Frustrated Lewis pairs beyond the main group: Synthesis, reactivity, and small molecule activation with cationic zirconocene-phosphinoaryloxide complexes

Article abstract of DOI:10.1021/ja207936p

The extension of the frustrated Lewis pair (FLP) concept to the transition series with cationic zirconocene-phosphinoaryloxide complexes is demonstrated. Such complexes mimic the reactivity of main group FLPs in reactions such as heterolytic hydrogen cleavage, CO₂ activation, olefin and alkyne addition, and ring-opening of tetrahydrofuran. The interplay between sterics and electronics is shown to have an important role in determining the reactivity of these compounds with hydrogen in particular. The Zr-H species generated from the heterolytic activation of hydrogen is shown to undergo insertion reactions with both CO₂ and CO. Crucially, these transition metal FLPs are markedly more reactive than main group systems in many cases, and in addition to the usual array of reactions they demonstrate unprecedented reactivity in the activation of small molecules. This includes S_N2 and E2 reactions with alkyl chlorides and fluorides, enolate formation from acetone, and the cleavage of C-O bonds to facilitate S_N2 type reactions with noncyclic dialkyl ethers.

Full text of DOI:10.1021/ja207936p

ARTICLE
pubs.acs.org/JACS
Frustrated Lewis Pairs beyond the Main Group: Synthesis,
Reactivity, and Small Molecule Activation with Cationic
ZirconoceneꢀPhosphinoaryloxide Complexes
Andy M. Chapman, Mairi F. Haddow, and Duncan F. Wass*
School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom
S Supporting Information
b
ABSTRACT: The extension of the frustrated Lewis pair (FLP)
concept to the transition series with cationic zirconoceneꢀ
phosphinoaryloxide complexes is demonstrated. Such com-
plexes mimic the reactivity of main group FLPs in reactions
such as heterolytic hydrogen cleavage, CO2 activation, olefin
and alkyne addition, and ring-opening of tetrahydrofuran. The
interplay between sterics and electronics is shown to have an
important role in determining the reactivity of these compounds with hydrogen in particular. The ZrꢀH species generated from the
heterolytic activation of hydrogen is shown to undergo insertion reactions with both CO2 and CO. Crucially, these transition metal
FLPs are markedly more reactive than main group systems in many cases, and in addition to the usual array of reactions they
demonstrate unprecedented reactivity in the activation of small molecules. This includes SN2 and E2 reactions with alkyl chlorides
and fluorides, enolate formation from acetone, and the cleavage of CꢀO bonds to facilitate SN2 type reactions with noncyclic dialkyl
ethers.
frustrated Lewis pairs where the Lewis acidic borane component is
replaced with an electrophilic transition metal center. Our initial
results have demonstrated chemistry which mimics main group
frustrated pairs in many regards but which also demonstrates
additional reactivity, for example, the catalytic dehydrogenation of
amine-boranes,20 a reaction only demonstrated in a stoichiometric
sense with main group FLP systems (Figure 1).21,22
Even though the novelty of metal-free catalysis cannot be
claimed for a zirconiumꢀphosphine pair, the FLP paradigm is
valuable in understanding the reactivity of this system. It is
our view that combining the ability of transition metal
complexes in catalysis with the capability of FLPs to activate
substrate molecules via ditopic activation offers exciting
possibilities for exploitation in new activation pathways and
reactivity patterns.
In this Article, we explore the reactivity of these transition
metal frustrated Lewis pairs more widely in some typical reac-
tions of main groups FLPs: hydrogen cleavage, CO2 activation,
alkene and alkyne addition, and tetrahydrofuran (THF) ring-
opening. In all cases, the analogy between these systems is robust
and valuable. However, we have also demonstrated new, more
potent reactivity in small molecule activation: CO reduction,
C-halide cleavage in alkyl chlorides and fluorides, and the
cleavage of CꢀO bonds in acyclic ethers. This rare reactivity is
still well-explained using the FLP analogy but unprecedented for
the main group FLPs.
1. INTRODUCTION
Solution phase combinations of sterically hindered (“frustrated”)
Lewis acidꢀLewis base pairs (FLPs) have been the subject of recent
interest because of the high latent reactivity of such species in the
activation of small molecules. Initial studies focused on the reversible
heterolytic cleavage of dihydrogen, which offers the promise of
metal-free catalytic hydrogenation.1ꢀ4 However, the diversity of the
reactions reported is now large and continues to grow.5 The
pioneering bulky phosphine and fluorinated borane systems
(PtBu3/B(C6F5)3) first reported by Stephan have been modified
so that the specific reactivity of FLP systems can be controlled by
subtle steric and electronic alterations to either the Lewis acidic or
basic components2,6 which, in the context of reversible reactions
with carbon dioxide and hydrogen, has attracted significant interest.7
A great deal of work has also focused on extending the range of main
group FLPs to other main group Lewis acids (e.g., simple alkyl
boranes, allanes,8,9 and allenes10) or bases (e.g., amines11 carbenes,12
and sulfides13). Linking the two components of the FLP into a single
amphoteric molecule has also led to interesting results.3,14
While main group FLPs offer a novel and possibly useful way
to activate unreactive substrates,7,14ꢀ17 such systems suffer from
a common limitation in that, apart from some stoichiometric
insertion chemistry,17,5 the products are often inert toward
further reaction. Subsequently, and to the best of our knowledge,
only two catalytic transformations with such systems have been
demonstrated (imine or enamine hydrogention18 and deoxy-
genative hydrogenation of CO2).19
Wehave been exploringthe chemistryofcationic zirconoceneꢀ
Received: August 30, 2011
Published: September 29, 2011
phosphinoaryloxide complexes as analogues of linked main group
r
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Figure 1. Amine-borane dehydrogenation with 1. Counterion =
[B(C6F5)4]ꢀ.
Scheme 1. Synthesis of Compounds 1ꢀ5a
Figure 2. POV-ray representation of the molecular structure of 2. All
hydrogen atoms and borate anion have been omitted for clarity. Thermal
ellipsoid is drawn at the 50% probability level. The minor component of
the disordered chlorobenzene solvent molecule has been omitted for
clarity. Selected bond lengths (Å) and angles (deg): Zr1 Cl1 2.740(1),
Zr1 O1 1.980(3), Zr1 P1 4.613(1), O1 C21 1.359(5). O1 Zr1 Cl1
95.4(1), C59 Cl1 Zr1 129.0(2), C21 O1 Zr1 161.7(3).
Figure 3. POV-ray representation of the molecular structure of 4. All
hydrogen atoms and borate anion have been omitted for clarity. Thermal
ellipsoid is drawn at the 50% probability level. Selected bonds length (Å)
and angles (deg): Zr1 P1 2.8215(8), Zr1 O1 2.025(2), C21 O1
1.368(4), P1 C22 1.818(3). P1 Zr1 O1 70.77(6), O1 C21 C22
119.2(3), C21 C22 P1 114.7(2), C22 P1 Zr1 89.9(1).
sterics and electronics to 1 and 2. The synthesis was achieved using
the previously reported protocol starting from CpCp*ZrMe2
(Scheme 1). The presence of a ZrꢀP bond is corroborated by
the near identical 31P NMR spectra of 1 and 3 (54.4 vs 53.3 ppm),
although efforts to grow crystals suitable for X-ray crystallography
to allow direct bond length comparison with 1 were unsuccessful.
However, the calculated distances at two levels of theory, 3.068 Å
(B3LYP) and 2.918 Å (M06-2X) support the expectation of an
elongated ZrꢀP bond relative to 1 (found to be 2.883 Å from the
X-ray, and calculated to be 2.935 Å from B3LYP and 2.870 Å from
M06-2X level simulations).
We have also modified the phosphine component of these
systems; substitution of the tert-butyl groups in 2 for iso-propyl
groups leads to the isolation of 4 via a similar method. As
expected for this less bulky phosphine, solution 31P NMR data
(23.9 ppm) and X-ray crystallography (Figure 3) confirm the
presence of a ZrꢀP bond. The ZrꢀP bond is shown to be
shorter than that in 1 by ca. 2% (2.821 vs 2.883 Å). Finally, the
synthesis of 5 was accomplished in an analogous way. The lack
of a ZrꢀP implicated by the similarity of the 31P NMR shifts of
a DTBP = 2,6-di-tert-butylpyridine. Counterion = [B(C6F5)4]ꢀ.
2. RESULTS AND DISCUSSION
2.1. Synthesis of ZirconoceneꢀPhosphinoaryloxide Com-
plexes. We recently reported20 the synthesis of the zirconoceneꢀ
phosphinoaryloxide complexes 1 and 2 (see Scheme 1). The
zirconium center in 1 was found to be stabilized by a long ZrꢀP
interaction. We reasoned that increasing the bulk of the zircono-
cene fragment with the permethylcyclopentadienyl analogue 2
would hinder this interaction, albeit at the supposed cost of
decreased electrophilicity of the zirconium center.23 We report
here the X-ray crystal structure of 2 (Figure 2) which confirms
the absence of a ZrꢀP interaction in the solid state, revealing the
presence of a coordinated chlorobenzene, disordered over two
positions with an occupancy ratio of 0.77:0.23. In order to
explore the limit of the ZrꢀP interaction in our system, we
chose to synthesize 3 which was expected to possess intermediate
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Figure 5. Tentative rotomers of 9 in solution. Counterion =
[B(C6F5)4]ꢀ.
Figure 4. Structures of compounds 6ꢀ9. Counterion = [B(C6F5)4]ꢀ.
5 relative to its neutral precursor (ꢀ26.8 vs ꢀ32.9 ppm). The
mesityl substituents of compound 5 are expected to give a
substantially less basic phosphine,24 while retaining the neces-
sary steric bulk to “frustrate” coordination25 to the zirconium
center.
2.2. Reactivity with Hydrogen. With this range of complexes
in hand, we sought initially to explore the heterolytic cleavage of
dihydrogen when the steric bulk of both the zirconocene and
phosphine components is varied. We have previously reported
the heterolytic activation of dihydrogen with 2, yielding the
surprisingly stable complex 6 (Figure 4). Interestingly, we found
that 1 was unreactive toward dihydrogen (2 bar, ambient
temperature), suggesting that the presence of a ZrꢀP interaction
was a key feature in such a system, as might be expected by
analogy to main group FLPs. Exposure of the intermediately
bulky complex 3 to low pressures of dihydrogen (1ꢀ2 bar) at
ambient temperature resulted in an immediate color change from
orange to yellow, and the 31P NMR spectrum revealed >99%
conversion to a new species at 20.1 ppm (1JPH = 467 Hz). Only
in situ characterization was possible, since attempts to isolate the
material lead only to recovery of 3, but based on NMR data the
compound is formulated as 7. The reconversion of 7 to 3 upon
isolation indicated the reaction was reversible, and indeed simply
degassing the solution via three freezeꢀpumpꢀthaw cycles gave
50% conversion to 3, while complete removal of the solvent
under reduced pressure gave >99% conversion to 3. The system
was cycled three times in this way, demonstrating that the
reaction is fully reversible at room temperature and requires
only mild vacuum to induce hydrogen release. Given the con-
trasting reactivity of the Cp system 1 (no reaction under these
conditions) and the Cp* system 2 (facile but irreversible H2
cleavage to give 6), the reversible nature of hydrogen addition in
the Cp/Cp* mixed system 3 shows how subtle ligand alterations
can have a big influence on reactivity. Compound 4, with a less
bulky phosphine moiety, reacts incompletely at 2 bar of hydro-
Figure 6. Calculated energies for [(C5R5)2Zr(PhCl)(O(C6H4)PtBu2)]
(1, 2, or 3) and [(C5R5)2Zr(H)(O(C6H4)PHtBu2)] (6, 7, or product
derived from 1) relative to [(C5R5)2Zr(O(C6H4)PtBu2)] compounds.
Blue lines, C5R5 = C5H5; red lines, C5R5 = C5H5/C5Me5; black lines,
C5R5 = C5Me5. Solid lines indicate B3LYP calculations; dashed lines
indicate M06-2X level calculations.
dihydrogen, giving 100% conversion to two (in ca. 1:9 ratio)
spectroscopically distinct PꢀH species with near identical 1JPH
coupling constants (493.8 and 494.4 Hz). By analogy to related
literature systems, we tentatively assign this to two rotomers of 9
(Figure 5).26 Degassing the solution and warming to 60 °C in an
open system resulted in complete regeneration of 5 within ca. 3 h.
As expected, by analogy with main group FLPs, increasing
steric bulk lengthens the interaction between the basic phosphine
and electrophilic Zr center until it becomes “frustrated” (albeit, as
is always observed with such zirconocenes, a “vacant” coordina-
tion site is not observed and a labile solvent27 or anion interaction
persists).28 However, this does not always correlate to increased
reactivity when kinetic stabilization of the ZrꢀP is considered.
Insight into the subtle differences observed in the hydrogenation
of these compounds can be drawn from the large body of work
concerning the hydrogenation of d0 metal complexes. Of parti-
cular relevance to this work are the studies concerning the rate of
hydrogenolysis of neutral and cationic metallocene alkyls. In
these studies, the rate of hydrogenolysis is noted to be strongly
dependent on the nature of the ancillary ligands and, more
specifically, is substantially faster for Cp* compounds compared
to the analogous Cp compounds. One argument is that the
relatively electron rich Cp* ligand provides extra electron density
for backbonding to η2-dihydrogen intermediates.29 This not only
serves to explain the observed trends in hydrogenation but may
help to explain why a CO complex is accessible with 2 but not
with 1 and why 2 reacts immediately with ethene while 1 is inert
(vide infra). Preliminary calculations comparing the relative
gen, giving ca. 10% conversion to a new species (15 ppm, 1JPH
=
459.6 Hz) assigned as 8 and concomitant broadening of the
original resonance assigned to 4. These observations are con-
sistent with a dynamic binding of H2 in solution. Such reactivity is
initially surprising when it is considered that 1, which also has a
ZrꢀP bond, was found to be unreactive under the same condi-
tions. It is possible that the bulkier tert-Bu-substituted phosphine
in 1, despite resulting in a thermodynamically weaker longer
ZrꢀP bond compared to 3, affords kinetic protection of this
bond which is not present in the less encumbered iso-Pr
derivative. Preliminary calculations (vide infra) also suggest an
electronic component. Compound 5, with a bulky but less basic
mesityl-substituted phosphine, reacts extremely rapidly with
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Figure 9. POV-ray representation of part of the molecular structure of
12. All hydrogen atoms and borate anion have been omitted for clarity.
The crystal structure of 12 contains disorder in the formate group, where
it is bound through either one or both oxygen atoms in a ratio of
0.53:0.47. An illustration of the other component is shown in the
Supporting Information. Thermal ellipsoid is drawn at the 50% prob-
ability level. Selected bond lengths (Å) and angles (deg): Zr1 C35
2.360(2), C35 O2 1.124(2), Zr1 O1 1.952(1), O1 C21 1.360(2), P1
C26 1.837(2). O2 C35 Zr1 179.1(2), O1 Zr1 C35 90.10(6), C35 Zr1
O1 90.10(6), Zr1 O1 C21 168.7(1), O1 C21 C26 121.9(1).
