Slip - Inversion - Slip mechanism of phosphametallocene isomerization. Spectroscopic characterization of an (η1-phospholyl)titanium complex. Synthesis and structures of chiral mono(phospholyl)titanium complexes

Article abstract of DOI:10.1021/om050357h

The first reported synthesis and spectroscopic characterization of a group 4 η¹-phospholyl complex, (η¹-dibenzophospholyl) tris(dimethylamido)titanium, are documented, which has an η¹- phospholyl ligand analogous to those proposed in the slip - inversion - slip mechanism of phosphametallocene isomerization.

Full text of DOI:10.1021/om050357h

Organometallics 2006, 25, 1079-1083
1079
Articles
Slip-Inversion-Slip Mechanism of Phosphametallocene
Isomerization. Spectroscopic Characterization of an
(η1-Phospholyl)titanium Complex. Synthesis and Structures of
Chiral Mono(phospholyl)titanium Complexes
Yi Joon Ahn,† Ramel J. Rubio, T. Keith Hollis,* Fook S. Tham,‡ and Bruno Donnadieu‡
Physical Sciences 1, Department of Chemistry, UniVersity of California, RiVerside, California 92521
ReceiVed May 6, 2005
The first reported synthesis and spectroscopic characterization of a group 4 η1-phospholyl complex,
(η1-dibenzophospholyl)tris(dimethylamido)titanium, are documented, which has an η1-phospholyl ligand
analogous to those proposed in the slip-inversion-slip mechanism of phosphametallocene isomerization.
detailed understanding of the mechanism of heterocyclic
π-ligand isomerization is important for the application of
complexes containing these ligands. Recently, we reported the
activation parameters for the isomerization of a phospha-
titanocene and proposed an intramolecular mechanism for the
isomerization.12,13 The mechanism involves ring slippage to the
η1(σ)-bound phospholyl 1 followed by inversion at P (2, Scheme
1). It is termed the slip-inVersion-slip mechanism.14,15 Such
an η1 structure is consistent with much literature precedent for
phospholyl and pyrrollyl complexes.16 The η1 structure has been
established by X-ray crystal structure determinations for Ti and
Zr pyrrollyl complexes.16b Recent reports have also demonstrated
a facile isomerization of certain phosphinoferrocenes.17 Herein
we report the first spectroscopic evidence for an η1-bound
phospholyl ligand of group 4.
Introduction
Heterocyclic π-complexes have been demonstrated to be
excellent ligands for asymmetric catalysis.1 Late-transition-metal
phosphametallocenes, including phosphaferrocene-2 and phos-
pharuthenocene-based3 diphosphines and mixed P, N phospha-
ferrocene ligands have numerous applications.4,5 Boratabenzenes
bound to transition metals as heterocyclic π-ligands have been
found to be excellent polymerization catalysts.6,7 More recently,
examples with multiple heteroatoms have been reported.8
We began developing chiral, bent early-transition-metal
phosphametallocenes as ligands for asymmetric catalysis and
in the process discovered their facile isomerization.9-11
A
* To whom correspondence should be addressed. Tel: 951-827-3024.
Fax: 951-827-4713. E-mail: keith.hollis@ucr.edu.
† Current address: Chemistry Department, University of Michigan, 930
N. University, Ann Arbor, MI 48109-1055.
(9) Hollis, T. K.; Wang, L. S.; Tham, F. J. Am. Chem. Soc. 2000, 122,
11737-11738.
(10) Bellemin-Laponnaz, S.; Lo, M. M. C.; Peterson, T. H.; Allen, J.
M.; Fu, G. C. Organometallics 2001, 20, 3453-3458.
‡ To whom all correspondence regarding the X-ray crystallography should
be addressed: fook.tham@ucr.edu (F.S.T.), brunod@ucr.edu (B.D.).
(1) For recent reviews of heterocyclic metallocenes see: (a) Mathey, F.
Phosphorus-Carbon Heterocyclic Chemistry: The Rise of a New Domain,
1st ed.; Pergamon: Amsterdam; New York, 2001. (b) Ganter, C. Dalton
Trans. 2001, 3541-3548. (c) Ashe, A. J.; Al-Ahmad, S. AdV. Organomet.
Chem. 1996, 39, 325-353. (d) Mathey, F. Coord. Chem. ReV. 1994, 137,
1-52. (e) Dillon, K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon
Copy. From Organophosphorus to Phospha-Organic Chemistry; Wiley:
New York, 1998.
