Imido-alkyne coupling in titanium complexes: New insights into the alkyne hydroamination reaction

Article abstract of DOI:10.1021/om700758v

Titanium imido complexes [Ti(NR)(N₂^ArN _py)(L)] (N₂^ArN_py = MeC(2-C ₅H₄N)(CH₂NAr)₂, Ar = 4-C ₆H₄-Me or 3,5-C₆H₃Me₂) have been prepared from the corresponding bis(amide) complexes [Ti(N ₂^ArN_py)-(NMe₂)₂]. The reaction chemistry of the imido ligand has been investigated with aryl acetylenes, affording the {2 + 2} cycloaddition products [Ti(N₂ ^ArN_py){κ²-N(^tBu)CH=CAr′} ] (Ar′ = Ph and 4-C₆H₄Me) which represent a catalytic intermediate in the anti-Markovnikov hydroamination of terminal alkynes. Reaction of these azatitanacyclobutene complexes with tert-butylamine completes the catalytic cycle, affording trans-cinnamyl(tert-butyl)amine; conversely, reaction with a second equivalent of alkyne afforded a second insertion product, an azatitanacyclohexadiene [Ti(N₂ ^ArN_py){κ²-N(^tBu)CH= C(Ar′)C(Ar′) = CH}], two examples of which have been characterized by X-ray crystallography. Studies into the catalytic hydroamination of phenyl acetylene with tert-butylamine have been performed and indicate that the formation of an azatitanacyclohexadiene complex represents a deactivation pathway in this catalytic reaction.

Full text of DOI:10.1021/om700758v

5522
Organometallics 2007, 26, 5522-5534
Imido-Alkyne Coupling in Titanium Complexes: New Insights into
the Alkyne Hydroamination Reaction
Nadia Vujkovic,# Benjamin D. Ward,# Aline Maisse-Franc¸ois,† Hubert Wadepohl,#
Philip Mountford,*,‡ and Lutz H. Gade*,#
Anorganisch-Chemisches Institut, UniVersita¨t Heidelberg, Im Neuenheimer Feld 270,
69120 Heidelberg, Germany, Institut de Chimie, UniVersite´ Louis Pasteur, Institut le Bel, 4 rue Blaise
Pascal, 67000 Strasbourg, France, and Chemical Research Laboratory, UniVersity of Oxford,
Mansfield Road, Oxford, OX1 3TA, U.K.
ReceiVed July 26, 2007
Ar
Ar
Titanium imido complexes [Ti(NR)(N2 Npy)(L)] (N2
N ) MeC(2-C5H4N)(CH2NAr)2, Ar ) 4-C6H4-
py
Ar
Me or 3,5-C6H3Me2) have been prepared from the corresponding bis(amide) complexes [Ti(N2 Npy)-
(NMe2)2]. The reaction chemistry of the imido ligand has been investigated with aryl acetylenes, affording
Ar
the {2 + 2} cycloaddition products [Ti(N2 Npy){κ2-N(tBu)CHdCAr′}] (Ar′ ) Ph and 4-C6H4Me) which
represent a catalytic intermediate in the anti-Markovnikov hydroamination of terminal alkynes. Reaction
of these azatitanacyclobutene complexes with tert-butylamine completes the catalytic cycle, affording
trans-cinnamyl(tert-butyl)amine; conversely, reaction with a second equivalent of alkyne afforded a second
Ar
insertion product, an azatitanacyclohexadiene [Ti(N2 Npy){κ2-N(tBu)CHdC(Ar′)C(Ar′) ) CH}], two
examples of which have been characterized by X-ray crystallography. Studies into the catalytic
hydroamination of phenyl acetylene with tert-butylamine have been performed and indicate that the
formation of an azatitanacyclohexadiene complex represents a deactivation pathway in this catalytic
reaction.
reported, a generally applicable catalytic system has thus far
remained elusive. Pioneering work by Bergman22,38 and Liv-
inghouse39 established the propensity of zirconocene complexes
Introduction
The catalytic hydroamination of carbon-carbon multiple
bonds has emerged as a powerful synthetic strategy in the
preparation of a wide variety of building blocks in synthetic
organic chemistry, both in an academic and industrial context.1-9
The anti-Markovnikov hydroamination of terminal alkynes in
particular is deemed to be useful, since this is used to form
aldimines, which find application as intermediates for further
chemical transformations. Despite considerable research efforts
in this field10-37 and a number of successful systems being
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* To whom correspondence should be addressed. E-mail: lutz.gade@
uni-heidelberg.de. Fax: +49-6221-545609. E-mail: philip.mountford@
chem.ox.ac.uk.
# Universita¨t Heidelberg.
† Universite´ Louis Pasteur.
‡ University of Oxford.
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10.1021/om700758v CCC: $37.00 © 2007 American Chemical Society
Publication on Web 10/12/2007

Imido-Alkyne Coupling in Titanium Complexes
Organometallics, Vol. 26, No. 23, 2007 5523
Ar
Scheme 1. Synthesis of [Ti(N2 Npy)(NMe2)2] 2a and 2b
to act as hydroamination catalysts, and subsequent work
naturally turned to titanium-based systems which has led to the
development of a number of promising systems in recent
years.2,3,6
However there remain unanswered questions regarding the
mechanism of hydroamination catalysis as well as the catalyst
degradation pathways.40-43 Such understanding is necessary for
the development of catalytic systems with greater scope and
substrate tolerance. It is in this context that we turned our
attention to the preparation and characterization of catalytic
intermediates for the hydroamination of aryl alkynes with tert-
butylamine. We recently reported the preparation and crystal-
lographic characterization of an azatitanacyclobutene com-
plex44 supported by the diamido-pyridine ligand MeC(2-
between the steric demand of tolyl and mesityl groups. The
synthesis was achieved using an analogous method to that
reported for the aforementioned derivatives and 1 was employed
in parallel to the tolyl ligand in the subsequent titanium
chemistry.
C5H4N)(CH2NSiMe3)22- (N2 Npy).45 This complex represents
TMS
a proposed intermediate in the catalytic anti-Markovnikov
hydroamination of terminal alkynes. In addition, the titanacy-
clobutene was shown to undergo several catalytic cycles when
reacted with 5 molar equiv of tert-butylamine and phenylacety-
lene. However, the complex was observed to undergo significant
degradation, mainly via desilylation of the diamido-pyridine
ligand. In general, the structural platform based on the diami-
dopyridyl ligand has been found to be particularly apt for the
stabilization (and isolation) of reaction intermediates in a range
of complex Ti-based transformations.44 We have therefore
TMS
Titanium imido complexes of the form [Ti(NR)(N2 Npy)-
(py)] (as well as related N-silylated derivatives) are readily
synthesized by the reaction of the easily prepared imido
precursor [Ti(NR)Cl2(py)3] with the lithium amide Li2N2TMSNpy.48
However, in the case of the arylated ligand congeners, we were
unable to prepare the corresponding lithium amides. Indeed, in
reports involving arylated polyamide ligands, the lithium amides
are conspicuous by their absence, the chemistry normally being
accessed Via the protonolysis of a metal-alkyl or -amide
precursor.46,47,49 Studies carried out in one of our laboratories
have indicated that this is due to complex undesired side
reactions involving metalation of the aryl groups and rearrange-
ment of the ligand backbone, thus rendering the lithium amides
inaccessible.50
embarked on studies using the more robust arylated ligands
Tol
MeC(2-C5H4N)(CH2NAr)22- (Ar ) 4-C6H4Me, N2
N or 3,5-
py
Xyl
C6H3Me2, N2 Npy) with the aim of improving the stability of
the system under catalytic conditions while retaining its features
in regard to the isolation of intermediates or catalyst degradation
products.
Ar
In light of the inaccessibility of the lithium amides Li2N2 Npy,
we chose an alternative route into the coordination chemistry
with titanium via the protonolysis of Ti(NMe2)4 with the protio
Ar
Results and Discussion
ligands H2N2 Npy. Forcing conditions were required to effect
a successful conversion, the reaction occurring only when carried
out in a melt, rather than in solution. This method afforded the
Synthesis and Structural Characterization of the [Ti-
Ar
(N2 Npy) (NMe2)2] Precursors. Arylated diamido-pyridine
Ar
corresponding titanium complexes [Ti(N2 Npy)(NMe2)2] (Ar )
Ar
protio ligand precursors H2N2
N
py
were prepared from the
Tol 2a or Xyl 2b) in good yield (Scheme 1). No reaction was
diamine MeC(2-C5H4N)(CH2NH2)2 and the appropriate aryl
bromide in a palladium-catalyzed Buchwald-Hartwig coupling
reaction. The p-tolyl46 and mesityl47 derivatives have been
previously reported by us and by Schrock et al., respectively.
Since these two aryl groups represent two extremes in terms of
steric demand, and since we found that the mesityl ligand was
too bulky for titanium (vide infra), we prepared the 3,5-
dimethylphenyl derivative MeC(2-C5H4N){CH2NH(3,5-C6H3-
Mes
observed between Ti(NMe2)4 and the mesityl ligand H2N2 Npy,
presumably owing to the excessive steric demands imposed by
the ortho methyl groups on the aromatic rings.
The NMR data for complexes 2a and 2b indicate molecular
Cs symmetry, consistent with the structure provided in
Scheme 1. The presence of two independent NMe2 resonances
is likewise fully in accordance with this coordination geometry.
Moreover, the details of the molecular structures were confirmed
by means of X-ray diffraction studies. The molecular structure
of 2b is depicted in Figure 1, and a comparative listing of
selected bond lengths and angles for 2a and 2b is provided in
Table 1.
Xyl
Me2)}2 (H2N2 Npy, 1), the methyl groups in the meta position
generating a substituent “bulkiness” which is intermediate
(39) McGrane, P. L.; Jensen, M.; Livinghouse, T. J. Am. Chem. Soc.
1992, 114, 5459.
The molecular structures of both 2a and 2b exhibit distorted
trigonal bipyramidal geometries at titanium. The sum of angles
subtended at the metal in the equatorial plane is 356.9(9)° and
(40) Motta, A.; Lanza, G.; Fragala`, I. L. Organometallics 2004, 23, 4097.
(41) Straub, B. F.; Bergman, R. G. Angew. Chem., Int. Ed. 2001, 40,
4632.
(42) Pohlki, F.; Doye, S. Angew. Chem., Int. Ed. 2001, 40, 2305.
(43) Straub, T.; Haskel, A.; Neyroud, T. G.; Kapon, M.; Botoshansky,
M.; Eisen, M. R. Organometallics 2001, 20, 5017.
(44) (a) Ward, B. D.; Maisse-Franc¸ois, A.; Mountford, P.; Gade, L. H.
Chem. Commun. 2004, 704. For a review of imido complexes containing
this type of ligand system, see: (b) Gade, L. H.; Mountford, P. Coord.
Chem. ReV. 2001, 216/217, 65. (c) For a recent review of titanium imido
chemistry in general see: Hazari, N.; Mountford, P. Acc. Chem. Res. 2005,
38, 839.
(45) (a) Friedrich, S.; Schubart, M.; Gade, L. H.; Scowen, I. J.; Edwards,
A. J.; McPartlin, M. Chem. Ber./Recl. 1997, 130, 1751. Review: (b) Gade,
L. H. Chem. Commun. 2000, 173.
(48) (a) Blake, A. J.; Collier, P. E.; Dunn, S. C.; Li, W.-S.; Mountford,
P.; Shishkin, O. V. J. Chem. Soc., Dalton Trans. 1997, 1549. (b) Blake, A.
J.; Collier, P. E.; Gade, L. H.; Mountford, P.; Pugh, S. M.; Schubart, M.;
Skinner, M. E. G.; Tro¨sch, D. J. M. Inorg. Chem. 2001, 40, 870. (c) Pugh,
S. M.; Tro¨sch, D. J. M.; Wilson, D. J.; Bashall, A.; Cloke, F. G. N.; Gade,
L. H.; Hitchcock, P. B.; McPartlin, M.; Nixon, J. F.; Mountford, P.
Organometallics 2000, 19, 3205. (d) Ward, B. D.; Orde, G.; Clot, E.;
Cowley, A. R.; Gade, L. H.; Mountford, P. Organometallics 2004, 23, 4444.
(e) Ward, B. D.; Orde, G.; Clot, E.; Cowley, A. R.; Gade, L. H.; Mountford,
P. Organometallics 2005, 24, 2368.
(46) Ward, B. D.; Maisse-Franc¸ois, A.; Dubberley, S. R.; Gade, L. H.;
Mountford, P., J. Chem. Soc., Dalton Trans. 2002, 2649.
(47) Mehrkhodavandi, P.; Bonitatebus Jr., P. J.; Schrock, R. R. J. Am.
Chem. Soc. 2000, 122, 7841.
(49) Mehrkhodavandi, P.; Schrock, R. R.; Pryor, L. L. Organometallics
2003, 22, 4569.
(50) Ward, B. D.; Gade, L. H.; Mountford, P. Acta Cryst. 2006, E62,
m472.

