Neutral and zwitterionic low-coordinate titanium complexes bearing the terminal phosphinidene functionality. Structural, spectroscopic, theoretical, and catalytic studies addressing the Ti-P multiple bond

Article abstract of DOI:10.1021/ja064853o

α-Hydrogen abstraction and α-hydrogen migration reactions yield novel titanium(IV) complexes bearing terminal phosphinidene ligands. Via an α-H migration reaction, the phosphinidene (^tBunacnac)Ti= P[Trip](CH₂^tBu) (^tBu

Full text of DOI:10.1021/ja064853o

Published on Web 09/22/2006
Neutral and Zwitterionic Low-Coordinate Titanium Complexes
Bearing the Terminal Phosphinidene Functionality. Structural,
Spectroscopic, Theoretical, and Catalytic Studies Addressing
the Ti-P Multiple Bond
Guangyu Zhao,† Falguni Basuli,† Uriah J. Kilgore,† Hongjun Fan,†
Halikhedkar Aneetha,† John C. Huffman,† Gang Wu,‡ and Daniel J. Mindiola*,†
Contribution from the Department of Chemistry and Molecular Structure Center,
Indiana UniVersity, Bloomington, Indiana 47405, and Department of Chemistry, Queen’s
UniVersity, 90 Bader Lane, Kingston, Ontario, K7L3N6 Canada
Received July 7, 2006; E-mail: mindiola@indiana.edu
Abstract: R-Hydrogen abstraction and R-hydrogen migration reactions yield novel titanium(IV) complexes
bearing terminal phosphinidene ligands. Via an R-H migration reaction, the phosphinidene (tBunacnac)Tid
t
P[Trip](CH2 Bu) (tBunacnac- ) [Ar]NC(tBu)CHC(tBu)N[Ar], Ar ) 2,6-(CHMe2)2C6H3, Trip ) 2,4,6-iPr3C6H2)
was prepared by the addition of the primary phosphide LiPH[Trip] to the nucleophilic alkylidene triflato
complex (tBunacnac)TidCHtBu(OTf), while R-H abstraction was promoted by the addition of LiPH[Trip] to
the dimethyl triflato precursor (tBunacnac)Ti(CH3)2(OTf) to afford (tBunacnac)TidP[Trip](CH3). Treatment of
(
tBunacnac)TidP[Trip](CH3) with B(C6F5)3 induces methide abstraction concurrent with formation of the first
titanium(IV) phosphinidene zwitterion complex (tBunacnac)TidP[Trip]{CH3B(C6F5)3}. Complex (tBunacnac)-
TidP[Trip]{CH3B(C6F5)3} [2 + 2] cycloadds readily PhCCPh to afford the phosphametallacyclobutene
[(tBunacnac)Ti(P[Trip]PhCCPh)][CH3B(C6F5)3]. These titanium(IV) phosphinidene complexes possess the
shortest TidP bonds reported, have linear phosphinidene groups, and reveal significantly upfielded solution
31P NMR spectroscopic resonances for the phosphinidene phosphorus. Solid state 31P NMR spectroscopic
data also corroborate with all three complexes possessing considerably shielded chemical shifts for the
linear and terminal phosphinidene functionality. In addition, high-level DFT studies on the phosphinidenes
suggest the terminal phosphinidene linkage to be stabilized via a pseudo TitP bond. Linearity about the
Ti-P-Cipso linkage is highly dependent on the sterically encumbering substituents protecting the
phosphinidene. Complex (tBunacnac)TidP[Trip]{CH3B(C6F5)3} can catalyze the hydrophosphination of
PhCCPh with H2PPh to produce the secondary vinylphosphine HP[Ph]PhCdCHPh. In addition, we
demonstrate that this zwitterion is a powerful phospha-Staudinger reagent and can therefore act as a
carboamination precatalyst of diphenylacetylene with aldimines.
Introduction
popularity given their ability to carry out important transforma-
tions such as phospha-Staudinger or -Wittig type reactions.1-6
In contrast to imides, high-oxidation state transition metal
phosphinidenes are still scant,1-13 and such systems draw
Specifically, phosphinidenes are particularly attractive synthons
in the design of low-coordinate phosphorus in phosphaorganic
molecules.1-6Inthecontextofd0-transitionmetalphosphinidenes,4-9
the phosphinidene functionality is expected to be nucleophilic,
and is often comparable in reactivity to Schrock-type alkylidenes
since phosphorus is slightly more electropositive than carbon.3
† Indiana University.
‡ Queen’s University.
(1) Lammertsma, K.; Vlaar, M. J. M. Eur. J. Org. Chem. 2002, 1127-1138.
(2) (a) Cowley, A. H. Acc. Chem. Res. 1997, 30, 445-451. (b) Cowley, A.
H.; Barron, A. R. Acc. Chem. Res. 1988, 21, 81-87.
(3) Mathey, F. Angew. Chem., Int. Ed. 2003, 42, 1578-1604 and references
therein.
(7) Urnezius, E.; Lam, K.-C.; Rheingold, A. L.; Protasiewicz, J. D. J.
Organomet. Chem. 2001, 630, 193-197.
(4) (a) Hou, Z. M.; Stephan, D. W. J. Am. Chem. Soc. 1992, 114, 10088-
10089. (b) Hou, Z. M.; Breen, T. L.; Stephan, D. W. Organometallics 1993,
12, 3158-3167. (c) Breen, T. L.; Stephan, D. W. J. Am. Chem. Soc. 1995,
117, 11914-11921. (e) Stephan, D. W. Angew. Chem., Int. Ed. Eng. 2000,
39, 314-329. (f) Pikies, J.; Baum, E.; Matern, E.; Chojnacki, J.; Grubba,
R.; Robaszkiewicz, A. Chem. Commun. 2004, 2478-2478.
(5) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Angew. Chem., Int. Ed.
1993, 32, 756-759.
(8) Other Zr phosphinidene complexes have been isolated by trapping
experiments. Mahieu, A.; Igau, A.; Majoral, J.-P. Phosphorus Sulfur 1995,
104, 235-239.
(9) Bonanno, J. B.; Wolczanski, P. T.; Lobkovsky, E. B. J. Am. Chem. Soc.
1994, 116, 11159-11160.
(10) A high oxidation state uranium phosphinidene has also been prepared.
Arney, D. S. J.; Schnabel, R. C.; Scott, B. C.; Burns, C. J. J. Am. Chem.
Soc. 1996, 118, 6780-6781.
(6) (a) Basuli, F.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. J. Am.
Chem. Soc. 2003, 34, 10170-10171. (b) Basuli, F.; Watson, L. A.;
Huffman, J. C.; Mindiola, D. J. J. Chem. Soc., Dalton Trans. 2003, 4228-
4229. (c) Bailey, B. C.; Huffman, J. C.; Mindiola, D. J.; Weng, W.; Ozerov,
O. V. Organometallics 2005, 24, 1390-1393. (d) Basuli, F.; Bailey, B.
C.; Huffman, J. C.; Baik, Mu-H.; Mindiola, D. J. J. Am. Chem. Soc. 2004,
126, 1924-1925.
(11) Hitchcock, P. B.; Lappert, M. F.; Leung, W. P. J. Chem. Soc., Chem.
Commun. 1987, 1282.
(12) Cowley, A. H.; Pellerin, B.; Atwood, J. L.; Bott, S. G. J. Am. Chem. Soc.
1990, 112, 6734-6735.
(13) Figueroa, J. S.; Cummins, C. C. Angew. Chem., Int. Ed. 2004, 43, 984-
988.
9
10.1021/ja064853o CCC: $33.50 © 2006 American Chemical Society
J. AM. CHEM. SOC. 2006, 128, 13575-13585
13575

A R T I C L E S
Zhao et al.
Scheme 1. Synthesis of the Titanium(IV) Phosphinidene 1 via an
R-H Migration Reaction
Although phosphinidenes have been pursued as synthons for
stoichiometric “PR” group transfer processes,1-5 examples of
phosphinidenes playing a role in catalytic reactions are exceed-
ingly rare.14 This fact is rather surprising since the closely related
imides15 and alkylidenes16 are commonly sought catalysts in
organotransition metal chemistry.
Unlike the 4d, 5d, and the late-transition metal series, titanium
phosphinidenes were, until very recently, an unknown class of
compounds.6 One could attribute the lack of stable titanium
phosphinidenes to be the result of the hard-soft contrast among
these elements.7,8 Theoretical studies by Lammertsma and co-
workers have proposed that the nature of the nucleophilic Md
P bond depends inter alia on the atomic size of the metal and
not on the nature of the ligand.17 Consequently, there is a much
stronger σ- and π-component in the MdP interaction when
moving from the first- to the second- and third-row transition
metals.17 Arguably, this would imply that TidP linkages are
more reactive than its heavier group congeners.
temperature precluded us from carrying out more thorough
analysis surrounding the nature of the TidP linkage. To block
thermal rearrangement via a phospha-Staudinger reaction,6a we
resorted to the much more sterically demanding â-diketiminate
ligand version, (tBunacnac- ) [Ar]NC(tBu)CHC(tBu)N[Ar], Ar
i
) 2,6- Pr2C6H3), previously reported by Budzelaar and co-
workers.18 Accordingly, treatment of LiPH[Trip] with (tBunacnac)-
TidCHtBu(OTf)19 resulted in immediate formation of the
t
phosphinidene (tBunacnac)TidP[Trip](CH2 Bu) (Trip ) 2,4,6-
iPr3C6H2 (1), 62% yield). Complex 1 is likely generated by
means of a putative neopentylidene-phosphide (tBunacnac)Tid
CHtBu(PH[Trip]), which subsequently undergoes R-hydrogen
migration to afford the phosphinidene scaffold in 1 (Scheme
1). Attempts to transmetalate (tBunacnac)TidCHtBu(OTf) with
the aliphatic substituted phosphide LiPH[cC6H11] or bulkier
arylphosphide LiPH[2,4,6-tBu3C6H2] resulted in decomposition
mixtures. Given the steric protection imposed by the NCCCN
â-carbon, complex 1 appears to be impervious to intramolecular
phospha-Staudinger rearrangements often encountered with the
more conventional Menacnac- system.6a The 1H NMR spectrum
of 1 displays two methine resonances, four diasteriotopic methyl
In light of the above proposition, we wish to report the
synthesis of the neutral and zwitterionic titanium(IV) phosphin-
idene complexes (tBunacnac)TidP[Trip](CH2 Bu), (tBunacnac)-
t
TidP[Trip](CH3),(tBunacnac)TidP[Trip]{CH3B(C6F5)3}(tBunacnac-
i
) [Ar]NC(tBu)CHC(tBu)N[Ar], Ar ) 2,6- Pr2C6H3, Trip )
i
2,4,6- Pr3C6H2), as well as catalytic studies surrounding the
TidP bond for the latent low-coordinate zwitterion (tBunacnac)-
TidP[Trip]{CH3B(C6F5)}. Solid-state structural studies reveal
all these titanium phosphinidenes to possess the shortest TidP
bonds ever reported, while 31P NMR spectroscopic data (both
in solution and solid state forms) indicate highly shielded 31P
NMR resonances for the terminal phosphinidene phosphorus.