Figure 7. Summary of reactivity of 1, 2, and 6 with CO2. Counterion =
[B(C6F5)4]ꢀ.
sharp stretch at 1694 and 1697 cmꢀ1 for 10 and 11, respectively,
which is similar to main group FLP systems.32 However, unlike
the two main group systems, these transition metal analogues do
not liberate CO2 upon thermolysis and are thermally stable up to
80 °C;33 instead they slowly decompose to as yet unidentified
products upon prolonged thermolysis. Although thermodyna-
mically robust, the CO2 is kinetically labile and was readily
displaced by THF or dichloromethane (DCM) to yield products
in which these solvents have reacted (see sections 2.5 and 2.6).
Treatment of 10 or 11 with hydrogen showed no reaction (2 bar,
ambient temperature). However, the dihydrogen activation
product 6 reacted immediately with CO2, to give the unusual
monomeric formate complex 12 in quantitative yield (Figure 9).
This intermediate for stepwise CO2 reduction suggests promise
for these systems in this important area, and the identification of
an η2 binding mode of the formate ligand in 12 illustrates a subtle
difference compared with main group analogues where only an
η1 bonding mode is noted.17,34 Recent work by Stephan and
Menard has demonstrated that stoichiometric reduction of CO2
to methanol using an FLP triad is possible using ammonia borane
as the reducing agent.35 Unfortunately, analogous attempts to
reduce the coordinated CO2 in 11 and 12 with amine boranes
were unsuccessful and resulted only in the previously observed
dehydrocoupling reactions.20
2.4. Reactivity with Carbon Monoxide. There is only one
example of CO activation with traditional main group FLPs.36
This may be in part due to the lack of a stable (C6F5)3BꢀCO
adduct.37,38 While in this instance 1 proved inert to CO, 2
reacted immediately, giving a bright red solution and a small but
noticeable change in the 31P{1H} NMR shift (from 7.4 ppm in 2
to 5.6 ppm) (Scheme 2). Isolation of this species confirmed its
identity as 13, and it constitutes a rare example of a Zr(IV)
carbonyl compound (Figure 10). Complex 13 is surprisingly
stable; although exceedingly air and moisture sensitive, it is
stable at room temperature and may be isolated as a solid by
drying in vacuo.
Figure 8. POV-ray representation of the molecular structure of 10. All
hydrogen atoms and borate anion have been omitted for clarity. Thermal
ellipsoids are drawn at the 50% probability level. Selected bond lengths
(Å) and angles (deg): Zr1 O1 2.019(2), Zr1 O2 2.086(2), O2 C11
1.298(4), C11 O3 1.208(5), C11 P1 1.892(4), P1 C12 1.822(4), O1
C13 1.355(4). O1 Zr1 O2 86.9(1), O2 C11 O3 127.9(3), O3 C11 P1
117.4(3), P1 C11 O2 114.5(3), P1 C12 C13 124.7(3), C13 O1 Zr1
134.2(2).
energies of 1, 2, and 3 (B3LYP and M06-2X) support our experi-
mental observations and imply that 6 and 7 possess fundamen-
tally different ground state energies (Figure 6).
2.3. Reactivity with Carbon Dioxide. One of the most
exciting examples of FLP induced reactivity is the reversible
binding of carbon dioxide, first reported by Stephan and Erker
et al.30 The potential of these systems to sequester and activate
CO2 implicates the utility of this substrate in catalytic reactions.
Advances have been made in this regard, although current
systems are unrealistic in terms of technological application
because of the reactive coreagents necessary. Exposure of chloro-
benzene solutions of 1 or 2 to 1 bar CO2 at room temperature
resulted, in both cases, in an immediate reaction. Interestingly,
and crucially in supporting the analogy with FLP systems, the
related Lewis baseꢀfree zirconium complexes, [Cp2ZrOR]-
t
[MeB(C6F5)3] (R = Me and Bu), are found to be completely
unreactive toward CO2, highlighting the pivotal role of the
phosphine in these systems.31 The products were fully character-
ized and unambiguously assigned to 10 and 11 (Figure 7), with
both compounds being structurally characterized (10 in Figure 8,
11 in the Supporting Information). The IR spectra exhibited a
The carbonyl ligand in 13 (Figure 10) is nonclassical in
nature39ꢀ41 with a νco higher than that of free CO (νco = 2163
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Scheme 2. Comparison of the Reactivity of 1 and 2 toward H2 and COa
a Counterion = [B(C6F5)4]ꢀ.
Figure 10. POV-ray representation of the molecular structure of 13. All
hydrogen atoms and borate anion have been omitted for clarity. Thermal
ellipsoids drawn at the 50% probability level. Selected bond lengths (Å)
and angles (deg): Zr1 C35 2.360(2), C35 O2 1.124(2), Zr1 O1
1.952(1), O1 C21 1.360(2), P1 C26 1.837(2). O2 C35 Zr1 179.1(2),
O1 Zr1 C35 90.10(6), C35 Zr1 O1 90.10(6), Zr1 O1 C21 168.7(1),
O1 C21.
Figure 11. POV-ray representation of the molecular structure of 15. All
hydrogen atoms and borate anion have been omitted for clarity. Thermal
ellipsoids drawn at the 50% probability level. Selected bonds length (Å)
and angles (deg): Zr1 O1 2.026(1), O1 C21 1.332(2), Zr1 C35
2.231(2), C35 C36 1.215(3), C36 C37 1.442(3). C35 Zr1 O1
91.92(6), Zr1 O1 C21 164.5(1), O1 C21 C26 122.1(1), C21 C26 P1
120.8(1), C35 C36 C37 175.9(2).
Scheme 3. Postulated Route to the Formation of 14 from 2,
a
CO, and H2
of 6 to CO results in elimination of H2 and formation of mixtures
of 6 and 13 (Scheme 2). Upon standing, 13 and 6 slowly react to
form the coordinated formaldehyde complex 14 (Scheme 3).
This transformation may be achieved more directly by leaving
solutions of 2 under 10 bar of 1:1 CO/H2 for ca. 14 days.
Although no other intermediates are observed during the course
of the reaction, we suggest that 14 forms via coordination of CO
to 6, followed by CO insertion and rearrangement. An indepen-
dent synthesis of 14 was carried out by reacting 2 with gaseous
formaldehyde. Analogous reactions of aldehydes with a linked
main group FLP has been demonstrated.45 This reactivity
represents a single stepwise reduction of CO with hydrogen,
and similar “double” reductions (to methoxide) have been
observed in Zr46 and recently in U47 sandwich complexes.
2.5. Reactivity with Alkenes and Alkynes. The reaction of FLPs
with alkenes48,49 and alkynes50,51 is a well documented and general9
reaction. Depending on the specific reagents, deprotonation (terminal
alkynes only), 1,2-addition, or (in one case)51 1,1-carboration may
occur. The selectivity has been correlated to the basicity of the Lewis
basic component, with less basic aryl-phosphines favoring a 1,2-
addition.50 The intramolecular phosphineꢀallane system developed
by Uhl et al.9 gives mixtures of deprotonation and 1,2-addition
products at room temperature and upon warming to 70 °C fully
a Counterion = [B(C6F5)4]ꢀ.
for 13 vs 2144 cmꢀ1 for free CO).43,42 It is also slightly higher
than data for the related d0 complexes [Cp3M(CO)]-
[MeB(C6F5)3] (M = Zr, Hf).43,44 Although stable to vacuum,
the CO ligand in 13 is kinetically very labile and is rapidly and
irreversibly replaced by THF or even DCM to yield the
corresponding reaction products (see sections 2.5 and 2.6).
Exposure of solutions of 13 to hydrogen results in rapid dis-
placement of CO and formation of 6, while exposure of solutions
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Figure 12. Compounds 15ꢀ18. Counterion = [B(C6F5)4]ꢀ.
Figure 14. Summary of the reactions of 1 and 2 with fluoro- and
chloroalkanes.
(quantitative in less than 1 min for 2, and ca. 30 min for 1) and
repeatable with stoichiometric amounts of CH2Cl2. In this way,
19 and 20 were isolated in quantitative yield (Figure 14, X-ray
structure of 20 in the Supporting Information). A similar reaction
was observed by Stephan et al. between a titanium complex with
P(o-tol)3,52 and Jordan et al. have also reported similar CꢀCl
cleavage reactions of zirconium cations in CH2Cl2.27 While these
reactions seem commonplace to transition metal Lewis acids, we
were surprised to find that no CꢀCl cleavage reactions have been
reported for the main group systems. The previous parallel
reactivity between our systems and the main group promoted a
Figure 13. POV-ray drawing of the molecular structure of 18. All
hydrogen atoms and borate anion have been omitted for clarity. Thermal
ellipsoids drawn at the 50% probability level. Selected bonds length (Å)
and angles (deg): Zr1 O1 2.0364(9), O1 C21 1.330(2), P1 C26
1.798(1), C35 P1 1.809(1), C35 C36 1.552(2), C36 Zr1 2.327(1).
C36 Zr1 O1 83.26(4), O1 C21 C26 123.1(1), C21 C26 P1 124.2(1), P1
C35 C36 119.6(1), C35 C36 Zr1 111.68(9).
t
brief investigation using Bu3P/B(C6F5)3. Mixing a toluene
t
solution of Bu3P, B(C6F5)3, and an excess of 1-chloropropane
led to no observed spectroscopic changes after ca. 1 h at room
temperature. However, after standing overnight, in addition
t
to unchanged Bu3P, several other unidentified species were
apparent by 31P and 31P{1H} NMR spectroscopy. Importantly,
no [ClB(C6F5)3]ꢀ53 was detected, which may have been
expected to form if an analogous reaction had taken place.
Building on the previous result, we explored the reactivity of
compounds 1 and 2 toward a range of alkyl chlorides. Both 1
and 2 were found to react rapidly with 1-chloropropane or
2-chloropropane to give products reminiscent of SN2-type
reactions 21ꢀ24 (Figures 14 and 15). The SN2-type reactions
were accompanied by a competing E2-type reaction giving 27
and 28 in varying quantities (see Experimental Section), and
consequently, isolation and purification of these compounds
was not possible.
In the case of reaction with tertiary alkyl chlorides, only elimina-
tion products are observed. The reaction of 1and 2with tBuCl yields
27 and 28, respectively, in 94% and 92% yield, with the expected
isobutylene side-product detected by 1H NMR spectroscopy.
Reaction of 2 with neopentyl chloride gives a ca. 1:2 mixture of
SN2 and E2 products (25 and 28). While the SN2 products must
arise from nucleophilic attack, we suggest that the E2 product arises
from a WagnerꢀMeerwein sigmatropic shift (Scheme 4).54,55
It is noteworthy that these reactions are performed in chloro-
benzene solvent in which the complexes are completely inert;
reactivity is orthogonal to the well-known palladium species for
coupling reactions with aryl halides.56
converts to the 1,2-addition product, suggesting that 1,2-addition is
the thermodynamic product.
Treatment of 2 with excess phenylacetylene immediately
decolorized the solution and gave rise to a characteristic PꢀH
resonance at 26.7 ppm (1JPH = 472.7 Hz). Isolation and
structural characterization of 15 confirmed that a deprotonation
rather than 1,2-addition type reaction to the alkyne had occurred
(Figures 11 and 12). Exactly the same result was observed with
the less bulky analogue 1 to give 16 (Figure 12). Given the
importance of Lewis basicity for this reaction in main group
systems, we also investigated compound 5. This reacts in exactly
the same way to give 17 (Figure 12), evidenced by a characteristic
PꢀH resonances at ꢀ20.6 ppm (1JPH = 468.9 Hz). All three
compounds 15ꢀ17 were found to be thermally stable to 100 °C,
showing no sign of rearrangement.
Similar trends to other reactions are observed when 1 or 2 are
treated with alkenes; 1 exhibited no reaction toward ethene
under mild conditions, whereas 2 reacted immediately to give 18
(Figures 12 and 13), which like its main group analogue tBu3P-
CH2CH2B(C6F5)3 is thermally stable. Attempts to insert CO
into the ZrꢀC bond in either 15, 16, 17, or 18 were unsuccessful
under the conditions examined (2 and 10 bar CO, 25 and 100 °C).
2.6. Reactivity with Alkyl Halides. In the course of defining
the solubility characteristics of these complexes, we discovered
that compounds 1 and 2 react rapidly and cleanly with CH2Cl2
to yield the CꢀCl cleaved products. This reaction is fast
The same reactivity patterns are observed even with alkyl
fluorides. Treatment of 2 with 1-fluoropentane cleanly gives 26
in 69% yield. Although SN2 reactions of alkyl fluorides are
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Figure 15. POV-ray representation of the molecular structure of 24. All hydrogen atoms and borate anion have been omitted for clarity. Thermal
ellipsoids drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg): Zr1 O1 2.051(5), Zr1 Cl1 2.458(2), O1 C21 1.328(9), P1 C31
1.87(1), P1 C26 1.815(7). Cl1 Zr1 O1 94.6(2), Zr1 O1 C21 149.0(5), C27 P1 C31 113.2(4).