(11) For early-transition-metal phosphametallocenes see: (a) Nief, F.;
Ricard, L.; Mathey, F. Organometallics 1989, 8, 1473-1477. (b) Buzin,
F.-X.; Nief, F.; Ricard, L.; Mathey, F. Organometallics 2002, 21, 259-
263. (c) Janiak, C.; Lange, K. C. H.; Marquardt, P. J. Mol. Catal. A: Chem.
2002, 180, 43-58. (d) de Boer, E. J. M.; Gilmore, I. J.; Korndorffer, F.
M.; Horton, A. D.; van der Linden, A.; Royan, B. W.; Ruisch, B. J.; Schoon,
L.; Shaw, R. W. J. Mol. Catal. A: Chem. 1998, 128, 155-165.
(12) Hollis, T. K.; Ahn, Y. J.; Tham, F. S. Chem. Commun. 2002, 2996-
2997.
(13) For isomerizations of other P-containing ligands see: (a) Heinemann,
F. W.; Zeller, M.; Zenneck, U. Organometallics 2004, 23, 1689-1697. (b)
Heinemann, F. W.; Pritzkow, H.; Zeller, M.; Zenneck, U. Organometallics
2001, 20, 2905-2915. (c) Heinemann, F. W.; Pritzkow, H.; Zeller, M.;
Zenneck, U. Organometallics 2000, 19, 4283-4288. (d) Cloke, F. G. N.;
Flower, K. R.; Jones, C.; Matos, R. M.; Nixon, J. F. J. Organomet. Chem.
1995, 487, C21-C23.
(14) The slip-inversion-slip terminology is proposed in analogy to the
π-σ-π mechanism for π-allyl rearrangements: (a) Faller, J. W.; Thomsen,
M. E.; Mattina, M. J. J. Am. Chem. Soc. 1971, 93, 2642-2653. (b) Faller,
J. W.; Tully, M. T. J. Am. Chem. Soc. 1972, 94, 2676-2679.
(15) Dias, A. R.; Ferreira, A. P.; Veiros, L. F. Organometallics 2003,
22, 5114-5125.
(16) (a) Mercier, F.; Ricard, L.; Mathey, F. Organometallics 1993, 12,
98-103. (b) Nief, F.; Ricard, L. Organometallics 2001, 20, 3884-3890.
(c) Tanski, J. M.; Parkin, G. Organometallics 2002, 21, 587-589.
(2) (a) Tanaka, K.; Qiao, S.; Tobisu, M.; Lo, M. M. C.; Fu, G. C. J. Am.
Chem. Soc. 2000, 122, 9870-9871. (b) Tanaka, K.; Fu, G. C. J. Org. Chem.
2001, 66, 8177-8186. (c) Qiao, S.; Hoic, D. A.; Fu, G. C. Organometallics
1997, 16, 1501-1502.
(3) (a) Carmichael, D.; Ricard, L.; Mathey, F. J. Chem. Soc., Chem.
Commun. 1994, 1167-1168. (b) Carmichael, D.; Mathey, F.; Ricard, L.;
Seeboth, N. Chem. Commun. 2002, 2976-2977.
(4) (a) Shintani, R.; Fu, G. C. Org. Lett. 2002, 4, 3699-3702. (b)
Shintani, R.; Lo, M. M. C.; Fu, G. C. Org. Lett. 2000, 2, 3695-3697.
(5) Ganter, C,; Glinsbo¨ckel, C.; Ganter, B. Eur. J. Inorg. Chem. 1998,
1163.
(6) Ashe, A. J.; Al-Ahmad, S.; Fang, X. G. J. Organomet. Chem. 1999,
581, 92-97. (b) Hoic, D. A.; Davis, W. M.; Fu, G. C. J. Am. Chem. Soc.
1996, 118, 8176.
(7) Bazan, G. C.; Rodriguez, G.; Ashe, A. J.; Al-Ahmad, S.; Muller, C.
J. Am. Chem. Soc. 1996, 118, 2291-2292.
(8) Ashe, A. J.; Bajko, Z.; Carr, M. D.; Kampf, J. W. Organometallics
2003, 22, 910-912.
10.1021/om050357h CCC: $33.50 © 2006 American Chemical Society
Publication on Web 01/26/2006

1080 Organometallics, Vol. 25, No. 5, 2006
Ahn et al.