5524 Organometallics, Vol. 26, No. 23, 2007
VujkoVic et al.
Xyl
Figure 2. Molecular structure of [Ti(NtBu)(N2 Npy)(py)] 3c.
Ellipsoids are drawn at the 25% probability level and H atoms are
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Ti(1)-N(1) 2.202(2), Ti(1)-N(2) 1.985(2), Ti(1)-N(3) 2.018(2),
Ti(1)-N(4) 1.706(3), Ti(1)-N(5) 2.241(2), N(1)-Ti(1)-N(2)
80.37(9), N(1)-Ti(1)-N(3) 81.83(10), N(2)-Ti(1)-N(3) 116.64-
(10), N(1)-Ti(1)-N(4) 102.82(10), N(2)-Ti(1)-N(4) 119.85(11),
N(3)-Ti(1)-N(4) 123.31(11), N(1)-Ti(1)-N(5) 163.22(9), N(2)-
Ti(1)-N(5) 89.94(10), N(3)-Ti(1)-N(5) 90.48(10), N(4)-Ti(1)-
N(5) 93.87(10), Ti(1)-N(4)-C(26) 170.5(2).
Xyl
Figure 1. Molecular structure of [Ti(N2 Npy)(NMe2)2] 2b.
Ellipsoids are drawn at 25% probability, and H atoms are omitted
for clarity.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Ar
[Ti(N2 Npy)(NMe2)2] (Ar ) Tol 2a and Xyl 2b)
2a
2b
2a
2b
Ti-N(1)
Ti-N(2)
Ti-N(3)
Ti-N(4)
Ti-N(5)
N(1)-Ti-N(4) 127.9(3)
N(1)-Ti-N(5) 126.9(3)
1.9916(6) 1.932(2)
N(4)-Ti-N(5) 102.1(2) 103.63(7)
1.919(6)
2.296(5)
1.975(5)
1.982(6)
1.928(2)
2.301(2)
1.989(2)
1.968(2)
N(1)-Ti-N(2) 94.8(3)
N(2)-Ti-N(4) 96.9(2)
N(2)-Ti-N(5) 95.9(3)
N(1)-Ti-N(3) 86.4(2)
94.20(8)
99.89(8)
95.42(8)
88.25(8)
81.81(7)
80.18(7)
of pyridine, the tert-butylamine-stabilized complexes were
122.80(7) N(3)-Ti-N(4) 82.4(2)
129.91(7) N(3)-Ti-N(5) 83.4(2)
Ar
t
obtained, [Ti(NtBu)(N2 Npy)(NH2 Bu)] (Ar ) Tol 3b or Xyl
3d).
Scheme 2. Synthesis of the Imido Complexes 3a - 3e
The identity of 3b and 3d as imido-amine complexes, rather
than the isomeric bis(amide) complexes [Ti(N2 Npy)(NHtBu)2]
Ar
was confirmed by analysis of the tert-butyl quarternary carbon
resonances in the 13C{1H} NMR spectra. The imido resonances
were observed at δ 68.9 and 69.1 for 3b and 3d, respectively,
whereas the coordinated amine quarternary resonances were
observed at 50.4 ppm for both. The significant downfield shift
of the tert-butyl quarternary resonance is characteristic of imido
complexes.48a-c The synthesis of the aryl imido complex [Ti-
Ar
(N-4-C6H4Me)(N2 Npy)(py)] (Ar ) Tol 3e) was found to
proceed only in a concentrated pyridine solution, when heated
to 80 °C for 1 h. Prolonged reaction times gave rise to an
increased amount of protio ligand in the reaction mixture.
Equally, reaction of the tert-butyl imido complexes 3a or 3c
with p-toluidine, with the aim of an imide exchange,48a afforded
only decomposition into the protio-ligand, presumably owing
to a competition between proton transfer to the imido nitrogen
and the amido nitrogen atoms, which have a greater propensity
to act as a proton acceptor site because of the π-loaded nature
of the system (vide infra).48b
356.3(2)° for 2a and 2b, respectively, indicating a modest
deviation from an ideal planar arrangement. The Namide atoms
all show an approximate trigonal planar arrangement, showing
that they can, in principle, act as π-donors to the metal center.
The Ti-Namide bond lengths are in the expected range for
titanium-amide bond lengths, although it is noteworthy that the
Ti-Namide distances of the N2Npy ligand (1.966-1.987 Å) are
significantly longer than those of the NMe2 ligands (1.916 -
1.930 Å).
The structure of the imido complex 3c was confirmed by
X-ray diffraction. The molecular structure of 3c is shown in
Figure 2 along with principal bond lengths and angles. Complex
3c exhibits a distorted trigonal bipyramidal coordination ge-
ometry, with the imido group occupying an equatorial position.
This geometry persists in solution, as inferred from a 1H NOESY
NMR spectrum. The bond lengths are almost identical to within
experimental error to those of the silylated congener [Ti-
Synthesis and Structural Characterization of the [Ti(NR)-
Ar
(N2 Npy) (py)] Complexes. The diamide complexes 2a and
2b were subsequently converted to the corresponding imido
complexes by reaction with tert-butylamine or para-toluidine,
with the concomitant elimination of dimethylamine as repre-
sented in Scheme 2. Incomplete reactions were observed when
carried out in hydrocarbon or halogenated solvents. However
when the reaction was carried out using tert-butylamine as the
solvent in the presence of pyridine, complete conversion was
observed after heating to 55 °C for 2 days, affording the imido
(NtBu)(N2 Npy)(py)].48b Interestingly, the plane of the amido
TMS
Ar
nitrogen atoms of the N2
N
py
moiety was found to have
somewhat different orientation in the case of 3c compared to
2a and 2b. In 3c, the plane spanned by the substituents of the
Namide is rotated by 11.7° with respect to the equatorial plane
(the plane spanned by the titanium atom, Nimide, and Namide),
complexes [Ti(NtBu)(N2 Npy)(py)] (Ar ) Tol 3a or Xyl 3c).
Ar
Interestingly, when the reaction was carried out in the absence

Imido-Alkyne Coupling in Titanium Complexes
Organometallics, Vol. 26, No. 23, 2007 5525
Figure 4. Eyring plot for the exchange of [Ti(NtBu)(N2 Npy)-
Xyl
(py)] 3c with one molar equivalent of pyridine.
undergoing imido ligand metathesis to afford the aryl imido
complexes [Ti(NAr)(N2 Npy)(py)].48d,e
Ar
In all reactions of the imido complexes with organic
substrates, a pre-equilibrium involving the dissociation of the
axially bonded pyridine ligand is assumed. To investigate this
Xyl
Figure 3. ONIOM calculated structure for [Ti(NtBu)(N2 Npy)-
(py)] 3c, showing the two orthogonal π-bonding orbitals of the
linear imido ligands (a) and the highest occupied molecular orbitals
(in a NBO analysis) which are dominated by the contributions of
the nonbonding p-orbitals at the amido-N atom (b).
pre-dissociation of the pyridine in [Ti(NtBu)(N2 Npy)(py)] 3c,
Xyl
a molar equivalent of pyridine was added to a solution of 3c in
toluene-d8, and the exchange was monitored by variable
temperature 1H NMR spectroscopy. At ambient temperature only
a single pyridine resonance was observed, indicating a fast
exchange on the NMR time scale between the coordinated and
free pyridine. On cooling to -25 °C however, decoalescence
was observed, giving rise to two sets of resonances for the
coordinated and free pyridine. The activation barrier to this
exchange process was determined by line shape analysis and
exchange modeling of the ortho pyridine resonance between
-15 and 5 °C, at intervals of 5 °C. For each temperature, the
rate of exchange was determined, and was used to construct an
Eyring plot, from which the enthalpy and entropy of activation
while the equivalent planes in 2a and 2b are rotated by 44.3°
and 36.8°, respectively.
The near linear angle subtended at the imido nitrogen atom
of 170.5(2)° indicates that the imido ligand acts as a four-
electron donor to the metal center. The sum of the angles
subtended at the Namide atoms is 360° to within experimental
error, showing that the amido nitrogens can, in principle, donate
three electrons to the titanium. It is usually assumed that the
presence of four π donors affords a π-loaded system, in which
only three of the four π donor orbitals can donate into an
appropriate metal-based π acceptor orbital.48
were obtained as 21.2 kcal mol-1 and 81 cal mol-1 K-1
respectively (Figure 4).
,
To further elucidate the electronic structure of the imido
complexes, the structure of complex 3c was computed using
ONIOM (B3PW91:UFF) calculations. The metric parameters
of the calculated structure were comparable to those obtained
in the X-ray structure analysis, thus allowing further calculations
to be regarded with greater certainty (vide infra). An analysis
of the molecular frontier orbitals indicates that the imido ligand
binds to the metal with two orthogonal π bonds, as suggested
by the X-ray structure (Figure 3a). However, the amido-
nitrogens show only partial bonding character. A natural bond
order (NBO) analysis of the optimized structure shows that the
two highest occupied molecular orbitals are dominated by the
contributions of nonbonding p orbitals based solely on the Namide
atoms. Figure 3b shows the two NBO orbitals superimposed,
in which it can be seen that there are two possible combina-
tions: the in-phase and the out-of-phase. In principle the out-
of-phase combination can interact with the 3dπ atomic orbitals,
whereas the in-phase combination cannot. It is inferred from
this that the Namide-centered lone pairs can only partially donate
into a metal π-acceptor orbital, as described above. The π-loaded
nature of these imido complexes explains the residual basicity
of the metal-bonded amido-N atoms and thus the observation
The large positive entropy of activation suggestssas expecteds
a strongly dissociative mechanism, and the extrapolated rate
constant of k(293 K) ) 90 s-1 indicates that pre-dissociation
occurs rapidly in relation to subsequent transformations (vide
infra).
Coupling Reactions of the Ti imido Complexes with Aryl
Acetylenes: The Formation of Four-Membered Titana-
Ar
cycles. The imido complexes [Ti(NtBu)(N2 Npy)(py)] (Ar )
Tol 3a and Xyl 3c) react with phenyl or tolyl acetylene,
affording the azatitanacyclobutene complexes [Ti(N2 Npy){κ2-
Ar
N(tBu)CHdCAr′}] (Ar ) Tol, Ar′ ) Ph 4a or Tol 4b; Ar )
Xyl, Ar′ ) Ph 4c or Tol 4d), where the imido ligands undergo
a formal {2 + 2} cycloaddition (Scheme 3). The formation of
such a metallacyclic species has been suggested as being a key
reaction step in the catalytic hydroamination of alkynes.40-42
Examples of imido-alkyne coupling products have been isolated
and crystallographically characterized for both internal and
terminal alkynes.22,44 As in our earlier report, the azatitanacy-
clobutene complexes form exclusively as the anti-Markovnikov
isomers which has been attributed to the steric bulk of the tert-
butyl N-subsituent.3,44 While the reaction with aryl acetylenes
gave the respective cycloaddition products in good yield, the
corresponding reaction with either terminal or internal alkyl
Ar
that the reaction of [Ti(NtBu)(N2 Npy)(py)] with anilines
resulted in protonation of the amido groups, rather than

