Reactions of cyclopentadienyl-amidinate titanium imido compounds with CO2: Cycloaddition-extrusion vs. cycloaddition-insertion

Article abstract of DOI:10.1039/b901774g

A combined experimental and DFT study of the reactions of cyclopentadienyl-amidinate titanium imido complexes with CO₂ is reported. Cycloaddition reactions of the aryl imido compounds Ti(η-C ₅R₄Me)(NAr){R²C(NR

Full text of DOI:10.1039/b901774g

View Article Online / Journal Homepage / Table of Contents for this issue
This paper is published as part of a Dalton Transactions themed issue on:
The Synergy between Theory and Experiment
Guest Editor John McGrady
University of Glasgow, UK
Published in issue 30, 2009 of Dalton Transactions
Image reproduced with permission of Christophe Coperet
Papers published in this issue include:
A combined picture from theory and experiments on water oxidation, oxygen reduction and proton
pumping
Per E. M. Siegbahn and Margareta R. A. Blomberg, Dalton Trans., 2009,
DOI: 10.1039/b903007g
Mechanisms of C–H bond activation: rich synergy between computation and experiment
Youcef Boutadla, David L. Davies, Stuart A. Macgregor and Amalia I. Poblador-Bahamonde,
Dalton Trans., 2009,
DOI: 10.1039/b904967c
Are tetrathiooxalate and diborinate bridged compounds related to oxalate bridged quadruply
bonded compounds of molybdenum?
Malcolm H. Chisholm and Namrata Singh, Dalton Trans., 2009
DOI: 10.1039/b901734h
Molecular recognition in Mn-catalyzed C–H oxidation. Reaction mechanism and origin of selectivity
from a DFT perspective
David Balcells, Pamela Moles, James D. Blakemore, Christophe Raynaud, Gary W. Brudvig,
Robert H. Crabtree and Odile Eisenstein, Dalton Trans., 2009
DOI: 10.1039/b905317d
Visit the Dalton Transactions website for more cutting-edge inorganic and organometallic research
www.rsc.org/dalton

PAPER
www.rsc.org/dalton | Dalton Transactions
Reactions of cyclopentadienyl-amidinate titanium imido compounds with
CO2: cycloaddition-extrusion vs. cycloaddition-insertion†
Aldo E. Guiducci,a Catherine L. Boyd,a Eric Clot*b and Philip Mountford*a
Received 27th January 2009, Accepted 24th March 2009
First published as an Advance Article on the web 27th April 2009
DOI: 10.1039/b901774g
A combined experimental and DFT study of the reactions of cyclopentadienyl-amidinate titanium
imido complexes with CO2 is reported. Cycloaddition reactions of the aryl imido compounds
Ti(h-C5R4Me)(NAr){R2C(NR1)2} (R = H or Me; R1, R2 = SiMe3, Ph or iPr, Me) with CO2 gave the
corresponding N,O-bound carbamate complexes Ti(h-C5R4Me){N(Ar)C(O)O}{R2C(NR1)2}. These
reacted further with CO2 by insertion into the Ti–N(Ar) bond to afford the new dicarboxylates
2
1
=
Ti(h-C5R4Me){OC(O)N(Ar)C(O)O}{R C(NR )2} in which the original Ti NAr bond has been
completely cleaved. The X-ray structures of two of these have been determined. The CO2 insertion
reactions of the para-substituted phenyl carbamate complexes Ti(h-C5Me5){N(-4-C6H4X)-
C(O)O}{MeC(NiPr)2} (X = Me, CF3 or NMe2) were first order with respect to both carbamate
complex and CO2 and the pseudo first order rate constants were effectively independent of the para
substituent. The corresponding tert-butyl imido compounds Ti(h-C5R4Me)(NtBu){R2C(NR1)2} also
reacted with CO2 to form N,O-bound carbamate complexes, Ti(h-C5R4Me){N(tBu)C(O)O}-
{R2C(NR1)2}. However, these did not insert a further molecule of CO2 and instead extruded tBuNCO
to form the crystallographically characterized oxo-bridged dimers [Ti(h-C5R4Me)(m-O){R2C(NR1)2}]2.
These reactions proceeded via transient terminal oxo intermediates, one of which was trapped by the
addition of TolNCO (Tol = p-tolyl). DFT (B3PW91) calculations on Ti(h-C5H5)(NR){MeC(NMe)2}
(R = Me, Ph, 4-C6H4Me, 4-C6H4NMe2, 4-C6H4CF3) reacting with CO2 showed that the second CO2
insertion is thermodynamically favoured over isocyanate extrusion, and that the rates of the two
processes are similar. Calculations on Ti(h-C5R5)(NtBu){MeC(NiPr)2} (R = H or Me) showed that
increasing the steric bulk increases the thermodynamic favourability of the isocyanate extrusion process
and significantly raises the activation barrier for the second CO2 insertion, making the latter process
impossible.
Introduction
Since being established at the start of the 1990s,1–4 the chemistry
of terminal titanium imido compounds has been advanced
enormously. In addition to aspects of their molecular and
supramolecular5,6 structures and bonding,7–13 applications in olefin
polymerisation14–21 and uses in materials chemistry,22–27 the main
focus of the chemistry of titanium imido compounds has con-
=
cerned transformations involving the polar and reactive Ti NR
bond itself. Some of this progress has been charted in a series
Chart 1
of reviews,17,28–32 and the unsaturated substrates stoichiometrically
or/and catalytically transformed by titanium imido compounds
include: alkenes,33 allenes,34 alkynes,34–39 nitriles,40 isonitriles,41,42
phospha-alkynes40,43–46 and heterocumulenes.47–57
We have been developing the chemistry of the half-sandwich
cyclopentadienyl-amidinate compounds shown in Chart 1.56,58,59
The straightforward and modular synthesis of these compounds
allows for facile variation of the cyclopentadienyl-amidinate
supporting ligand set and also the imido N-substituents. In this
contribution, we focus on the reactions of these compounds
with CO2. Although the reaction chemistry of CO2 in general
continues to be of considerable interest,60–66 comparatively little
has been reported for transition metal imido compounds67–69
and for group 4 in particular.47,48,51,53,54 The first structurally
aChemistry Research Laboratory, University of Oxford, Mansfield Road,
Oxford, U.K. OX1 3TA. E-mail: philip.mountford@chem.ox.ac.uk.
authenticated product for any metal was Cp*Ir{N(tBu)C(O)O}
68
bUniversite´ Montpellier 2, Institut Charles Gerhardt, CNRS 5253, Case
Courrier 1501, Place Euge`ne Bataillon, 34095 Montpellier, France. E-mail:
eric.clot@univ-montp2.fr
and the first from group 4 was Ti{N(Tol)C(O)O}(Me4taa).47
A
number of reports of reactions of group 4 imido compounds with
CO2 have since appeared.47,48,51,53,54 Both the tert-butyl and aryl
imido-derived cycloaddition products typically undergo thermally
promoted isocyanate extrusion,48,51,53,54 although in at least one
† Electronic supplementary information (ESI) available: Graphs used for
determination of kinetic parameters. CCDC reference numbers 718337–
718339. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/b901774g
5960 | Dalton Trans., 2009, 5960–5979
This journal is
The Royal Society of Chemistry 2009
©

case the reaction is promoted by ambient light.47 In some cases,
the reaction is very fast and an intermediate carbamate cannot be
observed. With the exception of Me4taa-supported47 and related51
systems, the metal oxo by-products self-trap by dimerization.48,53,54
It has also been shown for a cationic tantalum system that
the extruded tert-butyl isocyanate could undergo a C–H bond
activation reaction at the newly formed metal–oxygen bond.67
We have recently reported experimental and DFT computa-
tional results on pendant arm functionalised amidinate systems of
the type Ti(h-C5R4Me)(NtBu){Me3SiNC(Ph)NCH2CH2R¢} (R¢ =
NMe2 (1a,b) or Me (2) in Chart 1)). These specifically probed
t
=
for anchimeric effects of pendant donors on the Ti N Bu/CO2
cycloaddition/extrusion reaction.53 We also recently reported
complementary reactions of some cyclopentadienyl-amidinate
titanium imides with other substrates, including isocyanates,
CS2, COS, PhNO, ketones and aldehydes, and organic primary
amides.56 In our present contribution, we describe a detailed
experimental and computational study of the reactions of a
range of cyclopentadienyl-amidinate titanium imido complexes
with CO2. In particular, we focus on how the rates of the
cycloaddition/extrusion or cycloaddition/insertion reactions are
critically dependent on the imido and other ligand substituents.
Part of this work has been communicated.70
Scheme 1
pound Ti(h-C5Me5)(NtBu){PhC(NSiMe3)2} (3) does not undergo
imi◦de exchange reactions with anilines even after several days at
80 C (benzene-d6). This suggests that the PhC(NSiMe3)2 ligand
is significantly more sterically demanding than the acetamidinate
analogue MeC(NiPr)2 since compound 4 easily undergoes this
reaction (to form 7). Fortunately, an alternative starting com-
pound Ti(h-C5Me5)(N-2,6-C6H3Me2)Cl(py) (13) was available.71
Reaction of 13 with Li[PhC(NSiMe3)2] (eqn (1)) afforded the
target compound Ti(h-C5Me5)(N-2,6-C6H3Me2){PhC(NSiMe3)2}
(14) as a green powder in 36% yield and the X-ray structure has
been determined (see Fig. 1).
Results and discussion
Synthesis of new cyclopentadienyl-amidinate aryl imido compounds
As shown in Chart 1, a number of cyclopentadienyl-tert-butyl
(1–6) and aryl imido (7, 8) have been reported previously.56,58,59
However, our preliminary work with CO2 and complementary
studies with other heterocumulenes56 found that the reactions
of the tert-butyl and aryl imido systems differ considerably. We
therefore decided to extend the range of aryl imido systems
available so as to probe the effects of both steric and electronic
factors on their reactions with CO2. The syntheses of the new
compounds are summarized in Scheme 1 and eqn (1).
70
(1)
Reaction of the pentamethylcyclopentadienyl compound Ti(h-
C5Me5)(NtBu){MeC(NiPr)2} (4) with two para-substituted ani-
lines at room temperature afforded the compounds Ti(h-
C5Me5)(N-4-C6H4X){MeC(NiPr)2} (X = CF3 (9) or NMe2 (10)) in
87% yield (Scheme 1). These compounds complement compounds
7 and (especially) 8 (Chart 1) prepared previously by the same gen-
eral route.56 The less sterically protected monomethylcyclopenta-
dienyl compound Ti(h-C5H4Me)(N-2,6-C6H3Me2){MeC(NiPr)2}
(11) was also formed cleanly (71% yield as a green oil after high
vacuum distillation). The methylcyclopentadienyl-benzamidinate
analogue Ti(h-C5H4Me)(N-2,6-C6H3Me2){PhC(NSiMe3)2} (12)
was also made by room temperature imido ligand exchange
starting from the tert-butyl imido compound 5 (58% yield). In
contrast, the pentamethylcyclopentadienyl-benzamidinate com-
Fig. 1 Displacement ellipsoid plot (25% probability) of Ti(h-C5Me5)-
(N-2,6-C6H3Me2){PhC(NSiMe3)2}(14). H atoms omitted for clarity.
Compound 14 is monomeric with a three-legged piano stool
geometry, which is consistent with the solution NMR data.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5960–5979 | 5961
©

◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for Ti(h-C5Me5)(N-2,6-
C6H3Me2){PhC(NSiMe3)2}(14). Cpcent refers to the C5Me5 ring carbon
centroid
˚
Bond lengths/A
Ti(1)–N(1)
Ti(1)–N(2)
Ti(1)–N(3)
2.134(2)
2.107(2)
1.748(2)
Ti(1) ◊ ◊ ◊ Cpcent
C(1)–N(1)
C(1)–N(2)
2.079
1.327(4)
1.346 (4)
Bond angles/◦
Ti(1)–N(3)–C(14)
Cpcent ◊ ◊ ◊ Ti(1)–N(1)
165.9(2)
120.5
Cpcent ◊ ◊ ◊ Ti(1)–N(2)
Cpcent ◊ ◊ ◊ Ti(1)–N(3)
119.6
121.8
Selected bond distances and angles are given in Table 1 and are
very similar to those for 7 and are within the previously reported
ranges for titanium(IV) complexes of the three types of ligand
present.72–78 The approximately linear Ti N–Cipso linkage suggests
=
that the arylimido nitrogen N(3) is formally sp hybridized and able
to act as 4 electron donor to the titanium centre, which achieves
an overall valence electron count of 16.
The rest of this contribution describes the various reactions
of cyclopentadienyl-amidinate imido complexes with CO2 as a
function of the imido N-substitutents and the overall steric
properties of the complexes.
Reactions of aryl imido compounds with CO2: cycloaddition
Reactions of the 2,6-dimethylphenyl imido compounds Ti(h-
i
C5R4Me)(N-2,6-C6H3Me2){R2C(NR1)2} (R = Me: R1, R2 = Pr,
Me (7) or SiMe3, Ph (14); R = H: R1, R2 = Pr, Me (11) or SiMe3,
i
Scheme 2
Ph (12)) with an excess of CO2 at room temperature yielded
the corresponding cherry-red N,O-bound carbamate derivatives
Ti(h-C5R4Me){N(-2,6-C6H3Me2)C(O)O}{R2C(NR1)2} (R = Me:
analysis80 (see ESI†) gave the activation parameters DH‡ = 62.1
0.8 kJ mol-1 and DS‡ = -45 5 J mol-1 K-1, which correspond
to DG‡ = 75.5 2.3 kJ mol-1 at 298 K. The somewhat negative
activation entropy suggests a rather ordered transition state for
the rate limiting step for exchange.81
i
R1, R2 = Pr, Me (15) or SiMe3, Ph (16); R = H: R1, R2
=
iPr, Me (17) or SiMe3, Ph (18)) in 50–96% yield (Scheme 2).
=
The IR spectra of 15–18 contain intense new n(C O) stretches
in the range 1667–1671 cm-1, consistent with presence of the
proposed N,O-bound carbamate ligand,47,48,68 and the structures
proposed in Scheme 2 are analogous to that crystallographically
determined for the pendant arm amidinate homologue Ti(h-
C5Me5){N(tBu)C(O)O}{Me3SiNC(Ph)NCH2CH2CH2NMe2}.53
The compounds are stable in solution at room temperature and
only decompose at elevated temperatures. Thus heating a solution
of 15 in benzene-d6 at 80 ◦C for 8 h led to a mixture of products,
including the corresponding aryl isocyanate and the oxo-bridged
dimer trans-[Ti(h-C5Me5)(m-O}{MeC(NiPr)2}]2 (see below).
The 1H NMR spectra of 15 and 16 are sharp at room
temperature and clearly show a loss of molecular Cs symmetry
(e.g. inequivalent amidinate N–R groups) upon their formation.
In addition, the presence of two sharp resonances (each with
a relative integral of 3 H) for the ortho-methyl groups of the
N-aryl rings indicate restricted rotation about the N–Cipso bonds.
However, warming a solution of 15 to 60 ◦C in toluene-d8 led to
In contrast to the sharp NMR spectra of 15 and 16, the room
temperature spectra of the less sterically encumbered complexes
17 and 18 showed rapid pairwise exchange of the ortho-methyl
groups of the 2,6-C6H3Me2 substituents, the amidinate ligand
N-substituents and C5H4Me ring hydrogens (apparent AA¢BB¢
spin system) at room temperature on the NMR timescale. How-
ever, the low temperature limiting spectra (213–223 K in CD2Cl2)
are sharp and consistent with the structures proposed in Scheme 2
(inequivalent ortho methyl groups and amidinate N-substituents,
as well as four inequivalent C5H4Me ring C–H resonances). An
Eyring analysis (see ESI†) of five rate constants for SiMe3 group
exchange in 18 (toluene-d8; range -5 to -25 ◦C) gave the activation
parameters DH‡ = 51.6 1.0 kJ mol-1 and DS‡ = -10 5 J
mol-1 K-1, which correspond to DG‡ = 54.5 3.9 kJ mol-1 at
298 K. In comparison with the data for 15, the lower value of DH‡
for 18 is consistent with reduced unfavourable steric interactions
at the transition state geometry, and the less negative DS‡ suggests
that less ordering is necessary in the transition state.
◦
broadening and mutual pairwise exchange (kexch 4.2 s-1 at 60 C)
between the amidinate iso-propyl methine and methyl groups,
as well as between the ortho-methyl groups of the 2,6-C6H3Me2
substituent at the same rate, implying that the same mechanism
links the two exchange events. De◦termination79 of five exchange
rate constants in the range 49–71 C (toluene-d8) and an Eyring
The dynamic NMR data for 15–18 are consistent with the
overall equilibrium in eqn (2), which represents the intercon-
version of two enantiomeric forms. In principle these equilibria
could proceed via the corresponding monomeric oxo compounds
5962 | Dalton Trans., 2009, 5960–5979
This journal is
The Royal Society of Chemistry 2009
©