Figure 1. ORTEP representations (50% thermal ellipsoids) of the X-ray crystal structures of (a) 3 and (b) 4.
Scheme 1. Slip-Inversion-Slip Mechanism of
Scheme 2. Synthesis of Chiral Monophospholyl Titanium
Trichloride Complexes
Phosphametallocene Isomerization
Results and Discussion
Table 1. Crystal Data and Structure Refinement Details
Previous work by Basolo to identify ring slippage in
phospholyl complexes led to the conclusion that no ring slippage
occurred for the complexes evaluated.18 The electron-deficient
ring-slipped intermediate 1 appears ready to accept additional
ligands to produce a more stable molecule. Undoubtedly, such
coordination is responsible for the isomerization rate enhance-
ments seen in THF or when PMe3 is added.9,10 Despite this rate
enhancement, all efforts to isolate complexes such as 1 by
adding pyridine, bipy, or phen as trapping agents led, at best,
to broadened signals in the 31P NMR spectra and to recovery
of the η5-phosphametallocene. These results indicate a strong
preference for the π-complex as the thermodynamically most
favored state. Additionally, the η1:η5-bis(phospholyl) intermedi-
ates are relatively sterically congested, which would disfavor
strong coordination of the additional ligand. Therefore, we
decided to evaluate monophospholyl complexes for coordination
of exogenous ligand to induce ring slippage.19 The two chiral
monophospholyl Ti complexes 3 (31P NMR, δ 185, 82% from
Sn) and 4 (31P NMR, δ 198, 28% from Sn) were prepared as
illustrated in Scheme 2. Established synthetic methods were
employed.11 The molecular structures of 3 and 4 are depicted
in Figure 1. The crystal data and structural refinement details
may be found in Table 1, and selected bond distances and angles
are reported in Table 2. The data for (DMP)TiIVCl3 (DMP )
η5-3,4-dimethylphospholyl) are included in Table 2 for
comparison.11a The metric data on these compounds are similar
to those of previously reported achiral monophospholyl com-
plexes of Ti.
3
4
formula
C12H12Cl3PTi
341.44
0.31 × 0.22 × 0.09
C8H10Cl3PTi
291.38
0.47 × 0.41 × 0.31
formula wt
cryst dimens, mm
temp, K
wavelength (Å)
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
100(2)
0.71073
218(2)
0.71073
triclinic
P1h
monoclinic
P21/c
16.7957(13)
7.1120(5)
12.4481(9)
90
109.797(2)
90
1399.06(18)
4
6.7877(9)
6.9647(9)
12.9311(17)
102.390(2)
92.824(2)
109.062(2)
559.60(13)
2
γ, deg
V, Å3
Z
Dc, Mg/m3
abs coeff, mm-1
F(000)
1.621
1.272
688
1.729
1.573
292
θ range, deg
index ranges
1.29-30.51
-21 e h e 23
-8 e k e 10
-17 e l e 15
19445
4230 (R(int) )
0.0276)
4230/0/156
1.63-28.28
-9 e h e 9
-9 e k e 9
-17 e l e 17
9563
2754 (R(int) )
0.0225)
2754/0/128
no. of rflns
no. of indep rflns
no. of data/restraints/
params
goodness of fit on F2
final R indices (I > 2σ(I))
1.032
1.019
R1 ) 0.0270
wR2 ) 0.0729
R1 ) 0.0307
wR2 ) 0.0750
0.988 and
R1 ) 0.0281
wR2 ) 0.0768
R1 ) 0.0296
wR2 ) 0.0783
0.559 and
R indices (all data)
Addition of phosphine ligands to early-transition-metal piano-
stool complexes to generate higher coordinate complexes is well
established.20 Addition of 1,2-bis(dimethylphosphino)ethane
largest diff peak and
hole, e Å-3
-0.406
-0.348
(dmpe) to solutions of 3, 4, and the known (η5-3,4-dimethyl-
(17) (a) Curnow, O. J.; Fern, G. M.; Hamilton, M. L.; Zahl, A.; van
Eldik, R. Organometallics 2004, 23, 906-912. (b) Curnow, O. J.; Fern, G.
M. Organometallics 2002, 21, 2827-2829. (c) Fern, G. M.; Klaib, S.;
Curnow, O. J.; Lang, H. R. J. Organomet. Chem. 2004, 689, 1139-1144.