Scheme 4. Suggested WagnerꢀMeerwein Sigmatropic Shift
That Occurs during the Formation of 28 via Neopentyl
Chloride Activation
Scheme 5. Reaction of 1 and 2 with THF to Give the Ring-
Opened Products 29 and 30
THF in the same way leads to the same reactivity but a much slower
rate of reaction. Following the reaction by NMR initially revealed
signals consistent with opening of the ZrꢀP bond and formation of
a simple THF adduct. Only over the course of ca. 4 days does ring-
opening occur, with the concomitant decline of signals for this
adduct. Isolation of the sample after this time in the same manner to
30 confirmed that intramolecular ring-opening of THF had
occurred to give 29 (X-ray structure in the Supporting Information).
We suggest that this substantial difference in rate between 1 and 2 is
likely to be related to differences in the geometrical alignment of the
coordinated THF in 1 and 2. For example, in [Cp2Zr(Me)(THF)]-
[BPh4], the THF ligand is known to coordinate in an almost
perpendicular fashion with respect to the plane formed between the
two Cp rings. Although more sterically congested than a parallel
binding mode, the orientation maximizes a favorable OꢀZr π-
bonding interaction. Upon moving to a Cp* ligand set (for example,
in [Cp*2Zr(CH2TMS)(THF)][BPh4]), this orientation is too high
in energy and the THF adopts a parallel binding mode.65 If a similar
scenario exists in 1 and 2, then it is conceivable that 2 reacts so much
faster than 1 because the phosphine is orientated directly toward the
α-carbon of the coordinated THF, whereas in 1 a rotation is
required to achieved the same orientation.
known, there are very few examples.57 Clearly, the strength of the
ZrꢀF bond provides a strong driving force for this reaction in our
case, but, nevertheless, complexes capable of the cleavage of
unactivated CꢀF bonds are rare.58ꢀ60
2.7. Reactivity with Ethers. The activation of ethers and
CꢀO bonds in general has attracted recent interest because of
the ubiquity of such groups in biosustainable feedstocks.61 One
of the first reactions observed with main group FLPs was the
ring-opening of tetrahydrofuran.62 We were struck by the fact
that virtually identical reactivity patterns were observed many
years previously when Lewis bases were combined with electro-
philic transition metals. Although not recognized as such at the
time, these results could be thought of as an early example of a
frustrated Lewis pair, a connection made recently by Stephan and
co-workers.5
Treatment of 2 with excess THF immediately decolorizes the
bright orange solution. After ca. 5 min, the 31P{1H} NMR spectrum
of the colorless solution revealed 100% conversion of 2 to a new
singlet resonance at higher chemical shift (42.7 ppm), typical of
tetralkylphosphonium center. Layering the reaction mixture with
hexane and standing overnight yielded large colorless crystals which
were fully characterized and unambiguously identified as 30
(Scheme 5). The structural parameters (Figure 16) are similar to
related compounds previously reported.63,64 Treatment of 1 with
The ring-opening of THF by 1 and 2, while supporting the
analogy between frustrated Lewis pairs and our system, is well-
known for closely related complexes. More surprising results
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Figure 16. POV-ray representation of the molecular structure of 30. All
hydrogen atoms and borate anion have been omitted for clarity. Thermal
ellipsoids drawn at the 50% probability level. Selected bonds length (Å)
and angles (deg): Zr1 O1 2.0980(9), Zr1 O2 1.9599(9), O2 C38
1.410(1). O1 Zr1 O2 91.63(4), Zr1 O1 C21 143.57(8), Zr1 O2 C38
149.10(8).
Figure 17. POV-ray representation of the molecular structure of 32. All
hydrogen atoms, solvent, and borate anion have been omitted for clarity.
Thermal ellipsoids drawn at the 50% probability level. Selected bonds
length (Å) and angles (deg): Zr1 O2 2.069(2), Zr1 O1 1.968(2), O1
C37 1.421(5). O2 Zr1 O1 94.73(9), Zr1 O2 C21 146.5(2), Zr1 O1 C37
155.7(3).
rare SN2 type reaction where the nucleofugacity of ethoxide
appears to be drastically increased by the presence of the electron
deficient and oxophillic zirconium center, and draws parallels to
the well-known reaction of BCl3 with alkyl ethers to give
B(OR)Cl2 and alkyl chlorides68 and the reaction of [Cp2Zr-
(THF)N(tBu)][BPh4] with allylic ethers.69 It is noteworthy, and
indeed crucial to the concept we propose here, that related
zirconocene complexes which do not contain a pendant
phosphine70ꢀ73 form only the expected simple diethyl ether
adducts; a Lewis basic phosphine and electrophilic zirconium
center are both required for activation to occur.
Scheme 6. Reaction of 1 and 2 with Ethers
This powerful new reactivity for compound 2 in particular led
us to investigate if bulkier alkyl ethers could be cleaved in the
same way (Scheme 6). No reaction is observed when diisopropyl
ether is added to 2 at room temperature. However, after 4 days at
100 °C, 38% conversion to the unexpected product 33 is
observed by in situ 31P and 31P{1H} NMR spectroscopy and
ESI-MS. We speculate that this product arises from similar
elimination mechanisms to those described in section 2.5. The
facile elimination pathway for this derivative is presumably being
driven by relief of steric congestion from the bulkier tetraalk-
ylphosphonium intermediate. Methyl tert-butyl ether (MTBE)
reacts in a similar fashion: addition of MTBE to 2 and heating in
sealed tube at 60 °C for 16 h gives >98% conversion to 34 with
isobutene as the elimination side-product. Finally, reaction of 2
with the unstrained 6-membered heterocycle tetrahydropyran
(THP) ring-opens this cyclic ether to 35 in an analogous fashion
to THF in 100% conversion after ca. 48 h (X-ray structure in the
Supporting Information).
were obtained when we sought to investigate the reaction of 1
and 2 with diethyl ether, expecting this would allow isolation of
the simple ether adducts. Treatment of a chlorobenzene solution
of 2 with excess diethyl ether leads initially to NMR data
consistent with the simple diethyl ether adduct of 2. However,
after ca. 3 days at room temperature, this converts quantitatively
(>99% by NMR) to 32 (Scheme 6 and Figure 17). As in the case
of THF ring-opening, compound 1 reacts in a similar manner but
much more slowly, possibly for analogous reasons to those
suggested previously. Following the reaction by NMR spectros-
copy indicated that treatment of 1 with excess diethyl ether gives
The steric and electronic similarities that exist between cationic
group 4 and isolobal neutral group 3 complexes has led to exciting
discoveries in polymerization and CꢀH activation chemistry.74 We
hypothesized that neutral group 3 analogues of 1 and 2 would
express a similar analogy in their reactivity to main group FLPs. Our
preliminary investigations have been frustrated to some extent by
the dearth of reliable methods for obtaining complexes free from
coordinating solvents such as THF. However, we reasoned that the
isolation of THF adducts would at least allow us to explore the FLP-
type ring-opening chemistry previously described. Such THF
adducts were obtained by protonolysis of MCp3 compounds75,76
with phosphino-alcohols in THF.
an association complex 1 OEt2; the coordinated ether is rather
3
labile, and attempted isolation of this product by removal of the
solvent gave only 1. Only after monitoring a sample by 31P{1H}
NMR spectroscopy over the course of ca. 1 month did a new
singlet resonance at 45 ppm form, consistent with the cleaved
ether product 31. Precipitation of light yellow crystals allowed
unambiguous characterization of 31 by X-ray diffraction (see the
Supporting Information). Both 32 and 31 represent rare exam-
ples of species in which the ether CꢀO bond has been cleaved,
and are distinct from superficially similar CꢀO cleavage reac-
tions by other Zr(II)66 and Zr(IV) species.67 This represents a
For example, addition of t-Bu2P(C6H5)OH to Cp03La in THF
gives 36 as a highly sensitive off white solid (Scheme 7).
The absence of LaꢀP interaction is inferred from the minor
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Scheme 7. Synthesis of the Related Neutral La Compound 36
and Subsequent Thermolysis to Give the THF Ring-Opening
Product, 37
Scheme 8. Synthesis of Compound 38
Figure 19. POV-ray representation of the molecular structure of 38. All
hydrogen atoms, solvent, and borate anion have been omitted for clarity.
Thermal ellipsoids drawn at the 50% probability level. Selected bond
lengths (Å) and angles (deg): Zr1 O1 2.076(1), O1 C21 1.326(2), Zr1
O2 1.986(1), O2 C36 1.349(2), C36 C35 1.378(3), C36 C37 1.456(3).
O1 Zr1 O2 94.35(5), Zr1 O1 C21 154.96(9), Zr1 O2 C36 174.7(1), O2
C36 C35 121.8(2), O2 C36 C37 115.0(2), C35 C36 C37 123.2(2).
Figure 18. POV-ray representation of the molecular structure of 37. All
hydrogen atoms and borate anion have been omitted for clarity. Thermal
ellipsoid is drawn at the 50% probability level. Solvent molecules have
been omitted for clarity. Selected bonds length (Å) and angles (deg):
La1 O1 2.3924(1), La1 O2 2.2014(1), C19 O1 1.3026, P1 C24 1.7928,
P1 C33 1.8153(1), O2 C36 1.3902. La1 O1 C19 143.67, O1 La1 O2
92.97, C33 P1 C24 113.05, P1 C24 C19 123.12, C24 C19 O1 123.34.
phosphine. In fact, upon treating 2 with a slight excess of acteone,
the anticipated reaction occurred immediately and quantitatively
to yield the Zr-enolate 38 and phosphonium center (Scheme 8),
which was subsequently isolated and characterized crystallogra-
phically (Figure 19).
31P{1H} NMR shift upon protonolysis and is almost identical to
that observed in the neutral Zr precursors.20 The presence of the
3. CONCLUSIONS
1
expected 1 equiv of coordinated THF is confirmed by H and
We have extended the concept of frustrated Lewis pairs (FLPs)
from the main group to transition metal systems. The analogy to
FLPs provides a coherent and useful paradigm in rationalizing the
reactivity of cationic zirconoceneꢀphosphinoaryloxide complexes.
We consider these complexes to be FLPs where the usual main
group Lewis acid (typically a fluorinated aryl borane) is replaced by a
zirconocene fragment. Our complexes mirror the reactivity of main
group systems for the heterolytic cleavage of dihydrogen, activation
of CO2, alkenes, alkynes and aldehydes, and the ring-opening of
THF. However, they also go beyond the main group systems
reported to date in accessing more powerful reactivity, such as the
stepwise reduction of CO or CO2 under mild conditions, the
cleavage of aliphatic CꢀCl or even CꢀF bonds, and the cleavage
of CꢀO bonds in noncyclic ethers. It should be noted that such
reactivity is not observed in the absence of the integrated Lewis base
phosphine fragment. In many cases, we have been struck by the
good thermodynamic stability of what appear to be potentially
labile species, for example, the robust Zr-CO complex 13, albeit in
the presence of other substrates these species are highly kinetically
13C{1H} NMR spectroscopy. Attempts to remove the THF by
vacuum or heating were unsuccessful. Compound 36 proved to
be surprisingly stable in solution with respect to ring-opening of
coordinated THF by the pendant phosphine. However, after
ca. 3 days at 110 °C, 100% conversion to the ring-opened
product 37 (Figure 18) was observed. This markedly differing
stability is in direct contrast to 2 which reacts within seconds,
and even with 1 which reacts within days at room temperature;
however, it does confirm the analogy to the Zr system and
indeed main group FLPs.
2.8. Reactivity with Acetone. It has been shown that
coordination of a remote functionality to the Lewis acid site in
an FLP can increase the acidity of conjugatively linked protons to
such an extent that they may be deprotonated by relatively weak
bases.34 An ideal candidate for these reactions is ketones posses-
sing α-protons. We envisaged that, upon coordination of the
carbonyl-oxygen in acetone, the already relatively acidic CꢀH
protons (pKa ∼26.5)77 may be deprotonated by the proximal
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labile. As expected, the specific reactivity patterns observed are a
function of the substitution patterns of both the zirconocene and
phosphine moieties of our complexes; in general, more sterically
encumbered species have the higher intrinsic activity. We suggest
the remarkable reactivity of these species in small molecule activa-
tion, combined with the catalytic reactivity for amine borane
dehydrogenation (as opposed to only stoichiometric reaction for
main group systems), offers exciting possibilities which we continue
to explore.
(d, 1JCP = 25.7 Hz, C(CH3)3), 31.1 (d, 2JCP = 16.4 Hz, C(CH3)3), 30.9
(d, JCP = 16.4 Hz, C(CH3)3), 30.2 (d, JCP = 9.3 Hz,, ZrCH3), 11.6
2
(d, JCP = 1.6 Hz, C5(CH3)5). 31P{1H} (161 Hz, toluene-d8): δ 9.20 (s).
The tube was returned to the glovebox and combined with a chloro-
benzene solution [(DTBP)H][B(C6F5)4] (78.4 mg, 0.09 mmol), result-
ing in orange solutionandgasevolution. Thesolutionwasallowed tostand
for 16 h and analyzed by 31P NMR which showed quantitative conversion
to 3. The tube was again returned to the glovebox and then layered with
hexanes and allowed to stand for a further 16 h, precipitating an orange oil.
Decanting the supernatant and washing the residue with several portions
of hexanes before drying in vacuo afforded an amorphous yellow solid.
1
4. EXPERIMENTAL SECTION
Yield: 97.9 mg, 0.081 mmol, 90%. H NMR (500 Hz, chlorobenzene/
benzene-d6, 5:1): HC3, HC4, and HC6 aromatic signals are obscured by
chlorobenzene signals and could not be unambiguously identified. δ 6.41
(dd, 1H, 3JHH = 8.2 Hz, 4JHH = 4.9 Hz, 1H, HC5), 5.76 (s, 5H, C5H5), 1.78
(s, 15H, C5(CH3)5), 1.11 (br. d, 3JHP ∼ 55 Hz, 18H, C(CH3)3). 31P{1H}
(161 Hz, chlorobenzene/benzene-d6, 5:1): δ 53.34. 13C{1H} (125 Hz,
500 Hz, chlorobenzene/benzene-d6, 5:1): δ 168.0 (d, 2JCP = 15.2 Hz, C1),
133.9 (s, C4), 133.6 (d, 4JCP = 2.9 Hz, C5), 123.2 (s, d, 3JCP = 3.9 Hz, C6),
122.4 (d, 1JCP = 21.5 Hz, C2), 120.9 (C5(CH3)5), 117.9 (d, 1JCP = 4.9 Hz,
C3), 116.6 (s, C5H5), 32.1 (br.s, C(CH3)3), 29.8 (br. s, C(CH3)3), 12.8
(s, C5(CH3)5). 31P{1H} (161 Hz, chlorobenzene/benzene-d6, 5:1): δ
53.3 (s). ESI MS: 527.2 [M]. Elemental Analysis: Calcd: C, 52.70; H, 3.50.