Ti(h-C5R4Me)(O){R1C(NR2)2} and free ArNCO (Ar = 2,6-
C6H3Me2). However, the negative DS‡ values determined for
15 and 18 militate against a dissociative process on the NMR
timescale.
(2)
Reactions of aryl imido compounds with CO2: insertion of a 2nd
molecule of CO2
In the presence of an excess of CO2 (ca. 1.1 atm), com-
pounds 15–18 slowly react to form the Cs symmetrical dicar-
boxylate (azamalonate) complexes Ti(h-C5R4Me){OC(O)N(-2,6-
i
C6H3Me2)C(O)O}{R2C(NR1)2} (R = Me: R1, R2 = Pr, Me
i
(19); R = H: R1, R2 = Pr, Me (20) or SiMe3, Ph (21)) in 33–
82% isolated yields (Scheme 2). A pure dicarboxylate derivative
could not be obtained for the bulkiest carbamate, 16. The IR
spectra of 19, 20 and 21 are consistent with the incorporation of
a second carbonyl group into the molecule and each contains
two bands in the carbonyl stretching region (1694–1703 and
-1
=
1651–1657 cm ) corresponding to in- and out-of-phase n(C O)
stretching modes. The EI mass spectra of compounds 19 and 20
showed the expected parent ion and compounds 19 and 21 have
been structurally characterised. The NMR spectra are consistent
with Cs symmetrical products. The o-methyl groups of the 2,6-
C6H3Me2 substituents appeared as two singlets, indicative of
restricted rotation about the N–Cipso bonds.
Fig. 2 Displacement ellipsoid plots (25% probability) of Ti(h-5Me5)-
{OC(O)N(-2,6-6H3Me2)C(O)O}{MeC(NiPr)2} (19, top) and Ti(h-C5H4-
Me){OC(O)N(-2,6-C6H3Me2)C(O)O}{PhC(NSiMe3)2} (21, bottom). H
atoms omitted for clarity.
The molecular structures of 19 and 21 are shown in Fig. 2
and selected bond lengths and angles are given in Table 2. Each
contains a titanium atom in a four-legged piano stool geometry.
5
In addition to a h -bound cyclopentadienyl ring and bidentate
amidinate ligand, there is a bidentate azamalonate group. As far
as we are aware, this is a new type of ligand in transition metal
chemistry. The structures unambiguously confirm the complete
Table 2 Selected bond lengths (A) and angles (◦) for Ti(h-
˚
C5Me5){OC(O)N(-2,6-C6H3Me2)C(O)O}{MeC(NiPr)2} (19) and Ti(h-
C5H4Me){OC(O)N(-2,6-C6H3Me2)C(O)O}{PhC(NSiMe3)2} (21). Cpcent
refers to the C5Me5 or C5H4Me ring carbon centroid
=
cleavage of the Ti Nimide bonds of the original starting complexes
7 and 12 and the “double-insertion” of two CO2 molecules.
Overall, the two structures are very similar, with Ti–C, Ti–N and
Ti–O distances lying within the expected ranges.72,73 The atoms of
the hitherto unknown titana-azamalonate ring are approximately
Parameter
19
21
˚
Bond angles/A
˚
planar. The C(1)–O(2) (1.213(3) and 1.211(4) A for 19 and 21,
respectively) and C(2)–O(4) (1.210(3) and 1.206(4) A) distances
˚
Ti(1)–N(2)
Ti(1)–N(3)
Ti(1)–O(1)
Ti(1)–O(3)
Ti(1) ◊ ◊ ◊ Cpcent
C(1)–O(2)
C(2)–O(4)
2.064(2)
2.071(2)
1.932(2)
1.931(2)
2.046
1.213(3)
1.210(3)
2.079 (3)
2.095 (3)
1.925 (2)
1.915 (2)
2.026
1.211(4)
1.206(4)
are consistent with double bond (carbonyl) character in agreement
with the IR data discussed above. The 2,6-C6H3Me2 rings lie
perpendicular to the titana-azamalonate ring as expected from
the NMR data.
When followed by NMR spectroscopy, it was found that the
rates of reaction of 15–18 with CO2 follow the pattern expected
on steric grounds, with the more encumbered carbamates reacting
most slowly. Thus, the reaction of Ti(h-C5H4Me){N(-2,6-
C6H3Me2)C(O)O}{MeC(NiPr)2} (17) was complete within 12 h
whereas Ti(h-C5Me5){N(-2,6-C6H3Me2)C(O)O}{MeC(NiPr)2}
(15) requires 2 d. With the most crowded carbamate, Ti(h-
C5Me5){N(-2,6-C6H3Me2)C(O)O}{PhC(NSiMe3)2} (16), reac-
tion with CO2 eventually occurred after many days at room
Bond angles/◦
Cpcent ◊ ◊ ◊ Ti(1)–N(2)
Cpcent ◊ ◊ ◊ Ti(1)–N(3)
Cpcent ◊ ◊ ◊ Ti(1)–O(1)
Cpcent ◊ ◊ ◊ Ti(1)–O(3)
N(2)–Ti(1)–N(3)
118.9
111.8
110.8
112.2
64.09(7)
83.38(6)
117.2
115.7
110.9
113.1
64.9(1)
83.6 (1)
O(1)–Ti(1)–O(3)
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5960–5979 | 5963
©

temperature. As mentioned above, a pure product could not be
obtained on a preparative scale.
The double substrate insertion reactions of these aryl imido
=
complexes (i.e. complete cleavage of the Ti NAr bond) are
very uncommon in transition metal imido chemistry. Apart from
our own recently reported examples with certain isocyanates
for cyclopentadienyl-amidinate systems,56 the only well-defined
=
examples involving M NR cycloaddition reactions are for the
iridium compound Cp*Ir(NtBu) which reacts with two equiva-
4
lents of C2(CO2Me)2 to form Cp*Ir{h -C4(CO2Me)4NtBu}.68
A
double activation type reaction was implied in the isocyanate
exchange reaction between the unsymmetrical ureate complex
Ti(Me4taa){N(Ph)C(O)N(Tol)} and an excess of PhNCO, which
yields Ti(Me4taa){N(Ph)C(O)N(Ph)} and TolNCO via a pu-
tative biuret intermediate (not directly observed).47 Bergman
recently reported related heterocumulene insertion reactions of
iridium ureate and guanidinate complexes, although these did
not originate from metal imido complexes.82 This group has also
recently shown that certain alkynes and carbodiimides can be
=
sequentially coupled with a Zr NR bond to form six-membered
metallacycles.83 However, one should recall that the insertion of
CO2 into a metal–nitrogen single bond is in general very well
precedented and has been the subject of experimental, mechanistic
and computational investigations.69,84–93
In order to gain a better understanding of the second (inser-
tion) step of the reaction a series of kinetic experiments was
carried out. The rate of reaction of the p-tolylcarbamate Ti(h-
C5Me5){N(Tol)C(O)O}{MeC(NiPr)2} (22) with CO2 at room
temperature makes this a convenient system for determining
the rate expression. NMR samples in benzene-d6 were exposed
to CO2 at ambient temperature and then transferred to an
NMR spectrometer probe maintained at 25 ◦C, and spectra were
recorded over at least three half-lives of 22. Studies were carried out
at 5 different CO2 pressures under pseudo-first order conditions
in which at least a 10-fold excess of CO2 was present at the lowest
pressure studied (0.25 atm). The concentrations of the carbamate
22 and the product dicarboxylate 23 were monitored over time and
the results fitted first-order exponential relationships; the observed
rate constants kobs were extracted from linear plots of ln(I/I0) vs.
reaction time (see Fig. 3 for pCO2 = 0.50 atm and the ESI for other
systems studied).† The kobs values are summarised in Table 3. The
exponential decay of carbamate and evolution of dicarboxylate
product indicate that the rate determining step is first order in 22.
Fig.
3
Plot of normalized concentrations against time for the
insertion reaction of Ti(h-C5Me5){N(Tol)C(O)O}{MeC(NiPr)2} (22)
with CO2 (0.5 atm) (top). Values are given for starting car-
bamate 22 (represented as solid points) and product dicarboxy-
late Ti(h-C5Me5){OC(O)N(4-C6H4Me)C(O)O}{MeC(NiPr)2} (23, repre-
sented as hollow points). Plot of ln(I/I0) vs. reaction time for the
consumption of Ti(h-C5Me5){N(Tol)C(O)O}{MeC(NiPr)2} (22) (0.5 atm
CO2) where “I” and “I0” represent the normalized [22] at the reaction time
indicated or at time = 0 s, respectively (bottom).
The linear dependence of kobs on CO2 pressure (Fig. 4 and Table 3)
shows that it is also first order in CO2 and hence the overall rate
expression is bi-molecular.
Table 3 Pseudo-first order rate constants kobs and associated half-lives
(t1/2) for the CO2 insertion reaction of the carbamate complexes Ti(h-
C5Me5){N(-4-C6H4X)C(O)O}{MeC(NiPr)2} (X = Me (22), CF3 (24) or
NMe2 (25))
Carbamate
pCO2/atm
k ¥ 104/s-1
Fig. 4 Plot of kobs vs. CO2 pressure for the reaction of Ti(h-C5Me5)-
{N(Tol)C(O)O}{MeC(NiPr)2} (22) with CO2.
22
0.25
0.5
0.75
1.0
1.6
1.6
1.6
1.6
1.6
1.6
0.95 0.02
2.9 0.03
4.1 0.06
5.7 0.09
9.0 0.09
9.0 0.09
9.3 0.05
8.9 0.07
11.4 0.07
14.4 0.17
The effect of carbamate N-substituent electronic factors in
these reactions was also evaluated by comparing the reaction
rates for two other carbamate complexes Ti(h-C5Me5){N(-4-
C6H4X)C(O)O}{MeC(NiPr)2} (X = CF3 (24) or NMe2 (25)) in
which only the para-phenyl substituents were varied so that the
steric effects at the metal centre were the same. The substituents
24
25
5964 | Dalton Trans., 2009, 5960–5979
This journal is
The Royal Society of Chemistry 2009
©

chosen have very different electron-donating or -withdrawing
properties. The pseudo-first order reactions of 24 and 25 with
CO2 (pCO2 = 1.6 atm) to form the dicarboxylates 26 and 27,
respectively, (Scheme 2) were assessed as for 22 above. Rate
constants kobs are shown in Table 3 together with those for 22. They
are effectively independent of the N-phenyl para-substituent, and
do not fit a simple relationship with Hammett parameters.
Reactions of tert-butyl imido compounds with CO2
We have previously reported the reactions of CO2 with pendant
arm functionalised amidinates of the type 1 and 2 (Chart 1),
together with some DFT studies of the model compound Ti(h-
C5H5)(NMe){MeC(NMe)2}.53 For 2 (containing no pendant
t
=
amine donor), CO2 cycloaddition to Ti N Bu occurred readily at
-78 ◦C, whereas for 1a (R = H; pendant arm = CH2CH2NMe2) no
significant reaction occurred below -35 ◦C. Both systems formed
t
N,O-bound carbamates, which rapidly extruded BuNCO above
-25 ◦C to form oxo-bridged dimers. There was no significant
effect of the nature of the pendant arm on the extrusion
process, the rates of which were first order in carbamate and
concentration-independent. Although monomeric oxo interme-
diates were proposed, no direct evidence for their existence was
advanced. The carbamate formed from the bulkier amidinate Ti(h-
C5Me5)(NtBu){Me3SiNC(Ph)NCH2CH2NMe2} (1b) was more
t
stable to extrusion of BuNCO, which took place comparatively
slowly at room temperature (t1/2 = 30 min). There was no evidence
for double CO2 addition reactions of the type shown in Scheme 2.
Given the contrasting behaviour of 1a and 1b, and of the N-aryl
substituted carbamates (Scheme 2), we decided to explore further
the reactions of tert-butyl imido compounds with CO2.
Scheme 3
Reaction of the compounds Ti(h-C5Me5)(NtBu){PhC-
(NSiMe3)2} (3) and Ti(h-C5Me5)(NtBu){PhC(NiPr)2} (4) with
CO2 (ca.1.1 atm) at room temperature, followed by immediate
isolation, yielded the cherry-red N,O-bound carbamates
Ti(h-C5Me5){N(tBu)C(O)O}{PhC(NSiMe3)2} (28) and Ti(h-
C5Me5){N(tBu)C(O)O}{MeC(NiPr)2} (29) in 95 and 65% yields,
respectively, (Scheme 3). The NMR spectra of 28 and 29 are
consistent with the proposed structures and the IR spectra contain
intense new stretches at 1660 cm-1 and 1662 cm-1, respectively,
consistent with the incorporation of a new carbonyl unit into the
molecule. These values are slightly lower that those for the aryl
imido-derived homologues (e.g. 1667–1671 cm-1 for 15–18) and
similar values and trends have been found previously.47
ligand) requires about a week to undergo complete conversion
when followed by NMR spectroscopy.
The monomethylcyclopentadienyl complex 5 also reacts rapidly
with CO2 in benzene at room temperature. When the reaction
1
was followed by H NMR spectroscopy in benzene-d6 the spec-
trum after 5 min revealed that ca. 80% of the parent imido
complex had been consumed, while a new set of resonances
indicated the formation of a new carbamate complex Ti(h-
C5H4Me){N(tBu)C(O)O}{PhC(NSiMe3)2} (33, Scheme 3). How-
ever, the onset of tBuNCO extrusion from 33 also starts to occur
in this period, and after 30 min the only resonances visible were
t
for the oxo complexes 32 and 32a and BuNCO. Because of the
In contrast to their aryl imido-derived analogues 15–18, the
carbamates 28 and 29 are unstable in solution at ambient
temperature and cleanly eliminate tert-butyl isocyanate to form
rapid rate at which 33 undergoes extrusion, it could not be isolated
on a preparative scale.
In contrast to the very fluxional N-aryl homologue Ti(h-
C5H4Me){N(-2,6-C6H3Me2)C(O)O}{PhC(NSiMe3)2} (18), the 1H
NMR resonances for 33 are sharp at room temperature, showing
two clear SiMe3 groups (d -0.04 and -0.08 ppm) and four
C5H4Me ring hydrogen resonances. The NMR spectra for the
more sterically crowded C5Me5 homologues 28 and 29 are also
non-fluxional. Thus 28, 29 and 33 do not appear to undergo the
enantiomer interconversion process summarised in eqn (2) for the
N-aryl homologues 15–18, at least on the NMR timescale.
The oxo-bridged dimer formed from 33 exists as a mixture
trans-[Ti(h-C5Me5)(m-O){PhC(NSiMe3)2}]2 (30) and trans-[Ti(h-
i
=
C5Me5)(m-O){MeC(N Pr)2}]2 (31). The absence of terminal Ti O
stretching bands in the IR spectra of 30 and 31 are consistent
with the formation of dimeric oxo-bridged structures, and 31 has
been crystallographically characterised (see below). The tBuNCO
extrusion reaction still proceeds in the presence of an excess of CO2
and there is no evidence for insertion of a second molecule of CO2
into the Ti–Ncarbamate bonds of 28 or 29. The rates of disappearance
of 28 and 29 are markedly dependent upon the ancillary ligand
set. Thus the acetamidinate-supported compound 29 decays in
benzene-d6 solution at room temperature within 24 h, while
28 (having the more bulky N,N¢-bis(trimethylsilyl)benzamidinate
1
of trans- (32) and cis- (32a) isomers according to the H NMR
spectrum of the product mixture. This revealed twice as many
resonances as would be expected for a single product. The
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5960–5979 | 5965
©

formation of two isomers is possible because of the less sterically
demanding nature of the methylcyclopentadienyl ligands. Heating
the mixture of isomers in benzene-d6 to 80 ◦C for 30 min resulted
in quantitative conversion of 32a to the trans isomer 32, which has
been crystallographically characterized (see below).
Exposure of a benzene-d6 solution of the least sterically
protected imide Ti(h-C5H4Me)(NtBu){MeC(NiPr)2} (6) to CO2
(1 atm) resulted in an extremely rapid reaction sequence. The
solution briefly became cherry-red (consistent with a putative
carbamate intermediate) but lightened to dark amber almost
immediately. The 1H NMR spectrum recorded after 3 min
reaction time revealed complete consumption of 6 and resonances
t
attributable to BuNCO and the isomeric oxo species cis- and
trans- [Ti(h-C5H4Me)(m-O){MeC(NiPr)2}]2 (34 and 34a). These
were isolated on the preparative scale in 58% yield. The trans
isomer was successfully separated from the reaction mixture by
fractional crystallisation.
The X-ray structures of trans-[Ti(h-C5Me5)(m-O){MeC-
(NiPr)2}]2 (31) and trans-[Ti(h-C5H4Me)(m-O){PhC(NSiMe3)2}]2
(32) have been determined. The molecular structures are shown
in Fig. 5 and selected distances and angles and listed in Table 4.
Both compounds have a pseudo-four-legged piano stool geometry
about titanium and a trans arrangement of the cyclopentadienyl
rings. Compounds with Ti2(m-O)2 cores are well established, and
a number have been crystallographically characterized.72,73 The
bond lengths and angles for the two compounds are of comparable
magnitudes, with the metal–ligand distances in 31 on average being
slightly longer than in 32. This is attributed to the presence of the
more sterically demanding h-C5Me5 ligand in the former case.
Further aspects of the CO2 cycloaddition/isocyanate extrusion
reaction
The oxo-bridged dimers formed by isocyanate extrusion from
tert-butyl carbamate complexes are probably preceded by short-
lived monomeric terminal oxo intermediates. This is illustrated
in Scheme 4 for the formation of dimeric 31 from 29 via
a putative monomeric oxide 35. To explore the chemistry of
these systems further, a series of NMR tube scale reactions
Table 4 Selected bond lengths (A) and angles (◦) for trans-
˚
[Ti(h-C5Me5)(m-O){MeC(NiPr)2}]2 (31) and trans-[Ti(h-C5H4Me)(m-
O){PhC(NSiMe3)2}]2 (32). Cpcent refers to the C5Me5 or C5H4Me ring
carbon centroid
Fig. 5 Displacement ellipsoid plots (25% probability) of trans-[Ti(h-C5-
Me5)(m-O){MeC(NiPr)2}]2 (31, top) and trans-[Ti(h-C5H4Me)(m-O)-
{PhC(NSiMe3)2}]2 (32, bottom). H atoms omitted for clarity.
Parameter
31
32
on the representative tolyl and tert-butyl carbamates Ti(h-
t
C5Me5){N(R)C(O)O}{MeC(NiPr)2} (R = Tol (22) or Bu (29)
˚
Bond lengths/A
were carried out as summarized in Schemes 4 and 5.
Ti(1)–N(1)
Ti(1)–N(2)
Ti(1)–O(1)
Ti(1)–O(1B)
Ti(1)–Cpcent
2.188(3)
2.168(3)
1.855(2)
1.869(2)
2.130
2.154(1)
2.163(1)
1.842(1)
1.859(1)
2.087
To probe for any reversibility of tBuNCO extrusion reaction, the
effect of an excess of tBuNCO on the extent and rate of decay of 29
was examined. In the absence of any added tBuNCO, compound
t
29 underwent 30 and 70% conversion to BuNCO and the oxo
bridged dimer 31 after 3 and 16 h, respectively, in benzene-d6.
In the presence of an excess of BuNCO (5 equiv.) the extents of
Bond angles/◦
t
conversion were 28 and 69%, respectively. Hence, there is negligible
back reaction of the terminal oxo species 35 with tBuNCO.
We have shown previously47 that TolNCO reacts rapidly
Cpcent–Ti(1)–N(1)
Cpcent–Ti(1)–N(2)
Cpcent–Ti(1)–O(1)
Cpcent–Ti(1)–O(1B)
Ti(1)–O(1)–Ti(1B)
109.4
110.0
117.8
115.9
111.2
109.2
117.7
115.5
=
with the terminal Ti O group of Ti(Me4taa)(O) (36) to form
98.59(9)
97.01(4)
Ti(Me4taa){N(Tol)C(O)O} (37) as summarized in eqn (3) (the
5966 | Dalton Trans., 2009, 5960–5979
This journal is
The Royal Society of Chemistry 2009
©

itself does not react with TolNCO under these conditions, whereas
22 reacts wth TolNCO very rapidly, accounting for the formation
of 38 since an excess of TolNCO was used.56
(3)
These NMR experiments show that tBuNCO elimination from
29 (and probably all of the N-tert-butyl carbamates described
above) is irreversible. However, they also raise the possibility that
the N-aryl carbamates (e.g. 22) could exist in equilibrium with
trace amounts of monomeric oxo species 35 which might, in turn,
react back more readily with ArNCO than another terminal oxo
species (leading to irreversible formation of dimeric oxo species).
In a further NMR experiment, a small excess (3 equiv.) of
Ti(Me4taa)(O) (36) was therefore added to a sample of 22 in
benzene-d6. We have previously shown that Ti(O)(Me4taa) is an
efficient trap for TolNCO, reacting rapidly to form the carbamate
Ti(Me4taa){N(Tol)C(O)O} (37). Within 30 min, complete conver-
sion of 22 to trans-[Ti(h-C5Me5)(m-O){MeC(NiPr)2}]2 (31) and 37
had occurred. As illustrated in Scheme 5 this reaction probably
proceeds via the transient terminal oxo compound 35. In a control
experiment, a solution of pure 22 gave no formation of 31 over
24 h at room temperature under otherwise identical conditions.
Scheme 4
corresponding reaction of 36 with tBuNCO gave only 70%
conversion to Ti(Me4taa){N(tBu)C(O)O} after 17 d). In the hope
that an aryl isocyanate could likewise trap the transient oxo
species 35, TolNCO (5 equiv.) was added to a sample of 29 in
t
benzene-d6. As before, BuNCO was slowly eliminated but in
Computational studies
this instance Ti(h-C5Me5){OC(O)N(Tol)C(Tol)O}{MeC(NiPr)2}
(38, Scheme 4) was the only organometallic product and no oxo-
bridged dimer 31 was observed. Compound 38 was characterised
by comparison with an authentic sample independently pre-
pared from Ti(h-C5Me5){N(Tol)C(O)O}{MeC(NiPr)2} (22) and
TolNCO.56 The formation of 38 (via 22) provides firm evidence
for the the intermediate 35. Note that the oxo-bridged dimer 31 is
unreactive towards both tBuNCO and TolNCO. Furthermore, 29
The difference in reactivity with CO2 of the alkyl and aryl imido
complexes prompted us to carry a detailed DFT study of the reac-
tion mechanisms. The CO2 cycloaddition/isocyanate extrusion re-
action of Ti(h-C5H5)(NMe){MeC(NMe)2}, 1-Me, was previously
computed.53 The mechanism proceeds with an almost barrier-less
cycloaddition reaction of CO2 (DE# = 0.7 kJ mol-1, TS12-Me) to
yield the carbamate Ti(h-C5H5){N(Me)C(O)O}{MeC(NMe)2},
Scheme 5
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5960–5979 | 5967
©