5526 Organometallics, Vol. 26, No. 23, 2007
VujkoVic et al.
Figure 6. Plot of the initial rate versus concentration of alkyne
for the reaction of 10 µmol of [Ti(NtBu)(N2 Npy)(py)] 3c with
Xyl
varying amounts of phenyl acetylene.
counterbalanced by the release of pyridine. The entropic
contribution to the transition state is however not expected to
be negligible, although in this study no transition state structures
were located. The remaining isomers exhibit energies between
-1.7 and -6.5 kcal mol-1, and are thus less stable than the
experimentally observed isomer, although the computed values
should only be treated as semiquantitative estimates. Since there
is no indication of a reversibility of the {2 + 2} cycloaddition,
the four-membered metallacycles being stable even at high
temperatures (100-110 °C) and not showing any cycloreversion,
their formation is assumed to be kinetically controlled. As the
computational study shows, the kinetically preferred product
also happens to be also thermodynamically most stable. A
further analysis of the structures suggests that the anti-
Markovnikov isomer is preferred since this alleviates steric strain
between the phenyl ring and the tert-butyl group.
Figure 5. ONIOM calculated structures for the isomeric forms of
Xyl
[Ti(N2 Npy){κ2-N(tBu)CHC(Ph)} 4c. Energies are provided in kcal
mol-1
.
Scheme 3. Synthesis of the {2 + 2} Cycloaddition Products
4a - 4d
The four-membered titanacycle may adopt two orientations
in relation to the diamidopyridyl spectator ligand, and previous
studies on such five-coordinate complexes have shown them
to undergo exchange between the two remaining coordination
sites. The observation of the tert-butyl group trans to the pyridyl
ring in the pentacoordinate products 4a-d is likely to avoid
steric interaction with the pyridyl moiety, since there is more
open space between the aryl substituents of the diamido-pyridine
ligand.
acetylenes were either incomplete or did not occur at all under
these conditions. Subsequent tests with these substrates under
catalytic conditions (vide infra) proved to be equally unsuc-
cessful.
The NMR data of 4a-d were found to be consistent with
NMR data of the crystallographically characterized silyl deriva-
tive reported previously, with the metallacycle CH proton
resonance being observed as a singlet at around 10 ppm.
Given the py-dissociation pre-equilibrium, the overall reaction
of the imido complexes with phenyl acetylene is expected to
be as follows:
1
k1
Moreover, H NOESY NMR spectra of 4a-d allowed us to
Ar
Ar
[(N2 Npy)Ti(NR)(py)] y z [(N2 Npy)Ti(NR)] + py
k-1
place the tert-butyl group trans to the pyridyl moiety, as drawn
in Scheme 3.
k2
Ar
Ar
The relative stability of the four possible isomeric forms of
[(Ni2 Npy)Ti(NR)] + R′CCH
98 [(N2 Npy)Ti(NRHCCR′)]
Xyl
[Ti(N2 Npy){κ2-N(tBu)CHdCPh}] (4c) was computed using
ONIOM calculations. The relative electronic energies of the four
isomers are displayed in Figure 5, and are computed in relation
to the parent imido complex, the unreacted phenyl acetylene,
and the released pyridine. Although all four isomers represent
local energy minima, it can be clearly seen that the experimen-
tally observed isomer is the most stable, with a cycloaddition
enthalpy of 14.1 kcal mol-1. The entropic contribution to the
energies can be approximately ignored in this case, since the
entropy change due to the association of the alkyne is
Ar
k1k2[(N2 Npy)Ti(NR)(py)][R′CCH]
rate )
k-1[py] + k2[R′CCH]
Ar
Since k2 , k-1 the rate law simplifies to k1k2[(N2 Npy)Ti(NR)-
(py)][R′CCH]/k-1[py] in the absence of a large excess of the
alkyne. To determine the reaction order with respect to the
Xyl
alkyne under these conditions, 10 µmol of [Ti(NtBu)(N2 Npy)-
(py)] 3c was reacted with varying amounts of phenyl acetylene,

Imido-Alkyne Coupling in Titanium Complexes
Organometallics, Vol. 26, No. 23, 2007 5527
Scheme 4. Synthesis of the Azatitanacyclohexadiene Complexes 5a - 5d
from 0.5 to 4 molar equiv. The reaction was then monitored by
1H NMR spectroscopy. The initial rate (i.e., at time ) 0) was
determined from the conversion curves; a plot of the initial rate
versus concentration of alkyne is displayed in Figure 6, and
the linear nature of the plot clearly denotes a first-order reaction
in alkyne concentration.
to the two orientations of the second alkyne molecule (Scheme
5). Although only a single isomer is observed experimentally,
an ONIOM study indicated that there is no significant
thermodynamic preference for one of the two isomers, the
difference in energy being only 1.9 kcal mol-1, which is
considered to be less than (or about equal to) the precision
associated with the method. It is therefore evident that the
preference for the observed isomer is due to kinetic control as
was discussed above for the formation of the four-membered
titanacycles in 4a-d.
Furthermore, the linear dependence of the initial reaction rates
on 1/[py] upon varying the concentration of pyridine (at constant
concentrations of the complex and a tenfold excess of the
alkyne) is also consistent with the rate law proposed above.
The rate coefficient kobs ) k1k2/k-1[py] was determined by
carrying out the reaction with varying concentrations of 3c, in
each case with a 20-fold excess of alkyne, that is, under pseudo-
first-order conditions. The initial rates were plotted against the
concentration of 3c, which showed a linear relationship, thus
allowing kobs to be determined from the slope of the plot as 1.9
× 10-3 mol-1 s-1
.
The Insertion of a Second Alkyne Molecule into the
Azatitanacyclobutenes Giving Six-Membered Azatitanacy-
clohexadienes. The preparation of the azatitanacyclobutene
complexes was carried out with a slight excess of alkynes to
obtain optimal yields of the {2 + 2} coupling product. It was
noticed, however, that the crude material often contained a minor
as yet unknown component. This component was successfully
identified by reacting the imido complexes 3a and 3c with 2
equiv of aryl acetylene. After heating to 100 °C for 1 h, complete
conversion was observed to this second component, identified
Ar
as the azatitanacyclohexadiene complex [Ti(N2 Npy){κ2-
N(tBu)CHdC(Ar′)C(Ar′) ) CH}] (Ar ) Tol, Ar′ ) Ph 5a or
Tol 5b; Ar ) Xyl, Ar′ ) Ph 5c or Tol 5d), the product of a
second alkyne insertion into the Ti-C bond (Scheme 4).
The structural details of complexes 5b and 5d were estab-
lished by X-ray diffraction. Their molecular structures are
displayed in Figures 7 and 8, respectively, with a comparison
of selected bond lengths and angles being provided in Table 2.
The C-C bond lengths of the metallacyclic moiety clearly
indicate that the two double bonds are placed between the CH
and the CTol carbons; the longer TolC-CTol bond lengths are
typical of sp2-sp2 carbon-carbon single bonds.51 The bonds
to titanium are unremarkable compared with previously reported
examples. To the best of our knowledge, there has been only
one crystallographically characterized structural motif of this
kind, in which Odom et al. reported the reaction of group 6
imido complexes with the sterically highly strained cyclooc-
tyne.52
Tol
Figure 7. Molecular structure of [Ti(N2 Npy){κ2-N(tBu)CHd
C(Tol)C(Tol) ) CH}] 5b. Ellipsoids are drawn at the 25%
probability level, and H atoms are omitted for clarity.
There are two possible isomers for the second insertion of
alkyne into the azatitanacyclobutene complexes, corresponding
(51) Allen, F. H.; Kennard, O. Chem. Des. Autom. News 1993, 8, 1, 31.
Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf. Comput. Sci.
1996, 36, 746.
(52) Lokare, K. S.; Ciszewski, J. T.; Odom, A. L. Organometallics 2004,
23, 5386.
Xyl
Figure 8. Molecular structure of [Ti(N2 Npy){κ2-N(tBu)CHd
C(Tol)C(Tol) ) CH}] 5d. Ellipsoids are drawn at the 25%
probability level, and H atoms are omitted for clarity.

5528 Organometallics, Vol. 26, No. 23, 2007
VujkoVic et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
The Imidotitanium Complexes 3a and 3c as Model
Catalysts for the Hydroamination of Aryl Acetylenes. Given
their reactivity toward alkynes, the imido complexes [Ti(Nt-
Ar
[Ti(N2 Npy){K2-N(tBu)CHdC(Tol)C(Tol) ) CH}] (Ar ) Tol
5b and Xyl 5d)
Ar
5b
5d
5b
5d
Bu)(N2 Npy)(py)] (Ar ) Tol 3a or Xyl 3c) were investigated
as potential catalysts for the hydroamination of phenyl acetylene
with tert-butylamine, producing trans-cinnamyl(tert-butyl)-
amine. The reaction proceeded significantly faster than for the
Ti-N(1)
Ti-N(2)
Ti-N(3)
Ti-N(4)
Ti-C(4)
2.036(3) 2.031(2) C(4)-Ti-N(2) 132.1(2)
1.944(3) 1.958(2) C(4)-Ti-N(3) 116.0(2)
133.37(8)
113.60(8)
1.934(3) 1.922(2) N(2)-Ti-N(3) 109.04(14) 109.77(7)
2.257(3) 2.260(2) N(1)-Ti-C(4) 85.8(2)
86.24(8)
TMS
corresponding silylated derivative [Ti(NtBu)(N2 Npy)(py)],44
2.046(4) 2.056(2) N(1)-Ti-N(2) 93.89(14) 95.29(7)
but was still slower at ambient temperature than the most active
Ti-based catalysts reported in the literature.1-6 The conversion
curves for this reaction are presented in Figure 9.
Using 10 mol % catalyst (imido complex) loading, the
reaction proceeded to ca. 70-80% conversion after 24 h at 293
K (80-90% after 48 h), after which no further reaction was
observed. Under these conditions there was no significant
difference between 3a and 3c. Since the reaction did not go to
completion, the evolution of the catalyst was monitored by NMR
spectroscopy during the catalytic reaction.
N(1)-C(1) 1.363(5) 1.371(3) N(1)-Ti-N(3) 109.65(14) 109.15(8)
C(1)-C(2) 1.374(5) 1.370(3) N(4)-Ti-C(4) 87.8(2)
C(2)-C(3) 1.443(5) 1.449(3) N(4)-Ti-N(2) 81.03(13) 81.55(7)
C(3)-C(4) 1.365(6) 1.356(3) N(4)-Ti-N(3) 84.66(14) 82.64(7)
87.67(7)
Unfortunately, a transition-state structure for the reaction
could not be found using ONIOM and DFT studies. The
modeling of transition states of bimolecular reactions between
molecules of the complexity as those involved in the process
at hand is generally associated with difficulties arising from
the multitude of orientational intra- and intermolecular degrees
of freedom. However, a visual inspection of the in-plane
approach of the second alkyne may give some insight into the
observed structural preference. If it is assumed that the
experimentally observed isomers of 4a and 4b are the only
isomers present, as inferred from the results discussed above,
the second alkyne must presumably approach from the upper
side, nearest to the pyridyl group. For insertion into the Ti-C
bond, the alkyne triple bond must lie parallel to the Ti-C bond
in the transition state. As illustrated in Scheme 5, the two
possible transition states differ only in a 180° rotation of the
alkyne. Transition state A (leading to the experimentally
observed isomer) possesses an alkyne-aryl group directed away
from the diamido-pyridine ligand; conversely transition state B
possesses the same group pointing toward it, causing significant
steric repulsion. Should the pyridyl group dissociate from the
metal center, there would still be significant steric repulsion
for transition state B, although it should be noted that dissocia-
tion of the pyridyl moiety is likely to raise the transition-state
energy significantly.
A mixture of compounds derived from the catalyst precursor
was observed, including the respective imido complexes [Ti-
(NtBu)(N2 Npy)(L)] (L ) py or BuNH2, which are indistin-
guishable under the catalytic conditions, presumably owing to
the fluxional nature of the system) used as catalyst (precursor)
Ar
t
and the azatitanacyclobutene complexes [Ti(N2 Npy){κ2-N(t-
Ar
Bu)CHdC(Ph)}] (which were found to be catalytically active
species themselves in a separate such experiment with com-
pounds 4a and 4b). Futhermore, the azatitanacyclohexadiene
complexes [Ti(N2 Npy){N(tBu)CHdC(Ph)C(Ph) ) CH}] and
Ar
Ar
the protio ligand H2N2
N
py
were observed. Both of the latter
components are the result of catalyst deactivation (the azati-
tanacyclohexadiene being inert to aminolysis and the concomi-
tant re-formation of the imido complex) and decomposition,
respectively, and were observed to increase in intensity over
time.
The protio ligand was formed under the conditions of catalysis
by reaction of the imido intermediates with the primary amine
as a competitive reaction with the cycloaddition with alkyne
and ultimately the formation of the desired hydroamination
product. This observation was independently verified in the
absence of alkyne by reaction of with tert-butylamine with the
imido complex 3c (which afforded free protio ligand) and 4c
(which afforded no protio ligand).
Reaction of complexes 4a and 4b with the appropriate aryl
acetylene likewise gave quantitative conversion to the corre-
sponding azatitanacyclohexadiene complex, suggesting that the
conversion from 3a or 3c to 5a-d proceeds in a stepwise
manner. Interestingly, although the second alkyne insertion
proceeds only slowly at ambient temperature, the reaction is
deemed to be a deactivation pathway in the hydroamination of
alkynes. The second insertion (as the first) is irreVersible and
the azatitanacyclohexadiene complexes are stable toward ami-
nolysis,that is, 5a-d do not react with tert-butylamine to reform
the imido complexes 3a-d, the final step in the catalytic
hydroamination cycle. Consequently, the six-membered species
represents a mechanistic “cul de sac” and, as will be shown
below, compounds of type 5a-d do indeed represent dead ends
in the catalytic hydroamination with the Ti complexes reported
in this work.
To further investigate the amount of catalyst present, the
quantity of the two catalytically active species (the respective
imido complex and the four-membered metallacyclic intermedi-
ates) was measured by integration of the 1H NMR signals
corresponding to the H6 proton of the coordinated N2
N
Ar
py
Ar
ligand, as a proportion of the total number of N2
N
py
ligand
environments (as well an internal standard, 1,4-dimethoxyben-
zene).
A steady decrease in the catalyst concentrations over time
was observed, with almost total catalyst deactivation after ca.
24 h (Figure 10), corresponding to the cessation of the catalytic
Scheme 5. Transition States for the Formation of 5c from 4c