Found: C, 52.71; H, 3.90.
Unless otherwise stated, all manipulations were carried out under an inert
atmosphere of argon using standard Schlenk-line and glovebox (M-Braun,
O2 < 0.1 ppm, H2O < 0.1 ppm) techniques, and all glassware was oven-
dried (200 °C) overnight and allowed to cool under vacuum prior to use.
The compounds Cp*2ZrMe2,78 CpCp*ZrMe2,78 t-Bu2P(C6H4)OH,79
i-Pr2P(C6H4)OH,80 [DTBP][B(C6F5)4],20 1, 2, and 620 were prepared
according to the literature. Cp03La was purchased from Strem and sublimed
before use. Solvents were purified and predried using an Anhydrous
Engineering column purification system81 and then vacuum transferred
from the appropriate drying agent (K/benzophenone for aromatic and
ethers, CaH2 for hydrocarbons and chlorinated solvents) prior to use. NMR
spectra were recorded using a JEOL ECP 300 MHz spectrometer and
Varian 400 and 500 MHz spectrometers (using the appropriate deuterated
solvent, purchased from Cambridge Isotope Laboratories or Sigma-Aldrich
and purified by vacuum transfer from the appropriate desiccant) and
Compound 4. Compound 4 was prepared in an analogous fashion
to 2 (0.07 mmol scale). Orange crystals were grown from a chloroben-
zene solution layered with hexane. Yield: 77.5 mg, 0.062 mmol, 89%. 1H
NMR (500 Hz, chlorobenzene/toluene-d8, 5:1): HC3, HC4, and HC6
aromatic signals are obscured by chlorobenzene signals and could not be
unambiguously identified. δ 6.45 (ddd, 1H, 3JHH = 8.26 Hz, 4JHH = 4.5
1
referenced to an appropriate standard (residual solvent signal for H,
BF3 OEt2 for 11B, 85% H3PO4 for 31P, and FCCl3 for 19F NMR). Spectra
3
of air and moisture sensitive compounds where recorded using sealable
J-Youngs tap NMR tubes. Microanalysis was carried out by the Micro-
analytical Laboratory, University of Bristol using a Carlo Elba spectrometer.
2-(Dimesityl)phosphinophenol. 2-(Dimesityl)phosphinophenol
was prepared in a analogous fashion to a previously reported procedure
for i-Pr2P(C6H4)OH80 from o-methoxymethylphenol in two steps
(5 mmol scale). White solid, recrystallized from DCM/hexane at
ꢀ20 °C. Yield:59%. 1HNMR(400Hz, toluene-d8):δ7.14 (ddd, 1H, 3JHH
= 7.2 Hz, 4JHH = 5.0 Hz, 4JHH = 1.7 Hz, HC5), 7.00 (tm, 1H, 3JHH = 7.3 Hz,
HC3), 6.84 (overlapping ddd, 1H, 3JHH = 7.7 Hz, 3JHH = 6.5 Hz, 4JHH = 1.2
Hz, HC4), 6.67 (d, 4H, JHH = 3.2 Hz, m-H), 6.47 (tm, 1H, 3JHH = 7.3 Hz,
3
Hz, JHP = 1.1 Hz, H5, 1H, Hc5), 2.49 (sept, JHH = 7.34 Hz, 1H,
CH(CH3)2), 2.48 (sept, 3JHH = 7.34 Hz, 1H, CH(CH3)2), 1.57 (s, 30H,
3
3
C5(CH3)5), 0.96 (dd, JHP = 14.9, JHH = 7.34 Hz, 6H, CH(CH3)2),
0.95 (dd, 3JHP = 14.9 Hz, 3JHH = 7.34 Hz, 6H, CH(CH3)2). 13C{1H}
(125 Hz, chlorobenzene/toluene-d8, 5:1): δ 166.7 (d, 2JCP = 16.6 Hz,
C1), 133.8 (s, C5), 133.2 (s, C4), 122.6 (d, 3JCP = 3.9 Hz, C6), 121.7 (d,
1JCP = 28.4 Hz, C2), 119.7 (d, 2JCP = 5.9 Hz, C3), 127.16 (s, C5(CH3)5),
1
1
26.8 (d, JCP = 11.7 Hz, CH(CH3)2), 21.4 (d, JCP = 2.0 Hz, CH-
(CH3)2), 20.4 (d, JCP = 4.9 Hz, CH(CH3)2). 31P{1H} (161 Hz,
2
chlorobenzene/toluene-d8 5:1): δ 23.88 (s). ESI MS: 569.25 [M].
Elemental Analysis: Calcd: C, 62.60; H, 8.17. Found: C, 62.27; H, 8.31.
Compound 5. In this instance, the neutral precursor was prepared
in an identical fashion to that previously reported20 from Cp*2ZrMe2
(195 mg, 0.5 mmol) and Mes2P(C6H5)OH (181.2, 0.5 mmol). Yield:
339.5 mg, 0.46 mmol, 92%. 1H NMR (400 Hz, toluene-d8): δ 7.15 (ddd,
1H, 3JHH = 7.6 Hz, 4JHH = 4.2 Hz, 4JHH = 1.7 Hz, HC6), 7.06 (tm, 1H,
3JHH = 7.3 Hz, HC4), 6.73 (d, 4H, JHH = 2.5 Hz, m-H), 6.54 (tm, 1H, 3JHH
= 7.58 Hz, HC3), 6.47 (tm, 1H, 3JHH = 6.11 Hz, HC5), 2.36 (s, 12H, p-CH3),
2.13 (s, 6H, p-CH3), 1.78 (s, 30H, C5(CH3)5), ꢀ0.03 (s, 3H,
HC6), 6.14 (s, 1H, OH), 2.17 (s, 12H, p-CH3), 2.07 (s, 6H, p-CH3. 13
C
{1H} (100 Hz, toluene-d8): δ 164.8 (d, 2JCP = 20.6 Hz, C1), 147.5 (d, 2JCP
= 15.00 Hz, o-C), 143.1 (s, p-C), 135.2 (d, 3JCP = 3.9 Hz, m-C), 135.9 (s,
C3), 133.5 (d, 1JCP = 9.7 Hz, i-C), 138.7 (d, 2JCP = 2.7 Hz, C5), 126.6 (d,
3JCP = 4.3 Hz, C2), 125.4 (d, 3JCP = 1.6 Hz, C6), 120.5 (s, C4), 27.4 (d, JCP
= 16.5 Hz, o-CH3), 25.5 (s, p-CH3). 31P{1H} (161 Hz, toluene-d8): δ
ꢀ43.16 (s). ESI MS: 363.19 [M + H]. Elemental Analysis: Calcd: C, 79.53;
H, 7.51. Found: C, 79.56; H, 7.80.
Compound 3. CpCp*ZrMe2 (23.1 mg, 0.1 mmol) and t-Bu2
P(C6H5)OH (23.8 mg, 0.1 mmol) were loaded into an NMR tube fitted
with a Teflon needle valve and dissolved in toluene-d8 (0.7 mL),
immediately resulting in the slow evolution of gas as the reagents
dissolved. The tube was removed after gas evolution subsided (ca. 16 h),
and the relevant NMR spectra of the neutral precursor acquired. (Not
isolated, quantitative by NMR.)1H NMR (400 Hz toluene-d8): δ 7.62
(dt, 1H, 3JHH = 7.6 Hz, 4JHH = 2.0 Hz, HC6), 7.15 (ddd, 1H, 3JHH = 8.1
2
ZrCH3). 13C{1H} (100 Hz, toluene-d8): δ 167.3 (d, JCP = 23.4 Hz,
C1), 144.0 (d, 3JCP = 16.4 Hz, i-C), 137.5 (s, o-C), 134.4 (s, p-C), 132.6
(d, 2JCP = 21.8 Hz, C3), 130.5 (d, 3JCP = 3.1 Hz, m-C), 129.3 (s, C5),
125.6 (d, 3JCP = 11.7 Hz, C6), 120.7 (d, 3JCP = 11.7 Hz, C4), 118.7 (s,
C2), 118.6 (s, C5(CH3)5), 33.8 (d, JCP = 8.6 Hz, ZrCH3), 23.7 (d, JCP
=
16.4 Hz, o-CH3), 20.9 (s, p-CH3), 11.5 (s, C5(CH3)5). 31P{1H} (161
Hz, toluene-d8): δ ꢀ26.8 (s). ESI MS: 737.35 [M + H]. Elemental
Analysis: Calcd (1:1 hexane solvate): C, 74.31; H, 8.93. Found: C,
74.55; H, 8.90.
Hz, 4JHH = 7.1 Hz, 4JHH = 1.7 Hz HC3), 6.76 (dt, 1H, 3JHH = 7.2 Hz, 4JHH
=
1.2 Hz, HC4), 6.52 (ddd, 1H, 3JHH = 8.1 Hz, 4JHH = 6.4 Hz, 4JHH = 1.2 Hz
3
HC5), 5.83 (s, 5H, C5H5), 1.79 (s, 15H, C5(CH3)5), 1.27 (d, JHP
=
The neutral precursor (36.9 mg, 0.05 mmol) prepared above was
activated and isolated in an analogous fashion to 2 except the compound
was obtained as a deep red oil that could not be solidified despite
repeated precipitation into hexanes. Yield: 69.7 mg, 0.046 mmol, 92%.
1H NMR (500 Hz chlorobenzene/toluene-d8, 5:1): HC3 and HC4
aromatic signals are obscured by chlorobenzene signals and could not
11.3 Hz, 9H, C(CH3)3), 1.26 (d, 3JHP = 11.3 Hz, 9H, C(CH3)3), 0.35 (d,
JHP = 0.7 Hz, 3H, Zr CH3). 13C{1H} (100 Hz, toluene-d8): δ 169.9 (d,
2JCP = 24.1 Hz, C1), 136.1 (d, 3JCP = 3.9 Hz, C6), 130.3 (s, C5), 125.5 (d,
2JCP = 24.9 Hz, C3), 119.7 (d, 3JCP = 3.1 Hz, C4), 117.9 (s, C2), 118.4 (s,
C5(CH3)5), 111.6 (s, C5H5), 32.5 (d, 1JCP = 25.7 Hz, C(CH3)3), 32.4
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be unambiguously identified. 6.73 (d, 4H, JHH = 3.1 Hz, m-H), 6.64 (t,
1H, 3JHH = 7.55 Hz, HC6), 6.09 (pseudo t, 1H, 3JHH = 6.8 Hz, HC5), 2.17
(s, 12H, p-CH3), 2.16 (s, 6H, p-CH3), 1.64 (s, 30H, C5(CH3)5).
(s, C5(CH3)5), 123.5 (d, 3JCP = 7.8 Hz, C6), 119.7 (d, 3JCP = 9.8 Hz,
C4), 117.6 (s, C5H5), 104.5 (d, 1JCP = 49.9 Hz, C2), 38.6 (d, 1JCP = 26.4
Hz, C(CH3)3), 28.9 (s, C(CH3)3), 11.2 (s, C5(CH3)5). 31P{1H} (161
Hz, chlorobenzene/toluene-d8, 5:1): δ 37.02 (s). ESI-MS: 615.29 [M ꢀ
CO2 + H2O]. Elemental Analysis (1:1 PhCl solvate from crystal
structure): Calcd: C, 54.42; H, 4.00. Found: C, 54.78; H, 4.36.
2
13C{1H} (100 Hz, toluene-d8): δ 166.2 (d, JCP = 24.3 Hz, C1),
143.8 (d, 3JCP = 15.7 Hz, i-C), 139.2 (s, o-C), 135.6 (s, C6), 135.6 (s,
p-C), 129.4 (d, 3JCP = 2.6 Hz, m-C), 129.3 (s, C5(CH3)5), 125.3 (d, 2JCP
= 13.7 Hz, C3), 121.8 (s, C2), 122.6 (s, C4), 119.6 (s, C5), 23.7 (d, JCP
=
Compound 11. An identical procedure to 10 using 1 instead of 2
(45.5 mg, 0.04 mmol) was followed, giving pale yellow blocks. Yield: 42.7
mg, 0.0361 mmol, 73%. H NMR (500 Hz fluorobenzene/toluene-d8,
5:1): HC4 aromatic signal is obscured by fluorobenzene signals and could
not be unambiguously identified. δ 7.33 (overlapping ddt, 1H, 3JHH = 8.3
Hz, 3JHH = 7.1 Hz, 4JHH = 1.22 Hz, HC5), 7.04 (partial m, HC3), 6.48 (ddd,
1H, 3JHH = 8.31 Hz, 3JHH = 6.6 Hz 4JHH = 0.98 Hz, HC6), 6.02 (s, C5H5),
1.16 (d, 3JHP = 15.9 Hz, 18H, C(CH3)3). 13C{1H} (125 Hz, fluoroben-
15.0 Hz, o-CH3), 21.2 (s, p-CH3), 12.07 (s, C5(CH3)5). 31P{1H} (161
Hz, chlorobenzene/toluene-d8 5:1): δ ꢀ32.9 (s). ESI-MS not observed.
Satisfactory elemental analysis could not be obtained. We attribute the
depleted C and H determinations to be due to traces of chlorobenzene
that remain occluded in the oil. Calcd: C, 55.28; H, 4.13. Found: C,
55.12; H, 4.25.