In addition, high-level DFT studies for all three titanium-
phosphinidenes clearly depict the HOMO and HOMO-1 orbitals
to be the two orthogonal π-bonds comprising the TitP linkage.
Bond order analysis corroborate the short Ti-P linkage with a
bond order greater than two for all phosphinidene complexes
studied in this work.
t
groups on the isopropyls, as well as one Bu environment for
the â-carbons of the â-diketiminate backbone. As a result, all
NMR spectroscopic data are consistent with complex 1 retaining
Cs symmetry in solution. Most notably, the 31P and 31P{1H}
NMR solution spectra of 1 manifests a single resonance at 157
ppm, which is consistent with this system bearing a terminal
and linear TidPR functionality. To our knowledge, complex 1
represents a rare example of a group 4 complex having a highly
shielded 31P NMR chemical shift for the phosphinidene
phosphorus.1-3 The highly shielded 31P NMR resonance for 1
provided the impetus for examining the solid-state structure.
Large brown blocks of 1 were grown from hexane at -35
°C, and the single-crystal structure revealed a titanium complex
having Cs symmetry, a Ti(IV)-Calkyl bond (2.107(3) Å; Figure
1), and a short TidP bond (2.157(2) Å; Figure 1). As a result,
the former metrical parameters reflect an R-hydrogen migration
from the former primary phosphide ligand to the alkylidene
carbon (Table 1). The TidP bond length value is by far much
shorter to the computed Pauling and Schomaker-Stevenson
covalent radii with corrections for electronegativity differences,
which predicts a bond length of 2.288 Å for a double bond.20
In the structure of 1, the phosphinidene group is along the
σ-plane bisecting N-Ti-N, and oriented syn with respect to
the neopentyl ligand. A close interaction is also observed
between the titanium center and the â-carbon forming part of
the NCCCN ring (Ti1-C3, 2.638(4) Å). The metal center in 1
assumes its rightful position out of the NCCCN imaginary plane,
therefore making the neopentyl group endo relative to the
Results and Discussion
Synthesis and Structural Elucidation of Terminal Tita-
nium Phosphinidene Complexes. Recently, we reported that
four-coordinate titanium phosphinidenes could be generated via
an R-hydrogen migration reaction involving the nucleophilic
titanium alkylidene (Menacnac)TidCHtBu(OTf) (Menacnac-
)
[Ar]NC(Me)CHC(Me)N[Ar], Ar ) 2,6-iPr2C6H3) and the cor-
c
i
responding phosphide LiPH[R] (R ) C6H11, 2,4,6- Pr3C6H2,
2,4,6-tBu3C6H2).6a Unfortunately, these titanium phosphinidenes
Menacnac)TidP[R](CH2 Bu) were all kinetic products under N2
t
(
inasmuch as these species readily underwent intramolecular
phospha-Staudinger reactions (for R ) cC6H11, 2,4,6- iPr3C6H2)
(Scheme 1).6a However, when R ) 2,4,6-tBu3C6H2, the titanium
phosphinidene was moderately stable to isolate under low-
temperature conditions, but gradual decomposition at room-
(14) A phosphinidene anion has been implicated in the catalytic oligomerization
of primary phosphines via dyhydrocoupling of P-H bonds. Fermin, M.
C.; Stephan, D. W. J. Am. Chem. Soc. 1995, 117, 12645-12646.
(15) For some recent reviews of early-transition metal imides and their role in
catalytic reactions. (a) Duncan, A. P.; Bergman, R. G. Chem. Rec. 2002,
2, 431-445. (b) Hazari, N.; Mountford, P. Acc. Chem. Res. 2005, 38, 839-
849.
(18) Budzelaar, P. H. M.; von Oort, A. B.; Orpen, A. G. Eur. J. Inorg. Chem.
1998, 1485-1494.
(16) (a) Schrock, R. R. Chem. ReV. 2002, 102, 145-179. (b) Schrock, R. R.
(19) Basuli, F.; Bailey, B. C.; Huffman, J. C.; Mindiola, D. J. Organometallics
2005, 24, 1886-1906.
Acc. Chem. Res. 1990, 23, 158-165.
(17) Ehlers, A. W.; Baerends, E. J.; Lammertsma, K. J. Am. Chem. Soc. 2002,
124, 2831-2838.
(20) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell University
Press: Ithaca, NY, 1960.
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Neutral and Zwitterionic Titanium Complexes
A R T I C L E S
Figure 1. Crystal structures of complexes 1, 3, and 4 with thermal ellipsoids at the 50% probability level. H-atoms and solvent molecules have been
removed for simplicity.
Table 1. Selected Structural Parameters for Complexes 1, 3, and 4
complex
1
3
4
TidP
Ti(1)-P(39), 2.157(2)
Ti1-N2, 1.981(3)
Ti(1)-P(39), 2.1644(7)
Ti1-N2, 2.036(6)
Ti(1)-P(39), 2.1512(4)
Ti1-N2, 2.042(1)
Ti-N
Ti-N
Ti1-N6, 2.114(3)
Ti1-N7, 2.014(6)
Ti1-N6, 1.973(1)
Ti-CR
Ti(1)-C(55), 2.107(3)
Ti(1)-C(3), 2.638(4)
n/a
n/a
n/a
Ti(1)-P(39)-C(40), 176.64(7)
N(6)-Ti(1)-N(2), 98.8(1)
P39-Ti1-N2, 107.2(1)
P39-Ti1-N6, 109.29(9)
C(55)-Ti(1)-P(39), 112.2(1)
C(55)-Ti(1)-N(2), 116.05(9)
C(55)-Ti(1)-N(6), 112.38(9)
Ti1-C55-C56, 141.2(6)
Ti(1)-C(55), 2.155(2)
Ti(1)-C(3), 2.720(2)
Ti(1)-C(5), 2.665(2)
n/a
Ti(1)-C(55), 2.405(3)
Ti(1)-C(3), 2.677(3)
Ti(1)-C(5), 2.555(3)
Ti(1)-C(4), 2.606(4)
C(55)-B(56), 1.665(2)
Ti(1)-P(39)-C(40), 176.03(5)
N(6)-Ti(1)-N(2), 99.33(4)
P39-Ti1-N2, 103.79(3)
P39-Ti1-N6, 108.11(3)
C(55)-Ti(1)-P(39), 112.57(4)
C(55)-Ti(1)-N(2), 113.19(5)
C(55)-Ti(1)-N(6), 118.20(5)
Ti1-C55-B56, 175.44(10)
Ti-Câ
Ti-Câ
Ti-Cγ
CR-B
n/a
Ti-P-C
N-Ti-N
P-Ti-N
P-Ti-N
CR-Ti-P
CR-Ti-N
CR-Ti-N
Ti-CR-X
Ti(1)-P(39)-C(40), 159.95(7)
N(6)-Ti(1)-N(2), 98.78(6)
P39-Ti1-N2, 107.57(5)
P39-Ti1-N6, 109.65(5)
C(55)-Ti(1)-P(39), 111.26(8)
C(55)-Ti(1)-N(2), 115.68(8)
C(55)-Ti(1)-N(6), 113.14(9)
n/a
a Bond lengths are reported in Å and bond angles in deg. X represents the atoms carbon and boron for complexes 1 and 4, respectively. n/a ) not
available.
Scheme 2. Synthesis of the Titanium Phosphinidene 3 via an R-H
Abstraction Reaction of 2 with LiPH[Trip] and Subsequent
Formation of the Zwitterion 4 by Methide Abstraction of 3 with
B(C6F5)3
isopropyl methyl groups. This feature places the linear phos-
phinidene group (TidP-Cipso, 176.64(7)°) exo with respect to
the isopropyl methyl residues. As expected, the linear phos-
phinidene ligand is in accord with the observed upfielded 31P
NMR chemical shift (vide supra).
Interestingly, it was discovered that titanium phosphinidenes
could also be generated by an R-hydrogen abstraction reaction
utilizing the precursor (tBunacnac)Ti(CH3)2(OTf) (2) and LiPH-
[Trip]. Stephan4a,c and Protasiewicz7 have applied this same
strategy in the assembly of kinetically stable zirconium com-
plexes bearing a terminal phosphinidene ligand. In a similar
way, when an Et2O solution of 2, prepared readily from the
AgOTf oxidation of (tBunacnac)Ti(CH3)2 (Scheme 2),21 was
treated with LiPH[Trip], compound (tBunacnac)TidP[Trip](CH3)
(Trip ) 2,4,6-iPr3C6H2; 3) was isolated in 59% yield. Complex
3 also displays NMR spectroscopic features consistent with a
Cs symmetric system in solution. A diagnostic terminal phos-
phinidene 31P NMR chemical shift was located at 232 ppm,
while the alkyl methyl group was unambiguously confirmed as
for the isoelectronic imido analogue (tBunacnac)TidNR(CH3)
(R ) 2,6-iPr2C6H3), previously reported by our group (1.35
ppm).22 We propose that complex 3 is likely formed by a
transmetalation step to afford putative phosphide (tBunacnac)-
Ti(CH3)2(PH[Trip]) intermediate, which readily extrudes CH4
1
a broad resonance at 1.27 ppm in the H NMR spectrum. The
alkyl methyl chemical shift in 3 coincides with the same group
(22) (a) Basuli, F.; Clark, R. L.; Bailey, B. C.; Brown, D.; Huffman, J. C.;
Mindiola, D. J. Chem. Commun. 2005, 2250-2252. (b) Kilgore, U. J.;
Basuli, F.; Huffman, J. C.; Mindiola, D. J. Inorg. Chem. 2006, 45, 487-
489.