Imido-Alkyne Coupling in Titanium Complexes
Organometallics, Vol. 26, No. 23, 2007 5529
clobutene. Overall, a rate law which is first order with respect
to the complex and both substrates was deduced under the
conditions of the catalytic reaction, which is consistent with
the established mechanism.
Conclusion
We have demonstrated that the arylated diamido-pyridine
Ar
ligands N2
N are remarkably efficient at stabilizing catalytic
py
intermediates in the hydroamination of aryl acetylenes. In
addition, greater insight has been obtained into the catalyst
decomposition pathways, in particular the previously unobserved
double insertion of the alkyne which leads to an extremely stable
six-membered azatitanacycle. The latter aspect will have to be
considered in further research aimed at developing more efficient
catalytic systems for this class of reactions.
Experimental
Figure 9. Conversion for the reaction of phenyl acetylene with
tert-butylamine by 3a and 3c at 293 K using 10 mol % catalyst
loading (internal reference for the NMR integration, 1,4-dimethoxy-
benzene).
General Experimental. All manipulations of air- and moisture-
sensitive materials were performed under an inert atmosphere of
dry argon using standard Schlenk techniques or by working in a
glovebox. Solvents were dried over sodium (toluene), potassium
(hexanes), or sodium/potassium alloy (pentane, diethyl ether),
distilled, and degassed prior to use. Deuterated solvents were dried
over potassium (C6D6, toluene-d8), vacuum distilled, and stored in
Teflon valve ampoules under argon. Samples for NMR spectroscopy
were prepared under argon in 5 mm Wilmad tubes equipped with
1
J. Young Teflon valves. H, 13C{1H} and 15N{1H} NMR spectra
were recorded on Bruker Avance 200, 400, and 600 NMR
spectrometers and were referenced internally using the residual
protio solvent (1H) of solvent (13C) resonances or externally vs.
NH3. Where necessary, NMR assignments were confirmed by the
use of two-dimensional 1H-1H or 1H-13C NMR correlation experi-
ments or by 13C DEPT experiments. Elemental analyses were
recorded by the analytical service of the Heidelberg Chemistry
Department. Mass spectra were recorded on a Jeol JMS 700 mass
spectrometer by the mass spectrometry service of the Heidelberg
Chemistry Department. The diamido-pyridine protio-ligand H2N2TolNpy
was prepared according to published procedures.46 All other reagents
were obtained from commercial sources and used as received unless
explicitly stated.
Preparation of the Compounds. H2N2
Xyl
N
(1). A Schlenk
py
Figure 10. Catalyst decomposition for the reaction of phenyl
acetylene with tert-butylamine, catalyzed by 3a and 3c (+4a and
4c, respectively) at 293 K using 10 mol % catalyst loading (internal
reference for the NMR integration, 1,4-dimethoxybenzene).
flask was charged with MeC(2-C5H4N)(CH2NH2)2 (2.15 g, 13.0
mmol),45 5-bromo-m-xylene (4.81 g, 26.0 mmol), [Pd2(dba)3] (0.18
g, 0.33 mmol, dba ) dibenzylideneacetone), rac-BINAP (0.31 g,
0.50 mmol), and NaOtBu (5.00 g, 52.0 mmol) which were
suspended in toluene (100 mL). After the reaction mixture was
stirred at 110 °C for 3 days, the volatiles were removed under
reduced pressure and the brown residue was redissolved in Et2O
(75 mL). The resulting solution was washed with H2O (3 × 30
mL) and then with a saturated aqueous solution of NaCl (3 × 30
mL). The combined organic phases were dried over MgSO4 and
evaporated. The residue was purified by column chromatography
(SiO2, gradient pentane/ether started from 90/10 to 70/30; detection
was made by TLC pentane/ether 70/30 Rf ) 0.4) to give the desired
product as a pale yellow oil (3.47 g, 72%). 1H NMR (CDCl3, 199.9
MHz, 296 K): δ 1.51 (3 H, s, Me of N2Npy), 2.21 (12 H, s,
C6H3Me2), 3.46 (2 H, d, CHH, 3J ) 12.2 Hz), 3.58 (2 H, d, CHH,
3J ) 12.2 Hz), 4.15 (2 H, s, NH), 6.25 (4 H, s, o-C6H3Me2), 6.34
(2 H, s, p-C6H3Me2), 7.17 (1 H, m, H5), 7.38 (1 H, d, H3, 3J ) 8.0
reaction. Since the formation of the azatitanacyclohexadiene
complexes 5a-d is significantly faster at elevated temperatures,
the catalysis was repeated at 50 °C and monitored as above.
Under these conditions the conversion was indeed much more
rapid, with 60% conversion in 5 h but so was the deactivation
which took place concomitantly.
The aminolysis reaction which completes the catalytic cycle
was studied using the azatitanacyclobutene 4c and tert-buty-
lamine. This step was likewise found to be first order in amine
concentration, and the second-order rate constant for this step,
k
aminol, was found to be 1.1 × 10-3 s-1 mol-1. The relative
values of kobs for the {2 + 2} cycloaddition of the alkyne and
the imido complex (taking the predissociation of the donor in
the imido complex into account) as well as the second-order
rate constant for the subsequent aminolysis step (kaminol) of
approximately kobs/kaminol ≈ 2 correspond well to the empirical
observations made in NMR tube scale experiments, in which
{2 + 2} cycloaddition of alkyne with the imido complexes was
observed to be faster than the aminolysis of the azatitanacy-
Hz), 7.66 (1 H, app td, H4, J(H3H4H5) ) 7.3 Hz, J(H4H6) ) 1.9
3
4
3
4
Hz), 8.62 (1 H, dd, H6, J(H5H6) ) 4.8 Hz, J(H4H6) ) 1.2 Hz)
ppm. 13C{1H} NMR (CDCl3, 75.5 MHz, 296 K): δ 21.4 (C6H3Me2),
23.0 (Me of N2Npy), 45.4 [C(CH2NXyl)2], 52.3 [(CH2NXyl)2], 111.0
(o-C6H3Me2), 119.3 (p-C6H3Me2), 121.3 (C3), 121.6 (C5), 136.7
(C4), 138.8 (overlapping m-C6H3Me2 and ipso-C6H3Me2) 148.8 (C6),