(18) Kershner, D. L.; Basolo, F. J. Am. Chem. Soc. 1987, 109, 7396-
7402.
11a
phospholyl)TiCl3 resulted in quantitative generation of new
signals in the 31P NMR spectrum. The structures of the new
complexes were assigned on the basis of the chemical shift
(19) For a review of ring slippage see: O’Connor, J. M.; Casey, C. P.
Chem. ReV. 1987, 87, 307-318.
(20) Hughes, D. L.; Leigh, G. J.; Walker, D. G. J. Organomet. Chem.
1988, 355, 113-119.

Chiral Mono(phospholyl)titanium Complexes
Organometallics, Vol. 25, No. 5, 2006 1081
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Scheme 3. Preparation of the Dibenzophospholyl (DBP)
Derivative 9
3, 4, and (DMP)TiIVCl3 (DMP ) η5-3,4-Dimethylphospholyl)
a
3
4
(DMP)TiCl3
Ti-Ctr
2.068
2.065
2.058
2.549
2.386
2.442
2.432
2.379
2.233
2.232
2.216
Ti-P
2.5836(4)
2.4571(13)
2.4593(13)
2.3987(13)
2.3741(13)
2.2230(4)
2.497(4)
2.5796(6)
2.3594(17)
2.4053(16)
2.4457(16)
2.4696(16)
2.2269(5)
2.412(6)
Ti-C(1)
Ti-C(2)
Ti-C(3)
Ti-C(4),C(8)
Ti-Cl(1)
Ti-Cl(2)
Ti-Cl(3)
2.2244(4)
2.2312(5)
and thus isolable. Reductive cleavage of the Ph-P bond of 8
with K and protonation with AcOH yielded 9H-dibenzophos-
phole (Scheme 3).24 Subsequent reaction with Ti(NMe2)4, as
illustrated in Scheme 3, produced complex 9, which was first
indicated by the new 31P NMR signal at δ 16.8 and the 1H NMR
integral ratios. The 13C NMR data for 9 reveal significantly
smaller and fewer J(PC) couplings than were reported for
1-phenyldibenzophosphole.25 This observation is attributed to
an increased rate of inversion at P in 9. When the synthesis
was carried out in an NMR tube, 1 equiv of free Me2NH was
Ctr-Ti-Cl(1)
Ctr-Ti-Cl(2)
Ctr-Ti-Cl(3)
Cl(1)-Ti-Cl(2)
Cl(1)-Ti-Cl(3)
Cl(2)-Ti-Cl(3)
117.78
112.74
117.97
100.312(15)
102.756(16)
102.821(16)
114.47
113.29
118.56
102.82(2)
102.29(2)
102.34(2)
118.18
112.16
116.92
101.43
103.83
102.07
a See ref 11a.
position and P-P coupling to the coordinated dmpe and are
shown by 5 (31P NMR, δ 83.9), 6 (31P NMR, δ 82.7), and 7
(31P NMR, δ 64.7). The 31P NMR chemical shifts were in the
1
observed by H NMR spectroscopy. Mass spectral analysis
(LDIMS) of the product revealed a peak at m/z 773 and an
isotopic distribution that was consistent with the dimeric
molecular formula [C38H52N6P2Ti2 + Me2NH + 2H]+ in the
spectrometer. We propose a dimeric Ti structure with bridging
amido groups and a coordinated amine plus two protons. The
coordination of amines to such complexes has been documented
by X-ray structural determination.16b The available solution data
do not distinguish between a monomeric or dimeric structure.
It is known that Zr(NMe2)4 exists as a dimer in the solid state.26
Compound 9 is exceedingly air sensitive, and with proper
precautions satisfactory elemental analyses were obtained for
C and H.
The dibenzophospholyl complex 9 has a chemical shift
significantly different from those of other phospholyl Ti(IV)
complexes (δ 16.8 vs δ 65-190; vide supra). This unique
property was the first indication that an η1 complex had in fact
been achieved. Such an upfield shift is consistent with a
pyramidal P.27 This observation is attributed to an increased
rate of inversion at P in 9. Numerous attempts have been made
to obtain X-ray-quality crystals, but only thin plates that did
not diffract well were obtained. Attempts to obtain a satisfactory
elemental analysis were unsuccessful, due to the extreme air
sensitivity of the sample, which resulted in decomposition (see
Experimental Section). There are several precedents that support
the assignment of compound 9 as the η1(σ)-bound complex.