(21) The analogous complex (Menacnac)Ti(CH3)2 has been reported by Budzelaar
and co-workers, ref 15.
9
J. AM. CHEM. SOC. VOL. 128, NO. 41, 2006 13577

A R T I C L E S
Zhao et al.
Figure 2. Solid-state 31P MAS NMR spectra of complex 1 (top: 2084 transients, 8.737 kHz spinning), 3 (middle: 5050 transients, 15 kHz spinning), and
4 (bottom: 6140 transients, 14 kHz spinning). The isotropic peaks are indicated by asterisks. Tensors are reported to the right side of each spectrum.
upon R-hydrogen abstraction to furnish the TidP linkage
(Scheme 2). Such a method allows us to assemble phosphin-
idene-methyl surrogates as opposed to the sterically encum-
zwitterionic types were until now an unknown class of
molecules.4e,24
In lieu of elemental analysis, and to obtain an accurate
connectivity map for both the phosphinidene and zwitterionic
nature of 4, we collected single crystal X-ray diffraction data.
Single-crystal X-ray diffraction analysis of 4 exposes a
bered phosphinidene-neopentyl groups in compounds such as
t
(
Menacnac)TidP[Trip](CH2 Bu)6a (R ) 2,4,6-tBu3C6H2) or 1.
To ascertain an accurate connectivity in compound 3, we
(
tBunacnac)TidP[Trip] scaffold (TidP, 2.1512(4) Å; TidP-C,
collected single-crystal X-ray diffraction data. Salient features
for the structure of 3 include a very short TidP bond (2.1644-
(7) Å, Figure 1), and slightly distorted titanium phosphinidene
group (TidP-C, 159.95(7)°), which is also oriented exo relative
to the isopropyl methyl groups of the â-diketiminate ligand.
Unlike the TidP-C motif in 1, the phosphinidene group is not
linear in 3, hence hinting that sp hybridization of P in 1 might
be sterically enforced and a consequence of clashing of the bulky
aryl group on the phosphinidene P with both the neopentyl and
sterically encumbering substitutents on the â-diketiminate ligand.
As opposed to complex 1, the less sterically imposing methyl
group on Ti allows the phosphorus aryl motif to be oriented
almost parallel to the imaginary NCCCN plane defined by the
â-diketiminate ligand. Pertinent metrical parameters for the
molecular structure of complex 3 are listed in Table 1.
176.03(5)°) with an abstracted methyl ligand (Ti-CH3, 2.405-
(3) Å, Figure 1). Complex 4 contains a shorter TidP linkage
and linear phosphinidene moiety when compared to 3, thus
hinting that a pseudo TitP bond might be playing a role (Table
1). The perfluorinated aryls on the boron atom are twisted in a
propeller like fashion and deviations of the boron atom from
the aryl-C3 plane (∼0.54 Å) lend further support to charge
separation (or Lewis acid-base adduct formation) in 4. As
expected, methide abstraction in 4 results in an electron deficient
and latent low-coordinate Ti(IV) center, consequently leading
to a weak interaction of the latter with both the â- (2.677(3)
and 2.555(3) Å) and γ-carbons (2.606(4) Å) composing the
NCCCN ring (Table 1). The latter feature is further manifested
by deviation of the Ti atom from the NCCCN imaginary plane
(∼1.13 Å) when compared to 1 (∼1.01) and 3 (∼1.06). Complex
4 represents the pnictogen analogue of (tBunacnac)TidNR-
{CH3B(C6F5)3} R ) 2,6-iPr2C6H3), a highly reactive zwitterionic
titanium imido previously reported by us.22
Given the less-sterically congested environment in 3, we
decided to explore if such a complex could yield latent low-
coordinate phosphinidene templates. As a result, treatment of
3 with B(C6F5)3 in FC6H5 results in immediate methide
abstraction concomitant with formation of the phosphinidene
zwitterion (tBunacnac)TidP[Trip]{CH3B(C6F5)3} (4) in quantita-
tive yield (Scheme 2). Diagnostic spectroscopic features for 4
include a 31P NMR phosphinidene resonance at 207 ppm and a
11B NMR spectroscopic signal at -14 ppm, both of which are
consistent with a terminal phosphinidene zwitterion system
resulting from methide abstraction. To our knowledge, complex
4 represents the first d0 zwitterion featuring a terminal phos-
phinidene ligand. Although examples of cationic phosphinidene
complexes have been reported by Carty,23 high-oxidation state
Solid State 31P NMR Spectroscopic Studies. Isotropic solid-
state 31P NMR shifts of the terminal phosphinidene complexes
1 (137 ppm), 3 (220 ppm), and 4 (202 ppm) obtained with
(23) (a) Sterenberg, B. T.; Carty, A. J. J. Organomet. Chem. 2001, 617-618,
696. (b) Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. Organometallics
2001, 20, 2657-2659. (c) Sterenberg, B. T.; Udachin, K. A.; Carty, A. J.
Organometallics 2001, 20, 4463-4465. (d) Sanchez-Nieves, J.; Sterenberg,
B. T.; Udachin, K. A.; Carty, A. J. J. Am. Chem. Soc. 2003, 125, 2404-
2405. (e) Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. Organometallics
2003, 22, 3927-3932.
(24) Fermin, M. C.; Ho, J.; Stephan, D. W. Organometallics 1995, 14, 4247-
4256.
9
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Neutral and Zwitterionic Titanium Complexes
A R T I C L E S
Figure 3. Computed frontier orbitals for the phosphinidene complexes 1, 3, and 4. Full models have been cropped for drawing the orbitals: tBu to CH3 and
iPr to H.
Table 2. Selected Computed and X-ray Bond Distances (Å) and
presented in this work are exceedingly shielded when compared
Bond Angles (deg) of the Full Modelsa
to the solution 31P NMR spectra of the few terminal terminal
and linear phosphinidene complexes reported in the literature.5,12
It is also well-known that linear and terminal phosphinidenes
exhibit a much shielded environment than the corresponding
bent analogues.1-3,5,9,11,12 Hence, our solution and solid-state
31P NMR data are consistent with linear TidP-Cipso frame-
works, which are also in agreement with the solid-state crystal
structures (vide supra).
compd 1
compd 3
compd 4
atoms
calcd
X-ray
calcd
X-ray
calcd
X-ray
Ti1-P2
2.151
2.100
2.080
1.834
97.7
2.157
2.107
2.048
1.808
98.82
176.6
2.169
2.113
2.059
1.832
98.0
2.164
2.155
2.025
1.814
98.8
2.126
2.419
2.036
1.826
99.0
2.151
2.405
2.008
1.808
99.33
176.0
Ti1-C3
Ti1-N*
P2-C6
N4-Ti1-N5
Ti1-P2-C6
175.9
158.5
160.0
178.2
Computational Studies. To address the factors governing
structure and bonding in complexes 1, 3, and 4, we carried out
theoretical calculations using high level density functional theory
as implemented in the Jaguar 5.5 suite26 of ab initio quantum
chemistry programs. Geometry optimizations were performed
with the B3LYP27 functional and the 6-31G** basis set.
Titanium was represented using the Los Alamos LACVP basis.28
For all three phosphinidene complexes the optimized geometry
for the full model reproduced the key features of the solid state
structure expectedly well (Table 2). The structural features of
4 can also be reproduced accurately by simplifying the zwitterion
to its cationic component (tBunacnac)TidP[Trip], thus indicating
that the B(CH3)(C6F5)3 anion has no significant structural
influence to the core structure.
*Average of both Ti-N values.
magic-angle-spinning (MAS) are in agreement with the chemical
shifts observed in solution (Figure 2). These isotropic resonances
possess extended chemical shift anisotropies spread over a range
of ∼900 ppm, and from the rotational sidebands the chemical
shielding tensor components are obtained (Figure 2). On the
basis of the chemical shielding anisotropies (CSA) observed
for 1, 3, and 4, it is clear that the small isotropic chemical shifts
are primarily due to the fact that the tensor component along
the Ti-P-Cipso direction (δ33) is significantly shielded. The
latter value is relatively small when compared with the only
phosphinidene case in the literature reporting 31P CSA data,
namely the trinuclear cluster nido-Ru4(CO)13(µ3-PPh) bearing
a bridging phosphinidene ligand.25 In fact, the solid-state
isotropic 31P chemical shifts found for the TidP compounds
The frontier orbitals of complexes 1, 3, and 4 are shown in
Figure 3. In all systems, the HOMO and HOMO-1 are composed
(26) Jaguar, 5.5 ed.; Schro¨dinger, L. L. C: Portland, OR, 1991-2003.
(27) (a) Becke, A. D. Phys. ReV. A: At., Mol., Opt. Phys. 1988, 38, 3098-
3100. (b) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652. (c) Lee, C.
T.; Yang, W. T.; Parr, R. G. Phys. ReV. B: Condens. Matter Mater. Phys.
1988, 37, 785-789. (d) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys.
1980, 58, 1200-1211.
(25) (a) Eichele, K.; Wasylishen, R. E.; Corrigan, J. F.; Taylor, N. J.; Carty, A.
J. J. Am. Chem. Soc. 1995, 117, 6961-6969. (b) Solid state 31P NMR
studies have been also reported for terminal tungsten and molybdenum
phosphides. Wu, G.; Rovnyak, D.; Johnson, M. J. A.; Zanetti, N. C.;
Musaev, D. G.; Morokuma, K.; Schrock, R. R.; Griffin, R. G.; Cummins,
C. C. J. Am. Chem. Soc. 1996, 118, 10654-10655.
(28) Mayer, I. Chem. Phys. Lett. 1983, 97, 270-274.