5530 Organometallics, Vol. 26, No. 23, 2007
VujkoVic et al.
164.2 (C2) ppm. MS (EI): m/z (%) ) 373.2 [M]+ (8), 239.1 [M
(CH2-NH-xyl)]+ (25), 134.1 [M- ((CH2-NH-Xyl) - (Xyl))]+
(31), 121.0 [M- {MeC(2-C5H4N)(CH2NXyl)(CH2)}]+ (100). HRMS
(FAB) : m/z (%) ) 374.264 (100) [M + H]+. Anal. Found (calcd
for C25H31N3): C, 80.3 (80.4); H, 8.3 (8.4); N, 10.8 (11.3).
121.2 (C5), 123.3 (m-C5H5N), 124.5 (o-C6H4Me), 129.4 (m-C6H4-
Me), 129.7 and 137.7 (C4 and p-C5H5N), 149.8 (o-C5H5N), 150.4
(C6), 152.3 (p-C6H4Me) 159.8 (C2) ppm. Anal. Found (calcd for
C32H39N5Ti): C, 70.4 (71.0); H, 7.6 (7.3); N, 12.7 (12.9).
Tol
t
[Ti(NtBu)(N2 Npy)(NH2 Bu)] (3b). A Schlenk tube was charged
Tol
Tol
[Ti(N2 Npy)(NMe2)2] (2a). A Schlenk tube was charged with
with [Ti(N2 Npy)(NMe2)2] (209 mg, 0.43 mmol) and a large excess
Tol
H2N2
N
py
(2.77 mg, 8.02 mmol) and 1.2 equiv of Ti(NMe2)4 (2.27
of tert-butylamine (20 mL) and placed under partial vacuum. The
reaction mixture was stirred for 5 days at 55 °C. The volatiles were
removed under reduced pressure, and the residue was washed with
hexane. After the residue was dried in vacuo an orange-yellow
powder was obtained. Yield 171 mg (73%). 1H NMR (C6D6, 399.9
MHz, 296 K): δ 0.75 (9 H, s, NH2CMe3), 1.20 (3 H, s, Me of
N2Npy), 1.59 (9 H, s, CMe3), 2.26 (6 H, s, C6H4Me), 3.06 (2 H, d,
mL, 9.62 mmol), and placed under partial vacuum. The reaction
mixture was stirred overnight at 100 °C, affording a red-orange
solid, which was washed with pentane. After the residue was dried
in vacuo, an orange powder was obtained. Yield 3.34 g (87%).
Single crystals for X-ray diffraction study were grown from a
saturated pentane solution at 5 °C (200 mg in 4 mL of pentane).
1H NMR (C6D6, 399.9 MHz, 296 K): δ 1.28 (3 H, s, Me of N2Npy),
2.31 (6 H, s, C6H4Me), 3.26 (6 H, s, NMe2), 3.32 (2 H, d, CHH, 3J
3
CHH, J ) 12.4 Hz), 3.33-3.43 (2 H, br. s, NH2CMe3), 3.38 (2
H, d, CHH, 3J ) 12.3 Hz), 6.51 (1 H, ddd, H5, 3J(H4H5) ) 7.6 Hz,
3J(H5H6) ) 5.3 Hz, 4J(H3H5) ) 1.2 Hz), 6.71 (1 H, dt, H3, 3J(H3H4)
) 8.0 Hz, 4J(H3H4H5) ) 1.0 Hz), 6.90 (1 H, td, H4, 3J(H3H4H5) )
3
) 12.2 Hz), 3.37 (6 H, s, NMe2), 3.68 (2 H, d, CHH, J ) 12.2
3
Hz), 6.48 (1 H, app t, H5, J ) 6.4 Hz), 6.90 (4 H, d, o-C6H4Me,
3J ) 8.6 Hz), 6.95 (1 H, d, H3, 3J ) 8.3 Hz), 7.01 (1 H, app td, H4,
3J(H3H4H5) ) 7.8 Hz, 4J(H4H6) ) 1.7 Hz), 7.14 (4 H, d, m-C6H4-
Me, 3J ) 8.7 Hz), 7.77 (1 H, dd, H6, 3J(H5H6) ) 5.3 Hz, 4J(H4H6)
) 1.5 Hz) ppm. 13C{1H} NMR (C6D6, 100.5 MHz, 296 K): δ 20.7
(C6H4Me), 24.8 (Me of N2Npy), 42.0 (NMe2), 48.1 (NMe2), 52.9
[C(CH2NTol)2], 63.7 [(CH2NTol)2], 114.4 (o-C6H4Me), 119.4 (ipso-
C6H4Me), 121.9 (C5), 126.1 (p-C6H4Me), 128.9 (m-C6H4Me), 129.9
(C3), 138.2 (C4), 147.4 (C6), 163.2 (C2) ppm. Anal. Found (calcd
for C27H37N5Ti): C, 68.1 (67.6); H, 7.7 (7.8); N, 14.0 (14.6).
7.8 Hz, J(H4H6) ) 1.8 Hz), 7.13 (4 H, d, m-C6H4Me, J ) 8.6
4
3
Hz), 7.30 (4 H, d, o-C6H4Me, J ) 8.4 Hz), 9.60 (1 H, dd, H6,
3
3J(H5H6) ) 5.3 Hz, 4J(H4H6) ) 1.8 Hz, 5J(H3H6) ) 0.8 Hz) ppm.
13C{1H} NMR (C6D6, 100.5 MHz, 296 K): δ 20.7 (C6H4Me), 25.4
(Me of N2Npy), 31.2 (NH2CMe3), 33.6 (CMe3), 42.4 [C(CH2NTol)2],
50.4 (NH2CMe3), 62.6 [(CH2NTol)2], 68.9 (CMe3), 114.7 (ipso-
C6H4Me), 119.5 (C3), 121.5 (C5), 125.0 (o-C6H4Me), 129.9 (m-
C6H4Me), 137.8 (C4), 151.4 (C6), 152.8 (p-C6H4Me), 160.0 (C2)
ppm. Anal. Found (calcd for C31H45N5Ti): C, 69.1 (69.5); H, 8.4
(8.5); N, 12.7 (13.1).
Xyl
[Ti(N2 Npy)(NMe2)2] (2b). A Schlenk tube was charged with
Xyl
Xyl
H2N2
N
py
(3.28 g, 8.78 mmol) and 1.2 equiv of Ti(NMe2)2 (2.27
[Ti(NtBu)(N2 Npy)(py)] (3c). A Schlenk tube was charged with
Xyl
mL, 10.54 mmol) and placed under partial vacuum. The reaction
mixture was stirred overnight at 100 °C, affording an orange solid,
which was washed with pentane. After the residue was dried in
vacuo an orange powder was obtained. Yield 3.52 g (79%).
Diffraction-quality single crystals were grown from a saturated
[Ti(N2 Npy)(NMe2)2] (618 mg, 1.22 mmol), a large excess of tert-
butylamine (20 mL), and pyridine (0.20 mL) and placed under
partial vacuum. The reaction mixture was stirred for 2 days at
55 °C. The volatiles were removed under reduced pressure and the
residue was washed with diethyl ether. After the residue was dried
in vacuo a yellow powder was obtained. Yield 487 mg (70%).
Single crystals for X-ray diffraction were grown from a saturated
diethyl ether solution at 5 °C (300 mg in 4 mL of diethyl ether).
1H NMR (C6D6, 600.1 MHz, 296 K): δ 1.17 (3 H, s, Me of N2Npy),
1.65 (9 H, s, CMe3), 2.35 (12 H, s, C6H3Me2), 3.25 (2 H, d, CHH,
1
pentane solution at 5 °C (200 mg in 4 mL of pentane). H NMR
(C6D6, 600.1 MHz, 296 K): δ 1.27 (3 H, s, Me of N2Npy), 2.37
(12 H, s, C6H3Me2), 3.11 (6 H, s, NMe2,ax), 3.37 (2 H, d, CHH, 3J
3
) 12.3 Hz), 3.40 (6 H, s, NMe2,eq), 3.73 (2 H, d, CHH, J ) 12.2
3
4
Hz), 6.51 (1 H, app td, H5, J(H4H5H6) ) 5.8 Hz, J(H3H5) ) 1.1
3
Hz), 6.90 (2 H, s, p-C6H3Me2), 6.67 (4 H, s, o-C6H3Me2), 6.83 (1
H, d, H3, J ) 7.9 Hz), 7.01 (1 H, app td, H4, J(H3H4H5) ) 7.7
3J ) 12.2 Hz), 3.33 (2 H, d, CHH, J ) 12.2 Hz), 6.37 (2 H, app
3
3
t, m-C5H5N, 3J ) 7.7 Hz), 6.46 (2 H, br. s, p-C6H3Me2), 6.55 (1 H,
Hz, J(H4H6) ) 1.7 Hz), 7.79 (1 H, dd, H6, J(H5H6) ) 5.3 Hz,
4J(H4H6) ) 1.0 Hz) ppm. 13C{1H} NMR (C6D6, 100.5 MHz, 296
K): δ 21.8 (C6H3Me2), 24.6 (Me of N2Npy), 41.7 (NMe2), 44.1
[C(CH2NXyl)2], 47.9 (NMe2), 63.2 [(CH2NXyl)2], 110.0 (ipso-C6H3-
Me2), 112.5 (o-C6H3Me2), 119.1 (C3), 119.2 (p-C6H3Me2), 121.6
(C5), 136.7 (m-C6H3Me2), 137.9 (C4), 147.1 (C6), 154.4 (C2) ppm.
15N{1H} NMR (C6D6, 60.8 MHz, 296 K): δ 215.8 (N2Npy), 228.4
(NMe2,ax), 256.1 (NMe2,eq), 290.1 (N2Npy) ppm. Anal. Found (calcd
for C29H41N5Ti): C, 68.5 (68.6); H, 8.1 (8.1); N, 13.5 (13.8).
ddd, H5, J(H4H5) ) 7.6 Hz, J(H5H6) ) 5.3 Hz, J(H3H5) ) 1.2
4
3
3
3
4
Hz), 6.58 (1 H, t, p-C5H5N, J ) 7.7 Hz), 6.73 (1 H, d, H3, J )
3
3
8.3 Hz), 6.93 (1 H, app td, H4, J(H3H4H5) ) 7.8 Hz, J(H4H6) )
3
4
1.8 Hz), 7.22 (4 H, br. s, o-C6H3Me2), 8.96 (2 H, d, o-C5H5N, 3J )
4.7 Hz), 9.68 (1 H, dd, H6, J(H5H6) ) 5.2 Hz, J(H4H6) ) 1.0
Hz) ppm. 13C{1H} NMR (C6D6, 150.9 MHz, 296 K): δ 21.9
(C6H3Me2), 25.7 (Me of N2Npy), 33.7 (CMe3), 42.1 [C(CH2NXyl)2],
62.8 [(CH2NXyl)2], 69.6 (CMe3), 113.4 (o-C6H3Me2), 118.9 (p-
C6H3Me2), 119.8 (C3), 121.5 (C5), 123.7 (m-C5H5N), 137.2 (p-
C5H5N), 137.7 (C4), 137.9 (ipso-C6H3Me2), 150.0 (o-C5H5N), 150.8
(C6), 154.8 (m-C6H3Me2), 160.2 (C2) ppm. 15N{1H} NMR (C6D6,
60.8 MHz, 296 K): δ 193.4 (N2Npy), 284.4 (NC5H5), 292.1 (N2Npy),
442.9 (NtBu) ppm. Anal. Found (calcd for C34H43N5Ti): C, 71.8
(71.7); H, 7.6 (7.6); N, 12.3 (12.3).
3
4
Tol
[Ti(NtBu)(N2 Npy)(py)] (3a). A Schlenk tube was charged with
Tol
[Ti(N2 Npy)(NMe2)2] (203 mg, 0.40 mmol), a large excess of tert-
butylamine (10 mL), and pyridine (0.10 mL) and placed under
partial vacuum. The reaction mixture was stirred for 2 days at
55 °C. The volatiles were removed under reduced pressure and the
residue was washed with hexane. After the residue was dried in
vacuo an orange-yellow powder was obtained. Yield 131 mg (57%).
1H NMR (C6D6, 399.9 MHz, 296 K): δ 1.22 (3 H, s, Me of N2Npy),
1.63 (9 H, s, CMe3), 2.28 (6 H, s, C6H4Me), 3.18 (2 H, d, CHH, 3J
Xyl
t
[Ti(NtBu)(N2 Npy)(NH2 Bu)] (3d). A Schlenk tube was charged
Xyl
with [Ti(N2 Npy)(NMe2)2] (565 mg, 1.11 mmol) and a large excess
of tert-butylamine (40 mL) and placed under partial vacuum. The
reaction mixture was stirred for 5 days at 55 °C. The volatiles were
removed under reduced pressure, and the residue was washed with
ether. After the residue was dried in vacuo an orange-yellow powder
3
) 12.3 Hz), 3.28 (2 H, d, CHH, J ) 12.3 Hz), 6.43 (2 H, br. s,
3
m-C5H5N), 6.51 (2 H, app t, H5, J ) 7.0 Hz), 6.67 (1 H, br. s,
3
1
p-C5H5N), 6.72 (1 H, d, H3, J ) 7.9 Hz), 6.91 (1 H, app td, H4,
was obtained. Yield 454 mg (83%). H NMR (C6D6, 399.9 MHz,
3J(H3H4H5) ) 7.7 Hz, 4J(H4H6) ) 1.2 Hz), 7.11 (4 H, d, m-C6H4-
296 K): δ 0.84 (9 H, s, NH2CMe3), 1.28 (3 H, s, Me of N2Npy),
1.69 (9 H, s, CMe3), 2.43 (12 H, s, C6H3Me2), 3.18 (2 H, d, CHH,
3J ) 12.4 Hz), 3.48 (2 H, d, CHH, 3J ) 12.3 Hz), 3.53-3.63 (2 H,
br. s, NH2CMe3), 6.53 (2 H, br. s, p-C6H3Me2), 6.62 (1 H, ddd,
3
3
Me, J ) 8.2 Hz), 7.39 (4 H, d, o-C6H4Me, J ) 8.4 Hz), 8.78 (2
H, br. s, o-C5H5N), 9.62 (1 H, dd, H6, 3J(H5H6) ) 5.3 Hz, 4J(H4H6)
) 1.0 Hz) ppm. 13C{1H} NMR (C6D6, 100.5 MHz, 296 K): δ 20.4
(C6H4Me), 25.3 (Me of N2Npy), 33.5 (CMe3), 41.8 [C(CH2NTol)2],
62.5 [(CH2NTol)2], 69.1 (CMe3), 114.8 (ipso-C6H4Me), 119.5 (C3),
3
3
4
H5, J(H4H5) ) 7.6 Hz, J(H5H6) ) 5.3 Hz, J(H3H5) ) 1.2 Hz),
6.80 (1 H, d, H3, J ) 8.3 Hz), 7.01 (1 H, app td, H4, J(H3H4H5)
3
3