First, previous structural characterization of DBP anion com-
plexes revealed η1 coordination.22 Second, we have performed
a computational study using Gaussian 03 to evaluate the
potential bonding modes of the DBP complex 9 and (C4H4P)-
Ti(NMe2)3 (10) that support the structural assignment.28 The
structural minimizations for 9 and 10 were approached from
region typical of η5-phospholyl complexes of Ti.11a,12 The unique
chemical shifts for the coordinated dmpe ligand are consistent
with the pseudoequatorial and pseudoaxial shifts reported for
the crystallographically characterized example CpTiCl3(dmpe).20
Complexes 5-7 proved to be unstable over long periods in
solution and, hence, were not characterized further. This
instability may be due to increased access to the ring-slipped
complex, generating a more reactive metal center that leads to
decomposition. With no conclusive data to support the formation
of η1 coordination in the monophospholyl complexes, an
additional element to favor η1 coordination was needed.
This feature was found in a dibenzophospholyl (DBP) ligand
derived from phenyldibenzophosphole (8; Scheme 3).21,22 DBP
has two fused benzene rings that will rearomatize upon ring
slippage to an η1-phospholyl ligand, providing a double-indenyl
effect,23 which counterbalances the driving force for η5(π)-
complexation. The dibenzophospholyl anion was prepared
according to literature procedures and reacted with Me3SnCl
followed by TiCl4. Despite repeated attempts, no stable isolable
products were obtained. With an η1-dibenzophospholyl ligand,
(DBP)TiCl3 would be, formally, an eight-electron complex. Such
a complex would be extremely reactive, which would make
isolation difficult. Having successfully synthesized η5-mono-
phospholyl titanium trichlorides (Scheme 2), the decomposition
of the DBP complexes was attributed to their inherent instability.
Therefore, auxiliary ligands that were better π-donors were
sought. If each Cl is replaced with a 4-electron-donating amido
ligand the formal electron count for the complex would be 14,
which is still unsaturated but was anticipated to be less reactive
(24) Braye, E. H.; Caplier, I.; Saussez, R. Tetrahedron 1971, 27, 5523-
5537.
(25) Nelson, J. H.; Affandi, S.; Gray, G. A.; Alyea, E. C. Magn. Reson.
Chem. 1987, 25, 774-779. Gray, G. A.; Nelson, J. H. Org. Magn. Reson.
1980, 14, 14-19.
(26) For amido-bridged zirconium complexes see: (a) Chisholm, M. H.;
Hammond, C. E.; Huffman, J. C. Polyhedron 1988, 7, 2515-2520.; For
amido-bridged titanium complexes see: Smolensky, E.; Kapon, M.; Eisen,
M. S. Organometallics 2005, 24, 5495-5498.
(21) Cornforth, J. J. Chem. Soc., Perkin Trans. 1 1996, 2889-2893.
(22) For recent examples see: (a) Nief, F.; Ricard, L. J. Organomet.
Chem. 1994, 464, 149-154. (b) Decken, A.; Neil, M. A.; Dyker, C. A.;
Bottomley, F. Can. J. Chem. 2002, 80, 55-61. (c) Decken, A.; Neil, M.
A.; Bottomley, F. Can. J. Chem. 2001, 79, 1321-1329.
(23) Rerek, M. E.; Ji, L. N.; Basolo, F. J. Chem. Soc., Chem. Commun.
1983, 1208-1209. Ji, L. N.; Rerek, M. E.; Basolo, F. Organometallics 1984,
3, 740-745. Basolo, F. New J. Chem. 1994, 18, 19-24.
(27) For a discussion of 31P NMR shifts as a function of pyrimidalization
see: (a) Chesnut, D. B.; Quin, L. D. J. Am. Chem. Soc. 1994, 116, 9638-
9643. (b) Westerhausen, M.; Digeser, M. H.; Noth, H.; Ponikwar, W.;
Seifert, T.; Polborn, K. Inorg. Chem. 1999, 38, 3207-3214.
(28) Frisch, M. J.; Trucks, G. W.; et al. Gaussian 03, revision C.02;
Gaussian, Inc.: Wallingford, CT, 2004.

1082 Organometallics, Vol. 25, No. 5, 2006
Ahn et al.
Experimental Section
All reactions were carried out under an inert atmosphere of Ar
using standard Schlenk and glovebox techniques.31 [(η5-3,4-
dimethylphospholyl)TiCl3] was prepared according to the literature
procedure.11a
(η5-3,4-Dimethyl-2-phenylphospholyl)titanium Trichloride (3).