9
J. AM. CHEM. SOC. VOL. 128, NO. 41, 2006 13579

A R T I C L E S
Zhao et al.
simplified
Table 3. Full Models versus Simplified Models: Calculated Bond Distances (Å), Bond Angles (deg), and the Mayer Bond Order
compd 1
compd 3
compd 4
atoms
full
simplified
full
simplified
full
metrical parameter
bond order
Ti1-P2
2.151
175.9
2.24
106.4
2.169
158.5
2.26
95.9
2.126
178.2
2.24
68.5
Ti1-P2-C6
Ti1-P2
2.11
1.87
2.06
1.76
2.26
1.81
Scheme 3. Cycloaddition of the Titanium(IV) Zwitterion Complex
4 with PhCCPh to Provide 5, and Subsequent Protonation of the
Metallacycle with H2NPh to Afford the Secondary Vinylphosphine
HP[Trip]PhCdCHPh
of two orthogonal π-bonds invoking in the Ti-P linkage, and
the calculated Mayer bond orders29 for the Ti-P linkage are
2.06, 2.11, and 2.26 respectively (Table 3). These features
clearly suggest that the linear Ti-P-Cipso angle and short Ti-P
distance result from a pseudo TitP bond. The LUMO orbitals
of complexes 1 and 3 are â-diketiminate π* based augmented
with some metal d character. However, drastic differences arise
when the LUMO of 1 or 3 with that of the zwitterion 4 are
compared. Not surprisingly, methide abstraction in 4 results in
an open coordination site, hence the LUMO is composed
primarily of a nonbonding metal-based orbital. This feature
would suggest that complex 4 should be a system viable for
substrate binding, since the LUMO orbital has large direction-
ality along one lobe which is oriented toward the open
coordination site.
cycloadduct formation in 5 is provided by its reactivity with
protic media such as H2NPh, which results in extrusion of the
secondary vinylphosphine HP[Trip]PhCdCHPh30 (31P NMR:
-63.3 ppm, JP-H ) 221.9 Hz; MS (EI) M+ ) 414.25)
concurrent with traces of the free phosphine H2P[Trip] (Scheme
3). We have been unable to identify the metal-based product
resulting from protonolysis, but separation of HP[Trip]PhCd
CHPh from the mixture is facile given the limited solubility of
the metal byproduct in hydrocarbons. When judging from the
31P NMR spectrum, no isomer or phosphaalkene tautomer is
present with the secondary vinylphosphine. However, the
presence of some free phosphine suggests that complex 5 might
be in equilibrium with 4 and PhCCPh. Similar equilibrium
processes have been observed with azatitanocyclobutene species
generated from PhCCPh and the corresponding metal-imide.31,32
Albeit rare, stable phosphametallacyclobutene complexes of
zirconium have been previously reported by Stephan and co-
workers.33 These systems also [2 + 2] retrocycloadd the alkyne,
since tertiary phosphines cleanly transform the phosphametal-
lacyclobutene to the corresponding phosphinidene phosphine
adduct and the free alkyne.33
Geometry optimizations of 1, 3, and 4 indicate that alterations
i
t
of the all Pr groups of the full models to H’s or Bu to CH3
(the simplified model is displayed in Figure 3) result in
considerable discrepancies in the Ti-P-Cipso angles, together
with elongation of Ti-P bond lengths (Table 3). Consequently,
our computed bond orders (Table 3) for the simplified structures
are more consistent with a TidP bond as opposed to the TitP
linkage suggested in Table 2. This perturbation implies that
linearity at the Ti-P-Cipso motif and the bonding scheme
invoking the Ti-P linkage are possibly dominated by the
sterically imposing substituents on the phosphinidene and
â-diketiminate nitrogens. Clearly, a pseudo TitP bond results
in a lower energy species since the linear Ti-P-Cipso linkage
places both the P substituent outward to reduce the steric
repulsion with the neopentyl group and sterically encumbering
tBu groups of the â-diketiminate ligand. Similar features
involving the sterics at P have been discussed previously by
our group.6c To form the TitP bond, donation of the lone pair
of P: f Ti needs to occur. Perplexed by the TidP bond order
preference observed for the simplified models, we speculate that
there must be a greater energy penalty for rearrangement to a
linear Ti-P-Cipso linkage than the energy gained from forming
a pseudo-triple bond, TitP.
Catalytic Activity of Terminal Titanium Phosphinidenes.
Given the ability of 4 to undergo [2 + 2] cycloaddition with
PhCCPh to afford the phosphametallacyclobutene, we reasoned
that complex 4 could be poised to be a catalytic “PAr” transfer
reagent. Accordingly, when 4 (10 mol %) was treated with
PhCCPh and H2PPh in C6D6 at 80 °C for 12 h, the secondary
vinylphosphine HP[Ph]PhCdCHPh was isolated in 73% yield
Reactivity Studies of the Phosphinidene Zwitterion 4.
Compounds 1 and 3 fail to react with diphenylacetylene
presumably because of the sterically protected phosphinidene
functionality. Complex 4 however, contains a labile borate group
and would therefore be expected to be more reactive than its
neutral derivatives. Hence, complex 4 reacts rapidly with
PhCCPh to afford the phosphametallacyclobutene salt [(tBunacnac)-
Ti(P[Trip]PhCCPh)][CH3B(C6F5)3] (5) in >90% yields (Scheme
3). 31P and 13C NMR spectra are indicative of one isomer
present, which contains a three-coordinate phosphorus species
resulting from a [2 + 2] cycloaddition of the alkyne across the
TidP bond (see Experimental Section). Stronger evidence for
(30) This type of secondary vinylphosphine is unknown but the 1-phosphaallyl
anion [Aryl]PC(Ph)C(H)Ph (aryl ) 2,4,6-tBu3C6H2) has been reported.
Niecke, E.; Nieger, M.; Wenderoth, P. J. Am. Chem. Soc. 1993, 115, 6989-
6990. Secondary vinylphosphines of the type H2CdCHPHR have also been
reported. Gaumont, A. C.; Morise, X.; Denis, J. M. J. Org. Chem. 1992,
57, 4292-4295.
(31) The imide zwitterion (tBunacnac)TidNR{CH3B(C6F5)3} (R ) 2, 6-iPr2C6H3)
and PhCCPh are in equilibrium with the azametallacyclobutene complex
[(tBunacnac)Ti(NRPhCCPh)][CH3B(C6F5)3]. Basuli, F.; Aneetha, H.; Huff-
man, J. C.; Mindiola, D. J. J. Am. Chem. Soc. 2005, 127, 17992-17993.
(32) (a) Baranger, A. M.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc. 1993,
115, 2753-2763. (b) Walsh, P. J.; Baranger, A. M.; Bergman, R. G. J.
Am. Chem. Soc. 1992, 114, 1708-1719.
(33) (a) Breen, T. L.; Stephan, D. W. J. Am. Chem. Soc. 1996, 118, 4204-
4205. (b) Breen, T. L.; Stephan, D. W. Organometallics 1996, 15, 5729-
5737. (c) Transient ruthenium phosphametallacyclobutenes originated from
alkynes have been proposed as likely intermediates in the formation of
phosphaallyl moieties. (d) Termaten, A. T.; Nijbacker, T.; Schakel, M.;
Lutz, M.; Spek, A. T.; Lammertsma, K. Chem.sEur. J. 2003, 9, 2200-
2208.
(29) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270-283. (b) Wadt,
W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284-298.
9
13580 J. AM. CHEM. SOC. VOL. 128, NO. 41, 2006

Neutral and Zwitterionic Titanium Complexes
A R T I C L E S
Scheme 4. Catalytic Hydrophosphination Utilizing the
Phosphinidene Precatalyst 4a
Table 4. Carboamination Reactions to Prepare R,â-Unsaturated
Iminesa
entry
aldimine
product
yield (%)
1
6a; R1 ) CH3, R2 ) CH3
6b; R1 ) CH3, R2 ) NMe2
6c; R1 ) OCH3, R2 ) NMe2
7a
7b
7c
68
70
68
2b
3
a Reactions were carried out with 10 mol % catalyst in C6D6 at 135 °C.
Yield of the isolated product after column chromatography. b 5 mol %
catalyst was used.
exciting intermolecular transformations such as the hydroami-
nation of alkynes32,36-43 and alkenes,44 hydrohydrazination of
alkynes,45 three-component coupling reactions to form R,â-
unsaturated â-iminoamines,46 guanylation of amines,47 and more
recently carboamination,31,48,49 among other catalytic processes.15
Given our interest in catalytic carboamination,31,49 a process in
which an alkyne inserts into an aldimine CdN bond to form
an R,â-unsaturated imine, we reasoned whether complex 4 could
behave as an active precatalyst for this type of reaction.
a The â-diketiminate ligand and BCH3(C6F5)3 anion are not shown for
clarity. Formation of the cationic phenylphosphinidene catalyst [Ti])PPh
from 4 is proposed to occur via protonation and subsequent R-hydrogen
abstraction steps.
as a pale yellow oil. Compound HP[Ph]PhCdCHPh forms as a
monomer (MS (CI) MH+ ) 289.11) containing a mixture of E
and Z isomers in a 5:2 ratio when judged by 31P NMR
spectroscopy and GC-MS. 31P NMR (proton coupled) spectra
of HP[Ph]PhCdCHPh clearly reveals not only coupling of the
phosphorus to the proximal hydrogen (1JP-H ) 218-224 Hz),
but substantial coupling to the two ortho phenyl hydrogens
(3JP-H ∼6 Hz) as well as the vinylic hydrogen (3JP-H ) 14-
17 Hz). Compound HP[Ph]PhCdCHPh is a pale yellow oil
which is exceedingly reactive toward air and slowly decomposes
overtime to a mixture of products. A mechanism qualitatively
similar to the more common, intermolecular catalytic hydroami-
nation of alkynes appears likely to be operative for the system
studied herein (Scheme 4). We propose that H2PPh protonates
the phosphinidene ligand in 4 to form a bisphosphide intermedi-
ate, which subsequently undergoes R-hydrogen abstraction to
form the catalyst having a TidPPh linkage (Scheme 4).
Evidence for phosphametallacyclobutene formation as opposed
to the known 1,2-insertion mechanism34 appears to be the
favored route in this process since complex 4 fails to form a
phosphine product when treated with HPPh2 and PhCCPh under
similar conditions.35
Given the ability of 4 to catalytically generate the secondary
phosphine, we reasoned that this species was also suitable as a
low-coordinate “(tBunacnac)Ti3+” vehicle rather than a stoichio-
metric or catalytic phospha-Staudinger PAr delivery reagent.