2-Me, which is
a
reasonably exothermic process (DE
=
-113.1 kJ mol-1). This intermediate evolves into the oxo inter-
mediate Ti(h-C5H5)(O){MeC(NMe)2}, 3-O, and MeNCO in an
endothermic step (DE = 87.7 kJ mol-1) with an activation energy
through TS23-Me of 88 kJ mol-1. When Gibbs free energies are
considered, the energy diagram shown in Fig. 6 is obtained. The
carbamate 2-Me is more stable than the two extrusion pathways
1-Me + CO2 or 3-O + MeNCO, the latter being favoured over
the former. As a result, the overall transformation 1-Me + CO2
→ 3-O + MeNCO is exergonic (DG = -32.2 kJ mol-1). Once
the oxo complex 3-O is formed, it is known experimentally to
convert in an irreversible step into the oxo-bridged dimer. We did
not try to optimize the oxo-bridged dimer as it would have been
computationally prohibitive.
Fig. 7 Optimized geometry for 1-Ph, TS12-Ph, and 2-Ph and the
corresponding HOMO in each case.
reactants) are given in Table 5. The activation barrier for CO2
cycloaddition to 1-Ph is larger than that obtained with 1-Me, but
still very low (10.6 kJ mol-1 vs. 0.7 kJ mol-1, see Table 5), and the
reaction is less exothermic (-91.9 kJ mol-1 vs. -113.1 kJ mol-1,
see Table 5). The transition state for cycloaddition is earlier with
1-Me. As a consequence, TS12-Me and TS12-Ph present signifi-
cant differences in terms of geometrical parameters. The forming
Ti ◊ ◊ ◊ O and N ◊ ◊ ◊ C bonds are significantly longer in TS12-Me
˚
˚
˚
(2.442 A and 2.476 A, respectively) than in TS12-Ph (2.285 A
˚
and 2.277 A). Interestingly, the orientation of the phenyl ring in
TS12-Ph is different than in the reactant 1-Ph and the product
2-Ph (Fig. 7). In the imido complex 1-Ph, the orientation of the
phenyl ring (lying in the plane bisecting the Cp–Ti–amidinate
angle) allows the less stable out-of-plane 2p lone pair (LPp) on
N to interact with a high lying accepting orbital on Ti (HOMO
of 1-Ph, Fig. 7), whereas the more stable in-plane 2p lone pair
(LPp’) interacts with a low lying accepting orbital on Ti. Rotating
the phenyl group by 90◦ in TS12-Ph allows LPp on the nitrogen
to interact with the incoming CO2 molecule as illustrated by the
HOMO of TS12-Ph (Fig. 7). This rotation also reduces steric
interactions between the phenyl ortho C–H with the approaching
CO2.
The reaction can thus be described as a nucleophilic attack by
the imido nitrogen on the carbon atom of CO2. Furthermore,
the size of the activation barrier for CO2 cycloaddition is
influenced by the nature of the para substituent on the phenyl
ring. Three different para-substituted aryl imido complexes Ti(h-
C5H5)(NAr){MeC(NMe)2}, 1-PhX, have been considered (Ar = 4-
C6H4Me, X = Me; Ar = 4-C6H4CF3, X = CF3; Ar = 4-C6H4NMe2,
Fig. 6 Gibbs free energy diagram (kJ mol-1) for CO2 cycloaddi-
tion/isocyanate extrusion (solid lines) and second CO2 insertion (dotted
lines) for the methyl imido complex 1-Me (R = Me, black lines) and the
phenyl imido complex 1-Ph (R = Ph, blue lines).
The CO2 cycloaddition/isocyanate extrusion pathway was also
computed for CO2 reacting with Ti(h-C5H5)(NPh){MeC(NMe)2},
1-Ph, where the iso-propyl groups on the experimental acetamid-
inate ligand have been modelled by methyl groups to concentrate
on the basic electronic features of the reaction. The geometries of
the imido complex 1-Ph, the TS for CO2 cycloaddition TS12-Ph,
and the carbamate product 2-Ph are shown in Fig. 7, together
with the HOMO of the system in each case. The electronic
and Gibbs free energies (expressed with respect to separated
Table 5 Electronic energy (E) and Gibbs free energy (G) of the various extrema located expressed with respect to the separated reactants 1-R and CO2.
t
Energies are in kJ mol-1, and for R = Bu, 3-O is 3¢-O
TS12-R
2-R
TS23-R
3-O
TS24-R
4-R
DE#
DG#
DE
DG
DE#
DG#
DE
DG
DE#
DG#
34.1
73.8
65.7
74.8
73.2
101.0
DE
DG
R = Me
0.7
10.6
7.4
10.0
13.1
16.5
51.7
68.0
57.6
65.9
66.1
74.9
-113.1
-91.9
-93.1
-91.4
-88.8
-101.6
-55.4
-21.5
-27.9
-24.5
-23.5
-39.5
-25.1
2.0
-5.3
0.2
12.9
-7.7
29.7
65.0
52.6
62.2
72.5
49.1
-25.4
-1.6
-8.6
-3.2
8.7
-32.2
-3.7
-16.5
-7.4
2.0
-77.5
-45.9
-49.6
-46.7
-43.5
-20.1
-212.8
-151.8
-158.4
-153.7
-145.5
-171.4
-99.6
-31.6
-44.0
-34.5
-27.2
-53.1
R = Ph
R = PhNMe2
R = PhMe
R = PhCF3
t
R = Bu
-33.4
-49.1
5968 | Dalton Trans., 2009, 5960–5979
This journal is
The Royal Society of Chemistry 2009
©

X = NMe2). The calculated activation and reaction energies are
given in Table 5 together with the corresponding Gibbs free
energy values. The more electron releasing the para substituent
(NMe2, sp = -0.63; Me, sp = -0.14; CF3, sp = 0.53) the lower
the activation barrier, in agreement with the reaction being a
nucleophilic attack of the imido nitrogen on CO2.
87.7 kJ mol-1, 3-O + MeNCO; DE = 90.3 kJ mol-1, 3-O + PhNCO).
In contrast to the situation for the methyl imide 1-Me, the pathway
for CO2 or PhNCO extrusion from 2-Ph are competitive in terms
of activation barriers and reaction energies (DE# = 102.5 kJ mol-1,
DE = 91.9 kJ mol-1, 2-Ph → 1-Ph + CO2; DE# = 93.9 kJ mol-1,
DE = 90.3 kJ mol-1, 2-Ph → 3-O + PhNCO). As a result, the
reaction 1-Ph + CO2 → 3-O + PhNCO is only slightly exergonic
(DG = -3.7 kJ mol-1). The Gibbs free energy diagram for the
CO2 cycloaddition/PhNCO extrusion reaction of 1-Ph is shown
in Fig. 6 for a comparison with the results for 1-Me.
Estimation of the turnover frequency (TOF) at room tempera-
ture of the two consecutive processes with the procedure proposed
by Kozuch and Shaik94,95 yielded similar values (0.78 10-2 s-1,
1-Me; 0.20 10-2 s-1, 1-Ph). This shows that even though the TS¢s
are at higher energy in the phenyl case (Fig. 6), formation of a
less stable carbamate intermediate compensates and the overall
rates are similar. However, in stark contrast to these predictions,
the experimental results are different for the real tert-butyl and
aryl imido complexes. In the former cases, extrusion of tBuNCO
is observed. In the aryl cases, no extrusion of ArNCO is observed,
except under forcing conditions. Furthermore, in the presence of
an excess of CO2, insertion of a second CO2 molecule is generally
observed.
Formation of the carbamate is less exothermic for the aryl imido
complexes than for the methyl case (Table 5). The HOMO of
2-Ph (Fig. 7) shows that the lone pair LPp on nitrogen interacts
both with an empty d orbital on Ti and with a p-accepting orbital
=
on C O. In the starting imido complex 1-Ph, the two lone pairs
LPp and LPp’ are interacting with Ti, while in the product 2-Ph,
LPp’ is used to make the new N–C bond. The magnitude of the
reaction energy (Table 5) originates mainly from the creation of
two new s-bonds (Ti–O and N–C) at the expense of two p-bonds
=
=
(C O and Ti N). This negative value is further altered by the
reorganization of the framework of p interactions in the product
(2-Me or 2-Ph) with respect to the reactant (1-Me or 1-Ph). The Ti-
N bond becomes longer in the carbamate intermediate as a result
of the cycloaddition, but the increase is larger for the aryl case (Ti–
˚
˚
˚
N = 1.688 A, 1-Me; Ti–N = 1.710 A, 1-Ph; Ti–N = 1.916 A, 2-Me;
˚
Ti–N = 2.005 A, 2-Ph). There is thus a larger loss of p-donation
from N to Ti in 2-Ph than in 2-Me. This is only partly compensated
=
by increased p-donation from N to C O in the carbamate as
We therefore searched for a mechanism associated with the
insertion of CO2 into the Ti–NPh bond of the carbamate 2-Ph
to form the azamalonato complex 4-Ph. The geometries of the
TS for the second CO2 insertion, TS24-Ph, and of the product of
insertion, 4-Ph, are shown in Fig. 8. The electronic and Gibbs free
energies are given in Table 5. In TS24-Ph, the carbamate moiety is
twisted out of the “equatorial” plane of Ti(h-C5H5){MeC(NMe)2}
to allow attack by CO2. In the transition state, the forming
˚
illustrated by the shorter N–C bond in 2-Ph (1.384 A) than in
˚
2-Me (1.394 A), and also by the lower nCO vibrational frequency
in the carbamate (1825.6 cm-1, 2-Me; 1823.0 cm-1, 2-Ph). This
analysis is supported by the results for the para-substituted aryls
(Table 5) where the reaction energy is more exothermic for the
more electron releasing groups, and the nCO stretching frequencies
show the expected trend (1817.9 cm-1, 2-PhNMe2; 1820.7 cm-1,
2-PhMe; 1823.4 cm-1, 2-PhCF3).
˚
N ◊ ◊ ◊ C bond is 2.295 A and the oxygen atom interacts with Ti
˚
The geometry of the TS for extrusion of PhNCO, TS23-Ph,
is shown in Fig. 8 and the electronic and Gibbs free energies
associated with this process are given in Table 5 (see also Fig. 6).
The transition state TS23-Ph (leading to 3-O and PhNCO) could
(Ti ◊ ◊ ◊ O = 2.36 A). As for the first insertion, the reaction is best
described as a nucleophilic attack by the nitrogen lone pair on
the carbon atom of CO2. However, due to the steric interactions
imposed by the geometry of TS24-Ph, the reacting lone pair on
nitrogen is not conjugated with the phenyl ring as efficiently as
it was in TS12-Ph. The electronic activation barrier is thus larger
(46 kJ mol-1 vs. 10.6 kJ mol-1, Table 5) but is still indicative of
a facile process. Moreover, the formation of the product 4-Ph is
thermodynamically favoured (DE = -59.9 kJ mol-1 with respect
to 2-Ph and -151.8 kJ mol-1 with respect to 1-Ph). The transition
state for the second CO2 insertion was also computed for the para-
substituted phenyl groups and the activation barriers are very
close (43.5 kJ mol-1, TS24-PhNMe2; 44.7 kJ mol-1, TS24-PhMe;
45.3 kJ mol-1, TS24-PhCF3). There is thus a weaker influence
˚
be described as an N-adduct of PhNCO (Ti ◊ ◊ ◊ N = 2.304 A)
on the terminal oxo 3-O, and features a short C ◊ ◊ ◊ O contact
˚
(2.254 A). The geometry is typical of a [2 + 2] cycloaddition
product (PhNCO extrusion being the reverse of Ti O + PhNCO
=
cycloaddition) and the Cipso–N–CO angle in this TS (122◦) is ca.
20◦ less than in PhNCO itself (141◦). The activation barrier for
the extrusion process is slightly larger than in the methyl case
(DE# = 88 kJ mol-1, TS23-Me; DE# = 93.9 kJ mol-1, TS23-Ph),
and consequently the reaction is slightly more endothermic (DE =
of the para-substituent on the second CO2 insertion (DDE#
ª
2.5 kJ mol-1) than on the first one (DDE# ª 4.5 kJ mol-1) because
of the change of hybridisation at the nitrogen atom rendering the
lone pair less conjugated with the phenyl ring. This is in agreement
with the experimental results on kobs (Table 3) where no particular
influence of the para group was observed.
The Gibbs free energy diagram for the second CO2 insertion
on 2-Ph is given in Fig. 6 for comparison with the PhNCO
extrusion process. Even though the activation barrier for the
second insertion is ca. 10 kJ mol-1 larger than the activation
barrier for extrusion (DG# = 86.5 kJ mol-1, 2-Ph → 3-O +
PhNCO; DG# = 95.3 kJ mol-1, 2-Ph + CO2 → 4-Ph, Table 5),
there is a clear thermodynamic driving force toward insertion of
Fig. 8 Optimized geometry of the TS for PhNCO extrusion TS23-Ph,
the TS for second CO2 insertion TS24-Ph, and the product of second CO2
insertion 4-Ph.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5960–5979 | 5969
©

the second CO2 molecule (DG = 17.8 kJ mol-1, 2-Ph → 3-O +
PhNCO; DG = -10.1 kJ mol-1, 2-Ph + CO2 → 4-Ph, Table 5).
In the present case, comparison is made between processes in
which the changes of molecularity of each steps are different.
Extrusion of PhNCO is associated with creation of degrees of
freedom, whereas insertion of the second CO2 corresponds to
annihilation of degrees of freedom. As the major contributor to G
in the calculations is the loss or gain of translational entropy, the
DG# values should be only taken as qualitative indicators of the
respective reactivity. Nevertheless, the calculated values indicate
that the processes of CO2 cycloaddition/PhNCO extrusion and
CO2 cycloaddition/second CO2 insertion are competitive and are
both likely to occur at similar rates. The final outcome here is
dictated by the relative stability of the products with respect to
2-Ph, specifically the thermodynamically favourable formation of
the azamalonato complex 4-Ph and the unfavourable formation of
3-O and PhNCO. As a matter of fact the extrusion of PhNCO is
reversible (DG > 0) as illustrated by the trapping experiment shown
in Scheme 4 with TolNCO cycloaddition on the unobserved oxo
complex 35. Moreover the large excess of CO2 is likely to reduce
the effective activation barrier leading to 4-Ph.
˚
˚
t
TS12- Bu; Ti ◊ ◊ ◊ O = 2.442 A, N ◊ ◊ ◊ C = 2.476 A, TS12-Me). Based
on these shorter contacts, the apparent stronger interaction of CO2
with Ti in TS12-tBu is necessary to compensate for the larger steric
repulsion, thus allowing for a cycloaddition with still a low barrier.
Interestingly, the carbamate intermediate 2-tBu is not particularly
destabilized as the reaction energy DE = -101.6 kJ mol-1 is
only ca. 10 kJ mol-1 less exothermic than for the formation
of 2-Me.
The main difference between the two systems concerns the
extrusion pathway and in Fig. 9 is shown a comparison of the
Gibbs free energy diagram for 1-Me and 1-tBu. Increasing the
steric bulk results in a slightly larger activation barrier (DG#
=
85.1 kJ mol-1, 2-Me → 3-O + MeNCO; DG# = 88.6 kJ mol-1,
2-tBu → 3¢-O + BuNCO), but the main difference is the large
t
increase of thermodynamic stability of the extrusion product.
From the carbamate intermediate 2-tBu, the extrusion reaction
is now computed to be exergonic by DG = -9.6 kJ mol-1
(Table 5). Consequently the overall reaction 1-tBu + CO2 → 3¢-O +
tBuNCO is now exergonic by DG = -49.1 kJ mol-1, and the
calculated TOF is similar to that obtained with 1-Me (0.19 10-2 s-1,
1-tBu; 0.78 10-2 s-1, 1-Me). Compound 1-tBu is very close to the
experimental system 6 whose reaction with CO2 was extremely
rapid at room temperature (completion in less than 3 min). The
calculated TOF for 1-tBu corresponds to a half-reaction time of
ca. 6 min, qualitatively in very good agreement with the experi-
mental observation. The high energy of TS23-tBu with respect to
The results of the second CO2 insertion on the aryl carbamate
2-Ph prompted us to study the potential insertion of CO2 into the
Ti–NMe bond of the carbamate 2-Me. A transition state, TS24-
Me, similar to TS24-Ph, was located 35.6 kJ mol-1 above 2-Me +
CO2 (Table 5, Fig. 6). In this TS, the C ◊ ◊ ◊ N forming bond is
˚
t
3¢-O + BuNCO (98.2 kJ mol-1, which corresponds to DG# for
2.30 A, whereas the Ti ◊ ◊ ◊ O contact is longer than in TS24-Ph
˚
˚
the back-reaction 3¢-O + tBuNCO → 2-tBu) is consistent with the
experimental observation that the rate of tBuNCO extusion from
Ti(h-C5Me5){N(tBu)C(O)O}{MeC(NiPr)2} (29) is unaffected by
added tBuNCO (Scheme 4).
(2.515 A vs. 2.36 A). The TS is thus earlier in the methyl case
and this is confirmed by the value of the reaction energy DE =
-99.7 kJ mol-1, much larger than for the aryl case (-59.9 kJ mol-1,
Table 5). There is thus a strong electronic thermodynamic driving
force toward the insertion of a second CO2 molecule on the
carbamate 2-Me as illustrated by the Gibbs free energy profile
on Fig. 6. Thus, placed under the same experimental conditions
of excess of CO2, the methyl carbamate 2-Me should insert easily
a second CO2 molecule to yield 4-Me. However, such an outcome
t
was not observed experimentally and only BuNCO extrusion
was observed. Moreover, in the actual experimental systems, the
steric bulk has an influence on the reactivity. With the tert-butyl
imido complexes 3–6 (Scheme 3), the carbamate intermediate was
isolated only for the larger systems (28 and 29), while for the
smaller systems the carbamate was either only observed by NMR
(33) or not observed at all at room temperature. In all cases,
the system evolves to the oxo-bridged dimers (30–32, 34) after
tBuNCO extrusion.
In order to address the influence of the steric bulk on the
reactivity of the alkyl imido complexes toward CO2, DFT
calculations were carried out on the model system Ti(h-
C5H5)(NtBu){MeC(NiPr)2}, 1-tBu. This model is very close to
the experimental system 6 where the Cp ring has a single methyl
substituent, and differs from 4 by the use of Cp instead of Cp*.
The electronic and Gibbs free energies of the extrema located along
the pathway for CO2 cycloaddition/tBuNCO extrusion are given
in Table 5.
Fig. 9 Gibbs free energy diagram (kJ mol-1) of the CO2 cycloaddi-
tion/isocyanate extrusion (solid lines) and second CO2 insertion (dotted
lines) for the methyl imido complex 1-Me (R = Me, black lines) and the
t
t
bulky tert-butyl imido complex 1-tBu (R = Bu, blue lines). For R = Bu
As expected, the activation barrier for CO2 cycloaddition on 1-
tBu to form the carbamate 2-tBu is larger than with 1-Me (DE# =
16.5 kJ mol-1, TS12-tBu; DE# = 0.7 kJ mol-1, TS12-Me). The
Ti ◊ ◊ ◊ O and N ◊ ◊ ◊ C forming bonds in TS12-tBu are shorter than
i
and R¢= Pr, the oxo complex is 3¢-O.
Not only does the steric bulk favour the isocyanate formation
pathway by stabilizing the extrusion product, it also influences in
˚
˚
in the less bulky TS12-Me (Ti ◊ ◊ ◊ O = 2.351 A, N ◊ ◊ ◊ C = 2.363 A,
5970 | Dalton Trans., 2009, 5960–5979
This journal is
The Royal Society of Chemistry 2009
©