1-(Trimethylstannyl)-3,4-dimethyl-2-phenylphosphole12 (0.36 g, 1.0
mmol) in pentane (5 mL) was rapidly added to a solution of TiCl4‚
2THF (0.33 g, 1.0 mmol) in toluene (5 mL) at 0 °C. The solution
was warmed to room temperature and stirred overnight. All volatiles
were evaporated under high vacuum, and the resulting red residue
was extracted with toluene (30 mL) followed by removal of the
solvent to obtain a red crystalline solid (0.28 g, 82%). X-ray-quality
crystals were grown from a saturated toluene solution at -35 °C.
1H NMR (C6D6, 300.052 MHz): δ 7.38-6.94 (m, 6H, Ph and
PCH), 2.11 (s, 3H, CH3), 1.88 (s, 3H, CH3). 31P{1H} NMR (C6D6,
121.469 MHz): δ 185.0 (s).
Figure 2. Two views of the molecular structure of 9 calculated
with Gaussian 03 at the B3LYP/6-311+G(d,p) level. Carbon atoms
are shown in grey, phosphorus atoms in orange, and nitrogen atoms
in blue. Ti-P ) 2.56 Å, Ti-N ) 1.90 Å, and P-C ) 1.83 Å.
both η5 and η1 structures. The simple mono(phospholyl)
complex (C4H4P)Ti(NMe2)3 (10) minimized to an η5 structure,
regardless of the starting geometry. In contrast, the DBP
complex 9 minimized to an η1 complex in both cases. Final
optimizations were performed at the B3LYP/6-311+G(d,p)
level. The optimized structure for 9 is depicted in Figure 2.
The pyrimidalization of P can be noted in the sum of the angles,
296°. Additional geometric data are included in Figure 2.
Finally, we calculated the chemical shift for the η1 complex
9 and (η5-C4H4P)Ti(NMe2)3 (10) using the GIAO method at
the HF/6-311+G(d,p) level and using the minimized structures
as the input geometry and compared the results to those for
PH3.29 The 31P NMR chemical shift for 9 in C6H6 is δ 16.8,
and that for PH3 is δ 238,30 which gives ∆δ ) 255 ppm. The
calculated magnetic shielding was σ ) 350 for 9 and σ ) 587
for PH3, which gives ∆δ ) 237 ppm. The predicted chemical
shift for 9 is -1 ppm, which is very close to the observed value.
Considering solvent effects and the standard error in the
computations, the observed ∆δ values are in close agreement
(237 vs 255, a difference of 18 ppm). Additional confidence in
the structural and spectroscopic assignment was gained when a
comparison was made to the calculated absolute magnetic
shielding of σ ) 240 for the η5-phospholyl tris(amido) Ti
complex 10, which is 110 ppm further downfield. The predicted
31P chemical shift for 10 is 109 ppm, which is typical of η5-
Ti(IV) complexes (vide supra).
In conclusion, despite much effort, the η1 intermediates in
phosphametallocene isomerization have resisted trapping for bis-
(phospholyl)MCl2 and (phospholyl)MCl3 complexes. Strong
spectroscopic and computational evidence have been amassed
in support of an (η1-DBP)Ti(NMe2)3 structure, which is the first
reported confirmation of an η1-phospholyl ligand bonded to
group 4 metals, an important step in establishing viability for
the slip-inVersion-slip mechanism. A detailed understanding
of phosphametallocene isomerization is critical for applications
of phosphametallocenes as catalysts and as ligands in asym-
metric catalysis. It also provides insight into the behavior of
other heterocyclic π-ligands. The first chiral monophospholyl
complexes of group 4 have been prepared and spectroscopically
characterized. Work to structurally characterize an η1 complex
and to further establish the slip-inversion-slip mechanism is
ongoing.
(η5-Cyclohexa[b]phospholyl)titanium Trichloride (4). 1-Phen-
ylcyclohexa[b]phosphole32 (1.50 g, 7.0 mmol) and Li (220 mg, 32
mmol) were stirred in THF (10 mL) for 4 h at room temperature.