1
Compound 8. A sample of 3 dissolved in chlorobenzene
(∼0.7 mL) in a NMR tube equipped with a Teflon needle valve was
connected to a Schlenk line and subjected to three freezeꢀpumpꢀthaw
degassing cycles then backfilled with 1 bar hydrogen at room tempera-
ture via liquid nitrogen trap. The solution immediately changed color to
orange to yellow. The relevant spectra were recorded in situ. since
attempts to isolate the material resulted in quantitative recovery of 3. 1H
NMR (500 Hz, chlorobenzene/benzene-d6, 5:1): HC3, HC4, and HC6
aromatic signals are obscured by chlorobenzene signals and could not be
zene/benzene-d68, 5:1): δ 169.9 (d, 2JCP = 1.5 Hz, C1), 164.7 (d, 1JCP
=
94.4 Hz, ZrOC(O)P), 137.4 (d, 4JCP = 2.9 Hz, C5), 134.6 (d, 2JCP = 4.9
Hz, C3), 122.2 (d, 3JCP = 7.3 Hz, C6), 121.2(d, 3JCP = 10.3 Hz, C4), 117.6
1
1
(s, C5H5), 105.4 (d, JCP = 58.7 Hz, C2), 37.4 (d, JCP = 27.4 Hz,
C(CH3)3), 27.8 (s, C(CH3)3). 31P{1H} (161 Hz, fluorobenzene/
toluene-d8 5:1): δ 37.02 (s). ESI-MS:489.15[Mꢀ CO2 + O2]. Elemental
Analysis: Calcd: C, 49.80; H, 2.73. Found: C, 49.79; H, 2.78.
Compound 12. A sample of 6 (64.0 mg, 0.05 mmol) was loaded
into an NMR tube fitted with a Teflon needle valve and dissolved in
chlorobenzene (0.7 mL) giving a colorless solution. The tube was
removed, connected to a Schlenk line and subjected to three freezeꢀ
pumpꢀthaw degassing cycles and then backfilled with 1 bar carbon
dioxide at room temperature via trap cooled to ꢀ40 °C. After ca. 5 min, a
white precipitate began to form. The 31P{1H} NMR spectrum of the
supernatant revealed 100% conversion of 6. The sample was degassed
and then returned to the glovebox and poured into hexane (1 mL). The
resulting white powder was collected on a frit and washed with several
portions of hexane before drying in vacuo. Crystals suitable for X-ray
diffraction were grown from a DCM solution layered with hexane at
unambiguously identified. 6.61 (br. s, 1H, Zr-H), 6.28 (dd, 1H, 3JHH
=
8.2 Hz, 4JHH = 4.6 Hz, H5, 1H, HC5), 5.69 (s, 5H, C5H5), 1.77 (s, 15H,
C5(CH3)5), 0.90 (br. d, 3JHP = 17.2 Hz, 18H, C(CH3)3). 13C{1H} (125
Hz, 500 Hz, chlorobenzene/benzene-d6, 5:1): δ 168.4 (s, C1), 137.7 (s,
C3), 131.3 (s, C6), 121.4 (s, C5), 120.9 (C5(CH3)5), 120.5 (d, 3JCP
=
11.8 Hz, C4), 110.8 (s, C5H5), 100.2 (d, 1JCP = 72.4 Hz, C2), 34.6 (d,
1JCP = 36.2 Hz, C(CH3)2), 34.4 (d, 1JCP = 34.2 Hz, C(CH3)2), 27.7 (br.
s, C(CH3)2), 27.5 (br. s, C(CH3)2), 12.75 (s, C5(CH3)5). 31P{1H} (161
Hz, chlorobenzene/benzene-d6, 5:1): δ 19.61.
Compound 9. Compound 9 was prepared in an identical fashion to
6
20 using 5 (instead of 2) (30.3 mg, 0.02 mmol). The product could not
1
be isolated in pure form, since exposure to vacuum resulted in some
decomposition to 5, and thus, only in situ NMR data of the major species
are presented. 1H NMR (chlorobenzene/toluene-d8, 5:1): HC3 aromatic
signals are obscured by chlorobenzene signals and could not be
room temperature. Yield: 39 mg, 0.029 mmol, 59%. H NMR (500
MHz, DCM-d2): δ 8.76 (d, JHP = 2.4 Hz, 1H, OC(O)H), 7.77 (d, 1H,
1JHP = 492.2 Hz, P-H), 7.54 (t, 1H, 3JHH = 8.2 Hz, HC5), 7.39 (ddd, 1H,
3JHH = 10.5 Hz, 3JHH = 7.9 Hz, 4JHH = 1.7 Hz, HC3), 7.00 (dt, 1H, 3JHH
=
2
unambiguously identified. δ 7.80 (d, 1H, JHP = 484.4 Hz), 7.02 (m,
7.9 Hz, 4JHP = 2.2 Hz, HC4), 6.57 (ddd, 1H, 3JHH = 8.5 Hz, 3JHH = 5.7 Hz,
4JHH = 0.7 Hz, HC6), 1.95 (s, 30H, C5(CH3)5), 1.52 (br. d, 3JHP = 16.7
Hz, 18H, C(CH3)3). 13C{1H} (125 MHz, DCM-d2): δ 167.6 (s, C1),
166.6 (s, OC(O)H), 133.5 (s, C5), 133.3 (d, 2JCP = 6.9 Hz, C3), 124.8
(s, C5(CH3)5), 123.8 (d, 3JCP = 6.4 Hz, C6), 119.9 (d, 3JCP = 10.8 Hz,
C4), 102.4 (d, 1JCP = 73.9 Hz, C2), 37.2 (d, 1JCP = 37.2 Hz, C(CH3)3),
28.5 (s, 2JCP = 1.5 Hz, (C(CH3)3), 12.2 (s, C5(CH3)5). 31P{1H} (121
Hz, DCM-d2): δ 14.78 (s). ESI-MS: 643.29 [M]. Elemental Analysis:
Calcd: C, 53.52 H, 4.11. Found: C, 53.48; H, 4.34.
1H, HC5), 6.42 (d, 4H, JHH = 4.9 Hz, m-H), 6.37 (dt, 1H, 3JHH = 7.3 Hz,
4JHH = 2.4 Hz, HC4), 6.07 (t, 1H, 3JHH = 7.63 Hz, HC6), 1.81 (s, 12H,
p-CH3), 1.71 (s, 6H, p-CH3), 1.41 (s, 30H, C5(CH3)5). 13C{1H} (100 Hz,
3
chlorobenzene/toluene-d8, 5:1): δ 167.3 (s, C1), 146.5 (d, JCP = 2.9
Hz, i-C), 143.8 (s, 3JCP = 9.8 Hz o-C), 137.1 (s, p-C), 133.9 (s, C3), 132.1
(d, 3JCP = 11.8 Hz, m-C), 129.7 (s, C6), 121.8 (s, C5), 120.0 (d, 3JCP
=
13.7 Hz, C4), 119.6 (s, C5(CH3)5), 101.7 (d, 1JCP = 90 Hz, C2), 21.6 (d,
JCP = 7.8 Hz, o-CH3), 20.6 (s, p-CH3), 11.3 (s, C5(CH3)5). 31P{1H}
(161 Hz, chlorobenzene/toluene-d8, 5:1): δ ꢀ27.33 (s, minor 10%),
ꢀ29.23 (s, major 90%). ESI MS: not observed.
Compound 13. A sample of 6 (69.5 mg, 0.05 mmol) (compound 2
may also be conveniently used in the same manner) was loaded into an
NMR tube fitted with a Teflon needle valve and dissolved in
chlorobenzene (0.7 mL) giving a bright orange solution. The tube
was removed, connected to a Schlenk line via a three way valve
connected to a regulated 1 bar supply of CO. The tube was subjected
to three freezeꢀpumpꢀthaw degassing cycles, refilling with CO on
the last cycle once the tube had warmed to room temperature. Upon
shaking, the solution immediately became bright red. The tube was
again degassed and then returned to the glovebox. The solution was
layered with hexane, precipitating large red blocks. Yield: 64.0 mg,
0.049 mmol, 98%. 1H NMR (400 Hz chlorobenzene/toluene-d8, 5:1):
Compound 10. A sample of 2 (27.8 mg, 0.02 mmol) was loaded
into an NMR tube fitted with a Teflon needle valve and dissolved in
chlorobenzene (0.7 mL) giving a bright orange solution. The tube was
removed, connected to a Schlenk line via a three way valve connected to
a regulated 1 bar supply of CO2 via a ꢀ78 °C trap. The tube was
subjected to three freezeꢀpumpꢀthaw degassing cycles, refilling with
CO on the last cycle once the tube had warmed to room temperature.
Upon shaking, the solution immediately became bright red. The tube
was again degassed and then returned to the glovebox. The solution was
layered with hexane precipitating large yellow blocks. Yield: 25.2 mg,
0.0191 mmol, 96%. 1H NMR (500 Hz chlorobenzene/toluene-d8, 5:1):
HC3 and HC4 aromatic signals are obscured by chlorobenzene signals
δ 7.22 (m, 2H, HC5 and HC3), 6.74 (partialm, HC4), 6.44 (ddd, 1H,3JHH
=
and could not be unambiguously identified. δ 7.51 (dt, 1H, JHH
7.69 Hz, 4JHH = 1.83 Hz, HC6), 6.09 (ddd, 1H, 3JHH = 8.06 Hz, 3JHH
=
=
3
3
8.2 Hz, JHH = 5.2 Hz 4JHH = 0.9 Hz, HC6), 1.61 (s, 30H, C5(CH3)5),
3
1.18 (d, JHP = 15.9 Hz, 18H, C(CH3)3). 13C{1H} (125 Hz, chloro-
5.13 Hz 4JHH = 1.10 Hz, HC5), 1.66 (s, 30H, C5(CH3)5), 1.08 (d, 3JHP
1
benzene/toluene-d8, 5:1): δ 169.3 (s, C1), 161.9 (d, JCP = 85.1 Hz,
= 12.05 Hz, 18H, C(CH3)3). 13C{1H} (125 Hz, chlorobenzene/
2
3
ZrOC(O)P), 137.5 (s, C5), 128.9 (d, JCP = 8.8 Hz, C3), 126.2
toluene-d8, 5:1): δ 195.1 (s, ZrCO), 165.9 (d, JCP = 22.0 Hz, C1),
18473
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Journal of the American Chemical Society
ARTICLE
2
136.9 (s, C6), 126.1 (s, C5(CH3)5), 122.5 (d, JCP = 23.5 Hz, C3),
ESI-MS: 699.33 [M]. Elemental Analysis: Calcd: C, 57.44 H, 4.24.
Found: C, 57.83; H, 4.08.
121.4 (s, C2), 121.1 (s, C4), 118.5 (d, 4JCP = 3.4 Hz, C5), 33.1 (d, 1JCP
2
= 20.1 Hz, C(CH3)2), 30.9 (d, JCP = 14.2 Hz, C(CH3)2), 11.3
Compound 16. Conpound 16 was prepared in a analogous fashion
(s, C5(CH3)5). 31P{1H} (161 Hz, chlorobenzene/toluene-d8 5:1):
δ 5.63. ESI-MS: 615.29 [M ꢀ CO + H2O]. Elemental Analysis: Calcd:
C, 54.26; H, 4.01. Found: C, 54.25; H, 4.29.
to 15 but not isolated. 31P{1H} (121 Hz, unlocked, PhCl): δ 20.25. 31
(121 Hz, unlocked, PhCl): δ 20.23 (d, JPH = 481.95 Hz). ESI-MS:
559.17 [M].
P
1
Compound 14. Method A. 2 (69.5 mg, 0.05 mmol) was dissolved
in chlorobenzene (0.3 mL) then loaded into a high pressure NMR tube
fitted with a Teflon needle valve giving a bright orange solution. The
tube was removed, connected to a Schlenk line, and subjected to three
freezeꢀpumpꢀthaw degassing cycles and then backfilled with 10 bar
carbon monoxide/hydrogen (50:50) at room temperature via a column
(10 ꢁ 1 cm) of freshly activated powdered molecular sieves. The
solution immediately changed color to pale green. Once the reaction
was deemed complete by 31P{1H} NMR (ca. 14 days), the sample was
degassed, returned to the glovebox, and transferred to a standard NMR
tube where toluene-d8 (0.3 mL) was added. The tube was sealed and
removed, and the relevant spectra were acquired. The sample was
returned to the glovebox and layered with hexane. The colorless crystals
were separated from the supernatant via decantation and then washed
Compound 17. Compound 17 was prepared in a analogous fashion
to 15 but not isolated. 31P{1H} (121 Hz, unlocked, PhCl): δ ꢀ29.95.
31P (121 Hz, unlocked, PhCl): δ ꢀ29.95 (d, 1JPH = 513.59 Hz). ESI-MS:
825.25 [M].