a dramatic way the CO2 insertion pathway. The transition state
for CO2 insertion, TS24-tBu, in the carbamate 2-tBu was located
on the potential energy surface together with the azamalonato
complex 4-tBu. The electronic and Gibbs free energies are given in
Table 5 and the Gibbs free energy diagram is shown in Fig. 9 for
comparison with the extrusion pathway. In order to achieve the
required N ◊ ◊ ◊ C interactions between the carbamate and CO2 in
TS24-tBu, the tert-butyl group has to move toward the amidinate
ligand where the isopropyl groups exert some steric pressure.
Consequently, strong steric repulsion develops in the TS and the
activation barrier is dramatically increased (DE# = 35.6 kJ mol-1,
TS24-Me; DE# = 81.5 kJ mol-1, TS24-tBu). This translates into
a very unfavourable DG# = 140.1 kJ mol-1 from the carbamate
(Fig. 9). Even though the second CO2 insertion is an exergonic
reaction (DG = -13.6 kJ mol-1), the activation barrier is too high
for the process to be effective. This is reflected qualitatively by
the calculated TOF value for the process 1-tBu → 2-tBu → 4-
tBu of 0.16 ¥ 10-11 s-1 that would correspond to an extrusion
reaction being ca. 107 times faster than insertion. In the case of the
alkyl imido complexes, the steric bulk, in particular at the imido
(tBu), results in a complete shut down of the second CO2 insertion
pathway.
Conclusions
We have carried out a comprehensive experimental and compu-
tational study of the reaction of titanium alkyl and aryl imido
complexes with CO2. These complement our previous studies with
isocyanate and related unsaturated substrates.56 Experimentally,
the two reaction outcomes, namely CO2 cycloaddition/isocyanate
extrusion and CO2 cycloaddition/second CO2 insertion are found
to differ dramatically depending on whether tert-butyl or aryl
imides are under consideration. A second important factor is the
steric demands of the supporting ligand sets (C5H4Me vs. C5Me5
and PhC(NSiMe3)2 vs. MeC(NiPr)2). The DFT calculations repro-
duce the experimental data and reveal that the intrinsic electronic
differences between alkyl and phenyl imides (when modelled by
non-sterically demanding groups) are small in comparison with
the major changes to transition state and product energies which
occur upon introducing tert-butyl in place of methyl on the imido
nitrogen. Similarly, the electronic effects of para substituents in the
series Ti(h-C5R5)(N-4-C6H4X){MeC(NR’)2} are relatively minor.
Experimental
General methods and instrumentation
As a further attempt to probe the influence of the steric bulk on
the extrusion pathway, the experimental system 29 was computed
together with the TS for tBuNCO extrusion. The activation barrier
is larger than from 2-tBu (DG# = 88.6 kJ mol-1, TS23-tBu; DG# =
96.6 kJ mol-1, 29 → oxo complex + tBuNCO) and the reaction is
more exergonic (DG = -9.6 kJ mol-1 vs. DG = -40.7 kJ mol-1).
As expected there is a stronger thermodynamic driving force
All manipulations were carried out using standard Schlenk line
or drybox techniques under an atmosphere of argon or of
dinitrogen. Solvents were pre-dried over 4 A molecular sieves and
˚
were refluxed over appropriate drying agents under a dinitrogen
atmosphere and collected by distillation. Deuterated solvents were
dried over appropriate drying agents, distilled under reduced
pressure and stored under dinitrogen in Teflon valve ampoules.
NMR samples were prepared under dinitrogen in 5 mm Wilmad
t
for BuNCO extrusion when steric bulk is increased. However,
this is not accompanied by a lowering of the activation barrier.
As already described for TS23-Ph (Fig. 8), the TS for RNCO
extrusion could again be described as an N-adduct on the Ti
centre of the oxo complex. Therefore any increase of the steric
bulk at the nitrogen atom would result in a longer Ti ◊ ◊ ◊ N bond
in the transition state and thus to a higher barrier. This could
be compensated only in part by a stronger C ◊ ◊ ◊ O interaction in
the TS. This analysis is confirmed by the evolution of the Ti ◊ ◊ ◊ N
and C ◊ ◊ ◊ O bond distances in the TS for extrusion (Ti ◊ ◊ ◊ N =
507-PP tubes fitted with J. Young Teflon valves. 1H, 13C{ H}
1
and 13C NMR spectra were recorded on Varian Unity Plus
500 and Varian Mercury spectrometers. H and 13C assignments
1
were confirmed where necessary with the use of NOE, DEPT-
135, DEPT90, DEPT-45, and two dimensional 1H–1H and
13C–1H NMR experiments. All spectra were referenced internally
to residual protio-solvent (1H) or solvent (13C) resonances and
are reported relative to tetramethylsilane (d = 0 ppm). Chemical
shifts are quoted in d (ppm) and coupling constants in Hertz.
Infrared spectra were prepared as Nujol mulls or thin films
between KBr or NaCl plates and were recorded on Perkin-Elmer
1600 and 1700 series spectrometers. Infrared data are quoted in
wavenumbers (cm-1). Mass spectra were recorded by the mass
spectrometry service of the University of Oxford’s Inorganic
Chemistry Laboratory. Combustion analyses were recorded by
the analytical services of the University of Oxford’s Inorganic
Chemistry Laboratory.
˚
˚
˚
˚
2.224 A, C ◊ ◊ ◊ O = 2.161 A, TS23-Me; Ti ◊ ◊ ◊ N = 2.350 A, C ◊ ◊ ◊ O =
t
˚
˚
2.152 A, TS23- Bu; Ti ◊ ◊ ◊ N = 2.660 A, C ◊ ◊ ◊ O = 2.082 A, TS
from 29). Increasing the steric bulk at the cyclopentadienyl ring
has resulted in an increase of the activation barrier by 8 kJ mol-1,
which translates at room temperature into a reaction ca. 25 times
less rapid. This is in qualitative agreement with the experimental
results where 29 decays at room temperature within 24 h, whereas
reaction of 6 with CO2 to form 34 is complete within 3 min without
observation of the carbamate intermediate.
We return finally to the difference in dynamic NMR behaviour
of the aryl carbamates 15–18 (fluxional but dependent on steric
factors) and the tert-butyl carbamates 28, 29 and 33 (apparently
non-fluxional). The proposed fluxional process in eqn (2) appears
to proceed via a net rotation about the Ti ◊ ◊ ◊ Ccarbamate vector. This
motion is the same as that which brings the model carbamates
2-R to the second insertion transition states TS24-R (e.g., Fig. 8
for TS24-Ph). The higher barrier for the fluxional process in the
bulkier carbonates 15 and 16, and the absence of fluxionality
in the tert-butyl carbamates, are therefore consistent with the
calculations described above.
Starting materials and literature preparations
The compounds Ti(h-C5Me5)(NtBu){PhC(NSiMe3)2} (3),56
Ti(h-C5Me5)(NtBu){MeC(NiPr)2} (4),56 Ti(h-C5H4Me)(NtBu)-
{PhC(NSiMe3)2} (5),56 Ti(h-C5H4Me)(NtBu){MeC(NiPr)2}
(6),56 Ti(h-C5Me5)(N-2,6-C6H3Me2){MeC(NiPr)2} (7),56 Ti(h-
C5Me5)(NTol){MeC(NiPr)2} (8),56 Ti(h-C5Me5)(N-2,6-C6H3-
Me2)Cl(py) (13)71 and Li[PhC(NSiMe3)2]96 were prepared
according to published methods. All other compounds and
reagents were purchased and used without further purification.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5960–5979 | 5971
©

Ti(g-C5Me5)(N-4-C6H4CF3){MeC(NiPr)2}
(9). 680
mg
m-2,6-C6H3Me2), 6.72 (1 H, t, J = 7.5 Hz, p-2,6-C6H3Me2), 6.37
(2 H, virtual t, J = 2.7 Hz, C2H2(b)C2H2(a)CMe), 5.92 (2 H,
virtual t, J = 2.7 Hz, C2H2(b)C2H2(a)CMe), 3.50 (2 H, apparent
sept., J = 6.4 Hz, NCHMeMe), 2.38 (6 H, s, 2,6-C6H3Me2), 2.10
(3 H, s, C2H2(b)C2H2(a)CMe), 1.53 (3 H, s, MeCN2), 1.01 (6 H, d,
J = 6.4 Hz, NCHMeMe), 0.86 (6 H, d, J = 6.4 Hz, NCHMeMe).
(1.73 mmol) Ti(h-C5Me5)(NtBu){MeC(NiPr)2} (4) was dissolved
in ca. 15 mL benzene to give a red solution. To this was
added dropwise a solution of 217 mL (278 mg, 1.73 mmol)
4-(trifluoromethyl)aniline in ca. 5 mL benzene over 5 min to give
a green solution. After 18 h, all volatiles were removed under
reduced pressure. Compound 9 was isolated as a brown powder.
Yield: 728 mg (87%). 1H NMR data (benzene-d6, 500.0 MHz, 298
K) d: 7.34 (2 H, d, J = 8.0 Hz, m-(N-4-C6H4CF3)), 6.56 (2 H, d,
J = 8.0 Hz, o-(N-4-C6H4CF3)), 3.46 (2 H, apparent sept., J =
6.4 Hz, NCHMeMe), 1.98 (15 H, s, C5Me5), 1.47 (3 H, s, MeCN2),
0.96 (6 H, d, J = 6.4 Hz, NCHMeMe), 0.91 (6 H, d, J = 6.6 Hz,
1
13C–{ H} NMR data (benzene-d6, 125.7 MHz, 298 K) d: 160.3
(CN2), 131.6 (i-2,6-C6H3Me2), 128.3 (o-2,6-C6H3Me2), 127.6 (m-
2,6-C6H3Me2), 125.0 (p-2,6-C6H3Me2), 119.5 (C2(b)C2(a)CMe),
113.6 (C2(b)C2(a)CMe), 111.8 (C2(b)C2(a)CMe), 48.8
(NCHMeMe), 25.6 (NCHMeMe), 25.4 (NCHMeMe), 20.6
(N-2,6-C6H3Me2), 15.1 (C2(b)C2(a)CMe), 10.6 (MeCN2). IR data
(KBr plates, neat thin film, cm-1) 3170 (w), 3054 (m), 3028 (m),
2965 (s), 2927 (s), 2868 (s), 2720 (w), 2601 (w), 2365 (w), 2053 (w),
1827 (w), 1765 (w), 1640 (w, br), 1587 (m), 1467 (s, br), 1408 (s),
1378 (s), 1361 (s), 1336 (s), 1308 (s, br), 1227 (s), 1173 (m), 1143
(m), 1123 (m), 1094 (m), 1057 (m), 1049 (m), 1032 (m), 1019 (m),
980 (m), 963 (m), 936 (w), 915 (w), 885 (w), 845 (m), 816 (s), 786
(s), 758 (s), 742 (m), 624 (m), 585 (m), 564 (w), 550 (w), 503 (w),
435 (m). Anal. found (calcd for C22H33N3Ti): C 66.0 (68.2); H 8.7
(8.6); N 10.8 (10.9)%. Mass spec. (E.I.) m/z 387 [M]+.
1
NCHMeMe).13C–{ H} NMR data (benzene-d6, 75.5 MHz,
298 K) d: 164.2 (CN2), 162.8 (i-N-4-C6H4CF3), 126.3 (p-N-4-
C6H4CF3), 125.9 (m-N-4-C6H4CF3), 123.0 (o-N-4-C6H4CF3),
121.8 (C5Me5), 49.8 (NCHMeMe), 26.5 (NCHMeMe), 25.4
(NCHMeMe), 12.8 (C5Me5), 12.1 (MeCN2). CF3 resonance not
observed. 19F NMR data (benzene-d6, 282.4 MHz, 298 K) d:
-61.0 (CF3). IR data (KBr plates, Nujol mull, cm-1) 2726 (w),
2670 (w), 1892 (w), 1654 (m), 1601 (s), 1499 (s, br), 1412 (m), 1317
(s), 1275 (m, br), 1213 (m), 1159 (s), 1115 (s), 1066 (s), 1020 (w),
964 (m), 890 (w), 849 (m), 838 (m), 812 (w), 793 (w), 772 (w), 723
(m), 687 (m), 664 (w), 644 (w), 633 (w), 581 (w), 473 (w), 440 (w),
402 (w). Anal. found (calcd for C25H36F3N3Ti): C 61.8 (62.1) H
7.5 (7.5) N 8.9 (8.7)%. Mass spec. (E.I.) m/z 483 [M]+, 464 [M -
F]+, 445 [M - 2F]+, 426 [M - 3F]+.
Ti(g-C5H4Me)(N-2,6-C6H3Me2){PhC(NSiMe3)2} (12). 1.48 g
(3.21 mmol) Ti(h-C5H4Me)(NtBu){PhC(NSiMe3)2} (5) was dis-
solved in ca. 60 mL pentane, and to this was added 400 mL (394 mg,
3.25 mmol) 2,6-dimethylaniline via microlitre syringe. After 16 h,
all volatiles were removed under reduced pressure, and the residue
taken up in a minimum of pentane and cooled to -30 ◦C. 576 mg
(36% yield) was obtained from the first batch of crystals. Total yield
Ti(g-C5Me5)(N-4-C6H4NMe2){MeC(NiPr)2} (10). 549 mg
(1.40 mmol) Ti(h-C5Me5)(NtBu){MeC(NiPr)2} (4) was dissolved
in ca. 15 mL benzene to give a red solution. To this was
added 189 mg (1.39 mmol) freshly sublimed N,N-dimethyl-1,4-
phenylenediamine in ca. 15 mL benzene to afford a red solution
that quickly turned green. After 1 h, all volatiles were removed
under reduced pressure to give 10 as a green-brown solid. Yield:
555 mg (87%). 1H NMR data (benzene-d6, 500.0 MHz, 298 K) d:
6.80 (2 H, d, J = 9.0 Hz, m-N-4-C6H4NMe2), 6.56 (2 H, d, J =
9.0 Hz, o-N-4-C6H4NMe2), 3.58 (2 H, apparent sept., J = 6.4 Hz,
NCHMeMe), 2.51 (6 H, s, NMe2), 2.11 (15 H, s, C5Me5), 1.55 (3 H,
s, MeCN2), 1.16 (6 H, d, J = 6.4 Hz, NCHMeMe), 1.00 (6 H,
1
after a second crop was obtained: 943 mg (58%). H NMR data
(benzene-d6, 500.0 MHz, 298 K) d: 7.14–7.09 (3 H, m, aryl-H),
7.00-6.95 (5 H, m, aryl-H), 6.74 (2 H, virtual t, C5H2(b)H2(a)Me),
5.86 (2 H, virtual t, C5H2(b)H2(a)Me), 2.56 (6 H, s, N-2,6-
C6H3Me2), 2.10 (3 H, s, C5H2(b)H2(a)Me), -0.15 (18 H, s,
1
SiMe3).13C–{ H} NMR data (benzene-d6, 125.7 MHz, 298 K) d:
171.0 (CN2), 159.6 (i-2,6-C6H3Me2), 138.6 (i-C6H5CN2), 132.4 (o-
2,6-C6H3Me2), 128.9 (o-C6H5CN2), 127.6 (m-2,6-C6H3Me2), 127.5
(p-C6H5CN2), 125.2 (p-2,6-C6H3Me2), 119.9 (C2(b)C2(a)CMe),
114.5 (C2(b)C2(a)CMe), 111.7 (C2(b)C2(a)CMe), 20.6 (N-2,6-
C6H3Me2), 14.9 (C2(b)C2(a)CMe), 2.2 (SiMe3). IR data (KBr
plates, Nujol mull, cm-1) 2726 (w), 1589 (w), 1406 (m, br), 1308
(m, br), 1249 (s), 1171 (w, br), 1094 (w), 1033 (w), 1006 (m), 996
(m), 919 (w), 840 (s), 793 (m), 781 (m), 760 (m), 723 (w), 702 (w),
643 (w), 517 (m). Anal. found (calcd for C27H39N3Si2Ti): C 63.3
(63.6); H 8.3 (7.7); N 8.2 (8.2)%. Mass spec. (E.I.) m/z 509 [M]+,
495 [M - Me]+.
1
d, J = 6.4 Hz, NCHMeMe). 13C–{ H} NMR data (benzene-d6,
75.5 MHz, 298 K) d: 162.9 (CN2), 153.7 (i-N-4-C6H4NMe2) 144.6
(p-N-4-C6H4NMe2), 124.1 (m-N-4-C6H4NMe2), 120.1 (C5Me5),
113.9 (o-N-4-C6H4NMe2), 49.6 (NCHMeMe), 41.7 (NMe2), 26.7
(NCHMeMe), 25.7 (NCHMeMe), 12.8 (C5Me5), 12.0 (MeCN2).
IR data (KBr plates, Nujol mull, cm-1) 2956 (s), 2724 (w), 1655
(w), 1599 (w), 1499 (s), 1337 (w), 1313 (m), 1261 (m), 1218 (m),
1171 (w), 1123 (w), 1060 (w), 1021 (w), 969 (w), 947 (w), 858 (w),
814 (s), 753 (w), 724 (w), 625 (w), 555 (w), 470 (w). Anal. found
(calcd for C26H42N4Ti): C 67.2 (68.1) H 9.2 (9.2) N 12.2 (12.2)%.
Mass spec. (E.I.) m/z 458 [M]+.
Ti(g-C5Me5)(N-2,6-C6H3Me2){PhC(NSiMe3)2} (14). 409 mg
(0.98 mmol) Ti(h-C5Me5)(N-2,6-C6H3Me2)Cl(py) (13 and 267 mg
(0.99 mmol) Li[PhC(NSiMe3)2] were dissolved in ca. 40 mL
benzene and heated to 90 ◦C for 3 h. Volatiles were removed
under reduced pressure, and the residue extracted with 25 mL
benzene and filtered. The volatiles were again removed under
reduced pressure, the residue extracted into a minimum amount
of pent◦ane, and the compound further purified by crystallisation
at -30 C to afford 14 as a green powder. Yield: 225 mg (36%).
1H NMR data (benzene-d6, 500.0 MHz, 298 K) d: 7.17–7.13 (3 H,
m, o-, p-C6H5), 7.03-7.00 (4 H, m, m-C6H5, m-2,6-C6H3Me2), 6.73
(1 H, t, J = 7.4 Hz, p-2,6-C6H3Me2), 2.36 (6 H, s, 2,6-C6H3Me2),
[Ti(g-C5H4Me)(N-2,6-C6H3Me2){MeC(NiPr)2}]
(11). To
600 mg (1.77 mmol) Ti(h-C5H4Me)(NtBu){MeC(NiPr)2} (6) in
60 mL benzene was added 220 mL (216 mg, 1.79 mmol) 2,6-
dimethylaniline via microlitre syringe, resulting in an immediate
colour change from red to green. After 1 h, all volatiles were
removed under reduced pressure to gi◦ve a dark green oil. This
was purified via tube distillation (130 C, 1 ¥ 10-5 Torr, 4 h) to
1
afford 11 as a green oil. Yield: 485 mg (71%). H NMR data
(benzene-d6, 500.0 MHz, 298 K) d: 7.01 (2 H, d, J = 7.5 Hz,
1
2.02 (15 H, s, C5Me5), -0.08 (18 H, s, SiMe3). 13C–{ H} NMR
5972 | Dalton Trans., 2009, 5960–5979
This journal is
The Royal Society of Chemistry 2009
©