In other words, the propensity of 4 to undergo PAr group-
transfer renders this complex a convenient precursor for other
terminal functionalities confined in a low-coordination environ-
ment. Hence, one obvious functionality to conceive from the
phosphinidene group is the imide, since early-transition metal
complexes possessing this functionality play important roles in
Accordingly, when PhCCPh and corresponding aldimine
where heated at 135 °C with 5-10 mol % of 4, carboamination
proceeded smoothly to afford the R,â-unsaturated imine in
∼70% isolated yield (Table 4). All highly arylated R,â-
unsaturated imines had exclusive (E,E)-configuration at the
olefin and imine residues according to Table 4. Generation of
the R,â-unsaturated imine is proposed to occur initially by
phospha-Staudinger metathesis of 4 with the aldimine to
generate the putative phosphaalkene [Trip]PdCHR′ and the low-
coordinate imide (tBunacnac)TidNR{CH3B(C6F5)3}. While the
former byproduct appears to be kinetically incompetent through-
(36) (a) Anderson, L. L.; Arnold, J.; Bergman, R. G. Org. Lett. 2004, 6, 2519-
2522. (b) Lee, S. Y.; Bergman, R. G. Tetrahedron 1995, 51, 4255-4276.
(b) Ackermann, L. Organometallics 2003, 22, 4367-4368. (c) Straub, B.
F.; Bergman, R. G. Angew. Chem., Int. Ed. 2001, 40, 4632-4635.
(37) Lorber, C.; Choukroun, R.; Vendier, L. Organometallics 2004, 23, 1845-
1850.
(38) Ward, B. D.; Maisse-Francois, A.; Mountford, P.; Gade, L. H. Chem.
Commun. 2004, 704-705.
(39) Tillack, A.; Jiao, H.; Castro, I. G.; Hartung, C. G.; Beller, M. Chem.sEur.
J. 2004, 10, 2409-2420 and references therein.
(40) (3) Hill, J. E.; Profilet, R. D.; Fanwick, P. E.; Rothwell, I. P. Angew. Chem.,
Int. Ed. Engl. 1990, 29, 664-665.
(41) (a) Haak, E.; Bytschkov, I.; Doye, S. Angew. Chem., Int. Ed. 1999, 38,
3389-3391. (b) Pohlki, F.; Bytschkov, I.; Siebeneicher, H.; Heutling, A.;
Ko¨nig, W. A.; Doye, S. Eur. J. Org. Chem. 2004, 1967-1972. (c) Pohlki,
F.; Doye, S. Angew Chem., Int. Ed. 2001, 40, 2305-2308. (d) For a review
on hydroamination reactions involving alkynes: Pohlki, F.; Doye, S. Chem.
Soc. ReV. 2003, 32, 104-114.
(42) Ong, T.-G.; Yap, G. P. A.; Richeson, D. S. Organometallics 2002, 21,
2839-2841.
(43) Zhang, Z.; Schafer, L. L. Org. Lett. 2003, 5, 4733-4736 and references
therein.
(44) Ackermann, L.; Kaspar, L. T.; Gschrei, C. J. Org. Lett. 2004, 6, 2515-
2518.
(45) (a) Odom, A. J. Chem. Soc., Dalton Trans. 2005, 225-233 and references
therein. (b) Li, Y.; Shi, Y.; Odom, A. L. J. Am. Chem. Soc. 2004, 126,
1794-1803.
(34) Catalyzed intramolecular hydrophosphination of alkenes and alkynes
involving organolanthanide complexes have been reported. (a) Douglass,
M. R.; Marks, T. J. J. Am. Chem. Soc. 2000, 122, 1824-1825. (b) Kawaoka,
A. M.; Douglass, M. R.; Marks, T. J. Organometallics 2003, 22, 4630-
4632. (c) Motta, A.; Fragala, I. L.; Marks, T. J. Organometallics 2005, 24,
4995-5003. (d) Douglass, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem.
Soc. 2001, 123, 10221-10238.
(35) Intermolecular hydrophosphination of alkynes with HPPh2 has been
reported. Ohmiya, H.; Yorimitsu, H.; Oshima, K. Angew. Chem., Int. Ed.
2005, 44, 2368-2370 and references therein.
(46) Cao, C.; Shi, Y.; Odom, A. L. J. Am. Chem. Soc. 2003, 125, 2880-2881.
(47) Ong, T.-G.; Yap, G. P. A.; Richeson, D. S. J. Am. Chem. Soc. 2003, 125,
8100-8101.
(48) (a) Ruck, R. T.; Zuckermann, R. L.; Krska, S. W.; Bergman, R. G. Angew.
Chem., Int. Ed. 2004, 43, 5372-5374. (b) Ruck, R. T.; Bergman, R. G.
Organometallics 2004, 23, 2231-2233.
(49) Aneetha, H.; Basuli, F.; Huffman, J. C.; Mindiola, D. J. Organometallics
2006, 25, 2402-2404.
9
J. AM. CHEM. SOC. VOL. 128, NO. 41, 2006 13581

A R T I C L E S
Zhao et al.
Scheme 5. Catalytic Carboamination of Diphenylacetylene with
Aryl Aldimines Utilizing the Phosphinidene Precatalyst 4a
play a vital role in attractive catalytic processes such as the
intermolecular hydrophosphination and carboamination of diphe-
nylacetylene. We are currently exploring the intermolecular
hydrophosphination of alkynes with primary phosphines cata-
lyzed by titanium phosphinidenes, since secondary vinylphos-
phines have been demonstrated to tautomerize to the corre-
sponding phosphaalkene.50,51 The latter type of transformation
would allow a facile entry to low-coordinate phosphaalkene
moeties directly from the alkyne and the primary phosphine.
Experimental Section
General Considerations. Unless otherwise stated, all operations
were performed in a M. Braun Lab Master double-drybox under an
atmosphere of purified nitrogen or using high vacuum standard Schlenk
techniques under an argon atmosphere.52 Anhydrous n-hexane, pentane,
toluene, and benzene were purchased from Aldrich in sure-sealed
reservoirs (18 L) and dried by passage through two columns of activated
alumina and a Q-5 column.53 Diethyl ether was dried by passage through
a column of activated alumina.53 FC6H5 was purchased from Aldrich,
degassed, and dried by passage though a column of activated alumina.
THF was distilled, under nitrogen, from purple sodium benzophenone
ketyl and stored under sodium metal. Distilled THF was transferred
under vacuum into bombs before being pumped into a drybox. C6D6
was purchased from Cambridge Isotope Laboratory (CIL), degassed,
dried over CaH2, and vacuum transferred to 4 Å molecular sieves. THF-
d8 was purchased from CIL and stored over a sodium film. Celite,
alumina, and 4 Å molecular sieves were activated under vacuum
overnight at 200 °C. BrC6D5 was purchased from CIL and dried over
activated alumina. B(C6F5)3 was purchased from Boulder Scientific and
sublimed under reduced pressure prior to use. Li(tBunacnac) (tBunacnac-
) [Ar]NC(tBu)CHC(tBu)N[Ar], Ar ) 2,6-(CHMe2)2C6H3),18 LiCH2tBu,54
a The â-diketiminate ligand and BCH3(C6F5)3 anion are not shown for
clarity.
out the catalytic process via dimerization or oligomerization,
the latter subsequently undergoes [2 + 2] cycloaddition of the
internal alkyne to provide the azametallacyclobutene [(tBunacnac)-
TiNRCPhCPh][BCH3(C6F5)3]. The azametallacyclobutene in-
termediate then inserts the aldimine to yield a thermally unstable
six-membered ring metallacycle, which experiences [4 + 2]
retrocycloaddition to regenerate the TidNR linkage and extrude
the R,â-unsaturated imine (Scheme 5).
(
tBunacnac)TiCl2,19 tBunacnac)TidCHtBu(OTf),19 LiPH[Trip] (Trip )
(
Conclusions
2,4,6-(CHMe2)3C6H2),55-57 were prepared according to the literature.
All other chemicals were used as received. CHN analyses were
performed by Desert Analytics, Tucson, AZ. 1H, 13C, 31P, and 11B NMR
spectra were recorded on Varian 400 or 300 MHz NMR spectrometers.
1H and 13C NMR are reported with reference to solvent resonances
(residual C6D5H in C6D6, 7.16 and 128.0 ppm; proteo THF in THF-d8,
3.58, 1.73, and 67.4, 25.3; C6H5Br in C6D5Br 7.33, 7.05, 6.97 and 131.1,
129.6, 126.4, 122.4 ppm). 31P NMR chemical shifts are reported with
respect to external H3PO4 (aqueous solution, δ 0.0 ppm). 11B NMR
chemical shifts are reported with respect to external BF3‚OEt2 (δ 0.0
ppm). Solution magnetic moments were obtained by the method of
Evans.58 Electronic absorption spectra were obtained with a Perkin-
Elmer Lamba 19 spectrophotometer using UVWinlab software. Single-
crystal X-ray diffraction data were collected on a SMART6000 (Bruker)
system under a stream of N2(g) at low temperatures. Solid-state NMR
spectra were obtained on a Bruker Avance-500 NMR spectrometer
operating at 500.13 and 202.42 MHz for 1H and 31P nuclei, respectively.
All 31P chemical shifts were referenced to 85% H3PO4(aq) using a solid
sample of NH4H2PO4 as a secondary external reference. Powder samples
In summary, kinetically stable, neutral and zwitterionic
phosphinidene complexes of titanium(IV) have been prepared.