Compound 18. A sample of 2 (55.6 mg, 0.04 mmol) was loaded
into an NMR tube fitted with a Teflon needle valve and dissolved in
chlorobenzene (0.7 mL) giving a bright orange solution. The tube was
removed, connected to a Schlenk line via a three way valve connected to
a regulated 1 bar supply of ethene. The tube was subjected to three
freezeꢀpumpꢀthaw degassing cycles, refilling with ethene on the last
cycle once the tube had warmed to room temperature. Upon shaking,
the solution immediately became pale green. The tube was again
degassed and then returned to the glovebox. The solution was layered
with hexane, precipitating colorless needles. Yield: 39.2 mg, 0.03 mmol,
1
1
3
with hexane and dried in vacuo. Yield: 56 mg, 0.043 mmol, 86%. H
75%. H NMR (500 MHz, DCM-d2): δ 7.48 (t, 1H, JHH = 8.2 Hz,
HC5), 7.35 (ddd, 1H, 3JHH = 10.9 Hz, 3JHH = 7.9 Hz, 4JHP = 1.8 Hz, HC3),
NMR (500 Hz chlorobenzene/toluene-d8, 1:1): δ 7.23 (m, 1H, HC5),
HC3 obscured by chlorobenzene 13C satellites, 7.19 (tm, 1H, 3JHH = 7.0
Hz, HC4), 6.67 (tm, 1H, 3JHH = 8.24 Hz, HC6), 6.50 (dd, 1H, 3JHH = 8.55
6.95 (t, 1H, 3JHH = 7.93 Hz, HC4), 6.65 (ddd, 1H, 3JHH = 8.5 Hz, 3JHH
5.8 Hz, JHH = 1.2 Hz, HC6), 3.10 (br. d, 2H, JHP = 54.2 Hz,
ZrCH2CH2P), 1.97 (br. s, 15H, C5(CH3)5), 1.77 (br. s, 15H, C5-
=
4
2
4
Hz, JHH = 5.18 Hz HC3), 5.19 (br. s., 2H, OCH2P), 1.63 (s, 30H,
3
C5(CH3)5), 1.63 (d, 3JHP = 14.6 Hz, 18H, C(CH3)3). 13C{1H} (125 Hz,
chlorobenzene/toluene-d8, 1:1): δ 168.4 (d, 2JCP = 1.6 Hz, C1), 135.6
(s, C5), 124.4 (d, 2JCP = 8.8 Hz, C3), 123.9 (s, C5(CH3)5), 129.0 (s, C6),
118.9 (d, 3JCP = 10.8 Hz, C4), 103.1 (d, 1JCP = 59.7 Hz, C2), 64.6 (d,
(CH3)5), 1.70 (br. s, 9H, C(CH3)3), 1.50 (d, JHP = 17.0 Hz, 2H,
ZrCH2CH2P), 1.28 (br. s, 9H, C(CH3)3). 13C{1H} (125 MHz, DCM-d2):
δ 170.4 (s, C1), 135.9 (d, 2JCP = 1.9 Hz, C5), 135.3 (d, 3JCP = 5.9 Hz,
C3), 124.4 (d, 3JCP = 7.8 Hz, C6), 122.2 (s, C5(CH3)5) 119.2 (d, 3JCP
=
1
1
1JCP = 40.1 Hz,OCH2P), 37.6 (d, JCP = 31.3 Hz, C(CH3)3), 28.5
9.8 Hz, C4), 100.9 (d, JCP = 76.3 Hz, C2), 37.6 (br. m, C(CH3)3),
31.1 (br. s, C(CH3)3), 28.1 (br. s, C(CH3)3), 28.8 (d, JCP = 6.9 Hz,
ZrCH2CH2P), 21.7 (d, JCP = 36.2 Hz, ZrCH2CH2P), 11.9 (s,
1
(s, C(CH3)3), 11.5 (s, C5(CH3)5).31P{1H} (161 Hz, chlorobenzene/
toluene-d8, 1:1): δ 40.2 (s). ESI-MS: 627.29 [M]. Elemental Analysis:
Calcd: C, 54.18; H, 4.16. Found: C, 54.39; H, 4.00.
1
C5(CH3)5). 31P{1H} (121 Hz, DCM-d2): δ 45.07. ESI-MS: 625.31 [M].
Elemental Analysis: Calcd: C, 55.13; H, 4.40. Found: C, 55.49; H, 4.68.
Compound 20. Samples of [Cp*2Zr(Me)O(C6H4)PtBu2] (49.1
mg, 0.08 mmol) and [DTBP][B(C6F5)4] (69.7 mg, 0.08 mmol) were
weighed into two vials, dissolved in DCM (1 mL), and mixed,
immediately precipitating a white solid. After standing overnight, the
solids had dissolved, and the 31P{1H} NMR spectra of the pale green
solution revealed >99% conversion to 19. The sample was returned to
the glovebox and poured into hexane, and the resulting white solids were
collected on a frit and then washed with several portions of hexanes
before drying in vacuo. Large green crystals suitable for X-ray diffraction
were grown by layering a concentrated DCM solution with hexane.
Yield: 93.3 mg, 0.079 mmol, 99%. Compound 20 may also be con-
Method B. Paraformaldehyde (ca. 30 mg) was decomposed at 120 °C
under a 10ꢀ3 Torr static vacuum and collected in a liquid nitrogen trap
via a glass sinter (porosity 4). The trap was then connected to an NMR
tube containing 2 (27.8 mg, 0.02 mmol) and subjected to three
freezeꢀpumpꢀthaw degassing cycles. After the last cycle, the NMR
tube was allowed to remain frozen and fully submersed in liquid nitrogen
and then opened to the trap. Upon slow warming to ambient conditions,
excess formaldehyde gas was vacuum transferred to the NMR tube. The
tube was then allowed to warm to ambient where the color changed from
orange to yellow. Following the reaction by 31P{1H} NMR revealed ca.
60% conversion to 14 after 30 min, ca. 20% unidentified species
(s, 23.49; s, 23.04; s, 21.86; s, 21.52), and unreacted 2.
1
veniently obtained by dissolution of 2 in DCM. H NMR (500 Hz,
Compound 15. A sample of 2 (27.8 mg, 0.02 mmol) was loaded into
an NMR tube fitted with a Teflon needle valve and dissolved in chloro-
benzene (0.7 mL) giving a bright orange solution. Excess phenylacetylene
(ca. 3 drops) was added, immediately giving a pale green solution. The 31P
and 31P{1H} NMR spectra of the colorless solution revealed >99%
conversion of 3. The sample was returned to the glovebox, layered with
hexane, and allowed to stand for 16 h, precipitating large pale green needles.
The supernatant was decanted, and the solids washed with hexane before
drying in vacuo. Yield: 24.8 mg, 0.018 mmol, 90%. 1H NMR (500 MHz
DCM-d2): δ 7.51 (m, 2H, HC5 and HC3), 7.32 (m, 5H, HAr), 6.95
(overlapping ddd, 1H, 3JHH = 10.0 Hz, 3JHH = 7.7 Hz, 4JHP = 2.8 Hz, HC4),
6.65 (d, 1H, 1JHP = 471.5 Hz, P-H), 6.58 (dd, 1H, 3JHH = 8.5 Hz, 3JHH = 5.2
DCM-d2): δ 7.50 (tm, 1H, 3JHH = 8.0 Hz, HC5), 7.46 (ddd, 1H, 3JHH = 11.9
Hz, 3JHH = 8.2 Hz, JHP = 1.6 Hz, HC3), 6.97 (tm, 1H, 3JHH = 8.1 Hz, HC4),
6.16 (ddd, 1H, 3JHH = 8.2 Hz, 3JHH = 5.5 Hz, JHP = 0.9 Hz, HC6), 4.64
(d, 2H, 2JHP = 5.8 Hz, PCH2Cl), 1.95 (s, 30H, C5(CH3)5), 1.60 (d, 3JHP
=
15.9 Hz, 18H, C(CH3)3). 13C{1H} (125 Hz, DCM-d2): δ 168.0 (s, C1),
136.3 (d, 4JCP = 2.9 Hz, C5), 135.1 (d, 2JCP = 6.9 Hz, C3), 126.1 (d, 3JCP
=
7.8 Hz, C6), 125.4 (s, C5(CH3)5), 119.3 (d, 3JCP = 10.9 Hz, C4), 101.2 (d,
1JCP = 66.5 Hz, C2), 39.6 (d, 1JCP = 32.3 Hz, C(CH3)3), 31.7 (d, 1JCP = 43.0
Hz, PCH2C), 29.0 (s, C(CH3)3), 12.6 (s, C5(CH3)5). 31P{1H} (161 Hz,
DCM-d2): δ 41.5 (s). ESI-MS: 681.23 [M]. Elemental Analysis (DCM/
hexane 1:1 solvate from crystal structure): Calcd: C, 51.67; H, 4.60. Found:
C, 51.53; H, 4.85.
3
Hz, HC6), 2.04 (s, 30H, C5(CH3)5), 1.36 (d, JHP = 17.0 Hz, 18H,
C(CH3)3). 13C{1H} (125 MHz, DCM-d2): δ 167.7 (s, C1), 137.0 (d, 4JCP
= 2.45 Hz, C5), 132.9 (d, 2JCP = 7.8 Hz, C3), 132.2 (s, o-C), 130.4 (s, p-C),
129.3 (s, m-C), 128.7 (s, i-C), 127.1 (s, PhCCZr), 125.6 (s, PhCCZr),
123.3 (d, 3JCP =6.9 Hz, C6), 122.8 (s, C5(CH3)5), 119.9 (d, 3JCP = 11.7 Hz,
C4), 101.4 (d, 1JCP = 73.9 Hz, C2), 35.0 (d, 1JCP = 36.7 Hz, C(CH3)3), 28.5
(s,C(CH3)3),12.6(s,C5(CH3)5).31P{1H} (121 Hz, DCM-d2):δ20.49 (s).
Compound 21. A sample of 1 (0.05 mmol) was loaded into an
NMR tube fitted with a Teflon needle valve and dissolved in chloro-
benzene (0.7 mL) giving a bright orange solution. Excess PrCl (ca. 3
drops) was added, immediately causing the solution to turn pale green.
The 31P and 31P{1H} NMR spectra revealed >99% conversion of 1. The
NMR of the reaction mixture after standing overnight showed a 9:1
n
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Journal of the American Chemical Society
ARTICLE
mixture of 21:27. Attempts to crystallize the reaction mixture led only to
the isolation of pale green oils that were found to be mixtures of 21 and
27. 31P{1H} (121 Hz, unlocked, PhCl): δ 42.87. ESI-MS: 535.21 [M].
Compound 22. Compound 22 was prepared in a similar manner to
21 using nPrCl and 2 (0.02 mmol). The NMR of the reaction mixture
after standing overnight showed a 9:1 mixture of 28:22. Attempts to
crystallize the reaction mixture led only to the isolation of pale green oils
that were found to be mixtures of 28 and 22. 31P{1H} (121 Hz,
unlocked, PhCl): δ 42.63. ESI-MS: 675.30 [M].
Compound 23. Compound 23 was prepared in a similar manner to
21 using iPrCl and 1 (0.02 mmol). The NMR of the reaction mixture
after standing overnight showed a 10:1 mixture of 23:27. Attempts to
crystallize the reaction mixture led only to the isolation of pale green oils
that were found to be mixtures of 23 and 27. 31P{1H} (121 Hz,
unlocked, PhCl): δ 51.80. ESI-MS: 535.21 [M].
ESI-MS: 687.36 [M]. Elemental Analysis: Calcd: C, 55.31; H, 4.64.
Found: C, 55.32; H, 4.54.
Compound 27. Prepared in a similar way to 21 using an excess of
tBuCl (3 drops). The sample was layered with hexane and allowed to
stand for 16 h precipitating a white microcrystalline solid. The super-
natant was decanted, and the solids washed with hexane before drying in
vacuo. Yield: 22.0 mg, 0.0188 mmol, 94%. 1H NMR (500 MHz DCM-d2):
δ 7.64 (pseudo t, 1H, 3JHH = 8.3 Hz, HC5), 7.4 (overlapping dd, 1H,
3JHH = 7.47 Hz, JHP = 1.47 Hz HC3), 7.12 (overlapping dd, 1H, 3JHH
=
7.3 Hz, 4JHH = 2.5 Hz, HC4), 6.73 (d, 1H, 1JHP = 476.5 Hz, P-H), 6.63
(dd, 1H, 3JHH = 8.3 Hz, 3JHH = 4.9 Hz, HC6), 6.47 (s, 10H, C5H5), 1.49
(d, 3JHP = 17.4 Hz, 18H, C(CH3)3). 13C{1H} (125 MHz DCM-d2): δ
167.8 (s, C1), 137.4 (d, 4JCP = 2.0 Hz, C5), 131.9 (d, 2JCP = 7.0 Hz, C3),
121.2 (d, 4JCP = 10.9 Hz, C6), 119.9 (d, 3JCP = 5.5 Hz, C4), 115.5 (s,
1
1
C5H5), 102.6 (d, JCP = 75.5 Hz, C2), 34.4 (d, JCP = 35.0 Hz,
C(CH3)3), 27.5 (s, C(CH3)3). 31P{1H} (121 Hz, DCM-d2): δ 22.50
(s). ESI-MS: 493.11 [M]. Elemental Analysis: Calcd: C, 49.10; H, 2.83.
Found: C, 48.99; H, 2.94.
Compound 24. Compound 24 was prepared in an analogous
manner to 21 using excess iPrCl (0.05 mmol). The NMR of the reaction
mixture after standing overnight showed a 15:1 mixture of 24:28. Pale
green crystals were obtained after three recrystallizations from DCM
Compound 28. Compound 28 was prepared in a similar manner to
27 using 2 (0.02 mmol.) Yield: 24.2 mg, 0.0184 mmol, 92%. 1H NMR
(500 MHz DCM-d2). δ 7.53 (pseudo t, 1H, 3JHH = 7.1 Hz, HC5), 7.34
1
solutions layered with hexane. Yield: 24.0 mg, 0.0177 mmol, 35%. H
NMR (500 MHz DCM-d2): δ 7.46 (pseudo t, 1H, 3JHH = 8.4 Hz, HC5),
3
3
(overlapping dd, 1H, JHH = 7.5 Hz, JHP = 1.5 Hz HC3), 6.98
7.36 (overlapping dd, 1H, JHH = 7.47 Hz, JHP = 1.47 Hz HC3), 7.15
3
4
(overlapping dd, 1H, 3JHH = 7.1 Hz, 4JHH = 2.6 Hz, HC4), 6.06 (dd, 1H,
(overlapping dd, 1H, JHH = 8.0 Hz, JHH = 1.7 Hz, HC4), 6.61 (ddd,
1H, 3JHH = 8.1 Hz, 3JHH = 4.9 Hz, 3JHH = 1.0 Hz, HC6), 6.48 (d, 1H, 1JHP
= 471.7 Hz, P-H), 1.96 (s, 30H, C5(CH3)5), 1.51 (d, 3JHP = 16.9 Hz,
18H, C(CH3)3). 13C{1H} (125 MHz DCM-d2): δ 167.0 (s, C1), 136.3
3
3
3JHH = 7.6 Hz, JHH = 4.9 Hz, HC6), 3.67 (sept, 1H, JHH = 7.6 Hz,
CH(CH3)2), 1.95 (s, 30H, C5(CH3)5), 1.62 (partial dd, 3JHP = 15.7 Hz,
3JHH = 7.6 Hz, 6H, CH(CH3)2), 1.56 (d, JHP = 15.4 Hz, 18H,
3
4
2
C(CH3)3). 13C{1H} (125 MHz DCM-d2): δ 167.9 (s, C1), 135.4 (d,
2JCP = 3.1 Hz, C5), 130.6 (d, 3JCP = 7.8 Hz, C3), 124.7 (d, 3JCP = 3.1 Hz,
C4), 119.0 (d, 4JCP = 10.9 Hz, C6), 115.5 (s, C5H5), 103.6 (d, 1JCP = 66.2
Hz, C2), 39.5 (d, 1JCP = 31.1 Hz, C(CH3)3), 29.1 (s, C(CH3)3), 24.9 (d,
1JCP = 35.0 Hz, CH(CH3)2), 20.8 (br. s, CH(CH3)2), 12.6 (s,
C5(CH3)5). 31P{1H} (121 Hz, DCM-d2): δ 51.24. ESI-MS: 675.30 [M].