data (benzene-d6, 125.7 MHz, 298 K) d: 174.7 (CN2), 158.5 (i-2,6-
C6H3Me2), 138.9 (i-C6H5CN2), 132.0 (o-2,6-C6H3Me2), 128.9 (one
CH from o-, p-Ph or m-Me2C6H3), 128.5 (m-C6H5), 128.0 (one CH
from o-, p-Ph or m-Me2C6H3), 127.4 (one CH from o-, p-Ph or m-
Me2C6H3), 121.5 (C5Me5), 119.2 (p-C6H3Me2), 20.8 (C6H3Me2),
12.5 (C5Me5), 3.3 (SiMe3). IR data (KBr discs, Nujol mull, cm-1)
2726 (w), 1881 (w), 1651 (w), 1586 (w), 1307 (s), 1293 (s), 1248 (s),
1162 (w), 1093 (m), 1077 (w), 1031 (w), 1005 (m), 996 (m), 961 (w),
932 (w), 839 (s), 781 (m), 756 (s), 743 (s), 706 (m), 623 (w), 581 (w),
563 (w), 511 (m), 438 (m). Anal. found (calcd for C31H47N3Si2Ti:):
C 65.6 (65.8); H 8.6 (8.4); N 7.3 (7.4)%. Mass spec. (E.I.) m/z 565
[M]+.
(s), 1158 (m), 1098 (m), 1076 (m), 1004 (s), 991 (s), 913 (s), 841 (s,
br), 808 (s), 788 (s), 760 (s), 748 (s), 725 (s), 687 (m), 640 (w), 627
(w), 590 (w), 557 (w), 512 (w), 469 (w), 441 (w) cm-1. Mass spec.
(E.I.) m/z = 609 [M]+. A satisfactory elemental analysis was not
obtained.
Ti(g-C5H4Me){N(-2,6-C6H3Me2 )C(O)O}{MeC(NiPr)2}
(17). 100 mg (0.26 mmol) Ti(h-C5H4Me)(N-2,6-C6H3Me2)-
{MeC(NiPr)2} (11) was dissolved in 10 mL benzene to give a
green solution. The headspace was evacuated, and the solution
exposed to CO2 at a pressure of 1 atm, resulting in an immediate
colour change to deep red. After 5 min, all volatiles were
removed under reduced pressure to afford 17 as an olive-green
powder. Yield: 82 mg (74%). 1H NMR data (dichloromethane-d2,
500.0 MHz, 213 K) d: 6.93 (1 H, t, J = 4.7 Hz, p-2,6-C6H3Me2),
6.86 (2 H, d, J = 4.7 Hz, m-2,6-C6H3Me2), 6.80 (1 H, m,
CH(b1)CH(b2)C2H2(a)CMe), 6.49 (1 H, m, CH(b1)CH(b2)-
C2H2(a)CMe), 6.35 (1 H, m, C2H2(b)CH(a1)CH(a2)CMe), 6.23
(1H, m, C2H2(b)CH(a1)CH(a2)CMe), 3.50 (2 H, m, NCHMeMe),
2.43 (3 H, s, C5H4Me), 2.07 (3 H, s, 2,6-C6H3MeMe), 1.88
(3 H, s, MeCN2), 1.75 (3 H, s, 2,6-C6H3MeMe), 1.11 (3 H,
d, J = 6.7 Hz, NCHaMeMe), 1.09 (3 H, d, J = 6.7 Hz,
NCHbMeMe), 0.95 (3 H, d, J = 6.7 Hz, NCHaMeMe), 0.23
Ti(g-C5Me5){N(-2,6-C6H3Me2)C(O)O}{MeC(NiPr)2}
(15).
198 mg (0.45 mmol) Ti(h-C5Me5)(N-2,6-C6H3Me2){MeC(NiPr)2}
(7) was dissolved in ca. 10 mL pentane, the headspace evacuated,
and the solution exposed to CO2 at a pressure of 1 atm for
10 min. Volatiles were then removed under reduced pressure to
afford 15 as a brown powder. Yield: 71 mg (79%). 1H NMR
data (benzene-d6, 500.0 MHz, 298 K) d: 6.95–7.00 (3 H, m,
m-, p- 2,6-C6H3Me2), 3.23 (1 H, m, NCHaMeMe), 3.05 (1 H,
m, NCHbMeMe), 2.24 (3 H, s, 2,6-C6H3MeMe), 1.97 (3 H, s,
2,6-C6H3MeMe), 1.95 (15 H, s, C5Me5), 1.41 (3 H, s, MeCN2),
1.06 (3 H, d, J = 6.6 Hz, NCHaMeaMe), 1.00 (3 H, d, J =
6.6 Hz), NCHaMeMeb (0.79, 3 H, d, J = 6.4 Hz) NCHbMeaMe
1
(3 H, d, J = 6.7 Hz, NCHbMeMe). 13C–{ H} NMR data
(dichloromethane-d2, 125.7 MHz, 213 K) d: 166.4 (OCO),
159.2 (MeCN2), 144.8 (i-2,6-C6H3Me2), 135.7 (o-2,6-C6H3Me2),
133.5 (o-2,6-C6H3Me2), 132.5 (i-C5H4Me), 128.1 (m-2,6-
C6H3Me2), 127.2 (p-2,6-C6H3Me2), 124.5 (m-2,6-C6H3Me2),
119.8 (C2H2(b)CH(a1)CH(a2)CMe), 117.7 (CH(b1)CH(b2)-
C2H2(a)CMe), 117.3 (CH(b1)CH(b2)C2H2(a)CMe), 115.5
1
(0.52, 3 H, d, J = 6.4 Hz, NCHbMeMeb). 13C–{ H} NMR data
(benzene-d6, 125.7 MHz, 298 K) d: 168.5 (OCO), 159.2 (MeCN2),
147.1 (i- C6H3Me2), 134.2 (o- C6H3Me2), 133.6 (m- C6H3Me2),
129.4 (p- C6H3Me2), 124.7 (C5Me5), 50.5 (NCHaMeMe), 49.3
(NCHbMeMe), 25.7 (NCHbMeaMe), 24.6 (NCHaMeMeb), 24.2
(NCHaMeaMe), 24.0 (NCHbMeMeb), 19.7 (2,6-C6H3MeMe),
19.2 (2,6-C6H3MeMe), 13.6 (MeCN2), 13.0 (C5Me5). IR data
(KBr plates, Nujol mull, cm-1) 2955 (s), 2726 (w), 1669 (s, br),
1577 (w), 1405 (w), 1328 (w), 1309 (m), 1282 (m), 1247 (m), 1207
(m), 1172 (s, br), 1116 (w), 1002 (w), 910 (m), 821 (m), 790 (m),
762 (m), 723 (m, br), 687 (w), 631 (w), 587 (w), 549 (w), 467 (m),
443 (m). Anal. found (calcd for C27H47N3Si2Ti): C 61.0 (62.6), H
9.2 (9.2), N 7.6 (8.1)%.
(C2H2(b)CH(a1)CH(a2)CMe),
50.1
(NCHMeMe),
49.4
(NCHMeMe), 24.2 (NCHaMeMe), 24.0 (NCHbMeMe),
23.7 (NCHaMeMe), 22.9 (NCHbMeMe), 19.0 (2,6-C6H3MeMe),
18.1 (2,6-C6H3MeMe), 15.3 (C5H4Me), 11.0 (MeCN2). IR data
(KBr plates, Nujol mull): 2955 (s), 2726 (w), 2669 (w), 1733 (w),
1670 (s, br), 1615 (w), 1577 (w), 1499 (m), 1339 (m), 1309 (m),
1294 (m), 1261 (w), 1248 (w), 1218 (m), 1173 (w), 1138 (w), 1120
(w), 1096 (w), 1073 (w), 1020 (w), 1003 (w), 926 (w), 911 (w), 829
(m), 819 (m), 805 (m), 791 (m), 779 (w), 767 (w), 723 (m), 688 (w),
69 (w), 628 (w), 617 (w), 586 (w), 552 (w), 469 (w), 441 (w), 417
(w) cm-1. A satisfactory elemental analysis was not obtained.
Ti(g-C5Me5 ){N(-2,6-C6H3Me2 )C(O)O}{PhC(NSiMe3 )2}
(16). 57.3 mg (0.10 mmol) Ti(h-C5Me5)(N-2,6-C6H3Me2)-
{PhC(NSiMe3)2} (14) was dissolved in ca. 5 mL benzene, the
headspace evacuated, and the solution exposed to CO2 at a
pressure of 1 atm, which resulted in a colour change from dark
green to cherry red within 1 min. After 16 h, all volatiles were
removed under reduced pressure, affording 16 as a red powder.
Yield: 59.1 mg (96%). 1H NMR data (benzene-d6, 500.0 MHz, 298
K) d: 7.25 (1 H, d, J = 7.6 Hz, m-2,6-C6H3Me2), 7.08 (1 H, d, J =
7.6 Hz, m-2,6-C6H3Me2), 7.02 (1 H, t, J = 7.6 Hz, p-2,6-C6H3Me2),
7.02–6.94 (5 H, m, C6H5), 2.28 (3 H, s, 2,6-C6H3MeMe (a)), 2.26
(3 H, s, 2,6-C6H3MeMe (b)), 1.99 (15 H, s, C5Me5), -0.11 (9 H,
Ti(g-C5H4Me){N(-2,6-C6H3Me2 )C(O)O}{PhC(NSiMe3 )2}
(18). 167 mg (0.33 mmol) Ti(h-C5H4Me)(N-2,6-C6H3Me2)-
{PhC(NSiMe3)2} (12) was dissolved in ca. 10 mL benzene to
give a brown solution. The headspace was evacuated, and the
solution exposed to CO2 at a pressure of 1 atm. A colour change
from brown to red was observed. After 5 min, volatiles were
removed under reduced pressure to afford 18 as a hard brown
solid. This was triturated with ca. 5 mL pentane. 90 mg (50%
1
yield). H NMR data (dichloromethane-d2, 500.0 MHz, 223 K)
1
s, SiMe3), -0.36 (9 H, s, SiMe3). 13C–{ H} NMR data (benzene-
d: 7.40–7.46 (3 H, m, m-, p- C6H5), 7.20 (1 H, d, J = 6.6 Hz,
o-C6H5 (a)), 7.14 (1 H, d, J = 5.4 Hz, o-C6H5 (b)), 6.97 (2 H,
d, J = 7.6 Hz, m-N-2,6-C6H3Me2), 6.92 (1 H, t, J = 6.6 Hz,
p-N-2,6-C6H3Me2), 6.86 (1 H, s, CH(b1)CH(b2)C2H2(a)CMe),
6.63 (1 H, s, CH(b1)CH(b2)C2H2(a)CMe), 6.53 (1 H, s, C2H2(b)-
CH(a1)CH(a2)CMe), 6.20 (1 H, s, C2H2(b)CH(a1)CH(a2)CMe),
2.46 (3 H, s, C5H4Me), 2.13 (3 H, s, N-2,6-C6H3MeMe (a)),
2.04 (3 H, s, N-2,6-C6H3MeMe (b)), -0.22 (9 H,s, SiMe3),
d6, 125.7 MHz, 298 K) d: 177.3 (OCO), 158.8 (PhCN2), 147.1 (i-
2,6-C6H3Me2), 137.2 (i-C6H5), 134.7 (o-2,6-C6H3Me2 (a)), 133.5
(o- 2,6-C6H3Me2 (b)), 130.1 (C5Me5), 129.6 (o-C6H5), 128.2 (m-
C6H5), 128.0 (p-2,6-C6H3Me2), 127.9 (m-2,6-C6H3Me2 (a)), 127.3
(m-2,6-C6H3Me2 (b)), 125.0 (p-C6H5), 20.7 (2,6-C6H3MeMe), 19.6
(2,6-C6H3MeMe), 13.3 (C5Me5), 3.4 (SiMe3), 3.0 (SiMe3). IR data
(KBr plates, Nujol mull): 2727 (w), 2669 (w), 2208 (w), 1671 (s),
1634 (m), 1608 (m), 1577 (m), 1277 (s), 1260 (s), 1248 (s), 1171
1
-0.48 (9 H, s, SiMe3). 13C–{ H} NMR data (dichloromethane-d2,
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5960–5979 | 5973
©