Imido-Alkyne Coupling in Titanium Complexes
Organometallics, Vol. 26, No. 23, 2007 5531
3
) 7.8 Hz, 4J(H4H6) ) 1.8 Hz), 7.22 (4 H, br. s, o-C6H3Me2), 9.69
2.31 (3 H, s, 4-C6H4Me), 3.22 (2 H, d, CHH, J ) 11.9 Hz), 4.02
(1 H, dd, H6, J(H5H6) ) 5.2 Hz, J(H4H6) ) 1.0 Hz) ppm. 13C-
{1H} NMR (C6D6, 100.5 MHz, 296 K): δ 22.0 (C6H3Me2), 25.5
(Me of N2Npy), 31.3 (NH2CMe3), 33.7 (CMe3), 42.5 [C(CH2NXyl)2],
50.4 (NH2CMe3), 62.5 [(CH2NXyl)2], 69.1 (CMe3), 112.9 (o-C6H3-
Me2), 119.0 (p-C6H3Me2), 119.6 (C3), 121.6 (C5), 138.0 (C4), 138.2
(ipso-C6H3Me2), 151.6 (C6), 155.0 (m-C6H3Me2), 160.2 (C2) ppm.
Anal. Found (calcd for C33H49N5Ti): C, 69.2 (70.6); H, 8.3 (8.4);
N, 11.6 (12.5). Despite repeated attempts, we were unable to obtain
a more accurate elemental analysis. We attribute this inter alia to
the relatively weak coordination of tBuNH2 which leads to a slight
variation of the composition of the product.
3
4
(2 H, d, CHH, 3J ) 11.9 Hz), 6.34 (1 H, ddd, H5, J(H4H5) ) 7.1
3
Hz, 3J(H6H5) ) 5.4 Hz, 4J(H3H5) ) 1.3 Hz), 6.70 (4 H, d, o-C6H4-
Me, J ) 8.4 Hz), 6.82 (1 H, d, H3, J ) 7.9 Hz), 6.88 (1 H, td,
3
3
H4, 3J(H3H4H5) ) 7.9 Hz, 4J(H4H6) ) 1.7 Hz), 7.00 (4 H, d,
3
3
m-C6H4Me, J ) 8.3 Hz), 7.20 (2 H, d, m-4-C6H4Me, J ) 7.8
Hz), 7.40 (2 H, d, o-4-C6H4Me, J ) 8.2 Hz), 9.22 (1 H, d, H6,
3
3J(H5H6) ) 5.3 Hz), 10.03 (1 H, s, CdCH) ppm. 13C{1H} NMR
(C6D6, 150.9 MHz, 296 K): δ 20.8 (C6H4Me), 21.2 (4-C6H4Me),
24.3 (Me of N2Npy), 30.8 (CMe3), 44.1 [C(CH2NXyl)2], 59.8
(CMe3), 64.0 [(CH2NXyl)2], 115.1 (o-C6H4Me), 120.4 (C3), 121.9
(C5), 123.5 (p-C6H5), 126.3 (o-4-C6H4Me), 129.0 (m-4-C6H4Me),
129.4 (m-C6H4Me), 135.4 (p-C6H4Me), 138.4 (C4), 147.8 (C6), 150.7
(ipso-4-C6H4Me), 150.9 (CdCH), 152.3 (ipso-C6H4Me), 160.9 (C2),
197.4 (CdCH) ppm.
Tol
[Ti(N-4-C6H4Me)(N2 Npy)(py)] (3e). To a solution of [Ti-
Tol
(N2 Npy)(NMe2)2] (384 mg, 0.80 mmol) in pyridine (10 mL) was
added 1 equiv of p-toluidine (86 mg, 0.80 mmol), and the mixture
was placed under partial vacuum. The reaction mixture was stirred
for 1 h at 80 °C. The volatiles were removed under reduced
pressure, and the residue was washed with hexane. After the residue
was dried in vacuo an orange-red powder was obtained. Yield 370
Xyl
[Ti(N2 Npy){κ2-N(tBu)CHdCPh}] (4c). To a solution of [Ti-
(NtBu)(N2 Npy)(py)] (954 mg, 0.17 mmol) in toluene (50 mL)
Xyl
was added an equimolar amount of phenylacetylene (22 µL, 1.67
mmol) via syringe. The resulting brown solution was stirred over
night. Removing the volatiles under reduced pressure produced a
brown waxy solid, which was redissolved into pentane (20 mL).
After 2 days at -4 °C, the title compound was formed as a black
crystalline solid. Yield 553 mg (56%). 1H NMR (C6D6, 600.1 MHz,
296 K): δ 1.19 (9 H, s, CMe3), 1.22 (3 H, s, Me of N2Npy), 2.25
(12 H, s, C6H3Me2), 3.26 (2 H, d, CHH, 3J ) 12.0 Hz), 4.06 (2 H,
1
mg (81%). H NMR (C6D6, 399.9 MHz, 296 K): δ 1.30 (3 H, s,
Me of N2Npy), 2.13 (6 H, s, C6H4Me), 2,31 (3 H, s, N-4-C6H4Me),
3
3
3.30 (2 H, d, CHH, J ) 12.4 Hz), 3.59 (2 H, d, CHH, J ) 12.4
Hz), 6.30 (2 H, br. s, m-C5H5N), 6.35 (1 H, ddd, H5, J(H4H5) )
3
7.6 Hz, J(H5H6) ) 5.3 Hz, J(H3H5) ) 1.2 Hz), 6.66 (1 H, br. s,
3
4
p-C5H5N), 6.75 (1 H, d, H3, J ) 8.0 Hz), 6.91 (1 H, app td, H4,
3
3J(H3H4H5) ) 7.8 Hz, 4J(H4H6) ) 1.8 Hz), 6.99 (4 H, d, m-C6H4-
3
3
d, CHH, J ) 12.0 Hz), 6.31 (1 H, ddd, H5, J(H4H5) ) 7.2 Hz,
3
3
Me, J ) 8.2 Hz), 7.20 (2 H, d, m-N-4-C6H4Me, J ) 8.2 Hz),
3J(H6H5) ) 5.4 Hz, 4J(H3H5) ) 1.4 Hz), 6.45 (2 H, s, p-C6H3Me2),
3
7.32 (4 H, d, o-C6H4Me, J ) 8.4 Hz), 7.47 (2 H, d, o-N-4-C6H4-
6.46 (4 H, s, o-C6H3Me2), 6.81 (1 H, d, H3, J ) 7.6 Hz), 6.86 (1
3
Me, J ) 8.4 Hz), 8.53 (2 H, br. s, o-C5H5N), 9.46 (1 H, dd, H6,
3
H, td, H4, 3J(H3H4H5) ) 7.9 Hz, 4J(H4H6) ) 1.7 Hz), 7.13 (1 H, m
obscured by solvent, p-C6H5), 7.38 (2 H, app. t, m-C6H5, J ) 7.5
Hz), 7.46 (2 H, dd, o-C6H5, 3J ) 8.2 Hz, 4J ) 1.3 Hz), 9.19 (1 H,
3J(H5H6) ) 5.3 Hz, 4J(H4H6) ) 1.0 Hz) ppm. 13C{1H} NMR (C6D6,
100.5 MHz, 296 K): δ 20.7 (C6H4Me), 21.2 (N-4-C6H4Me), 25.3
(Me of N2Npy), 42.9 [C(CH2NTol)2], 63.3 [(CH2NTol)2], 114.5
(ipso-C6H4Me), 119.6 (C3), 122.2 (C5), 123.5 (p-C5H5N), 124.0 (o-
N-4-C6H4Me), 126.0 (ipso-N-4-C6H4Me), 128.3 (m-C5H5N), 129.6
(m-C6H4Me), 129.9 (m-N-4-C6H4Me), 135.2 (o-C6H4Me), 138.4
(C4), 150.4 (o-C5H5N), 151.0 (C6), 151.8 (p-C6H4Me), 160.1 (p-
N-4-C6H4Me), 160.2 (C2) ppm. Anal. Found (calcd for C34H43N5-
Ti): C, 72.0 (71.7); H, 6.5 (7.6); N, 12.3 (12.3).
ddd, H6, J(H5H6) ) 5.4 Hz, J(H4H6) ) 1.7 Hz, J(H3H6) ) 0.8
Hz), 9.99 (1 H, s, CdCH) ppm. 13C{1H} NMR (C6D6, 150.9 MHz,
296 K): δ 21.8 (C6H3Me2), 24.3 (Me of N2Npy), 30.6 (CMe3), 44.1
[C(CH2NXyl)2], 59.8 (CMe3), 63.8 [(CH2NXyl)2], 112.9 (o-C6H3-
Me2), 120.4 (C3), 121.4 (p-C6H3Me2), 121.9 (C5), 123.8 (p-C6H5),
126.4 (o-C6H5), 128.8 (m-C6H5), 137.7 (m-C6H3Me2), 138.4 (C4),
147.7 (C6), 150.0 (ipso-C6H5), 150.8 (CdCH), 152.8 (ipso-C6H3-
Me2), 160.9 (C2), 196.6 (CdCH) ppm. 15N{1H} NMR (C6D6, 60.8
MHz, 296 K): δ 240.9 (N2Npy), 274.6 (NtBu), 286.6 (N2Npy) ppm.
Anal. Found (calcd for C37H44N4Ti): C, 74.9 (75.0); H, 7.4 (7.5);
N, 8.9 (9.5).
3
4
5
Tol
[Ti(N2 Npy){κ2-N(tBu)CHdCPh}] (4a). To a solution of [Ti-
Tol
(NtBu)(N2 Npy)(py)] 3a (12 mg, 22.2 mmol) in C6D6 (0.5 mL)
was added phenyl acetylene (2.7 µL, 24.4 mmol, 1.1 equiv).
Analysis by NMR spectroscopy indicated that the formation of 4a,
along with a small quantity of [Ti(N2 Npy){κ2-N(tBu)CHdC(Ph)C-
Tol
Xyl
[Ti(N2 Npy){κ2-N(tBu)CHdCTol}] (4d). To a solution of [Ti-
(NtBu)(N2 Npy)(py)] (611 mg, 1.07 mmol) in toluene (50 mL)
(Ph) ) CH}] (5a) which could not be completely removed by
repeated recrystallization. 1H NMR (C6D6, 399.9 MHz, 296 K): δ
1.20 (9 H, s, CMe3), 1.23 (3 H, s, Me of N2Npy), 2.15 (6 H, s,
Xyl
was added an equimolar amount of tolylacetylene (150 µL, 1.18
mmol) via syringe. The resulting brown solution was stirred over
night. Removing the volatiles under reduced pressure produced a
brown, waxy solid, which was redissolved into pentane (20 mL).
After 2 days at -4 °C, the title compound was formed as a black
crystalline solid. Yield 337 mg (52%). 1H NMR (C6D6, 600.1 MHz,
296 K): δ 1.21 (9 H, s, CMe3), 1.24 (3 H, s, Me of N2Npy), 2.26
(12 H, s, C6H3Me2), 2.31 (3 H, s, 4-C6H4Me), 3.28 (2 H, d, CHH,
3J ) 12.0 Hz), 4.06 (2 H, d, CHH, 3J ) 12.0 Hz), 6.36 (1 H, ddd,
3
C6H4Me), 3.22 (2 H, d, CHH, J ) 11.9 Hz), 4.02 (2 H, d, CHH,
3J ) 11.9 Hz), 6.31 (1 H, ddd, H5, 3J(H4H5) ) 7.2 Hz, 3J(H6H5) )
4
3
5.3 Hz, J(H3H5) ) 1.4 Hz), 6.69 (4 H, d, o-C6H4Me, J ) 8.4
Hz), 6.81 (1 H, d, H3, 3J ) 7.9 Hz), 6.85-6.92 (1 H, m, H4), 6.46
(4 H, d, m-C6H4Me, 3J ) 8.2 Hz), 7.10-7.16 (1 H, m obscured by
solvent, p-C6H5), 7.35-7.44 (4 H, m, m-C6H5 and o-C6H5), 9.17
(1 H, d, H6, 3J(H5H6) ) 5.3 Hz), 10.00 (1 H, s, CdCH) ppm. 13C-
{1H} NMR (C6D6, 150.9 MHz, 296 K): δ 20.7 (C6H4Me), 24.3
(Me of N2Npy), 30.7 (CMe3), 44.1 [C(CH2NXyl)2], 59.7 (CMe3),
64.0 [(CH2NXyl)2], 115.1 (o-C6H4Me), 120.3 (C3), 121.8 (C5), 123.5
(p-C6H5), 126.3 (o-C6H5), 128.8 (m-C6H5), 129.4 (m-C6H4Me),
135.2 (p-C6H4Me), 138.4 (C4), 147.7 (C6), 150.2 (ipso-C6H5), 150.8
(CdCH), 152.2 (ipso-C6H4Me), 160.7 (C2), 196.3 (CdCH) ppm.
3
3
4
H5, J(H4H5) ) 7.2 Hz, J(H6H5) ) 5.4 Hz, J(H3H5) ) 1.2 Hz),
6.46 (2 H, s, p-C6H3Me2), 6.48 (4 H, s, o-C6H3Me2), 6.83 (1 H, d,
H3, 3J ) 7.9 Hz), 6.88 (1 H, td, H4, 3J(H3H4H5) ) 7.9 Hz, 4J(H4H6)
) 1.7 Hz), 7.21 (2 H, d, m-4-C6H4Me, 3J ) 8.0 Hz), 7.40 (2 H, d,
o-4-C6H4Me, 3J ) 7.7 Hz), 9.26 (1 H, dd, H6, 3J(H5H6) ) 5.4 Hz,
4J(H4H6) ) 1.7 Hz), 10.03 (1 H, s, CdCH) ppm. 13C{1H} NMR
(C6D6, 150.9 MHz, 296 K): δ 21.2 (4-C6H4Me), 21.9 (C6H3Me2),
24.4 (Me of N2Npy), 30.6 (CMe3), 44.1 [C(CH2NXyl)2], 59.8
(CMe3), 63.8 [(CH2NXyl)2], 112.9 (o-C6H3Me2), 120.4 (C3), 121.3
(p-C6H3Me2), 121.9 (C5), 126.4 (o-4-C6H4Me), 128.3 (m-4-C6H4-
Me), 129.5 (m-C6H3Me2), 132.8 (p-4-C6H4Me), 137.7 (ipso-4-C6H4-
Me) 138.4 (C4), 147.8 (C6), 150.5 (CdCH), 152.9 (ipso-C6H3Me2),
161.0 (C2), 197.7 (CdCH) ppm. 15N{1H} NMR (C6D6, 60.8 MHz,
Tol
[Ti(N2 Npy){κ2-N(tBu)CHdCTol}] (4b). To a solution of [Ti-
Tol
(NtBu)(N2 Npy)(py)] 3a (12 mg, 22.2 mmol) in C6D6 (0.5 mL)
was added tolyl acetylene (3.1 µL, 24.4 mmol, 1.1 equiv). Analysis
by NMR spectroscopy indicated the formation of 4a, along with a
small quantity of [Ti(N2 Npy){κ2-N(tBu)CHdC(Tol)C(Tol) )
Tol
CH}] (5b) which could not be completely removed by repeated
1
recrystallization. H NMR (C6D6, 399.9 MHz, 296 K): δ 1.20 (9
H, s, CMe3), 1.23 (3 H, s, Me of N2Npy), 2.25 (6 H, s, C6H4Me),