Satisfactory elemental analysis could not be obtained. We attribute the
depleted C and H determinations to be due to traces of elimination
product (evident in ESI-MS and NMR) that could not fully be removed
despite recrystallization. Calcd: C, 54.01; H, 4.38. Found (average of five
determinations): C, 53.50; H, 4.51.
(d, JCP = 2.0 Hz, C5), 132.3 (d, JCP = 7.8 Hz, C3), 124.23 (s,
C5(CH3)5), 122.6 (d, 3JCP = 6.2 Hz, C6), 119.7 (d, 3JCP = 11.7 Hz, C4),
102.1 (d, 1JCP = 76.5 Hz, C2), 34.8 (d, 1JCP = 36.6 Hz, C(CH3)3), 28.2
(s, C(CH3)3), 11.9 (s, C5(CH3)5). 31P{1H} (121 Hz, DCM-d2): δ
21.55 (s). ESI-MS: 635.43 [M]. Elemental Analysis: Calcd: C, 53.00; H,
4.06. Found: C, 53.11; H, 4.16.
Compound 29. A sample of 2 (27.8 mg, 0.02 mmol) was loaded
into an NMR tube fitted with a Teflon needle valve and dissolved in
chlorobenzene (0.7 mL) giving a bright orange solution. Excess THF
(ca. 3 drops) was added, immediately causing the solution to decolorize
over the course of ca. 5 min. The 31P{1H} NMR spectrum of the
colorless solution revealed >99% 29. The sample was returned to the
glovebox, layered with hexane, and allowed to stand for 16 h precipitat-
ing large colorless crystals. The supernatant was decanted, and the
crystals were washed with hexane before drying in vacuo. Yield: 22.1 mg,
0.0162 mmol, 81%. 1H NMR (500 Hz DCM-d2): δ 7.45 (m, HC6 and
HC3), 6.88 (ddd, 1H, 3JHH = 8.2 Hz, 4JHH = 2.3 Hz JHP = 1.2 Hz, HC4),
6.32 (ddd, 1H, 3JHH = 7.32 Hz, 4JHH = 6.0 Hz, JHP = 1.1 Hz, HC5), 4.46
(t, 1H, 3JHH = 5.7 Hz, α-H), 2.72 (m, 2H, δ-H), 2.1 (br. m, 2H, γ-H),
1.93 (s, 30H, C5(CH3)5), 1.86 (m, 2H, β-H), 1.49 (d, 18H, 3JHH = 14.9
Hz, C(CH3)3). 31P{1H} (121 Hz, DCM-d2): δ 42.76. 13C{1H}
Compound 25. Compound 25 was prepared in a similar manner to
22 using neopentyl chloride (0.02 mmol). The NMR of the reaction
mixture after standing overnight showed a 1:4 mixture of 25:28.
Attempts to crystallize the reaction mixture led only to the isolation of
a pale green powder that was found to be mixtures of 25 and 28. 31P{1H}
(121 Hz, unlocked, PhCl): δ 55.85. ESI-MS: 703.34 [M].
Compound 26. A sample of 2 (83.4 mg, 0.06 mmol) was loaded
into an NMR tube fitted with a Teflon needle valve and dissolved in
chlorobenzene (0.7 mL) giving a bright orange solution. Excess 1-fluoro-
pentane (ca. 3 drops) was added, immediately giving a pale green
solution and a white precipitate. The 31P{1H} NMR spectra of the
colorless solution revealed >99% conversion of 3 in the supernatant. The
sample was returned to the glovebox and poured into hexane, and the
resulting white solids were collected on a frit and then washed with
several portions of hexanes before drying in vacuo. Yield: 56.6 mg, 0.041
mmol, 69%. 1H NMR (500 Hz, DCM-d2): δ 7.47 (m, 1H, HC5), 7.34
2
(125 Hz, DCM-d2): δ 169.9 (s, C1), 135.5 (d, JCP = 2.9 Hz, C3),
3
4
135.0 (d, JCP = 6.9 Hz, C6), 126.7 (d, JCP = 8.8 Hz, C5), 122.8 (s,
C5(CH3)5), 117.7 (d, 3JCP =10.76Hz,C4), 102.1 (d, 1JCP = 69.5 Hz, C2) 67.3
(s, α-C), 37.2 (d, 1JCP = 37.1 Hz, C(CH3)3), 33.4 (d, 3JCP = 14.7 Hz, β-C),
28.8 (s, C(CH3)3), 21.3 (d, 2JCP = 5.9 Hz γ-C), 19.4 (d 1JCP = 41.1 Hz δ-C),
12.1 (s, C5(CH3)5). ESI-MS: 669.336 [M]. Elemental Analysis: Calcd: C,
55.16; H, 4.48. Found: C, 55.31; H, 4.48.
(m, 1H, HC3), 6.92 (tm, 1H, 3JHH = 8.1 Hz, HC6), 6.20 (dd, 1H, 3JHH
=
8.2 Hz, 4JHH = 5.4 Hz, HC4), 2.81 (m, 2H, Ha), 1.95 (partial m, Hb), 1.92
(s, 30H, C5(CH3)5), 1.68 (pseudo q, 3JHH = 7.7 Hz, 2H, Hd), 1.52 (d,
3JHP = 15.1 Hz, 18H, C(CH3)3), 1.44 (pseudo q, 3JHH = 7.4 Hz, 2H, Hc),
0.99 (t, 3JHH = 7.3 Hz, 3H, He). 13C{1H} (125 Hz, DCM-d2): δ 168.6 (s,
C1), 135.6 (d, 4JCP = 2.3 Hz, C5), 135.2 (d, 2JCP = 7.0 Hz, C3), 126.2 (d,
3JCP = 8.6 Hz, C6), 123.7 (s, C5(CH3)5), 118.5 (d, 3JCP = 10.9 Hz, C4),
103.4 (d, 1JCP = 68.5 Hz, C2), 38.7 (d, 1JCP = 35.8 Hz, C(CH3)3), 28.5
Compound 30. An identical procedure to 29 was followed except
using 1 and an extended reaction time of ca. 7 days was required for
complete conversion. Colorless crystals were obtained. Yield: 24.8 mg,
0.0186 mmol, 93%. 1H NMR (400 MHz DCM-d2): δ 7.58 (t, 1H, 3JHH
=
7.2 Hz, HC6), 7.51 (ddd, 1H, 3JHH = 10.8 Hz, 3JHH = 8.1 Hz, JHP = 1.59
Hz, HC3), 6.98 (ddd, 1H, 3JHH = 8.19 Hz, 4JHH = 2.38 Hz, JHP = 1.10 Hz,
HC4), 6.49 (dd, 1H, 3JHH = 8.4 Hz, 4JHH = 5.6 Hz HC5), 6.35 (s, 10H,
C5H5), 4.22 (t, 1H, 3JHH = 6.0 Hz, α-H), 2.59 (m, 2H, δ-H), 1.93 (br. m,
2H, γ-H), 1.84 (m, 2H, β-H), 1.48 (d, 18H, 3JHH = 14.9 Hz, C(CH3)3).
31P{1H} (161 MHz, DCM-d2): δ 43.01. 13C{1H} (100 MHz, DCM-d2): δ
(s, C(CH3)3), 33.7 (br. s, Cc), 26.2 (br. s, Cb), 23.0 (s, Cd), 20.1 (d, 1JCP
=
39.7 Hz, Ca), 14.2 (s, Ce), 11.7 (s, C5(CH3)5). 31P{1H} (161 Hz,
DCM-d2): δ 43.9 (br. s). 19F (470 Hz, DCM-d2): δ ꢀ207.2 (br. s, ZrꢀF).
18475
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ARTICLE
170.2 (d, 2JCP = 1.6 Hz C1), 136.8 (d, 2JCP = 3.1 Hz, C3), 135.2 (d, 3JCP
=
and HC3), 6.89 (ddd, 1H, 3JHH = 8.2 Hz, 4JHH = 2.3 Hz, JHP = 1.2 Hz,
HC4), 6.22 (ddd, 1H, 3JHH = 7.32 Hz, 4JHH = 5.95 Hz, JHP = 1.07 Hz,
HC5), 4.53 (t, 1H, 3JHH = 5.1 Hz, α-H), 2.57 (m, 2H, ε -H), 2.18 (br. m,
2H, δ-H), 1.92 (s, 30H, C5(CH3)5), 1.82 (m, 2H, β-H), 1.66 (m, 2H,
γ-H), 1.48 (d, 18H, 3JHH = 15.0 Hz, C(CH3)3). 31P{1H} (121 Hz, DCM-
d2): δ 40.31. 13C{1H} (125 Hz, DCM-d2): δ 169.7 (s, C1), 135.3 (d,
2JCP = 2.5 Hz, C3), 134.9 (d, 3JCP = 6.85 Hz, C6), 126.6 (d, 4JCP = 8.3 Hz,
6.23 Hz, C6), 123.3 (d, 4JCP = 7.8 Hz, C5), 118.9 (d, 3JCP = 10.90 Hz,
C4), 113.9 (s, C5H5), 102.1 (d, 1JCP = 70.1 Hz, C2), 70.3 (s, α-C), 36.8
(d, 1JCP = 37.3 Hz, C(CH3)3), 31.9 (d, 3JCP = 14.8 Hz, β-C), 28.6 (s,
C(CH3)3), 20.4 (d, 2JCP = 6.2 Hz γ-C), 18.8 (d 1JCP = 42.0 Hz δ-C).
ESI-MS: 529.19 [M]. Elemental Analysis: Calc.d: C, 51.62; H, 3.33.
Found: C, 51.19; H, 4.69.
C5), 122.7 (s, C5(CH3)5), 117.5 (d, 3JCP = 11.3 Hz, C4), 102.2 (d, 1JCP
=
Compound 32. A sample of 2 (27.8 mg, 0.02 mmol) was loaded
into an NMR tube fitted with a Teflon needle valve and dissolved in
fluorobenzene (0.7 mL) and diethyl ether (20 μL) giving a bright yellow
solution. The tube was sealed, removed from the glovebox, and followed
by NMR. The procedure was repeated on a preparative scale (278.1 mg,
0.2 mmol) in chlorobenzene. Once the reaction was deemed complete
by 31P{1H} NMR, the sample was precipitated by layering with hexane.
The white microcrystalline precipitate was recrystallized by layering a
concentrated DCM solution with hexanes and leaving to stand for 16 h.
The supernatant was decanted form the large colorless crystals before
drying in vacuo. Yield: 211.2 mg, 0.158 mmol, 79%. 1H NMR (400 Hz
69.5 Hz, C2), 71.91 (s, α-C), 37.6 (d, 1JCP = 38.2 Hz, C(CH3)3), 30.7 (d,
3JCP = 15.2 Hz, β -C), 28.8 (s, C(CH3)3), 28.5 (s, γ-C), 23.1 (d, 2JCP
=
6.4 Hz δ-C), 20.4 (d 1JCP = 42.0 Hz ε-C), 12.1 (s, C5(CH3)5). ESI-MS:
683.35 [M]. Elemental Analysis: Calcd: C, 55.47; H, 4.58. Found: C,
55.98; H, 4.90.
Compound 36. A silylated swivel frit apparatus was charged with
Cp03La (251.3 mg, 0.5 mmol) and THF (5 mL). The resulting yellow
suspension was stirred for 10 min to give a fine white suspension. To this,
a solution of t-Bu2P(C6H5)OH (119.1, 0.5 mmol) in THF (5 mL) was
added dropwise over 30 min. After 10 min, all the solids had dissolved to
give a light yellow solution (the reaction was deemed complete by
following the 31P{1H} spectrum of an identical NMR scale experiment).
The flask was removed from the glovebox and connected to a Schlenk
line where the solvent was removed in vacuo to leave a light yellow oil
which began to crystallize upon prolonged exposure to vacuum. Benzene
was vacuum transferred onto the solids, and the resulting yellow solution
filtered. The solvent was removed once more to leave a light yellow oil.
Pentane (∼10 mL) was vacuum transferred onto the solids at ꢀ78 °C
and then allowed to warm to room temperature giving a light yellow
suspension. The solids were stirred at room temperature for 1 h then and
collected on a frit and washed by back distillation of the solvent, leaving a
white solid that was dried under high vacuum (10ꢀ3 Torr) for 1 h before
being transferred to the glovebox and isolated. A second crop was
isolable by cooling the pentane supernatant down to ꢀ20 °C. Combined
yield: 241.8, 0.35 mmol, 70%. 1H NMR (400 Hz, toluene-d8): δ 7.56 (dt,
1H, 3JHH = 7.6 Hz, 4JHH = 2.2 Hz, HC6), 7.22 (dt, 1H, 3JHH = 8.5 Hz,
DCM-d2): δ 7.46 (m, HC6 and HC3), 6.89 (ddd, 1H, 3JHH = 8.2 Hz, 4JHH
=
2.2, JHP = 1.2 Hz HC4) 6.18 (ddd, 1H, 3JHH = 7.1 Hz, 3JHH = 6.1 Hz,
4JHH = 1.0 Hz, HC5) 4.37 (q, 2H, 3JHH = 7.1 Hz, OCH2CH3), 2.90 (m,
2H, PCH2CH3), 1.91 (s, 30H, C5(CH3)5), 1.60 (dt, 3H, 2JHP = 16.4 Hz,
3
3JHH = 7.6 Hz PCH2CH3), 1.52 (d, JHP = 14.9 Hz, 18H, C(CH3)3),
1.29 (t, 3JHH = 7.1 Hz, 3H, OCH2CH3).31P{1H} (161 Hz, DCM-d2): δ
2
44.31. 13C{1H} (125 Hz, DCM-d2): δ 168.4 (d, JCP = 1.6 Hz, C1),
135.2 (d, 2JCP = 2.3 Hz, C3), 135.1 (d, 3JCP = 7.0 Hz, C6), 126.7 (d, 4JCP
=
8.9 Hz, C5), 122.8 (s, C5(CH3)5), 117.7 (d, 3JCP = 10.9 Hz, C4), 102.0
(d, 1JCP = 68.9 Hz, C2), 67.0 (s, OCH2CH3), 37.8 (d, 1JCP = 36.6 Hz,
1
C(CH3)3), 29.0 (s, C(CH3)3), 21.0 (s, OCH2CH3), 12.85 (d JCP
=
56.4 Hz, PCH2CH3), 12.74 (s, PCH2CH3), 12.3 (s, C5(CH3)5). ESI-
MS: 671.37 [M]. Elemental Analysis: Calcd: C, 55.07; H, 4.62. Found:
C, 55.27; H, 4.74.