125.7 MHz, 223 K) d: 173.2 (OCO), 159.1 (C6H5CN2), 144.6 (i-
2,6-C6H3Me2), 135.3 (i-C6H5), 134.3 (o-2,6-C6H3Me2 (a)), 133.5 (o-
2,6-C6H3Me2 (b)), 132.8 (C5Me5), 129.5 (m-/p-C6H5), 128.4 (p-/m-
C6H5), 127.5 (m-2,6-C6H3Me2), 126.7 (o-C6H5 (b)), 125.8 (o-C6H5
(a)), 125.0 (p-2,6-C6H3Me2), 121.9 (C2H2(b)CH(a1)CH(a2)CMe),
120.5 (CH(b1)CH(b2)C2H2(a)CMe), 116.8 (CH(b1)CH(b2)-
C2H2(a)CMe) 116.3 (C2H2(b)CH(a1)CH(a2)CMe), 19.0 (2,6-
C6H3MeMe), 18.5 (2,6-C6H3MeMe), 15.6 (C5H4Me), 0.9 (SiMe3
(¥ 2)), i-C5H4Me resonance not observed. IR data (KBr plates,
Nujol mull, cm-1): 2954 (s), 2725 (w), 2670 (w), 2361 (w), 2209 (w),
1667 (s), 1610 (m), 1590 (m), 1571 (m), 1496 (m), 1289 (s), 1246
(s), 1185 (w), 1165 (m), 1097 (w), 1067 (w), 1034 (m), 1004 (s), 994
(m), 927 (m), 914 (m), 838 (s), 785 (m), 763 (s), 723 (s), 687 (s), 614
(w), 587 (w), 518 (m), 461 (m), 444 (m) cm-1. Anal. found (calcd
for C28H39N3O2Si2Ti): C 60.5 (60.7); H 7.1 (7.1); N 7.3 (7.6)%.
(adj. Mea)), 128.5 (m-N-2,6-C6H3Me2 (adj. Meb)), 127.4 (p-N-
2,6-C6H3Me2), 119.5 (C2(b)C2(a)CMe), 119.4 (C2(b)C2(a)CMe),
50.6 (NCHMeMe), 23.7 (NCHMeMe), 23.4 (NCHMeMe), 18.5
(Mea), 18.4 (Meb), 18.0 (MeCN2), 9.9 (C2(b)C2(a)CMe). IR data
(KBr plates, Nujol mull): 2956 (s), 2726 (w), 2671 (w), 1700 (s),
1651 (s, br), 1611 (m), 1583 (m), 1557 (m), 1262 (m), 1244 (m),
1216 (s), 1173 (s), 1122 (m), 1085 (m), 1071 (m), 1031 (m), 1003
(m), 936 (w), 920 (w), 811 (s), 767 (m), 722 (s), 703 (m), 585 (w),
549 (w), 532 9w), 458 (w), 426 (w) cm-1. Anal. found (calcd for
C24H33N3O4Ti): C 61.0 (60.6); H 7.4 (7.0); N 9.1 (8.8)%. Mass
spec. (E.I.): m/z = 475 [M]+.
Ti(g-C5H4Me){OC(O)N(-2,6-C6H3Me2 )C(O)O}{PhC(NSi-
Me3)2} (21). 142 mg (0.28 mmol) Ti(h-C5H4Me)(N-2,6-
C6H3Me2){PhC(NSiMe3)2} (12) was dissolved in ca. 15 mLben-
zene to give a brown solution. The headspace was evacuated,
and the solution exposed to CO2 at a pressure of 1 atm,
resulting in an immediate colour change to red. After 43 h, all
volatiles were removed under reduced pressure, and the residue
triturated with ca. 5 mL pentane. Compound 21 was obtained as
Ti(g-C5Me5){OC(O)N(-2,6-C6H3Me2)C(O)O}{MeC(NiPr)2}
(19). 125 mg (0.28 mmol) Ti(h-C5Me5)(N-2,6-C6H3Me2)-
{MeC(NiPr)2} (7) was dissolved in ca. 10 mL benzene, the
headspace evacuated, and the solution exposed to CO2 at a
pressure of 1 atm for a period of 24 h. Volatiles were then removed
under reduced pressure to afford 19 as a red powder. Yield: 122 mg
1
a brown powder. Yield: 55 mg (33%). H NMR data (benzene-
d6, 500.0 MHz, 298 K) d: 7.12 (1 H, d, J = 7.3 Hz, Ha), 7.09
(1 H, t, J = 7.3 Hz, Hb), 7.04 (1 H, d, J = 7.3 Hz, Hc),
6.95–6.90 (3 H, m, o-, p-C6H5), 6.86–6.81 (2 H, m, m-C6H5),
6.43 (2 H, virtual t, J = 2.7 Hz, C5H2(b)H2(a)Me), 6.05
(2 H, virtual t, J = 2.7 Hz, C5H2(b)H2(a)Me, 2.48 (3 H, s,
Mea), 2.34 (3 H, s, Meb), 2.12 (3 H, s, C5H2(b)H2(a)Me), -0.02
1
(82%). H NMR data (benzene-d6, 300.0 MHz, 298 K) d: 7.12
(1 H, d, J = 8.0 Hz, Ha), 7.09 (1 H, t, J = 8.0 Hz, Hb), 7.04
(1 H, d, J = 8.0 Hz, Hc), 3.51 (2 H, apparent sept, NCHMeMe),
2.55 (3 H, s, Mea), 2.20 (3 H, s, Meb), 1.97 (15 H, s, C5Me5), 1.42
(3 H, s, MeCN2), 1.12 (6 H, d, J = 7.0 Hz), NCHMeMe (1.07,
6 H, d, J = 7.0 Hz, NCHMeMe). 13C–{ H} NMR data (benzene-
(18 H, s, SiMe3). 13C–{ H} NMR data (benzene-d6, 125.7 MHz,
1
1
d6, 125.7 MHz, 298 K) d: 169.4 (MeCN2), 153.3 ({O(CO)}2N),
139.6 (i-N-2,6-C6H3Me2), 136.3 (o-N-2,6-C6H3Me2 (adj. Mea)),
135.9 (o-N-2,6-C6H3Me2 (adj. Meb)), 130.9 (C5Me5), 128.6 (m-N-
2,6-C6H3Me2 (adj. Mea)), 128.4 (m-N-2,6-C6H3Me2 (adj. Meb)),
127.2 (p-N-2,6-C6H3Me2), 50.5 (NCHMeMe), 24.2 (NCHMeMe),
23.3 (NCHMeMe), 18.7 (Mea), 18.1 (Meb), 14.4 (MeCN2), 12.7
(C5Me5). IR data (KBr plates, Nujol mull): 2725 (w), 1694 (s),
1651 (s), 1556 (w), 1314 (w), 1262 (w, br), 1234 (w), 1206 (m), 1173
(m), 1158 (m), 1124 (w), 1030 (w), 1004 (s), 811 (m), 782 (w), 771
(m), 742 (w), 724 (m), 685 (w), 652 (w), 611 (m), 587 (w), 528 (m),
511 (w), 453 (m, br) cm-1. Mass spec. (E.I.): m/z = 531 [M]+. Anal.
found (calcd for C28H41N3O4Ti): C 63.4 (63.3); H 7.3 (7.8); N 8.1
(7.9)%.
298 K) d:175.0 (C6H5CN2), 152.8 (OCO), 139.1 (i-2,6-C6H3Me2),
136.6 (i-C6H5), 136.0 (o-2,6-C6H3Me2 (adj. Mea)), 135.9 (o-2,6-
C6H3Me2 (adj. Meb)), 133.8 (C2(b)C2(a)CMe), 128.6 (m-2,6-
C6H3Me2 (adj. Mea)), 128.3 (m-2,6-C6H3Me2 (adj. Meb)), 128.2
(m-C6H5), 128.1 (o-/p-C6H5), 127.9 (p-/o-C6H5), 127.5 (p-2,6-
C6H3Me2), 120.7 (C2(b)C2(a)CMe), 119.8 (C2(b)C2(a)CMe), 18.5
(Mea), 18.0 (Meb), 15.7 (C2(b)C2(a)CMe), 1.7 (SiMe3). IR data
(KBr plates, Nujol mull): 3106 (w), 2728 (w), 2671 (w), 2336 (w),
2273 (w), 1944 (w), 1703 (s), 1657 (s), 1624 (m), 1590 (m), 1558
(m), 1524 (m), 1500 (m), 1407 (s), 1366 (s), 1301 (s), 1248 (s), 1229
(m), 1172 (m), 1094 (m), 1075 (m), 1032 (m), 1003 (s), 992 (s), 913
(s, br), 842 (s, br), 812 (s), 780 (s), 765 (s), 724 (s), 637 (w), 615
(w), 587 (w), 536 (w), 519 (w), 438 (w) cm-1. Anal. found (calcd for
C29H39N3O4Si2Ti): C 58.4 (58.3); H 6.5 (6.6); N 6.8 (7.0)%.
Ti(g-C5H4Me){OC(O)N(-2,6-C6H3Me2)C(O)O}{MeC(NiPr)2}
(20). 100 mg (0.26 mmol) Ti(h-C5H4Me)(N-2,6-C6H3Me2)-
{MeC(NiPr)2} (11) was dissolved in 10 mL benzene to give a
green solution. The headspace was evacuated, and the solution
exposed to CO2 at a pressure of 1 atm, resulting in an immediate
colour change to dark red. After 24 h, all volatiles were removed
Ti(g-C5Me5){N(Tol)C(O)O}{MeC(NiPr)2} (22). 371 mg
(0.87 mmol) Ti(h-C5Me5)(NTol){MeC(NiPr)2} (8) was dissolved
◦
in ca. 30 mL benzene. The solution was frozen at -196 C, and
the headspace evacuated. 0.86 mmol CO2 was condensed onto
the frozen solution using a volumetrically calibrated manifold,
and the solution warmed to room temperature. Volatiles were
removed under reduced pressure after ca. 10 min to afford the
1
to afford 20 as a red-brown solid. Yield: 75 mg (61%). H NMR
data d: (benzene-d6, 300.0 MHz, 298 K): 7.10 (1 H, d, J =
7.2 Hz, Ha), 7.08 (1 H, t, J = 7.2 Hz, Hb), 7.03 (2 H, d, J =
7.2 Hz, Hc), 6.30 (2 H, virtual t, J = 2.7 Hz, C5H2(b)H2(a)Me),
5.96 (2 H, virtual t, J = 2.7 Hz, C5H2(b)H2(a)Me), 3.16 (2 H,
sept, J = 6.4 Hz, NCHMeMe), 2.46 (3 H, s, Mea), 2.19 (3 H,
s, Meb), 2.12 (3 H, s, C5H2(b)H2(a)Me), 1.13 (3 H, s, MeCN2),
1.11 (6 H, d, J = 6.4 Hz, NCHMeMe), 1.04 (6 H, d, J = 6.4 Hz,
1
product as a red powder. Yield: 225 mg (55%). H NMR data
(benzene-d6, 500.0 MHz, 298 K) d: 7.35 (2 H, d, J = 8.5 Hz,
m-4-C6H4Me), 7.03 (2 H, d, J = 8.5 Hz, o-4-C6H4Me), 3.65 (1 H,
m, br, NCHaMeMe), 3.29 (1 H, m, br, NCHbMeMe), 2.14 (3 H,
s, ArMe), 1.94 (15 H, s, C5Me5), 1.35 (3 H, s, MeCN2), 1.08
(6 H, d, J = 6.2 Hz, NCHbMeMe), 0.98 (3 H, d, J = 5.9 Hz,
1
1
NCHMeMe). 13C–{ H} NMR data (benzene-d6, 125.7 MHz, 298
NCHaMeMe), 0.64 (3 H, d, J = 6.1 Hz, NCHaMeMe. 13C–{ H}
K) d:167.1 (MeCN2), 152.9 ({O(CO)}2N), 139.3 (i-2,6-C6H3Me2),
136.1 (o-2,6-C6H3Me2 (adj. Mea)), 136.0 (o-2,6-C6H3Me2 (adj.
Meb)), 134.2 (C2H2(b)C2H2(a)CMe), 128.6 (m-N-2,6-C6H3Me2
NMR data (125.7 MHz, 298 K, benzene-d6) d: 169.9 (MeCN2),
157.7 (OCO), 146.1 (i-4-C6H4Me), 131.0 (p-4-C6H4Me), 129.4
(o-4-C6H4Me), 129.0 (C5Me5), 122.6 (m-4-C6H4Me), 50.5
5974 | Dalton Trans., 2009, 5960–5979
This journal is
The Royal Society of Chemistry 2009
©

(NCHbMeMe), 49.5 (NCHaMeMe), 24.3 (NCHaMeMe), 24.1
(NCHaMeMe), 23.9 (NCHbMeMe), 20.9 (ArMe), 15.0 (MeCN2),
12.6 (C5Me5). IR data (KBr plates, Nujol mull): 2955 (s), 2726
(w), 2673 (w), 2360 (w), 1701 (w), 1672 (s), 1609 (w, br), 1575
(w), 1508 (s), 1339 (w), 1307 (m), 1207 (m), 1177 (w), 1160 (w),
1128 (w), 1064 (w), 1006 (m), 934 (w), 915 (m), 818 (m), 791 (m),
724 (s), 681 (w), 612 (w), 586 (w), 516 (w), 476 (m), 424 (w) cm-1.
Anal. found (calcd for C26H39N3O2Ti): C 65.8 (65.6); H 8.1 (8.3);
N 8.4 (8.9)%.
(10) was dissolved in ca. 10 mL benzene to give a green solution.
The headspace was evacuated, and the solution exposed to CO2
at a pressure of 1 atm, resulting in an immediate colour change to
cherry red. After 20 s, all volatiles were removed under reduced
pressure to afford 25 as a dark red solid which was triturated
with ca. 5 mL pentane and dried in vacuo. Yield: 60 mg (50%).
1H NMR data (benzene-d6, 500.0 MHz, 298 K) d: 7.31 (2 H,
d, J = 9.0 Hz, m-4-C6H4NMe2), 6.66 (2 H, d, J = 9.0 Hz,
o-4-C6H4NMe2) 3.62 (1 H, m, br, NCHaMeMe), 3.27 (1 H, m, br,
NCHbMeMe), 2.54 (6 H, s, NMe2), 1.98 (15 H, s, C5Me5), 1.40
(3 H, s, MeCN2), 1.15 (3 H, d, br, NCHbMeMe), 1.11 (3 H, d, br,
NCHbMeMe), 0.98 (3 H, d, br, NCHaMeMe), 0.73 (3 H, d, br,
Ti(g-C5Me5){OC(O)N(Tol)C(O)O}{MeC(NiPr)2}
(23).
197 mg (0.46 mmol) Ti(h-C5Me5)(NTol){MeC(NiPr)2} (8) was
dissolved in ca. 15 mL benzene to give a green solution. The
headspace was evacuated, and the solution exposed to CO2 at a
pressure of 1 atm for a period of 16 h. The volatiles were then
removed under reduced pressure to afford 23 as a brown solid.
1
NCHaMeMe). 13C–{ H} NMR data (benzene-d6, 75.5 MHz, 298
K) d: 169.8 (MeCN2), 158.2 (OCO), 146.9 (i-4-C6H4NMe2), 139.8
(p-4-C6H4NMe2), 130.0 (o-4-C6H4NMe2), 129.0 (C5Me5), 123.8
(m-4-C6H4NMe2), 50.8 (NCHbMeMe), 49.8 (NCHaMeMe),
41.3 (NMe2), 24.6 (NCHaMeMe), 24.5 (NCHaMeMe), 24.3
(NCHbMeMe), 15.0 (MeCN2), 13.1 (C5Me5). IR data (KBr
plates, Nujol mull): 2726 (w), 2671 (w), 1656 (m), 1603 (m), 1511
(s), 1341 (s), 1309 (s), 1261 (m), 1206 (m), 1162 (m), 1129 (m),
1065 (w), 1022 (w), 947 (m), 908 (w), 817 (m), 789 (w), 723 (m),
596 (w), 533 (w), 464 (w), 404 (w) cm-1. Anal. found (calcd for
C27H42N4O2Ti): C 64.2 (64.5); H 8.3 (8.4); N 10.7 (11.2)%.
1
Yield: 145 mg (61%). H NMR data (benzene-d6, 300.0 MHz,
298 K): 7.39 (2 H, d, J = 8.4 Hz, o-C6H4Me), 7.04 (2 H, d,
J = 8.4 Hz, m-C6H4Me), 3.42 (1 H, apparent sept, J = 6.8 Hz,
NCHMeMe), 2.05 (3 H, s, C6H4Me), 1.94 (15 H, s, C5Me5), 1.32
(3 H, s, MeCN2), 1.10 (6 H, d, J = 6.8 Hz, NCHMeMe), 1.07 (6 H,
1
d, J = 6.8 Hz, NCHMeMe). 13C–{ H} NMR data (benzene-d6,
125.7 MHz, 298 K) d: 169.5 (MeCN2), 154.4 ({O(CO)}2N),
139.2 (i-4-C6H4Me), 136.3 (p-4-C6H4Me), 130.9 (C5Me5), 129.4
(o-4-C6H4Me), 129.3 (o-4-C6H4Me), 128.3 (m-4-C6H4Me), 50.5
(NCHMeMe), 24.0 (NCHMeMe), 23.8 (NCHMeMe), 21.0
(C6H4Me), 13.2 (MeCN2), 12.7 (C5Me5). IR data (KBr plates,
Nujol mull): 2955 (s), 1698 (m), 1656 (m), 1265 (m), 1206 (w),
1154 (m), 1124 (w), 1005 (m), 784 (w), 723 (w), 610 (w), 526
(w) cm-1. Anal. found (calcd for C27H39N3O4Ti): C 63.0 (62.7); H
7.9 (7.6); N 7.9 (8.1)%.
Ti(g-C5Me5 ){OC(O)N(-4-C6H4CF3 )C(O)O}{MeC(NiPr)2}
(26). 117 mg (0.24 mmol) Ti(h-C5Me5)(N-4-C6H4CF3)-
{MeC(NiPr)2} (9) was dissolved in ca. 5 mL benzene to give
a dark green solution. The headspace was evacuated, and the
solution exposed to CO2 at a pressure of 1 atm for a period of
4 h. All volatiles were removed under reduced pressure to afford
1
26 as an oily brown solid. Yield: 85 mg (62%). H NMR data
(benzene-d6, 500.0 MHz, 298 K) d: 7.40 (2 H, d, J = 8.5 Hz,
o-4-C6H4CF3), 7.34 (2 H, d, J = 8.5 Hz, m-4-C6H4CF3), 3.41
(2 H, apparent sept, J = 6.5 Hz, NCHMeMe), 1.92 (15 H,
s, C5Me5), 1.31 (3 H, s, MeCN2), 1.08 (6 H, d, J = 6.5 Hz,
NCHMeMe), 1.05 (6 H, d, J = 6.5 Hz, NCHMeMe). 19F NMR
Ti(g-C5Me5){N(-4-C6H4CF3)C(O)O}{MeC(NiPr)2}
(24).
153 mg (0.31 mmol) Ti(h-C5Me5)(N-4-C6H4CF3){MeC(NiPr)2}
(9) was dissolved in ca. 10 mL benzene to give a dark green
solution. The headspace was evacuated, and the solution exposed
to CO2 at a pressure of 1 atm, resulting in an immediate colour
change to red. After 25 s, all volatiles were removed under
reduced pressure to afford 24 as a brown solid. Yield: 110 mg
1
data (benzene-d6, 282.4 MHz, 298 K) d: -62.40 (CF3). 13C–{ H}
NMR data (benzene-d6, 125.7 MHz, 298 K) d: 169.5 (MeCN2),
153.8 ({O(CO)}2N), 144.7 (i-4-C6H4CF3), 131.5 (C5Me5), 130.1
(o-4-C6H4CF3), 125.8 (m-4-C6H4CF3), 50.6 (NCHMeMe), 24.0
(NCHMeMe), 23.7 (NCHMeMe), 14.1 (MeCN2), 12.7 (C5Me5),
CF3, p-4-C6H4CF3 resonances not observed. IR data (CsBr plates,
Nujol mull): 2955 (s), 2728 (w), 1704 (s), 1658 (s), 1642 (s), 1632
(s), 1604 (s), 1548 (m), 1513 (m), 1494 (s), 1411 (s), 1323 (s),
1261 (s), 1208 (m), 1159 (s), 1107 (s), 1067 (s), 1007 (m), 918 (w),
890 (w), 846 (w), 795 (m), 723 (w), 677 (w), 663 (w), 633 (w),
595 (w), 534 (w), 454 (w), 409 (w) cm-1. Anal. found (calcd for
C27H36F3N3O4Ti·0.20(C6H6)): C 57.6 (57.7); H 6.6 (6.4); N 7.0
(7.2)%.
1
(67%). H NMR data (benzene-d6, 500.0 MHz, 298 K) d: 7.47
(2 H, d, J = 8.5 Hz, m-4-C6H4CF3), 7.43 (2 H, d, J = 8.8 Hz,
o-4-C6H4CF3), 3.57 (1 H, m, J = 6.6 Hz, NCHaMeMe), 3.22
(1 H, m, J = 6.6 Hz, NCHbMeMe), 1.85 (15 H, s, C5Me5), 1.29
(3 H, s, MeCN2), 1.04 (3 H, d, J = 6.6 Hz, NCHbMeMe), 1.01
(3 H, d, J = 6.6 Hz, NCHbMeMe), 0.98 (3 H, d, J = 6.6 Hz,
NCHaMeMe), 0.44 (3 H, d, J = 6.6 Hz, NCHaMeMe). 19F NMR
data (benzene-d6, 282.4 MHz, 298 K): -61.33 (CF3). 13C–{ H}
1
NMR data (benzene-d6, 125.7 MHz, 298 K) d: 169.6 (MeCN2),
151.3 (OCO), 130.4 (i-/p- 4-C6H4CF3), 128.5 (C5Me5), 125.8
(o-4-C6H4CF3), 121.5 (m-4-C6H4CF3), 50.9 (NCHbMeMe), 49.8
(NCHaMeMe), 24.3 (NCHaMeMe), 24.2 (NCHbMeMe), 23.7
(NCHaMeMe), 15.8 (MeCN2), 13.0 (C5Me5). IR data (KBr
plates, Nujol mull): 2727 (w), 1655 (m), 1603 (m), 1499 (m), 1322
(s), 1208 (m), 1160 (m), 1108 (m), 1066 (s), 1012 (m), 914 (w),
890 (w), 846 (w), 789 (w), 723 (w), 678 (w), 663 (w), 644 (w),
632 (w), 580 (w), 508 (w), 469 (w) cm-1. Anal. found (calcd for
C26H36F3N3O2Ti): C 59.5 (59.2); H 7.0 (6.9); N 7.7 (8.0)%.
Ti(g-C5Me5){OC(O)N(-4-C6H4NMe2)C(O)O}{MeC(NiPr)2}
(27). 110 mg (0.24 mmol) Ti(h-C5Me5)(N-4-C6H4NMe2)-
{MeC(NiPr)2} (10) was dissolved in ca. 5 mL benzene to give
a green solution. The headspace was evacuated, and the solution
exposed to CO2 at a pressure of 1 atm for a period of 4 h. All
volatiles were then removed under reduced pressure to give a
dark red solid. Trituration with ca. 2 mL pentane afforded the
product as a very fine red-brown powder. Yield: 71 mg (54%).
1H NMR data (benzene-d6, 500.0 MHz, 298 K) d: 7.43 (2 H,
d, J = 8.9 Hz o-4-C6H4NMe2), 6.62 (2 H, d, J = 8.9 Hz,
Ti(g-C5Me5){N(-4-C6H4NMe2)C(O)O}{MeC(NiPr)2}
(25).
111 mg (0.24 mmol) Ti(h-C5Me5)(N-4-C6H4NMe2){MeC(NiPr)2}
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5960–5979 | 5975
©