5532 Organometallics, Vol. 26, No. 23, 2007
VujkoVic et al.
296 K): δ 265.8 (N2Npy), 302.4 (NtBu), 314.5 (N2Npy) ppm. Anal.
Found (calcd for C38H46N4Ti): C, 75.2 (75.2); H, 7.7 (7.6); N, 8.9
(9.2).
3.71 (2 H, d, CHHN, 3J ) 12.5 Hz), 6.48-6.52 (3 H, overlapping
m, H5 and p-3,5-C6H3Me2), 6.85 (1 H, d, H3, 3J ) 7.9 Hz), 6.89 (4
H, s, o-3,5-C6H3Me2), 6.99-7.12 (3 H, overlapping m, H4and
p-C6H5), 7.26 (4 H, m obscured by the solvent, o-C6H5), 7.70 (4
H, t, m-C6H5, 3J ) 8.2 Hz), 8.07 (1 H, s, Ha), 9.29 (1 H, d, H6, 3J
(H5H6) ) 5.9 Hz), 10.16 (1 H, s, Hb) ppm. 13C{1H} NMR (C6D6,
100.5 MHz, 296 K): δ 21.8 (3,5-C6H3Me2), 25.3 (Me of N2Npy),
31.5 (CMe3), 42.0 [C(CH2NXyl)2], 62.4 (CMe3), 63.1 [(CH2NXyl)2],
113.8 (o-3,5-C6H3Me2), 119.9 (C3), 122.3 (CdCHa), 122.5 (C5),
122.6 (p-3,5-C6H3Me2), 124.2 (p-C6H5), 126.1 (p-C6H5), 127.9 (o-
C6H5), 128.1 (o-C6H5), 129.7 (m-C6H5), 130.2 (m-C6H5), 137.8 (m-
3,5-C6H3Me2), 138.4 (C4), 145.5 (ipso-C6H5), 145.9 (ipso-C6H5),
147.6 (C6), 149.2 (CdCHa), 151.4 (CdCHb), 154.2 (ipso-3,5-C6H3-
Me2), 160.3 (C2), 228.2 (CdCHb) ppm. Anal. Found (calcd for
C45H50N4Ti): C, 77.2 (77.8); H, 7.3 (7.3); N, 7.9 (8.1).
Tol
[Ti(N2 Npy){κ2-N(tBu)CHdC(Ph)C(Ph)dCH}] (5a). To a
Tol
solution of [Ti(NtBu)(N2 Npy)(py)] (758 mg, 1.40 mmol) in toluene
(50 mL) was added 3 equiv of phenylacetylene (460 µL, 1.40 mmol)
via syringe. The resulting brown solution was stirred for 60 min at
100 °C. Removing the volatiles under reduced pressure produced
a brown waxy solid, which was redissolved into diethyl ether (20
mL). After 2 days at -4 °C, the title compound was formed as a
black crystalline solid. Yield 345 mg (37%). 1H NMR (C6D6, 399.9
MHz, 296 K): δ 1.14 (9 H, s, CMe3), 1.18 (3 H, s, Me of N2Npy),
3
2.03 (6 H, s, C6H3Me), 3.27 (2 H, d, CHHN, J ) 12.5 Hz), 3.69
(2 H, d, CHHN, 3J ) 12.5 Hz), 6.39 (1 H, ddd, H5, 3J(H4H5) ) 7.3
3
4
3
Hz, J(H6H5) ) 5.4 Hz, J(H3H5) ) 1.1 Hz), 6.74 (1 H, d, H3, J
) 7.9 Hz), 6.87-7.03 (11 H, overlapping m, H4, p-C6H5, o-C6H4-
Me and m-C6H4Me), 7.12-7.21 (4 H, m obscured by the solvent,
Xyl
[Ti(N2 Npy){κ2-N(tBu)CHdC(Tol)C(Tol)dCH}] (5d). To a
Xyl
solution of [Ti(NtBu)(N2 Npy)(py)] (1.18 g, 2.1 mmol) in toluene
3
o-C6H5), 7.60 (4 H, t, m-C6H5, J ) 8.2 Hz), 8.08 (1 H, s, Ha),
(50 mL) was added 3 equiv of tolylacetylene (0.79 mL, 6.2 mmol)
via syringe. The resulting brown solution was stirred for 60 min at
100 °C. Removing the volatiles under reduced pressure produced
a brown, waxy solid, which was redissolved into diethyl ether (20
mL). After 2 days at -4 °C, the title compound was formed as a
black crystalline solid. Yield 275 mg (18%). Diffraction-quality
single crystals were grown from a saturated diethyl ether solution
9.29 (1 H, d, H6, J (H5H6) ) 5.9 Hz), 10.38 (1 H, s, Hb) ppm.
3
13C{1H} NMR (C6D6, 100.5 MHz, 296 K): δ 20.7 (C6H4Me), 25.3
(Me of N2Npy), 31.7 (CMe3), 42.9 [C(CH2NTol)2], 62.5 (CMe3),
63.5 [(CH2NTol)2], 115.9 (o-C6H4Me), 120.0 (C3), 121.8 (CdCHa),
122.6 (C5), 124.4 (p-C6H5), 126.2 (p-C6H5), 128.0 (o-C6H5), 128.4
(o-C6H5), 129.4 (p-C6H4Me), 129.5 (m-C6H4Me), 130.1 (m-C6H5),
130.4 (m-C6H5), 138.4 (C4), 145.7 (ipso-C6H5), 145.9 (ipso-C6H5),
147.5 (C6), 149.9 (CdCHa), 151.6 (CdCHb), 152.2 (ipso-C6H4-
Me), 160.3 (C2), 228.9 (CdCHb) ppm. Anal. Found (calcd for
C43H46N4Ti): C, 77.2 (77.5); H, 7.2 (6.9); N, 8.1 (8.4).
1
at 5 °C (600 mg in 4 mL of diethyl ether). H NMR (C6D6, 600.1
MHz, 296 K): δ 1.17 (9 H, s, CMe3), 1.19 (3 H, s, Me of N2Npy),
2.07 (3 H, s, 4-C6H4Me), 2.11 (3 H, s, 4-C6H4Me), 2.17 (12 H, s,
3
3,5-C6H3Me2), 3.32 (2 H, d, CHHN, J ) 12.4 Hz), 3.72 (2 H, d,
3
CHHN, J ) 12.4 Hz), 6.44 (3 H, overlapping m, H5 and p-3,5-
Tol
[Ti(N2 Npy){κ2-N(tBu)CHdC(Tol)C(Tol)dCH}] (5b). To a
3
C6H3Me2), 6.78 (1 H, d, H3, J ) 7.6 Hz), 6.83 (4 H, s, o-3,5-
Tol
solution of [Ti(NtBu)(N2 Npy)(py)] (1,00 g, 1.85 mmol) in toluene
C6H3Me2), 6.94 (1 H, td, H4 3J ) 7.8 ,4J ) 1.8), 7.01 (4 H, t,
(50 mL) was added 3 equiv of tolylacetylene (0.70 µL, 1.81 mmol)
via syringe. The resulting brown solution was stirred for 60 min at
100 °C. Removing the volatiles under reduced pressure produced
a brown, waxy solid, which was redissolved into diethyl ether (20
mL). After 2 days at -4 °C, the title compound was formed as a
black crystalline solid. Diffraction-quality single crystals were
grown from a saturated diethyl ether solution at 5 °C (400 mg in
4 mL of diethyl ether). Yield 379 mg (30%). 1H NMR (C6D6, 399.9
MHz, 296 K): δ 1.16 (9 H, s, CMe3), 1.19 (3 H, s, Me of N2Npy),
2.04 (12 H, s, C6H3Me), 2.06 (3 H, s, 4-C6H4Me), 2.12 (3 H, s,
3
3
m-4-C6H4Me, J ) 8.4 Hz), 7.58 (4 H, dd, o-4-C6H4Me, J ) 8.1
Hz, J ) 6.4 Hz), 8.08 (1 H, s, Ha), 9.36 (1 H, dd, H6, J (H5H6)
4
3
) 5.4 Hz, J (H4H6) ) 1.6 Hz), 10.25 (1 H, s, Hb) ppm. 13C{1H}
4
NMR (C6D6, 150.9 MHz, 296 K): δ 21.1 (4-C6H4Me), 21.2 (4-
C6H4Me), 21.8 (3,5-C6H3Me2), 25.3 (Me of N2Npy), 31.5 (CMe3),
42.0 [C(CH2NXyl)2], 62.3 (CMe3), 63.1 [(CH2NXyl)2], 113.8 (o-
3,5-C6H3Me2), 119.9 (C3), 122.4 (CdCHa), 122.5 (C5 and p-3,5-
C6H3Me2 overlapping), 128.7 (m-4-C6H4Me), 128.9 (m-4-C6H4Me),
129.7 (o-4-C6H4Me), 130.2 (o-4-C6H4Me), 133.1 (p-4-C6H4Me),
135.3 (p-4-C6H4Me), 137.8 (m-3,5-C6H3Me2), 138.4 (C4), 142.9
(ipso-4-C6H4Me), 143.1 (ipso-4-C6H4Me), 147.6 (C6), 148.7 (Cd
CHa), 151.3 (CdCHb), 154.3 (xyl-ipso-C), 160.4 (C2), 227.5 (Cd
CHB) ppm. 15N{1H} NMR (C6D6, 60.8 MHz, 296 K): δ 246.2
(N2Npy), 287.0 (NtBu), 288.3 (N2Npy) ppm. Anal. Found (calcd for
C47H54N4Ti): C, 78.5 (78.1); H, 7.7 (7.5); N, 7.8 (7.8).
3
4-C6H4Me), 3.27 (2 H, d, CHHN, J ) 12.5 Hz), 3.69 (2 H, d,
3
3
CHHN, J ) 12.5 Hz), 6.42 (1 H, ddd, H5, J(H4H5) ) 7.4 Hz,
3J(H6H5) ) 5.4 Hz, 4J(H3H5) ) 1.1 Hz), 6.76 (1 H, d, H3, 3J ) 7.9
Hz), 6.88-7.04 (13 H, overlapping m, H4, C6H3Me and m-4-C6H4-
Me), 7.56 (4 H, dd, o-4-C6H4Me, 3J ) 8.1 Hz, 4J ) 5.3 Hz), 8.09
(1 H, s, Ha), 9.35 (1 H, d, H6, 3J (H5H6) ) 5.2 Hz), 10.46 (1 H, s,
Hb) ppm. 13C{1H} NMR (C6D6, 100.5 MHz, 296 K): δ 20.7
(C6H4Me), 21.1 (4-C6H4Me), 21.2 (4-C6H4Me), 25.3 (Me of N2Npy),
31.7 (CMe3), 42.0 [C(CH2NTol)2], 62.4 (CMe3), 63.5 [(CH2NTol)2],
115.9 (o-C6H4Me), 119.9 (C3), 1218 (CdCHa), 122.5 (C5), 128.6
(m-4-C6H4Me), 129,1 (m-4-C6H4Me), 129.3 (p-C6H4Me), 129.5 (m-
C6H4Me), 130.1 (o-4-C6H4Me), 130,3 (o-4-C6H4Me), 133.3 (p-4-
C6H4Me), 135.3 (p-4-C6H4Me), 138.3 (C4), 142.7 (ipso-4-C6H4Me),
143.2 (ipso-4-C6H4Me), 147.6 (C6), 149.5 (CdCHa), 151.5 (Cd
CHb), 152.3 (ipso-C6H4Me), 160.3 (C2), 229.6 (CdCHB) ppm. Anal.
Found (calcd for C45H50N4Ti): C, 77.3 (77.8); H, 7.4 (7.3); N, 7.9
(8.1).
Kinetic Studies of the {2 + 2} Addition of Phenylacetylene
to the Ti Imido Complex 3c and of the Reaction of the
Azatitanacycle 4a with tert-Butylamine. A solution of [Ti(NtBu)-
Xyl
(N2 Npy)(py)] (3c) (5.7 mg, 10 µmol) and 1,4-dimethoxybenzene
(3.0 mg, internal standard) in toluene-d8 (0.5 mL) was transferred
to a J. Young NMR tube. After cooling the sample to -20 °C, 0.5
to 4 equiv of phenylacetylene (5 to 40 µmol) was added. The tube
was transferred to an NMR spectrometer probe that had been
precooled to 0 °C. 1H NMR spectra were recorded every 3 min for
a period of up to 30 min. The concentration of the reaction product
was plotted against time, and the conversion curve was line-fitted
to a first-order exponential decay Ae-x/b. The initial rate was
estimated from -A/b, derived from differentiation of the fitted line
for x ) 0. A plot of the initial rate versus alkyne concentration
indicated a linear relationship.
Xyl
[Ti(N2 Npy){κ2-N(tBu)CHdC(Ph)C(Ph)dCH}] (5c). To a
Xyl
solution of [Ti(NtBu)(N2 Npy)(py)] (1.03 mg, 1.8 mmol) in toluene
(50 mL) was added 3 equiv of phenylacetylene (0.60 mL, 5.4 mmol)
via syringe. The resulting brown solution was stirred for 60 min at
100 °C. Removing the volatiles under reduced pressure produced
a brown, waxy solid, which was redissolved into diethyl ether (20
mL). After 2 days at -4 °C, the title compound was formed as a
black crystalline solid. Yield 492 mg (39%). 1H NMR (C6D6, 399.9
MHz, 296 K): δ 1.14 (9 H, s, CMe3), 1.18 (3 H, s, Me of N2Npy),
2.15 (12 H, s, 3,5-C6H3Me2), 3.30 (2 H, d, CHHN, 3J ) 12.5 Hz),
Xyl
A solution of [Ti(NtBu)(N2 Npy)(py)] (3c) (5 to 25 µmol) and
1,4-dimethoxybenzene (3.0 mg, internal standard) in toluene-d8 (0.5
mL) was transferred to a J. Young NMR tube. After the sample
was cooled to -20 °C, 20 equiv of phenylacetylene (0.1-0.5 mmol)
was added. The tube was transferred to an NMR spectrometer probe
1
that had been precooled to 0 °C. H NMR spectra were recorded