The TidP linkage can be generated by two independent routes,
one via R-hydrogen migration, while the second synthetic
approach applies R-hydrogen abstraction. The phosphinidene
complexes reported in this paper contain exceedingly short Tid
P distances, linear Ti-P-Cipso linkages, and highly shielded
31P NMR resonances. These are the first terminal transition metal
phosphinidenes to be elucidated by a combination of single-
crystal X-ray diffraction, solid-state and solution 31P NMR, and
DFT analysis. On the basis of both solid-state structural and
DFT studies, we propose that part of the stability of the
titanium-phosphorus linkage arises from steric protection and
not the formation of a pseudo TitP bond since linearity at the
Ti-P-C linkage in systems such as 1 could originate from
clashing of the phosphorus sterically demanding aryl motif with
other sterically demanding ligands such as neopentyl or bulky
groups on the â-diketiminate ligand. Although TitP formation
is not prerequisite for these systems, spectroscopic, structural,
and theoretical data point to a pseudo-triple bond between Ti
and P which is operative for all the phosphinidenes systems
presented in this work. We have demonstrated that a zwitterionic
titanium complex possessing a terminal phosphinidene func-
tionality can deliver the phosphinidene group in a catalytic
fashion to generate the secondary vinylphosphine HP[Ph]PhCd
CHPh. Taking advantage of the reactive nature of the TidP
linkage we can also generate other functionalities capable of
mediating other catalytic reactions such as the carboamination
of diphenylacetylene with aldimines. Our work demonstrates
for the first time that an early-transition MdP functionality can
(50) Mercier, F.; Hugel-Le Goff, C.; Mathey, F. Tetrahedron Lett. 1989, 30,
2397-2398.
(51) Yam, M.; Tsang, C.-W.; Gates, D. P. Inorg. Chem. 2004, 43, 3719-3723.
(52) For a general description of the equipment and techniques used in carrying
out this chemistry see: Burger, B. J.; Bercaw, J. E. In Experimental
Organometallic Chemistry; Wayda, A. L., Darensbourg, M. Y., Eds.; ACS
Symposium Series 357; American Chemical Society: Washington DC,
1987; pp 79-98.
(53) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers,
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Chem. Soc. 1959, 2003-2005.
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Neutral and Zwitterionic Titanium Complexes
A R T I C L E S
were packed into zirconium oxide rotors (4 mm o.d.) in a drybox.
Typical sample spinning frequencies for the MAS experiments are 8-15
kHz. The recycle time was 10 s and all spectra were recorded with
cross polarization (2 ms contact time) and TPPM proton decoupling
(70 kHz B1 field). Variable sample spinning frequencies were used to
identify the isotropic peak in each spectrum.
(10 mL) and the solution was cooled to -35 °C. To the cold solution
was added a cold ether solution (∼10 mL) containing LiPH[Trip] [166
mg, 0.69 mmol]. After stirring for 20 min the solution was dried under
reduced pressure, the brown powder was extracted with hexane and
filtered, and the filtrate was concentrated under reduced pressure. The
concentrated solution was then cooled to -35 °C to afford large purple
crystals of (tBunacnac)TidP[Trip](CH3) (3) in two crops [325 mg, 0.41
Synthesis of Complex (tBunacnac)TidP[Trip](CH2 Bu) (1). In a
t
1
vial was dissolved (tBunacnac)TidCHtBu(OTf) [100 mg, 0.13 mmol]
in Et2O (10 mL), and the solution was cooled to -35 °C. To the cold
solution was added an ether solution (∼5 mL) containing LiPH[Trip]
[32 mg, 0.13 mmol]. After stirring for 30 min the solution was dried
under reduced pressure. The brown powder was extracted with hexane
and filtered, and the filtrate was concentrated and cooled to -35 °C to
mmol, 59.4% yield]. H NMR (23 °C, 399.8 MHz, C6D6): δ 7.08-
6.83 (m, C6H3, C6H2, 8H), 5.40 (s, C(tBu)CHC(tBu), 1H), 4.00 (septet,
CHMe2, 2H), 3.58 (septet, CHMe2, 4H), 2.65 (septet, CHMe2, 1H), 1.75
(d, CHMe2, 6H), 1.42 (d, CHMe2, 6H), 1.36 (d, CHMe2, 6H), 1.29 (d,
CHMe2, 6H), 1.27 (s, Ti-CH3, 3H), 1.10 (d, CHMe2, 18H), 1.04 (s,
C(tBu)CHC(tBu), 18H). 13C NMR (25 °C, 100.6 MHz, C6D6): δ.173.7
(C(tBu)CHC(tBu)), 155.3 (ipso-C6H2, JC-P ) 28 Hz,), 149.4 (C6H3),
149.1 (C6H3), 147.0 (C6H3), 142.2 (C6H3), 140.2 (C6H3), 126.5 (C6H3),
124.1 (C6H3), 124.0 (C6H3), 119.9 (C6H3), 90.0 (C(tBu)CHC(tBu)), 45.0
(C(CMe3)CHC(CMe3)), 41.4 (Ti-CH3), 34.6 (CHMe2), 32.5 (CHMe2),
32.0 (C(CMe3)CHC(CMe3)), 29.5 (CHMe2), 29.0 (CHMe2), 27.6 (Me),
afford in two crops purple crystals of (tBunacnac)TidP[Trip](CH2 Bu)
t
(1) [72 mg, 0.08 mmol, 61.5% yield].1H NMR (23 °C, 399.8 MHz,
C6D6): δ 7.05-6.74 (m, C6H3, C6H2, 8H), 5.39 (s, C(tBu)CHC(tBu),
1H), 4.14 (septet, CHMe2, 2H), 3.59 (septet, CHMe2, 2H), 3.30 (septet,
CHMe2, 2H), 2.60 (septet, CHMe2, 1H), 1.68 (d, CHMe2, 6H), 1.58 (s,
25.5 (Me), 24.6 (Me), 24.5 (two Me groups), 24.3 (Me), 24.2 (Me). 31
P
t
t
Ti-CH2 Bu, 9H), 1.56 (s, Ti-CH2 Bu, 2H), 1.39 (d, CHMe2, 6H), 1.28
(d, CHMe2, 6H), 1.24 (d, CHMe2, 6H), 1.08 (d, CHMe2, 6H), 1.05 (s,
C(tBu)CHC(tBu),18H), 1.01 (d, CHMe2, 12H). 13C NMR (25 °C, 100.6
MHz, C6D6): δ.173.0 (C(tBu)CHC(tBu)), 154.5 (ipso-C6H2, JC-P ) 28
Hz), 150.3 (C6H3), 149.5 (C6H3), 146.3 (C6H3), 141.8 (C6H3), 140.0
(C6H3), 137.1 (C6H3), 126.1 (C6H3), 124.6 (C6H3), 123.7 (C6H3), 98.3
NMR (25 °C, 161.9 MHz, C6D6): δ 231.5 (s, P[Trip]). Anal. Calcd
for C51H79N2TiP: C, 76.66; H, 9.97; N, 3.51. Found: C, 76.71; H,
10.20; N, 3.87. UV-vis (C6H6, 25 °C): 315 (ꢀ ) 27886 L‚mol-1‚cm-1),
368 (ꢀ ) 13743 L‚mol-1‚cm-1), 502 (ꢀ ) 2237 L‚mol-1‚cm-1) nm.
Synthesis of Complex (tBu
nacnac)TidP[Trip]{CH3B(C6F5)3} (5).
(Ti-CH2 Bu, JC-H ) 100 Hz), 87.8 (C(tBu)CHC(tBu)), JC-H ) 151),
t
Flurobenzene was added to the mixture of (tBunacnac)TidP[Trip](CH3)
[1.00 g, 1.25 mmol] and B(C6F5)3 [640 mg, 1.25 mmol]. After allowing
the reaction to proceed at room temperature for 10 min, the solution
was layered with pentane and cooled to -35 °C to afford large brown
crystals of (tBunacnac)TidP[Trip]{CH3B(C6F5)3} (5) in two crops [1.17
45.1 (C(CMe3)CHC(CMe3)), 36.9 (Ti-CH2CMe3), 35.5 (Ti-CH2CMe3),
34.4 (CHMe2), 32.2 (CHMe2), 31.8 (C(CMe3)CHC(CMe3)), 29.2
(CHMe2), 28.7 (CHMe2), 28.2 (Me), 27.7 (Me), 26.0 (Me), 24.9 (Me),
24.7 (Me), 24.5 (Me), 24.0 (Me). 31P NMR (25 °C, 161.9 MHz, C6D6):
δ 157.0 (s, P[Trip]). Anal. Calcd for C55H87N2TiP: C, 77.25; H, 10.25;
N, 3.28. Found: C, 76.93; H, 10.56; N, 3.20. UV-vis (C7H8, 25 °C):
319 (ꢀ ) 25344 L‚mol-1‚cm-1 ), 365 (ꢀ ) 13915 L‚mol-1‚cm-1), 490
(br shoulder) nm.
1
g, 0.89 mmol, 71.2% yield]. H NMR (23 °C, 399.8 MHz, C6D5Br):
δ 7.46-6.81 (m, C6H3, C6H2 and C(tBu)CHC(tBu) 9H), 3.50 (septet,
CHMe2, 2H), 3.28 (septet, CHMe2, 2H), 3.00 (septet, CHMe2, 2H),
2.73 (septet, CHMe2, 1H), 1.70 (d, CHMe2, 6H), 1.41 (d, CHMe2,6H),
1.25-0.96 (CHMe2, CH3, C(tBu)CHC(tBu), 51H). 13C NMR (25 °C,
100.6 MHz, C6D5Br): δ 175.8 (C(tBu)CHC(tBu)), 153.8 (C6H3), 151.7
(C6H3), 148.8 (br, B(C6F5)3), 140.9 (C6H3), 138.8 (C6H3), 136.8 (br,
B(C6F5)3), 131.7 (C6H3), 128.4 (C6H3), 128.0 (C6H3), 124.7 (C6H3),
124.4 (C6H3), 120.3 (C6H3), 113.6 (C(tBu)CHC(tBu)), 44.6 (C(CMe3)-
CHC(CMe3)), 34.3 (CHMe2), 31.8 (CHMe2), 31.0 (CHMe2), 30.8
(C(CMe3)CHC(CMe3)), 28.9 (CHMe2), 25.3 (Me), 24.5 (two Me
groups), 24.4 (Me), 23.7 (Me), 23.5 (Me), 23.3 (Me). 31P NMR (25 °C,
161.9 MHz, C6D5F): δ 206.8 (s, P[Trip]). 19F NMR (23 °C, 282.3
MHz, C6D5Br): δ -131.8 (B(C6F5)3), -164.9 (B(C6F5)3), -166.6
(B(C6F5)3). 11B NMR (23 °C, 128.4 Hz, C6D5Br): δ -14.2 (B(C6F5)3).