m-4-C6H4NMe2), 3.43 (2 H, apparent sept, J = 6.8 Hz,
NCHMeMe), 2.44 (6 H, s, NMe2), 1.97 (15 H, s, C5Me5), 1.32
(3 H, s, MeCN2), 1.11 (6 H, d, J = 6.8 Hz, NCHMeMe), 1.08 (6 H,
(m,br), 681 (w), 656 (w, br), 597 (w), 578 (w), 527 (w, br), 466 (s),
431 (w), 410 (m). Anal. found (calcd for C23H41N3O2Ti): C 62.7
(62.9) H 9.3 (9.4) N 9.1 (9.6)%. Mass spec. (E.I.) m/z 439 [M]+.
1
d, J = 6.8 Hz, NCHMeMe). 13C–{ H} NMR data (benzene-d6,
[Ti(g-C5Me5)(l-O){PhC(NSiMe3)2}]2
(30). 497
mg
125.7 MHz, 298 K) d: 154.8 ({O(CO)}2N), 131.1 (i-4-C6H4NMe2),
130.7 (p-4-C6H4NMe2), 129.8 (o-4-C6H4NMe2), 124.7 (C5Me5),
113.0 (m-4-C6H4NMe2), 50.5 (NCHMeMe), 40.4 (NMe2), 24.1
(NCHMeMe), 23.9 (NCHMeMe), 14.1 (MeCN2), 12.7 (C5Me5),
MeCN2 resonance not observed. IR data (KBr plates, Nujol mull):
2727 (w), 1774 (w), 1698 (s), 1653 (s), 1614 (m), 1558 (w), 1521 (m),
1263 (m), 1212 (m), 1183 (m), 1157 (m), 1129 (m), 1067 (m), 1025
(w), 998 (m), 947 (w), 918 (w), 820 (m), 790 (s), 751 (w), 723 (m),
676 (w), 596 (m), 533 (m), 454 (m) cm-1. Anal. found (calcd for
C28H42N4O4Ti): C 62.0 (61.5); H 7.8 (7.8); N 10.7 (10.3)%. Mass
spec. (E.I.): m/z = 546 [M]+. Accurate mass E.I. mass spectrum
found (calcd for C28H42N4O4Ti): 546.2689 (546.2686).
(0.96 mmol) [Ti(h-C5Me5)(NtBu){PhC(NSiMe3)2}] (3) was
dissolved in 25 mL benzene, the headspace evacuated, and the
solution exposed to CO2 at 1 atm. Immediate colour change
of the solution from red to cherry red occurred, followed by a
further colour change to brown over ca. 2 d. After 2 d, the brown
solution was removed by decantation and the remaining yellow
powder was washed with pentane (3 ¥ 10 mL). Drying under
vacuum yielded the product (a mixture of cis and trans isomers)
as a yellow solid. Yield: 80 mg (19%). IR data (KBr plates, Nujol
mull, cm-1) 2955 (s), 2720 (w), 2359 (w), 1952 (w), 1816 (w), 1771
(w), 1682 (w), 1651 (w), 1615 (w), 1575 (w), 1456 (s), 1258 (m),
1244 (m), 1162 (w), 1074 (w), 1020 (w), 1002 (m), 985 (m), 908
(m), 837 (m), 781 (m), 762 (m), 722 (m), 680 (w), 639 (m), 628
(m), 609 (m), 597 (m), 491 (m), 430 (m). Anal. found (calcd for
C46H76N4O2Si4Ti2): C 60.1 (59.7); H 8.6 (8.3); N 5.5 (6.1)%.
Ti(g-C5Me5){N(tBu)C(O)O}{PhC(NSiMe3)2} (28). 184 mg
(0.36 mmol) Ti(h-C5Me5)(NtBu){PhC(NSiMe3)2} (3) was dis-
solved in ca. 5 mL benzene, the headspace evacuated, and the
solution exposed to CO2 at a pressure of 1 atm for 20 min. The
volatiles were then removed under reduced pressure to afford 28
as a red powder. Yield: 189 mg (95%). 1H NMR data (benzene-d6,
500.0 MHz, 298 K) d: 7.00–7.03 (1 H, m, p-C6H5), 6.95–6.99 (2 H,
m, o-C6H5), 6.84–6.91 (2 H, m, m-C6H5), 1.99 (15 H, s, C5Me5),
1.49 (9 H, s, NtBu), 0.03 (9 H, s, SiMe3 (NOE tBu)), -0.10 (9 H,
Trans-[Ti(g-C5Me5)(l-O){MeC(NiPr)2}]2
(31). 250
mg
(0.64 mmol) Ti(h-C5Me5)(NtBu){MeC(NiPr)2} (4) was dissolved
in ca. 5 mL benzene. The headspace was evacuated, and the
solution was exposed to CO2 at a pressure of 1 atm, resulting in an
immediate colour change from red to cherry red. The solution was
left standing for 72 h, after which time all volatiles were removed
under reduced pressure. The residue was washed with 2 ¥ 5 mL
pentane, to afford 31 as a yellow powder. Yield: 152 mg (70%).
1H NMR data (benzene-d6, 500.0 MHz, 298 K) d: 3.46 (2 H,
apparent sept., J = 6.4 Hz, NCHMeMe), 2.01 (15 H, s, C5Me5),
1.61 (3 H, s, MeCN2), 1.40 (6 H, d, J = 6.4 Hz, NCHMeMe),
1
s, SiMe3). 13C–{ H} NMR data (benzene-d6, 125.7 MHz, 298 K)
d: 180.5 (OC(O)), 159.4 (CN2), 138.0 (i-C6H5), 129.6 (C5Me5),
129.2, 128.7 (o-C6H5), 128.5, 127.7 (m-C6H5), 127.4 (p-C6H5), 57.8
(NCMe3), 31.5 (NCMe3), 13.0 (C5Me5), 5.7 (SiMe3), 2.4 (SiMe3).
IR data (CsBr plates, Nujol mull, cm-1) 2855 (s, br), 2726 (w), 2360
(w), 1854 (w), 1839 (w), 1807 (w), 1787 (w), 1766 (w), 1739 (w),
1726 (w), 1711 (w), 1660 (s), 1592 (m), 1549 (w), 1513 (w), 1250
(m, br), 1157 (w, br), 1065 (w), 1002 (w), 988 (m), 938 (m), 920 (w),
838 (s), 798 (w), 787 (w), 767 (m, br), 721 (s), 675 (m), 596 (w), 514
(m), 465 (m), 404 (w). Anal. found (calcd for C28H47N3O2Si2Ti): C
59.8 (59.9); H 8.5 (8.4), 6.4 (7.5)%.
1.16 (6 H, d, J = 6.4 Hz, NCHMeMe). 13C–{ H} NMR data
1
(benzene-d6, 125.7 MHz, 298 K) d: 170.0 (CN2), 121.9 (C5Me5),
48.7 (NCHMeMe), 26.4 (NCHMeMe), 24.4 (NCHMeMe), 14.2
(C5Me5), 13.2 (MeCN2). IR data (NaCl plates, Nujol mull, cm-1)
2360 (w), 2342 (w), 1652 (w), 1495 (m), 1325 (m), 1306 (m), 1261
(m), 1201 (m), 1172 (w), 1094 (m, br), 1012 (m), 809 (s), 722 (w),
637 (m), 611 (w), 557 (w), 442 (w), 423 (w). Anal. found (calcd for
C36H64N4O2Ti2): C 63.8 (63.5); H 9.3 (9.5); N 8.3 (8.2)%. Mass
spec. (E.I.) m/z 340 [1/2M]+.
Ti(g-C5Me5){N(tBu)C(O)O}{MeC(NiPr)2} (29). 127 mg
(0.32 mmol) Ti(h-C5Me5)(NtBu){MeC(NiPr)2} (4)was dissolved
in ca. 10 mL pentane and cooled to -78 ◦C (CO2–acetone bath).
The headspace was evacuated, and the solution exposed to CO2
at a pressure of 1 atm for 2 min, during which time the solution
was removed from the cold bath. Volatiles were then immediately
removed under reduced pressure to give 29 as a dark red powder.
Yield: 92 mg (65%). 1H NMR data (benzene-d6, 500.0 MHz, 298
K) d: 3.73 (1 H, apparent sept., J = 6.4 Hz, NCHbMeaMeb),
3.47 (1 H, apparent sept., J = 6.4 Hz, NCHaMeaMeb), 1.90
(15 H, s, C5Me5), 1.50 (3 H, s, MeCN2), 1.39 (9 H, s, C5Me5),
1.15 (3 H, d, J = 6.4 Hz, NCHbMeaMeb), 1.13 (3 H, d, J =
6.4 Hz, NCHaMeaMeb), 1.05 (3 H, d, J = 6.4 Hz, NCHbMeaMeb),
Trans- and cis-[Ti(g-C5H4Me)(l-O){PhC(NSiMe3)2}]2 (32
and 32a). 242 mg (0.52 mmol) Ti(h-C5H4Me)(NtBu){PhC-
(NSiMe3)2} (6) was dissolved in ca. 5 mL benzene, the headspace
evacuated, and the solution exposed to CO2 at a pressure of
1 atm for 1 h. Volatiles were then removed under reduced
pressure to afford the product (a mixture of cis and trans
isomers) as a very fine beige powder. Yield: 194 mg (91%).
Full conversion to the trans isomer 32 was effected by disso-
lution in benzene and heating to 80 ◦C for 1 h. Trans-[Ti(h-
1
1
1.04 (3 H, d, J = 6.4 Hz, NCHaMeaMeb). 13C–{ H} NMR
C5H4Me)(m-O){PhC(NSiMe3)2}]2 (32). H NMR data (benzene-
data (benzene-d6, 125.7 MHz, 298 K) d: 172.4 (OC(O)), 158.8
(CN2), 127.7 (C5Me5), 57.5 (NCMe3), 50.2 (NCHaMeaMeb),
48.3 (NCHbMeaMeb), 30.7 (NCMe3), 24.8 (NCHbMeaMeb), 24.5
(NCHbMeaMeb), 23.7 (NCHaMeaMeb), 22.9 (NCHaMeaMeb),
16.7 (MeCN2), 12.5 (C5Me5). IR data (KBr plates, Nujol
mull, cm-1) 2723 (w), 1662 (s), 1646 (s, br), 1589 (m), 1494 (m),
1355 (s), 1313 (w), 1243 (m), 1208 (m), 1174 (w), 1127 (m), 1066
(w), 1024 (w, br), 940 (m), 923 (w), 826 (w), 797 (m), 782 (w), 722
d6, 500.0 MHz, 298 K) d: 7.31 (4 H, m, m-C6H5), 7.04 (6 H, m,
o-, p-C6H5), 6.54 (4 H, virtual t, J = 2.6 Hz, C5H2(b)H2(a)Me),
6.22 (4 H, virtual t, J = 2.6 Hz, C5H2(b)H2(a)Me), 2.35
1
(6 H, s, C5H4Me), 0.12 (36 H, s, SiMe3). 13C–{ H} NMR
data (benzene-d6, 75.5 MHz, 298 K) d: 177.9 (CN2), 140.9 (i-
C6H5CN2), 128.5 (o-C6H5CN2), 126.9 (m-C6H5CN2), 126.5 (p-
C6H5CN2), 114.0 (C2(b)C2(a)CMe), 112.5 (C2(b)C2(a)CMe), 16.1
(C2(b)C2(a)CMe), 2.5 SiMe3. Resonance from C2(b)C2(a)CMe
5976 | Dalton Trans., 2009, 5960–5979
This journal is
The Royal Society of Chemistry 2009
©

1
not observed. Cis-[Ti(h-C5H4Me)(m-O){PhC(NSiMe3)2}]2 (32a)
1H NMR data (benzene-d6, 500.0 MHz, 298 K) d: 7.46 (4 H,
d, J = 7.8 Hz, m-C6H5), 7.04 (6 H, m, o-, p-C6H5), 6.46 (4 H,
virtual t, J = 2.6 Hz, C5H2(b)H2(a)Me), 6.12 (4 H, virtual t, J =
2.6 Hz, C5H2(b)H2(a)Me), 2.30 (6 H, s, C5H4Me), 0.08 (36 H, s,
NCHMeMe). 13C–{ H} NMR data (benzene-d6, 75.5 MHz,
298 K) d: 167.8 (MeCN2), 126.3 (C2(b)C2(a)CMe), 113.1
(C2(b)C2(a)CMe), 111.5 (C2(b)C2(a)CMe), 48.1 (NCHMeMe),
25.0 (NCHMeMe), 23.9 (NCHMeMe), 15.1 (C2(b)C2(a)CMe),
10.0 (MeCN2). IR data on mixture of isomers (KBr plates, Nujol
mull, cm-1) 2726 (w), 1652 (w), 1338 (m), 1310 (m), 1216 (m), 1173
(w), 1037 (w), 847 (w), 793 (m), 679 (w), 590 (w), 445 (w), 421
(w) cm-1. Anal. found (calcd for C28H48N4O2Ti2): C 59.5 (59.2), H
8.4 (8.5), N 9.8 (9.9)%.
1
SiMe3). 13C–{ H} NMR data (benzene-d6, 75.5 MHz, 298 K) d:
177.1 (CN2), 141.4 (i-C6H5CN2), 128.5 (o-C6H5CN2), 126.7 (m-
C6H5CN2), 126.4 (p-C6H5CN2), 113.7 (C2(b)C2(a)CMe), 112.3
(C2(b)C2(a)CMe), 15.3 (C2(b)C2(a)CMe), 2.2 (SiMe3). Resonance
from C2(b)C2(a)CMe not observed. IR data on isomeric mixture
(KBr plates, Nujol mull, cm-1) 2726 (w), 2671 (w), 2094 (w), 1733
(w), 1576 (w), 1500 (m), 1305 (m, br), 1260 (m), 1246 (m), 1175
(w), 1074 (w), 1055 (w), 1038 (w), 1002 (m), 990 (m), 938 (w), 918
(w), 890 (w), 840 (s), 795 (m), 784 (w), 760 (m), 740 (w), 723 (s), 700
(w), 677 (m), 634 (w), 616 (w), 591 (m, br), 503 (s), 433 (w). Anal.
found (calcd for C38H60N4O2Si4Ti2): C 56.0 (56.1), H 7.3 (7.4), N
6.7 (6.9). Anal. found (calcd for C38H60N4O2Si4Ti2): C 56.0 (56.1),
H 7.3 (7.4), N 6.7 (6.9)%.
Reaction of Ti(g-C5Me5){N(Tol)C(O)O}{MeC(NiPr)2} (22)
with Ti(Me4taa)(O) (36). A solution of 22 in CD2Cl2 (0.6 ml)
was prepared in situ in an NMR tube equipped with a
J. Young Teflon valve from 8 (8.4 mg, 2.0 ¥ 10-5 mol) and CO2
(1 atm). To this was added. Ti(Me4taa)(O) (36, 3.0 equiv, 23.7 mg,
6.0 ¥ 10-5 mol). The H NMR spectrum recorded after 30 min
1
contained no resonances for 22 but new resonances attributed to
the previously reported Ti(Me4taa){N(Tol)C(O)O} (37) and trans-
[Ti(h-C5Me5)(m-O){MeC(NiPr)2}]2 (31).
NMR tube scale synthesis of Ti(g-C5H4Me){N(tBu)-
C(O)O}{PhC(NSiMe3)2} (33). 55.9 mg (0.12 mmol) Ti(h-
C5H4Me)(NtBu){PhC(NSiMe3)2} (5) was dissolved in 0.6 mL
benzene-d6, and freeze-pump-thawed three times. The solution
was then exposed to CO2 at a pressure of ca. 0.5 atm, resulting in
an immediate colour change to cherry red. The product 33 formed
Crystal structure determinations of Ti(g-C5Me5)(N-2,6-
C6H3Me2){PhC(NSiMe3)2}(14), Ti(g-C5H4Me){OC(O)N(-2,6-
C6H3Me2)C(O)O}{PhC(NSiMe3)2} (21) and trans-[Ti(g-
C5H4Me)(l-O){PhC(NSiMe3)2}]2 (32). Crystal data collection
and processing parameters are given in Table 6. Crystals were
mounted on a glass fibre using perfluoropolyether oil and cooled
rapidly to 150 or 175 K in a stream of cold N2. Diffraction
data were measured using either an Enraf-Nonius DIP2000 or
KappaCCD diffractometer. Intensity data were processed using
the DENZO package.97 The structures were solved with SIR9298
and subsequent full-matrix least-squares refinements were carried
out using CRYSTALS.99 Coordinates and anisotropic thermal
parameters of all non-hydrogen atoms were refined. Hydrogen
atoms were placed in calculated positions. Further details of the
structure solution and refinements are given in the Supporting
Information (CIF data). A full listing of atomic coordinates,
bond lengths and angles and displacement parameters for all the
structures have been deposited at the Cambridge Crystallographic
Data Centre. Details of the X-ray structures of 19 and 31 have
been reported previously.70
1
1
quantitatively and characterized by H NMR spectroscopy. H
NMR data (benzene-d6, 500.0 MHz, 298 K) d: 6.95 (1 H, d,
J = 7.3 Hz, CH(b1)CH(b2)C2H2(a)CMe), 6.92 (3 H, m, o-,
p-C6H5), 6.80 (1 H, d, J = 7.3 Hz, CH(b1)CH(b2)C2H2(a)CMe),
6.29 2 H, dd, J = 2.7 Hz, m-C6H5), 6.15 (1 H, d, J =
2.4 Hz, C2H2(b)CH(a1)CH(a2)CMe), 6.01 (1 H, d, J = 2.4 Hz,
C2H2(b)CH(a1)CH(a2)CMe), 2.19 (3 H, s, C5H4Me), 1.42 (9 H,
s, NtBu), -0.04 (9 H, s, SiMe3), -0.08 (9 H, s, SiMe3).
Trans- and cis-[Ti(g-C5H4Me)(l-O){MeC(NiPr)2}]2 (34 & 34a).
250 mg (0.74 mmol) [Ti(h-C5H4Me)(NtBu){MeC(NiPr)2} (6) was
dissolved in 25 mL benzene, the headspace evacuated, and the
solution exposed to CO2 at 1 atm. Immediate colour change
of the solution from red to cherry red occurred, followed
by a further colour change to brown over ca. 2 min. After
16 h, all volatiles were removed under reduced pressure, and
the residue triturated with ca. 10 mL pentane. The product
(a mixture of cis and trans isomers) was afforded as a light
brown solid. Yield: 121 mg (58%). Trans-[Ti(h-C5H4Me)(m-
O){MeC(NiPr)2}]2 (34). 1H NMR data (benzene-d6, 500.0 MHz,
298 K) d: 6.33 (4 H, virtual t, J = 2.7 Hz, C5H2(b)H2(a)Me),
6.09 (4 H, virtual t, J = 2.7 Hz, C5H2(b)H2(a)Me), 3.47
(4 H, virtual sept, J = 6.4 Hz, NCHMeMe), 2.18 (6 H,
s, C5H2(b)H2(a)Me), 1.52 (6 H, s, MeCN2), 1.27 (12 H, d,
J = 6.4 Hz, NCHMeMe), 1.13 (12 H, d, J = 6.4 Hz,
Computational details
All calculations were performed with the Gaussian 03 set of
programs100 within the framework of hybrid DFT (B3PW91).101,102
The titanium atom was represented by the relativistic effective core
potential (RECP) from the Stuttgart group (12 valence electrons)
and its associated basis set,103 augmented by an f polarization
function (a = 0.869).104 The remaining atoms (C, H, N, O) were
represented by a 6-31G(d,p) basis set.105 Full optimizations of
geometry without any constraint were performed, followed by
analytical computation of the Hessian matrix to confirm the nature
of the located extrema as minima or transition states. The nature
of the reactants and products connected by a given transition
state was checked by optimization of a slightly distorted geometry
of the TS along both directions of the transition state vector.
Calculations of TOF values were performed on the gas phase
Gibbs free energies at room temperature (298.15 K).
1
NCHMeMe). 13C–{ H} NMR data (benzene-d6, 75.5 MHz,
298 K) d: 167.9 (MeCN2), 126.2 (C2(b)C2(a)CMe), 112.7
(C2(b)C2(a)CMe), 112.1 (C2(b)C2(a)CMe), 48.4 (NCHMeMe),
25.2 (NCHMeMe), 24.9 (NCHMeMe), 15.8 (C2(b)C2(a)CMe),
10.5 (MeCN2). Cis-[Ti(h-C5H4Me)(m-O){MeC(NiPr)2}]2 (34a). 1H
NMR data (benzene-d6, 500.0 MHz, 298 K) d: 6.44 (4 H, virtual
t, J = 2.7 Hz, 2.4 Hz, C5H2(b)H2(a)Me), 6.08 (4 H, virtual t,
J = 2.7 Hz, 2.4 Hz, C5H2(b)H2(a)Me), 3.36 (4 H, virtual sept, J =
6.4 Hz, NCHMeMe), 2.15 (6 H, s, C5H4Me), 1.45 (6 H, s, MeCN2),
1.17 (12 H, d, J = 6.3 Hz, NCHMeMe), 1.13 (12 H, d, J = 6.3 Hz,
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5960–5979 | 5977
©