Imido-Alkyne Coupling in Titanium Complexes
Organometallics, Vol. 26, No. 23, 2007 5533
Table 3. X-ray Data for 2a, 2b, 3c, 5b, and 5d
2a
2b
3c
5b
5d
empirical formula
formula weight
crystal size /mm
crystal system
space group
a /Å
C27H37N5Ti‚C7H8
571.67
0.16 × 0.08 × 0.03
monoclinic
P21/c
10.7877(2)
11.6261(3)
25.8717(7)
90
98.831(5)
90
3206.3(1)
4
1.180
0.297
0.995, 0.968
0 to 14,
C29H41N5Ti
507.58
0.10 × 0.15 × 0.25
monoclinic
P21/c
10.637(2)
22.176(4)
11.572(2)
90
91.32(3)
90
C34H43N5Ti
569.65
0.15 × 0.15 × 0.15
monoclinic
P21/n
8.650(6)
20.362(13)
17.777(11)
90
93.924(14)
90
C45H50N4Ti
694.82
0.25 × 0.25 × 0.25
monoclinic
C2/c
30.081(6)
13.029(3)
21.530(4)
90
102.73(3)
90
C47H54N4Ti
722.84
0.10 × 0.20 × 0.20
monoclinic
C2/c
31.3967(18)
12.6357(8)
22.2022(13)
90
114.867(1)
90
b /Å
c /Å
R /deg
â /deg
γ /deg
V /Å3
2729.1(9)
4
1.235
3124(3)
4
1.211
8231(3)
8
1.121
7991.4(8)
8
1.202
Z
Dc /Mg m-3
µ /mm-1
max, min trans.
index ranges,
h,k,l
0.340
0.304
0.242
0.252
0.97, 0.95
-15 to 15,
0 to 31,
0 to 16
1.8 to 30.5
100(2)
0.959, 0.952
-10 to 10,
0 to 25,
0 to 22
1.5 to 26.7
100(2)
0.942, 0.929
-41 to 40,
0 to 18,
0 to 29
1.7 to 29.6
100(2)
0.7464, 0.6786
-40 to 36,
0 to 16,
0 to 28
1.7 to 27.5
100(2)
0 to 15,
-33 to 33
1.8 to 27.5
173(2)
θ /deg
T /K
F(000)
1224
1088
1216
2960
3088
reflns collected
reflns independent
7708
7708 [0.04]
26059
8335 [0.051]
77092
6633 [0.094]
203516
11545 [0.0749]
80120
9162 [0.0840]
[Rint
]
data/rest./par.
7708/0/343
1.009
8335/0/316
0.9674
6606/0/361
0.8625
11514/0/451
1.035
9162/0/479
1.087
GOF on F2
final R indices
[I > 2σ(I)]
R1 ) 0.087
wR2 ) 0.101
R1 ) 0.087
wR2 ) 0.101
1.071 and -0.876
R1 ) 0.056
wR2 ) 0.141
R1 ) 0.082
wR2 ) 0.161
0.83 and -0.87
R1 ) 0.056
wR2 ) 0.127
R1 ) 0.083
wR2 ) 0.155
0.60 and -0.76
R1 ) 0.099
wR2 ) 0.230
R1 ) 0.123
wR2 ) 0.237
0.79 and -1.21
R ) 0.050
wR2 ) 0.133
R ) 0.079
wR2 ) 0.148
0.457 and -0.536
R indices (all data)
Larg. res. peak /e. Å-3
every 3 min for a period of up to 30 min. The concentration of the
reaction product was plotted against time, and the conversion curve
was line-fitted to a first-order exponential decay Ae-x/b. The initial
rate was estimated from -A/b, derived from differentiation of the
fitted line for x ) 0. A plot of the initial rate versus titanium
concentration indicated a linear relationship, from which the
rate coefficient was obtained from the slope of the graph as 1.9 ×
tert-butylamine (0.1 to 5 mmol). The mixture was transferred to a
J. Young NMR tube and then to an NMR spectrometer. H NMR
1
spectra were recorded at 1 h intervals for up to 48 h.
Ar
To a solution of [Ti(NtBu)(N2 Npy)(py)] (3a and 3c) (10 µmol,
10 mol %) and 1,4-dimethoxybenzene (3.0 mg, internal standard)
in C6D6 (0.5 mL) was added 10 equiv of tert-butylamine (0.1
mmol). The mixture was transferred to a J. Young NMR tube and
then to an NMR spectrometer probe that had been preheated to
10-3 s-1
.
To a solution of [Ti(N2 Npy){κ2-N(tBu)CHdCPh}] (4a) (5.9
mg, 10 µmol) and 1,4-dimethoxybenzene (3.0 mg, internal standard)
in toluene-d8 (0.5 mL) was added 0.5-4 equiv of tert-butylamine
(5 to 40 µmol). The mixture was transferred to a J. Young NMR
Xyl
1
50 °C. H NMR spectra were recorded at 1 h intervals for up
to 24 h.
Crystal Structure Determinations Suitable crystals of 2a, 2b,
3c, 5b, and 5d were obtained from saturated solutions at 0 °C.
Intensity data were collected at low temperature on a Bruker AXS
Smart 1000 CCD (2b, 3d, 5b, 5d) or a Enraf-Nonius Kappa-CCD
(2a) diffractometer. The structures were solved using direct methods
with absorption corrections being applied as part of the data scaling
procedure.53 After refinement of the heavy atoms, difference Fourier
maps revealed the maxima of residual electron density close to the
positions expected for the hydrogen atoms. They were introduced
as fixed contributors in the structure factor calculations and treated
with a riding model, with isotropic temperature factors but not
refined. A final difference map revealed no significant maxima of
residual electron density. Structure solution and refinement were
performed by using the programs SIR,54 SHELXS-86,55 SHELXL-
97,56 or CRYSTALS.57 The crystal of 5b was found to possess a
disordered molecule of diethyl ether. Various models were em-
1
tube and then to an NMR spectrometer. H NMR spectra were
recorded every 3 min for a period of up to 30 min. The
concentration of the reaction product was plotted against time, and
the conversion curve was line-fitted to a first-order exponential
decay Ae-x/b. The initial rate was estimated from -A/b, derived
from differentiation of the fitted line for x ) 0. A plot of the initial
rate versus amine concentration indicated a linear relationship.
Xyl
A solution of [Ti(N2 Npy){κ2-N(tBu)CHdCPh}] (4a) (5-25
µmol) and 1,4-dimethoxybenzene (3.0 mg, internal standard) in
toluene-d8 (0.5 mL) was transferred to a J. Young NMR tube. After
the sample was cooled to 0 °C, 20 equiv of tert-butylamine (0.1-
0.5 mmol) was added. The tube was transferred to an NMR
spectrometer probe that had been precooled to 0 °C. 1H NMR
spectra were recorded every 3 min for a period of up to 30 min.
The concentration of the reaction product was plotted against time,
and the conversion curve was line-fitted to a first-order exponential
decay Ae-x/b. The initial rate was estimated from -A/b, derived
from differentiation of the fitted line for x ) 0. A plot of the initial
rate versus titanium concentration indicated a linear relationship,
from which the rate coefficient was obtained from the slope of the
(53) (a) Sheldrick, G. M. SADABS-2004/1, Bruker AXS, 2004. (b)
Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter, C. W., Sweet,
R. M., Eds.; Academic Press: San Diego, CA, 1997; Vol. 276, p 307.
(54) (a) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Cryst. 1999, 32, 115. (b) Burla, M. C.; Caliandro, R.; Camalli,
M.; Carrozzini, B.; Cascarano, G. L.; De Caro, L.; Giacovazzo, C.; Polidori,
G.; Spagna, R. J. Appl. Cryst. 2005, 38, 381.
(55) Sheldrick, G. M. SHELXS-86; University of Go¨ttingen: Go¨ttingen,
Germany, 1986.
(56) Sheldrick, G. M. SHELXL-97, University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
graph as 1.1 × 10-3 s-1
.
Catalytic Hydroamination of Phenylacetylene with tert-
Butylamine. To a solution of [Ti(NtBu)(N2 Npy)(py)] (3a and 3c)
Ar
(10 µmol, 0.5-10 mol %) and 1,4-dimethoxybenzene (3.0 mg,
internal standard) in C6D6 (0.5 mL) was added 10-500 equiv of

5534 Organometallics, Vol. 26, No. 23, 2007
VujkoVic et al.
ployed to model this molecule, of which none adequately fitted
the electron density. Therefore it was removed and the correspond-
ing electron density was modeled with SQUEEZE58 in the advanced
mode, with the A and B parts of the structure factors being passed
back to CRYSTALS for inclusion in Fc, rather than being removed
from Fo. Crystal data and experimental details are provided in Table
3.
Computational Details
All calculations were performed using the Gaussian 03 program.59
All calculated structures were optimized without geometry con-
straints, with each optimization being followed by a frequency
calculation (for quantum mechanical calculations) to confirm the
nature of the located extrema (minimum or transition state). Where
possible, molecular parameters of optimized structures were
compared to available X-ray data and exhibited no significant
Xyl
differences. For ONIOM calculations involving the N2
N ligand,
py
(57) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge, P. W.;
Cooper, R. I. CRYSTALS; Chemical Crystallography Laboratory: Oxford,
U.K. 2001 (11).
(58) Sluis, P. van der; Spek, A. L. Acta Cryst. 1990, A46,
194.
the apical methyl group and the aryl methyl groups were calculated
at the UFF level, with the remainder of the molecule calculated
with the B3PW91 method, in which the metal, the coordinated
atoms, and the alkyne CtC fragment were modeled with the
6-311G(d,p) basis set, with the remainder of the atoms modeled
with the 6-31G basis set.
(59) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A.
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Acknowledgment. We would like to thank the Deutsche
Forschungsgemeinschaft, the EU (Marie Curie EIF fellowship
for B.D.W.), and the EPSRC for financial assistance. Support
by BASF (Ludwigshafen) is gratefully acknowledged.
Supporting Information Available: Crystallographic informa-
tion in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
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