Compound 33. Reaction was carried out in an analogous fashion to
32 except using iPr2O and an extended reaction time of ca. 4 days and a
temperature of 100 °C. The 31P and 31P{1H} NMR spectra of the
resultant light yellow solution indicated ca. 38% conversion to a new
species. 31P{1H} NMR (unlocked): δ 18.5. 31P NMR (121 Hz,
unlocked, PhCl): δ 18.59 (d, 1JPH = 450 Hz). ESI-MS: 657.33 [M].
Compound 34. A sample of 2 (27.8 mg, 0.02 mmol) was loaded
into an NMR tube fitted with a Teflon needle valve and dissolved in
chlorobenzene (0.7 mL) giving a bright orange solution. Excess MTBE
(ca. 3 drops) was added. The tube was then sealed, removed, and
warmed to 60 °C for ca. 16 h. The 31P and 31P{1H} NMR spectra of the
colorless solution revealed >99% conversion of 3. The sample was
returned to the glovebox, layered with hexane, and allowed to stand for
16 h, precipitating a white microcrystalline solid. The supernatant was
decanted, and the solids were washed with hexane before drying under in
vacuo. Yield: 17.0 mg, 0.013 mmol, 65%. 1H NMR (500 MHz DCM-d2):
δ 7.53 (ddd, 1H, 3JHH = 7.2 Hz, 4JHH = 1.8 Hz, JHP = 1.0 Hz HC6), 7.36
(ddd, 1H, 3JHH = 10.99 Hz, 4JHH = 7.63 Hz, JHP = 1.5 Hz HC3), 6.92
(ddd, 1H, 3JHH = 7.9 Hz, 4JHH = 2.9 Hz, JHP = 0.76 Hz, HC4), 6.67 (ddd,
4JHH = 1.7 Hz, HC4), 6.82 (ddd, 1H, 3JHH = 6.9 Hz, 3JHH = 5.9 Hz 4JHH
=
1.2 Hz, HC5), 6.69 (dt, 1H, 3JHH = 7.6 Hz, 4JHH = 1.0 Hz, HC3), 5.67 (s,
2H, C2(CH3)2C2(CH3)2CH), 3.90 (m, 4H, α-HTHF), 2.14 (s, 12H,
C2(CH3)2C2(CH3)2CH), 1.97 (s, 12H, C2(CH3)2C2(CH3)2CH), 1.49
(m, 4H, β-HTHF), 1.23 (d, 3JHP = 11.3 Hz, 18H, C(CH3)3). 31P{1H}
(161 Hz, toluene-d8): δ 15.60 (s). 13C{1H} (100 Hz, toluene-d8): δ
171.0 (d, 2JCP = 24.1 Hz, C1), 135.5 (d, 3JCP = 3.9 Hz, C6), 130.6 (s, C4),
121.7 (d, 4JCP = 3.1 Hz, C5), 122.4 (d, 1JCP = 11.7 Hz, C2), 121.3 (s,
C2(CH3)2C2(CH3)2CH), 119.3 (s, C2(CH3)2C2(CH3)2CH), 115.2 (s,
C3), 112.9 (s, C2(CH3)2C2(CH3)2CH), 70.7 (s, α-CTHF), 32.7 (d, 1JCP
= 21.8 Hz, C(CH3)3), 31.1 (d, 2JCP = 14.8 Hz, C(CH3)3), 25.2 (s, β-
CTHF), 13.4 (s, C2(CH3)2C2(CH3)2CH), 11.2 (s, C2(CH3)2C2-
(CH3)2CH). Elemental Analysis: Calcd: C, 62.60; H, 8.17. Found: C,
62.27; H, 8.31.
Compound 37. A sample of 36 dissolved in toluene-d8 (34.5 mg,
0.05 mmol) was heated to 140 °C for ca. 3 days (the reaction was
deemed complete by following the 31P{1H} spectrum). The relevant
NMR spectra were acquired in situ. Crystals suitable for X-ray diffraction
were obtained by slow diffusion of hexane into the benzene solution at
room temperature. The supernatant was decanted, and the crystals were
washed with hexane Yield: 26.9 mg, 0.039 mmol, 78%. 1H NMR (400
Hz, toluene-d8): δ 7.19 (tm, 1H, 3JHH = 6.85 Hz, HC5), 6.87 (ddd, 1H,
1H, 3JHH = 6.7 Hz, 4JHH = 6.0 Hz, JHP = 0.8 Hz HC5), 6.26 (d, 1H, 1JHP
=
462.5 Hz, P-H), 4.12 (s, 3H, ZrOCH3), 1.94 (s, 30H, C5(CH3)5), 1.53
3
(d, JHP = 16.9 Hz, 18H, C(CH3)3). 31P{1H} (121 Hz, DCM-d2): δ
23.42. 13C{1H} (125 MHz DCM-d2): δ 168.6 (s, C1), 136.8. (d, 2JCP
=
2.0 Hz, C3), 132.4 (d, 3JCP = 8.80 Hz, C6), 123.9 (d, 4JCP = 5.9 Hz, C5),
122.5 (s, C5(CH3)5), 118.9 (d, 3JCP = 11.7 Hz, C4), 100.9 (d, 1JCP = 76.3
Hz, C2), 58.1 (s, ZrOCH3), 35.25 (d, 1JCP = 36.2 Hz, C(CH3)3), 28.7 (s,
C(CH3)3), 12.0 (s, C5(CH3)5). ESI-MS: 629.31 [M]. Elemental
Analysis: Calcd: C, 54.09; H, 4.31. Found: C, 53.90; H, 4.54.
3JHH = 9.8 Hz, 3JHH = 8.1 Hz 4JHH = 1.7 Hz, HC3), 6.81 (ddd, 1H, 3JHH
8.6 Hz, 3JHH = 5.9 Hz 4JHH = 1.0 Hz, HC6), 6.87 (overlapping ddd, 1H,
=
3
4
3JHH = 6.9 Hz, JHH = 4.2 Hz JHH = 1.2 Hz, HC4), 5.84 (s, 2H,
C(CH3)C(CH3)C0(C0H3)C0(C0H3)CH), 4.26 (t, 3JHH = 5.4 Hz, 2H, α-
H), 2.61 (m, 2H, δ-H), 2.40 (s, 6H, C(CH3)C(CH3)C0(C0H3)C0-
(C0H3)CH), 2.38 (s, 6H, C(CH3)C(CH3)C0(C0H3)C0(C0H3)CH),
2.27 (s, 6H, C(CH3)C(CH3)C0(C0H3)C0(C0H3)CH), 2.08 (s, 6H,
C(CH3)C(CH3)C0(C0H3)C0(C0H3)CH), 1.83 (m, 2H, γ-H),
Compound 35. Reaction was carried out and isolated in an
analogous fashion to 29 using 2 (27.8 mg, 0.02 mmol) and an excess
of THP (ca. 3 drops) and a reaction time of ca. 2 days. Yield: 20.1 mg,
0.0146 mmol, 73%. 1H NMR (500 Hz DCM-d2): δ 7.46 (m, 2H, HC6
18476
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Journal of the American Chemical Society
ARTICLE
1.65 (m, 2H, β-H), 0.86 (d, 3JHP = 14.2 Hz, 18H, C(CH3)3). 31P{1H}
(161 Hz, toluene-d8): δ 45.8 (s). 13C{1H} (100 Hz, toluene-d8): δ 174.0
(d, 2JCP = 3.4 Hz, C1), 135.0 (d, 4JCP = 2.3 Hz, C5), 133.7 (d, 2JCP = 7.8
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Trans. 2009, 7179.
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(14) Spies, P.; Schwendemann, S.; Lange, S.; Kehr, G.; Fr€ohlich, R.;
Erker, G. Angew. Chem., Int. Ed. 2008, 47, 7543.
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Commun. 2010, 46, 8947.
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3
Hz, C3,), 126.4 (d, JCP = 8.6 Hz, C6), 117.2 (s, C(CH3)C(CH3)C0-
(C0H3)C0(C0H3)CH), 116.5 (s, C(CH3)C(CH3)C0(C0H3)C0(C0H3)-
3
CH), 110.9 (s, C(CH3)C(CH3)C0(C0H3)C0(C0H3)CH), 112.8 (d,
JCP = 11.7 Hz, C4), 97.8 (d, 1JCP = 72.4 Hz, C2), 63.5 (s, α-C), 35.8 (d,
1JCP = 38.9 Hz, C(CH3)3), 35.1 (d, JCP = 14.0 Hz, β-C), 27.9 (s,
3
C(CH3)3), 20.9 (d, 2JCP = 6.2 Hz, γ-C), 18.9 (d, 1JCP = 42.0 Hz, δ-C),
13.6 (s, C(CH3)C(CH3)C0(C0H3)C0(C0H3)CH), 13.5 (s, C(CH3)C-
(CH3)C0(C0H3)C0(C0H3)CH), 11.5 (s, C(CH3)C(CH3)C0(C0H3)C0-
(C0H3)CH), 11.4 (s, C(CH3)C(CH3)C0(C0H3)C0(C0H3)CH),). ESI-
MS: Not observed. Elemental Analysis: Calcd: C, 62.60; H, 8.17. Found:
C,62.81; H, 8.10.
Compound 38. A sample of 2 (0.1 mmol) was loaded into an NMR
tube fitted with a Teflon needle valve and dissolved in chlorobenzene
(0.7 mL) giving a bright orange solution. Excess acetone (ca. 3 drops)
was added, immediately giving a pale green solution. The 31P and
31P{1H} NMR spectra of the colorless solution revealed >99% conver-
sion of 2. The sample was returned to the glovebox, layered with hexane,
and allowed to stand for 16 h precipitating large pale green blocks. The
supernatant was decanted, and the solids washed with hexane before
drying in vacuo. Recrystallization from DCM/hexane afforded colorless
blocks. Yield: 21.5 mg, 0.0161 mmol, 81%. 1H NMR (500 MHz, DCM-d2):
δ 7.55 (m, 1H, HC5), 7.38 (m, 1H, HC3), 6.96 (dt, 1H, 3JHH = 7.3 Hz,
4JHP = 2.0 Hz, HC4), 6.58 (m, 1H, HC6), 6.56 (d, 1H, 1JHP = 459.5 Hz,
P-H), 4.02 (br. s, 1H, CH3C(O)CHH), 3.86 (br. s, 1H, CH3C-
(O)CHH), 1.98 (s, 30H, C5(CH3)5), 1.92 (s, 1H, CH3C(O)CHH),
1.52 (br d., 3JHP = 17.0 Hz, 18H, C(CH3)3). 31P{1H} (121 Hz, DCM-d2):
δ 20.05. 13C{1H} (125 MHz, DCM-d2): δ 167.7 (s, C1), 162.5 (s,
CH3C(O)CHH), 136.6 (br. s, C5), 132.7 (br. s, C3), 124.4 (br. s, C6),
(18) Stephan, D. W.; Greenberg, S.; Graham, T. W.; Chase, P.;
Hastie, J. J.; Geier, S. J.; Farrell, J. M.; Brown, C. C.; Heiden, Z. M.;
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2011, 133, 8826.
3
1
119.4 (d, JCP = 10.8 Hz, C4), 124.0 (s, C5(CH3)5), 100.9 (d, JCP
=
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80.2 Hz, C2), 89.5 (br. s, CH3C(O)CHH), 35.5 (br. d, 1JCP = 39.1 Hz,
C(CH3)3), 28.6 (s, C(CH3)3), 25.8 (br. s, CH3C(O)CHH), 12.3 (s,
C5(CH3)5). ESI-MS: 629.30 [M ꢀ CH3C(O)CH2 + O2]. Elemental
Analysis (1:1 DCM solvate from crystal structure): Calcd: C, 52.73 H,
4.35. Found: C, 52.32; H, 4.46.
(25) Welch, G. C.; Stephan, D. W. J. Am. Chem. Soc. 2007, 129, 1880.
(26) Such a phenomenon is known to produce two distinct 31P
environments. The observation that only 5 is obtained upon degassing
the solution supports the notion.
(27) Sydora, O. L.; Kilyanek, S. M.; Jordan, R. F. Organometallics
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(28) Horton, A. D.; Orpen, A. G. Organometallics 1991, 10, 3910.
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’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic data and CIF
b
files. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
(30) M€omming, C. M.; Otten, E.; Kehr, G.; Fr€ohlich, R.; Grimme, S.;
Stephan, D. W.; Erker, G. Angew. Chem., Int. Ed. 2009, 48, 6643. Mꢀenard,
G.; Stephan, D. W. Angew. Chem., Int. Ed. 2011, 50, 8396.
(31) Hill, M.; Wendt, O. F. Organometallics 2005, 24, 5772.
Corresponding Author
duncan.wass@bristol.ac.uk
1
(32) Furthermore, 13C{1H} NMR shifts for OC(O) and JCP
’ ACKNOWLEDGMENT
coupling constants are almost identical compared with those reported
in ref 34: δ 161.6 (d, 1JCP = 93 Hz 164.7; d, 1JCP = 94.4 Hz) in 10 and
δ 161.9 (d, 1JCP = 85.1 Hz) for 11.
(33) We note that the allane based compounds in ref 9 are also
reported to be thermally stable.
(34) Tran, S. D.; Tronic, T. A.; Kaminsky, W.; Heinekey, D.; Mayer,
J. M. Inorg. Chim. Acta 2011, 369, 126.
(35) Menard, G.; Stephan, D. W. J. Am. Chem. Soc. 2010, 132, 1796.
(36) Dureen, M. A.; Stephan, D. W. J. Am. Chem. Soc. 2010,
132, 13559.
The University of Bristol is thanked for funding. Natalie Fey
(University of Bristol) is thanked for assistance with calculations.
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