Table 6 X-Ray data collection and processing parameters for Ti(h-C5Me5)(N-2,6-C6H3Me2){PhC(NSiMe3)2}(14), Ti(h-C5H4Me){OC(O)N(-2,6-
C6H3Me2)C(O)O}{PhC(NSiMe3)2} (21), and trans-[Ti(h-C5H4Me)(m-O){PhC(NSiMe3)2}]2 (32)
Compound
14
21
32
Empirical formula
FW/g mol-1
T/K
C31H47N3Si2Ti
565.81
150
0.71073
P21/n
11.672(5)
15.361(2)
18.018(7)
90
100.92(4)
90
3172(1)
18 449
88
C29H39N3O4Si2Ti
597.72
150
0.71073
P21/n
10.7126(2)
17.2231(4)
16.6483(4)
90
90.704
90
C50H72N4O2Si4Ti2
969.30
150
0.71073
¯
P1
10.1320(4)
10.4210(7)
15.3100(11)
92.248(4)
104.045(5)
118.207(4)
1359.4(2)
22 600
˚
l/A
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
3071.5
11 752
99
Reflections measured
Data completeness (%)
89
Unique reflections
Rint
6934
0.04
4
1.18
7025
0.05
4
1.29
5134
0.02
1
1.184
0.421
R1 = 0.0694
Rw = 0.0432
1.03
Z
D
calcd/Mg m-3
m/mm-1
0.37
0.39
R indices R1, Rw [I > 3s(I)]a
R1 = 0.0401
Rw = 0.0489
1.06
R1 = 0.0396
Rw = 0.0478
0.98
GOF
√
ꢀ
a R1 ꢀFo| - |Fcꢀ/R|Fo|; Rw
=
{Rw(|Fo| - |Fc|)2/R(w|Fo|2}.
15 A. J. Nielson, M. W. Glenny and C. E. F. Rickard, J. Chem. Soc.,
Dalton Trans., 2001, 232.
Acknowledgements
16 N. Adams, H. J. Arts, P. D. Bolton, D. Cowell, S. R. Dubberley,
N. Friedrichs, C. M. Grant, M. Kranenburg, A. J. Sealey, B. Wang,
P. J. Wilson, A. R. Cowley, P. Mountford and M. Schroder, Chem.
Commun., 2004, 434.
17 P. D. Bolton and P. Mountford, Adv. Synth. Catal., 2005, 355.
18 N. Adams, H. J. Arts, P. D. Bolton, D. Cowell, S. R. Dubberley, N.
Friederichs, C. M. Grant, M. Kranenburg, A. J. Sealey, B. Wang, P. J.
Wilson, M. A. Zuideveld, A. J. Blake, M. Schro¨der and P. Mountford,
Organometallics, 2006, 25, 3888.
We thank the EPSRC and the CNRS for support, Dr N H Rees
for assistance with the VT NMR analysis and Dr A R Cowley
for help with the crystallography. E C and P M thank the Royal
Society of Chemistry for International Authors Travelling Grants
and the British Council for support. We acknowledge the use of the
EPSRC National Service for Computational Chemistry Software
and the UK Computational Chemistry Facility.
19 H. R. Bigmore, S. R. Dubberley, M. Kranenburg, S. C. Lawrence, A. J.
Sealey, J. D. Selby, M. Zuideveld, A. R. Cowley and P. Mountford,
Chem. Commun., 2006, 436.
20 C. T. Owen, P. D. Bolton, A. R. Cowley and P. Mountford,
Organometallics, 2007, 26, 83.
21 G. J. Hayday, C. Wang, N. H. Rees and P. Mountford, Dalton Trans.,
2008, 3301.
22 C. J. Carmalt, A. Newport, I. P. Parkin, A. J. Sealey and S. R.
Dubberley, J. Mater. Chem., 2003, 13, 84.
References
1 J. E. Hill, R. D. Profilet, P. E. Fanwick and I. P. Rothwell, Angew.
Chem., Int. Ed. Engl., 1990, 29, 664.
2 H. W. Roesky, H. Velker, M. Witt and M. Noltemeyer, Angew. Chem.,
Int. Ed. Engl., 1990, 29, 669.
3 C. C. Cummins, C. P. Schaller, G. D. Van Duyne, P. T. Wolczanski,
A. W. E. Chan and R. Hoffmann, J. Am. Chem. Soc., 1991, 113, 2985.
4 P. L. McGrane, M. Jensen and T. Livinghouse, J. Am. Chem. Soc.,
1992, 114, 5459.
23 C. J. Carmalt, S. R. Whaley, P. S. Lall, A. H. Cowley, R. A. Jones,
B. G. McBurnett and J. G. Ekdert, J. Chem. Soc., Dalton Trans., 1998,
553.
5 N. Adams, A. R. Cowley, S. R. Dubberley, A. J. Sealey, M. E. G.
Skinner and P. Mountford, Chem. Commun., 2001, 2738.
6 N. Adams, H. R. Bigmore, T. L. Blundell, C. L. Boyd, S. R. Dubberley,
A. J. Sealey, A. R. Cowley, M. E. G. Skinner and P. Mountford, Inorg.
Chem., 2005, 44, 2882.
24 T. S. Lewkebandara, P. H. Sheridan, M. J. Heeg, A. L. Rheingold and
C. H. Winter, Inorg. Chem., 1994, 33, 5879.
25 C. H. Winter, P. H. Sheridan, T. S. Lewkebandara, M. J. Heeg and
J. W. Proscia, J. Am. Chem. Soc., 1992, 114, 1095.
26 P. J. McKarns, G. P. A. Yap, A. L. Rheingold and C. H. Winter, Inorg.
Chem., 1999, 35, 5968.
7 T. R. Cundari, Chem. Rev., 2000, 100, 807.
8 A. J. Blake, A. R. Cowley, S. C. Dunn, J. C. Green, N. Hazari, N. M.
Jones, A. G. Moody and P. Mountford, Chem.–Eur. J., 2005, 2111.
9 N. Kaltsoyannis and P. Mountford, J. Chem. Soc., Dalton Trans., 1999,
781.
10 P. E. Collier, S. C. Dunn, P. Mountford, O. V. Shishkin and D. Swallow,
J. Chem. Soc., Dalton Trans., 1995, 3743.
11 T. E. Hanna, I. Keresztes, E. Lobkovsky, W. H. Bernskoetter and P. J.
Chirik, Organometallics, 2004, 23, 3448.
12 P. D. Bolton, E. Clot, A. R. Cowley and P. Mountford, Chem.
Commun., 2005, 3313.
13 P. D. Bolton, E. Clot, A. R. Cowley and P. Mountford, J. Am. Chem.
Soc., 2006, 128, 15005.
14 N. A. H. Male, M. E. G. Skinner, S. Y. Bylikin, P. J. Wilson, P.
Mountford and M. Schroder, Inorg. Chem., 2000, 39, 5483.
27 C. J. Carmalt, A. Newport, I. P. Parkin, A. J. P. White and D. J.
Williams, J. Chem. Soc., Dalton Trans., 2002, 4055.
28 D. E. Wigley, Prog. Inorg. Chem., 1994, 42, 239.
29 P. Mountford, Chem. Commun., 1997, 2127 (feature article review).
30 L. H. Gade and P. Mountford, Coord. Chem. Rev., 2001, 216–217, 65.
31 N. Hazari and P. Mountford, Acc. Chem. Res., 2005, 38, 839.
32 A. R. Fout, U. J. Kilgore and D. J. Mindiola, Chem.–Eur. J., 2007, 13,
9428.
33 J. L. Bennett and P. T. Wolczanski, J. Am. Chem. Soc., 1994, 116, 2179.
34 A. Bashall, P. E. Collier, L. H. Gade, M. McPartlin, P. Mountford and
D. J. M. Trosch, Chem. Commun., 1998, 2555.
35 Y. Li, Y. Shi and A. L. Odom, J. Am. Chem. Soc., 2004, 126, 1794.
36 E. Haak, I. Bytsschkov and S. Doye, Angew. Chem., Int. Ed., 1999,
38, 3389.
5978 | Dalton Trans., 2009, 5960–5979
This journal is
The Royal Society of Chemistry 2009
©

37 B. D. Ward, A. Maisse-Francois, P. Mountford and L. H. Gade, Chem.
Commun., 2004, 704.
38 N. Vujkovic, B. D. Ward, A. Maisse-Francois, H. Wadepohl, P.
Mountford and L. H. Gade, Organometallics, 2007, 26, 5522.
39 N. Vujkovic, J. L. Fillol, B. D. Ward, H. Wadepohl, P. Mountford and
L. H. Gade, Organometallics, 2008, 27, 2518.
40 S. M. Pugh, D. J. M. Trosch, D. J. Wilson, A. Bashall, F. G. N.
Cloke, L. H. Gade, P. B. Hitchcock, M. McPartlin, J. F. Nixon and P.
Mountford, Organometallics, 2000, 19, 3205.
41 A. J. Blake, P. E. Collier, L. H. Gade, M. McPartlin, P. Mountford,
M. Schubart and I. J. Scowen, Chem. Commun., 1997, 1555.
42 A. Bashall, P. E. Collier, L. H. Gade, M. McPartlin, P. Mountford,
S. M. Pugh, S. Radojevic, M. Schubart, I. J. Scowen and D. J. M.
Trosch, Organometallics, 2000, 19, 4784.
74 R. Gomez, R. Duchateau, A. N. Chernega, A. Meetsma, F. T.
Edelmann, J. H. Teuben and M. L. H. Green, J. Chem. Soc., Dalton
Trans., 1995, 217.
75 J. R. Babcock, C. Incarvito, A. L. Rheingold, J. C. Fettinger and L.
Sita, Organometallics, 1999, 18, 5729.
76 L. A. Koterwas, J. C. Fettinger and L. Sita, Organometallics, 1999, 18,
4183.
77 W. J. van Meerendonk, K. Schroder, E. A. C. Brussee, A. Meetsma,
B. Hessen and J. H. Teuben, Eur. J. Inorg. Chem., 2003, 427.
78 M. Sotoodeh, I. Leichtweis, H. W. Roesky, M. Noltemeyer and H.-G.
Schmidt, Chem. Ber., 1993, 126, 913.
79 P. H. M. Budzelaar, gNMR for Windows v4.1, Cherwell Scientific Ltd.,
Oxford, 1999.
80 J. Sandstrom, Dynamic NMR Spectroscopy, Academic Press, London,
43 F. G. N. Cloke, P. B. Hitchcock, J. F. Nixon, D. J. Wilson and P.
Mountford, Chem. Commun., 1999, 661.
44 F. G. N. Cloke, P. B. Hitchcock, J. F. Nixon, D. J. Wilson, F. Tabellion,
U. Fischbeck, F. Preuss, M. Regitz and L. Nyulaszi, Chem. Commun.,
1999, 2363.
1982.
81 R. B. Jordan, Reaction Mechanisms of Inorganic and Organometallic
Systems, Oxford University Press, Oxford, 1998.
82 A. W. Holland and R. G. Bergman, J. Am. Chem. Soc., 2002, 124,
9010.
45 S. M. F. Asmus and M. Regitz, Tetrahedron Lett., 2001, 42, 7543.
46 F. G. N. Cloke, J. C. Green, N. Hazari, P. B. Hitchcock, P. Mountford,
J. F. Nixon and D. J. Wilson, Organometallics, 2006, 25, 3688.
47 A. J. Blake, J. M. McInnes, P. Mountford, G. I. Nikonov, D. Swallow
and D. J. Watkin, J. Chem. Soc., Dalton Trans., 1999, 379.
48 S. R. Dubberley, A. Friedrich, D. A. Willman, P. Mountford and U.
Radius, Chem.–Eur. J., 2003, 9, 3634.
49 T.-G. Ong, G. P. Yap and D. S. Richeson, Chem. Commun., 2003, 2612.
50 T. E. Hanna, I. Keresztes, E. Lobkovsky, W. H. Bernskoetter and P. J.
Chirik, Organometallics, 2004, 23, 3448.
51 S.-H. Hsu, C. Chang, C.-L. Lai, C.-H. Hu, H. M. Lee, G.-H. Lee,
S.-M. Peng and J.-H. Huang, Inorg. Chem., 2004, 43, 6786.
52 H. Wang, H. Chan and Z. Xie, Organometallics, 2005, 24, 3772.
53 C. L. Boyd, E. Clot, A. E. Guiducci and P. Mountford,
Organometallics, 2005, 24, 2347.
54 C. L. Boyd, T. Toupance, B. R. Tyrrell, B. D. Ward, C. R. Wilson,
A. R. Cowley and P. Mountford, Organometallics, 2005, 24, 309.
55 S. C. Dunn, N. Hazari, A. R. Cowley, J. C. Green and P. Mountford,
Organometallics, 2006, 25, 1755.
83 R. L. Zuckerman and R. G. Bergman, Organometallics, 2001, 20,
1792.
84 D. J. Darensbourg, B. J. Frost and D. L. Larkins, Inorg. Chem., 2001.
85 W. D. Mcghee, D. P. Riley, M. E. Christ and K. M. Christ,
Organometallics, 1993, 40, 1993.
86 J. Fournier, C. Bruneau, P. H. Dixneuf and S. Lecolier, J. Org. Chem.,
1991, 56, 4456.
87 W. D. Mcghee and D. P. Riley, Organometallics, 1992, 11, 900.
88 M. H. Chisolm and M. W. Extine, J. Am. Chem. Soc., 1977, 99,
782.
89 M. H. Chisolm and M. W. Extine, J. Am. Chem. Soc., 1977, 99,
792.
90 J. F. Hartwig, R. G. Bergman and R. A. Andersen, J. Am. Chem. Soc.,
1991, 113, 6499.
91 S. Park, A. L. Rheingold and D. M. Roundhill, Organometallics, 1991,
10, 615.
92 P. Legzdins, S. J. Rettig and K. J. Ross, Organometallics, 1994, 13, 569.
93 M. H. Chisolm, F. A. Cotton, M. W. Extine and W. W. Reichert, J. Am.
Chem. Soc., 1978, 100, 1727.
56 A. E. Guiducci, C. L. Boyd and P. Mountford, Organometallics, 2006,
26, 1167.
57 A. J. Blake, P. E. Collier, L. H. Gade, P. Mountford, J. Lloyd, S. M.
Pugh, M. Schubart, M. E. G. Skinner and D. J. M. Trosch, Inorg.
Chem., 2001, 40, 870.
94 S. Kozuch and S. Shaik, J. Am. Chem. Soc., 2006, 128, 3355.
95 S. Kozuch and S. Shaik, J. Phys. Chem. A, 2008, 112, 6032.
96 R. T. Boere, R. T. Oakley and R. W. Reed, J. Organomet. Chem., 1987,
331, 161.
97 Z. Otwinowski and W. Minor, Processing of X-Ray Diffraction Data
Collected in Oscillation Mode, Academic press, New York, 1997.
98 A. Altomare, G. Cascarano, J. R. Carrithers, P. W. Betteridge and R. I.
Cooper, J. Appl. Crystallogr., 1994, 27, 435.
58 P. J. Stewart, A. J. Blake and P. Mountford, Organometallics, 1998, 17,
3271.
59 P. J. Stewart, A. J. Blake and P. Mountford, J. Organomet. Chem.,
1998, 564, 209.
99 D. J. Watkin, C. K. Prout, J. R. Carruthers, P. W. Betteridge and R. I.
Cooper, CRYSTALS, Chemical Crystallography Laboratory, Oxford,
UK, 2001.
60 D. J. Darensbourg and R. A. Kudaroski, Adv. Inorg. Chem., 1983, 22,
129.
61 D. A. Palmer and R. van Eldik, Chem. Rev., 1983, 83, 651.
62 H. Arakawa, M. Aresta, J. M. Armor, M. A. Barteau, E. J. Beckman,
E. T. Bell, J. E. Bercaw, C. Creutz, E. Dinjus, D. A. Dixon, K. Domen,
D. L. DuBois, J. Eckert, E. Fujita, G. H. Gibson, W. A. Goddard,
D. W. Goodman, J. Keller, G. J. Kubas, H. H. Kung, J. E. Lyons, L. E.
Manzer, T. J. Marks, K. Morokuma, K. M. Nicholas, R. Periana, L.
Que, J. Rostrup-Nielson, W. M. H. Sachtler, L. D. Schmidt, A. Sen,
G. A. Somorjai, P. C. Stair, B. R. Stults and W. Tumas, Chem. Rev.,
2001, 101, 953.
63 M. Torrent, M. Sola and G. Frenking, Chem. Rev., 2000, 100, 439.
64 W. Leitner, Coord. Chem. Rev., 1996, 153, 257.
65 X. Yin and J. R. Moss, Coord. Chem. Rev., 1999, 181, 27.
66 D. Gibson, Chem. Rev., 1996, 96, 2063.
67 R. E. Blake, D. M. Antonelli, L. M. Henling, W. P. Schaefer, K. I.
Hardcastle and J. E. Bercaw, Organometallics, 1998, 17, 718.
68 D. S. Glueck, J. Wu, F. J. Hollander and R. G. Bergman, J. Am. Chem.
Soc., 1991, 113, 2041.
69 B. D. Ward, G. Orde, E. Clot, A. H. Cowley, L. H. Gade and P.
Mountford, Organometallics, 2005, 24, 2368.
100 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N.
Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone,
B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene,
X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. Ochterski, P. Y. Ayala, K. Morokuma, G. A.
Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-
Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W.
Gill, B. G. Johnson, W. Chen, M. W. Wong, C. Gonzalez and J. A.
Pople, GAUSSIAN 03 (Revision C.02), Gaussian, Inc., Wallingford,
CT, 2004.
101 A. D. Becke, J. Chem. Phys., 1992, 98, 5648.
70 A. E. Guiducci, A. R. Cowley, M. E. G. Skinner and P. Mountford,
J. Chem. Soc., Dalton Trans., 2001, 1392.
71 A. E. Guiducci, D. Phil, Thesis, University of Oxford, 2002.
72 F. H. Allen and O. Kennard, Chem. Des. Automat. News, 1993, 8, 1
and 31.
102 J. P. Perdew and Y. Wang, Phys. Rev. B, 1992, 45, 13244.
103 D. Andrae, U. Haussermann, M. Dolg, H. Stoll and H. Preuss, Theor.
Chim. Acta, 1990, 77, 123.
104 A. W. Ehlers, M. Bohme, S. Dapprich, A. Gobbi, A. Hollwarth, V.
Jonas, K. F. Kohler, R. Stegmann, A. Veldkamp and G. Frenking,
Chem. Phys. Lett., 1993, 208, 111.
73 D. A. Fletcher, R. F. McMeeking and D. J. Parkin, J. Chem. Inf.
Comput. Sci., 1996, 36, 746.
105 P. C. Hariharan and J. A. Pople, Theor. Chim. Acta, 1973, 28, 213.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5960–5979 | 5979
©