UV-vis (C6H6, 25 °C): 315 (ꢀ ) 3718 L‚mol-1‚cm-1), 365 (ꢀ ) 3974
L‚mol-1‚cm-1), 500 (broad shoulder) nm. Multiple attempts to obtain
satisfactorily elemental analysis have failed presumably because of the
thermal sensitivity of 4.
Synthesis of (tBunacnac)Ti(CH3)2. In a reaction vessel was dissolved
(
tBunacnac)TiCl2 [2.04 g, 3.29 mmol] in hexane (50 mL) and the solution
cooled to -35 °C. To the cold solution was added an ether solution
containing CH3MgCl [2.19 mL, 6.57 mmol]. After stirring for 20 min
the solution was filtered, and the filtrate was concentrated under reduced
pressure, and cooled to -35 °C to afford in two crops green crystals
of (tBunacnac)Ti(CH3)2 (2) [1.339 g, 2.31 mmol, 70.3% yield]. 1H NMR
(23 °C, 399.8 MHz, C6D6): δ 6.12 (∆ν1/2 ) 363 Hz), 5.50 (∆ν1/2
)
330 Hz), 4.90 (∆ν1/2 ) 72 Hz), 2.46 (∆ν1/2 ) 69 Hz); µeff ) 1.85 µB
(C6D6, 298 K, Evans’ method). Anal. Calcd for C37H59N2Ti: C, 76.65;
H, 10.26; N, 4.83. Found: C, 76.94; H, 10.61; N, 4.80.
Synthesis of (tBunacnac)Ti(CH3)2(OTf) (2). In a vial was dissolved
(
tBunacnac)Ti(CH3)2 [1.00 g, 1.73 mmol] in THF (10 mL) and the
solution was cooled to -35 °C. To the cold solution was added a THF
solution (∼10 mL) containing AgOTf [443 mg, 1.73 mmol] causing
precipitation of Ag0. After stirring for 15 min the solution was filtered,
the filtrate was dried under reduced pressure and was washed several
times with hexane to afford (tBunacnac)Ti(CH3)2(OTf) (3) [952 mg, 1.31
mmol, 75.7% yield] as an orange solid. 1H NMR (23 °C, 399.8 MHz,
THF-d8): δ 7.11-7.21 (m, C6H3, 6H), 6.47 (s, C(tBu)CHC(tBu), 1H),
3.34-3.60 (br, CHMe2, 4H), 1.77 (s, Me2Ti, 3H), 1.73 (s, Me2Ti, 3H),
1.10-1.59 (m, CHMe2 and C(tBu)CHC(tBu), 42H). 13C NMR (25 °C,
100.6 MHz, THF-d8): δ 173.6 (C(tBu)CHC(tBu)), 150.3 (C6H3), 147.2
(C6H3), 144.7 (C6H3), 142.3 (C6H3), 139.7 (C6H3), 136.0 (C6H3), 127.0
(C6H3), 125.2 (C6H3), 124.4 (C6H3), 121.3 (C6H3), 118.1 (C6H3), 114.9
(C6H3), 97.0 (C(tBu)CHC(tBu), JC-H ) 160 Hz), 82.4 (Me2Ti), 68.6
(Me2Ti), 43.1 (C(CMe3)CHC(CMe3)), 42.3 (C(CMe3)CHC(CMe3)), 29.6
(C(CMe3)CHC(CMe3)), 28.7 (C(CMe3)CHC(CMe3)), 27.0 (br), 26.7
(br), 25.6 (br), 24.0 (br). 19F NMR (23 °C, 282.3, MHz, THF-d8): δ
-78.9 (s, O3SCF3). Anal. Calcd for C38H59N2TiSO3F3: C, 62.62; H,
8.16; N, 3.84. Found: C, 62.62; H, 8.17; N, 3.62.
Synthesis of Complex [(tBunacnac)Ti(P[Trip]PhCCPh)][CH3B-
(C6F5)3] (6). C6D5Br was added to the mixture of 4 [75.7 mg, 0.06
mmol] and PhCCPh [10.8 mg, 0.06 mmol] in a J. Yong NMR tube.
After allowing the reaction to proceed at room temperature for 10 min,
the crude NMR spectrum revealed quantitative formation of [(tBunacnac)-
1
Ti(P[Trip]PhCCPh)][CH3B(C6F5)3] (5). H NMR (23 °C, 399.8 MHz,
C6D5Br): δ 7.30-6.38 (m, aryl, 18H), 6.04 (C(tBu)CHC(tBu),1H), 2.82
(septet, CHMe2, 2H), 2.41(mixture of septets, CHMe2, 3H), 1.88 (septet,
CHMe2, 2H), 0.96 (d, CHMe2, 12H), 0.93 (s, CH3, 3H), 0.85 (d, CHMe2,
12H), 0.78 (s, C(tBu)CHC(tBu), 18H), 0.71 (d, CHMe2, 6H), 0.41 (d,
CHMe2, 6H), 0.22 (d, CHMe2, 6H), 13C NMR (25 °C, 100.6 MHz,
C6D5Br): δ 253.5 (Ti-CPhCPh), 175.3 (C(tBu)CHC(tBu), 156.9, 156.4,
148.8 (CH3B(C6F5)3), 142.3, 140.6, 140.5, 140.0, 137.7 (CH3B(C6F5)3),
136.6 (CH3B(C6F5)3), 133.4, 131.7, 130.1, 129.1, 128.9, 128.7, 128.4,
128.3, 126.1, 124.7, 124.5, 122.8, 115.2, 88.6 (C(tBu)CHC(tBu)), 45.1
(C(CMe3)CHC(CMe3)), 34.6 (CHMe2), 34.3 (CHMe2), 31.0 (C(CMe3)-
CHC(CMe3)), 29.3 (CHMe2), 28.2 (CHMe2), 26.0 (Me), 25.8 (Me), 25.0
(Me), 24.1 (Me), 24.0 (Me), 23.4 (Me), 21.6 (Me). 31P NMR (25 °C,
Synthesis of Complex (tBunacnac)TidP[Trip](CH3) (3). In a vial
was dissolved (tBunacnac)Ti(CH3)2(OTf) [500 mg, 0.69 mmol] in ether
9
J. AM. CHEM. SOC. VOL. 128, NO. 41, 2006 13583

A R T I C L E S
Zhao et al.
161.9 MHz, C6D5Br): δ 160.7 (s, P[Trip]). 19F NMR (23 °C, 282.3
Hz, C6D5Br): δ -132.7 (CH3B(C6F5)3), -165.3 (CH3B(C6F5)3), -167.7
(CH3B(C6F5)3). 11B NMR (23 °C,128.4 MHz, C6D5Br): δ -14.9
(CH3B(C6F5)3). Anal. Calcd for C83H89N2TiPBF15: C, 66.94; H, 6.02;
N, 1.88. Found: C, 66.44; H, 6.07; N, 1.94.
Table 5. Summary of Crystallographic Data and Structure
Refinement for Complexes 1‚C6H14, 3, and 4‚1.5FC6H5
1‚
C6H14
3
4‚1.5FC6H5
formula
FW
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C58H94N2PTi C51H79N2PTi C78H85BF16.57N2PTi
898.22
P2(1)/n
13.854(18)
21.04(2)
18.74(3)
90.00
799.03
P2(1)/n
11.104(2)
21.191(4)
21.135(4)
90.00
1455.04
P2(1)/c
14.5495(10)
20.0614(14)
24.8462(17)
90.00
Treatment of 6 with H2NPh to form HP[Trip]PhCdCHPh. To
a stirring solution of 6 in fluorobenzene was added 1.2 equiv of aniline.
The solution was allowed to stir for 4 h after which, the solvent was
removed under vacuo. The organic product was extracted from the
remaining brown residue with hexane. The hexane solution was filtered
93.21(8)
90.00
102.302(5)
90.00
90.677(2)
90.00
1
and dried under reduced pressure resulting in a yellow oil. H NMR
5453(12)
4
4859.2(16)
4
7251.7(9)
4
(25 °C, 499.8 MHz, C6D12): δ 7.40 (m, aryl, 1), 7.15 (m, aryl, 5), 7.07
(s, aryl, 2), 6.86 (m, aryl, 3), 6.73 (m, aryl, 2), 6.19 (d, JP-H ) 6 Hz,
HCdC, 1), 4.80 (d, JP-H ) 221 Hz, PH, 1), 3.77 (septet, CHMe2, 2H),
2.86 (septet, CHMe2, 1H), 1.26 (d, CH3, 12H), 1.18 (d, CH3, 6H). 13C
NMR (25 °C, 125.69 MHz, C6D12): δ 155.01 (JP-C ) 14 Hz), 151.23,
142.14 (JP-C ) 15 Hz) 141.77 (JP-C ) 21 Hz), 137.88, 133.68 (JP-C
) 17 Hz), 132.16, 129.52, 129.03, 128.68 (JP-C ) 4 Hz), 128.49,
128.14, 127.33, 122.03, 35.40 (CHMe2), 35.67 (d, CHMe2, JP-C ) 14
Hz,), 25.28 (CHMe2), 24.70 (CHMe2), 24.29 (CHMe2). 31P NMR (25
°C, 161.9 MHz, C6D6): δ -62.72 (s, P[Trip]). MS-EI: M+ ) 414.25.
Crystallographic Details. Inert atmosphere techniques were used
to place the crystal onto the tip of a diameter glass capillary (0.03-
0.20 mm) and mounted on a SMART6000 (Bruker) at 113-140 K. A
preliminary set of cell constants was calculated from reflections obtained
from three nearly orthogonal sets of 20-30 frames. Data collections
were carried out using graphite monochromated Mo KR radiation with
a frame time of 3 s with a detector distance of 5.0 cm. A randomly
oriented region of a sphere in reciprocal space was surveyed. Three
sections of 606 frames were collected with 0.30° steps in ω at different
φ settings with the detector set at -43° in 2θ. Final cell constants were
calculated from the xyz centroids of strong reflections from the actual
data collection after integration (SAINT).59 The structure was solved
using SHELXS-97 and refined with SHELXL-97.60 A direct-methods
solution was calculated which provided most non-hydrogen atoms from
the E-map. Full-matrix least squares/difference Fourier cycles were
performed which located the remaining non-hydrogen atoms. All non-
hydrogen atoms were refined with anisotropic displacement parameters,
and all hydrogen atoms were refined with isotropic displacement
parameters (unless otherwise specified, vide infra). A summary of
crystal data and refinement details for all structures are given in Table
5.
(1)‚C6H14. A dark crystal of approximate dimensions 0.30 × 0.25
× 0.25 mm3 was selected and mounted on a glass fiber. A total of
11975 reflections (-13 e h e 17, -27 e k e 8, -22 e l e 24) were
collected at T ) 125(2) K in the range of 2.03-27.52° of which 7099
were unique (Rint ) 0.0472); Mo KR radiation (λ ) 0.71073 Å). A
direct-methods solution was calculated which provided most non-
hydrogen atoms from the E-map. All non-hydrogen atoms were refined
with anisotropic displacement parameters. A disordered hexane solvent
is located in the unit cell. The residual peak and hole electron densities
were 0.317 and -0.341 eÅ-3. The absorption coefficient was 0.223
mm-1. The least squares refinement converged normally with residuals
of R(F) ) 0.0426, wR(F2) ) 0.0658, and a GOF ) 0.797 (I > 2σ(I));
C58H94N2PTi; space group P2(1)/n; monoclinic; a ) 13.85(8), b )
21.04(2), c ) 18.74(3), â ) 93.21(8)°; V ) 5453(12) A3; Z ) 4; Dcalcd
) 1.094 mg/m3; F(000) ) 1972.
Z
Dcalcd
linear abs coeff
F(000)
1.094
0.223
1972
deep red
hexane
irregular
1.092
0.242
1744
1.333
0.227
3033
deep red FC6H5/
hexane
cryst color/solvent
dark brown
hexane
multifaceted irregular fragment
cryst form
cryst size (mm)
0.30 × 0.25 × 0.30 × 0.30 × 0.30 × 0.30 ×
0.25 0.25 0.25
Θ range (lattice, deg)
index range
2.03-27.52
2.11-27.55
2.14-30.03
-13 e h e 17 -13 e h e 14 -20 e h e 20
-27 e k e 8 -27 e k e 27 -28 e k e 28
-22 e l e 24 -25 e l e 27 -34 e l e 34
reflns collected
unique reflns F > 4σ(F) 11975
obsd reflns
18817
34306
11176
7118
164162
21184
14120
0.0767
7099
0.0472
Rint
0.0868
Final R indices [I > 2σ(I)] R1 ) 0.0426 R1 ) 0.0442 R1 ) 0.0367
wR2 ) 0.0658 wR2 ) 0.0977 wR2 ) 0.0846
R indices (F2, all data)
GOF on F2
R1 ) 0.0815 R1 ) 0.0815 R1 ) 0.0666
wR2 ) 0.0735 wR2 ) 0.1097 wR2 ) 0.0942
0.797
0.911
0.935
hydrogen atoms from the E-map. All non-hydrogen atoms were refined
with anisotropic displacement parameters. The residual peak and hole
electron densities were 0.345 and -0.257 eA-3. The absorption
coefficient was 0.242 mm-1. The least squares refinement converged
normally with residuals of R(F) ) 0.0442, wR(F2) ) 0.0977, and a
GOF ) 0.911 (I > 2σ(I)); C51H79N2PTi; space group P2(1)/n;
monoclinic; a ) 11.104(2), b ) 21.191(4), c ) 21.135(4), â ) 102.302-
(5)°; V ) 4859.2(16) Å3; Z ) 4; Dcalcd ) 1.092 mg/m3; F(000) ) 1744.
(4)‚1.5FC6H5. A deep red crystal of approximate dimensions 0.30
× 0.30 × 0.25 mm3 was selected and mounted on a glass fiber. A
total of 21184 reflections (-20 e h e 20, -28 e k e 28, -34 e l e
34) were collected at T ) 119(2) K in the range of 2.14 to 30.03° of
which 14120 were unique (Rint ) 0.0767); Mo KR radiation (λ )
0.71073 Å). A direct-methods solution was calculated which provided
most non-hydrogen atoms from the E-map. All non-hydrogen atoms
were refined with anisotropic displacement parameters. Two FC6H5
solvent molecules are present, both slightly disordered and one lying
at a symmetry site. The residual peak and hole electron densities were
0.499 and -0.297 eÅ-3. The absorption coefficient was 0.227 mm-1
.
The least squares refinement converged normally with residuals of R(F)
) 0.0367, wR(F2) ) 0.0846, and a GOF ) 0.935 (I > 2σ(I)); C78H85-
BF16.57N2PTi; space group P2(1)/c; monoclinic; a ) 14.550(1), b )
20.061(4), c ) 24.846(7), â ) 90.677(2)°; V ) 7251.7(9) Å3; Z ) 4,
Dcalcd ) 1.333 mg/m3, F(000) ) 3033.
Computational Details. All calculations were carried out using
density functional theory as implemented in the Jaguar 5.5 suite25 of
ab initio quantum chemistry programs. Geometry optimizations were
performed with the B3LYP26 functional and the 6-31G** basis set.
Titanium was represented using the Los Alamos LACVP basis.27 The
bond order is calculated using the definition of Mayer.28 Geometry
optimizations have been carried out beginning with the crystal structures
for complexes 1, 3, and 4, and without symmetry restrictions, and
optimized geometries are in good agreement with the X-ray structures.
The full models consist of 134-168 atoms which represent the
nonsimplified ligands that were also used in the experimental portion
of this work. These calculations challenge the current state of
(3). A dark brown crystal of approximate dimensions 0.30 × 0.25
× 0.25 mm3 was selected and mounted on a glass fiber. A total of
11176 reflections (-13 e h e 14, -27 e k e 27, -25 e l e 27)
were collected at T ) 120(2) K in the range of 2.11 to 27.55° of which
7118 were unique (Rint ) 0.0868); Mo KR radiation (λ ) 0.71073 Å).
A direct-methods solution was calculated which provided most non-
(59) SAINT 6.1; Bruker Analytical X-ray Systems: Madison, WI.
(60) SHELXTL-Plus, version 5.10; Bruker Analytical X-ray Systems: Madison,
WI.
9
13584 J. AM. CHEM. SOC. VOL. 128, NO. 41, 2006

Neutral and Zwitterionic Titanium Complexes
A R T I C L E S
1
computational capabilities, whereas the numerical efficiency of the
Jaguar program allows us to accomplish this task in a bearable time
frame.
reaction progress was monitored by H NMR spectroscopy. After the
reaction was completed, the NMR tube was cooled to room temperature,
and the product purified by silica gel column chromatography (5% ether/
hexanes) to afford yellow R,â-unsaturated imine product (7a-c, 68-
70% yield). 1H and 13C NMR spectra of R,â-unsaturated imine product
were compared to samples prepared independently.49 NOTE: It is
imperative that both substrates and inert atmospheres be free of
moisture, oxygen, coordinating solvents (Et2O, THF, pyridine, etc), and
Cl sources (CH2Cl2, CHCl3, CCl4, etc). Traces of these elements will
reduce the catalytic activity. It is highly recommended that substrates,
solvents, and titanium precursors be freed of coordinating solvents prior
to usage in catalytic reactions.
Catalytic Reactions Hydrophosphination and Carboamination
of PhCCPh. Hydrophosphination. In a typical experiment, 4 [0.025
mmol, 10 mol %], alkyne [0.275 mmol], and H2PPh [0.25 mmol] were
mixed in a J. Young NMR tube in C6D6 (0.8 mL) inside the glovebox.
The NMR tube was removed from the glovebox and was heated to
∼80 °C for approximately 14-16 h. The reaction progress was
1
monitored by H and 31P NMR spectroscopy. After the reaction was
completed, the NMR tube was cooled to room temperature, the product
purified by silica gel column chromatography (under an inert atmo-
sphere) to afford the secondary vinylphosphine HP[Phenyl]PhCdCHPh
as a mixture of E and Z isomers [58 mg, 73% yield].
Acknowledgment. This work was supported by Indiana
University, the Camille and Henry Dreyfus Foundation (Teacher-
Scholar Award to D.J.M.), the Alfred P. Sloan Foundation
(Fellowship to D.J.M.), and the National Science Foundation
(Grant CHE-0348941 and PECASE award to D.J.M.). G.W.
thanks the Natural Sciences and Engineering Research Council
(NSERC) of Canada for research and equipment grants. The
authors would like to thank the referees for helpful suggestions.
1
Major Isomer. H NMR (25 °C, 300.059 MHz, C6D6): 7.5-6.8
(m, aryl-H), 7.06 (d, JP-H ) 13.5 Hz vinyl-H, 1H), 5.07 (d, JP-H
)
218 Hz, P-H, 1H). 31P[1H] NMR (25 °C, 161.9 MHz, C6D6): δ -16.40
(s, Ar-P). MS-CI: MH+ ) 289.11, and GC-MS M+ ) 288.
1
Minor Isomer. H NMR (25 °C, 300.059 MHz, C6D6): 7.5-6.8
(m, aryl-H), 7.25 (d, JP-H ) 16.6 Hz, vinyl-H, 1H), 5.38 (d, JP-H
)
224 Hz, P-H, 1H). 31P[1H] NMR (25 °C, 161.9 MHz, C6D6): δ -52.78
(s, Ar-P). MS-CI: MH+ ) 289.11, and GC-MS M+ ) 288.
Mixture of E + Z Isomers. 13C NMR (25 °C, 100.6 MHz, C6D12):
δ 145.5, 141.7, 141.0, 140.2, 139.0, 138.4, 138.3, 137.7, 137.6, 137.1,
134.6, 134.2, 133.4, 131.9, 130.6, 129.7, 129.6, 129.2, 129.1, 128.9,
128.7, 128.6, 128.5, 128.4, 128.3, 127.9, 127.3, 126.9.
Supporting Information Available: Complete crystallo-
graphic data for compounds 1, 3, and 4 (CIF files) and complete
geometrical parameters for their optimized geometries. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Carboamination. In a typical experiment, 4 [0.025 mmol, 10%],
alkyne [0.275 mmol], and aldimine [6a-c, 0.25 mmol] were mixed in
a J. Young NMR tube in C6D6 (0.8 mL) inside the glovebox. The NMR
tube was removed from the glovebox and was heated at 125 °C. The
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J. AM. CHEM. SOC. VOL. 128, NO. 41, 2006 13585