The resulting dark violet solution was filtered, and then t-BuCl (1.8
mL, 17 mmol) was added and this mixture heated for 45 min at 55
°C. The light brown solution was cooled, and trimethyltin chloride
(1.37 g, 6.9 mmol) was added. The reaction mixture was stirred
for 15 min, and the solvent was removed under vacuum. The residue
was extracted with pentane (80 mL) and concentrated, yielding
1-(trimethylstannyl)cyclohexa[b]phosphole as a yellow oil (1.84 g,
84%). 1H NMR (C6D6, 300.052 MHz): δ 6.93 (dd, 3JPH ) 10.8, J
) 6.9 Hz, 1H, H-C2), 6.77 (dd, 2JPH ) 41.1, J ) 6.9 Hz, 1H, H-C3),
2.53 (bd, J ) 13.2 Hz, 4H), 1.59 (m, 4H), 0.04 (d, 3JPH ) 2.1 Hz,
9H, Sn(CH3)3). 31P{1H} NMR (C6D6, 121.469 MHz): δ -51.96
(s).
A solution of stannylphosphole (0.30 g, 1.0 mmol) in pentane
(10 mL) was rapidly added to a solution of TiCl4‚2THF (0.33 g,
1.0 mmol) in toluene (10 mL) at 0 °C. The resulting red solution
was stirred for 10 h at room temperature, and the solvent was
removed under vacuum. The residue was filtered through Celite
with toluene (50 mL) and concentrated, yielding a red powder
(0.073 g, 28%). X-ray-quality crystals were grown from a saturated
1
toluene solution at -35 °C. H NMR (CDCl3, 300.052 MHz): δ
7.93 (dd, 2JPH ) 36.0 Hz, 3JHH ) 5.6 Hz, 1H, H-C2), 7.52 (m, 1H,
H-C3), 3.59-2.83 (m, 4H, H-C4, H-C7), 1.93-1.83 (m, 4H, H-C5,
H-C6). 31P{1H} NMR (CDCl3, 121.469 MHz): δ 197.8 (s). 13C-
{1H} NMR (CDCl3, 75.456 MHz): δ 163.8 (d, JPC ) 60.1 Hz),
1
150.9 (d, 2JPC ) 7.8 Hz), 142.9 (d, 1JPC ) 60.7 Hz), 136.2 (d, 2JPC
2
3
) 6.5 Hz), 29.4 (d, JPC ) 17.5 Hz), 28.0, 25.6 (d, JPC ) 5. 7
Hz), 21.7.
(3,4-Dimethyl-2-phenylphospholyl)titanium Trichloride Bis-
(dimethylphosphino)ethane (5). (3,4-Dimethyl-2-phenylphos-
pholyl)titanium trichloride (3; 7 mg, 0.02 mmol) and bis(dimeth-
ylphosphino)ethane (8.0 µL, 0.04 mmol) were mixed in THF (1
2
mL). 31P{1H} NMR (C6D6, 121.469 MHz): δ 83.9 (d, JPP ) 9.9
2
2
Hz, Pphospholyl), 35.1 (dd, JPP ) 47.1 Hz, JPP ) 9.9 Hz,
2
P
pseudo-equatorial), 26.5 (d, JPP ) 47.1 Hz, Ppseudo-axial).
(η5-Cyclohexa[b]phospholyl)titanium Trichloride Bis(di-
methylphosphino)ethane (6). (η5-Cyclohexa[b]phospholyl)titanium
trichloride (4; 5 mg, 0.019 mmol) and bis(dimethylphosphino)ethane
(3.0 µL, 0.019 mmol) were mixed in THF (1 mL). 31P{1H} NMR
2
2
(121.469 MHz): δ 82.7 (dd, JPP ) 9.2 Hz, JPP ) 4.2 Hz,
P
phospholyl), 33.3 (dd, 2JPP ) 49.8 Hz, 2JPP ) 9.4 Hz, Ppseudo-equatorial),
2
2
25.9 (dd, JPP ) 49.6 Hz, JPP ) 4.2 Hz, Ppseudo-axial).
(3,4-Dimethylphospholyl)titanium Trichloride Bis(dimeth-
ylphosphino)ethane (7). Bis(dimethylphosphino)ethane (48 mg,
(29) van Wullen, C. Phys. Chem. Chem. Phys. 2000, 2, 2137. HF results
were closer to experimental results than did B3LYP in our case.
(30) (a) In the gas phase PH3 has a chemical shift of -266.1 ppm
extrapolated to zero pressure. Jameson, C. J.; De Dios, A.; Jameson, A. K.
Chem. Phys. Lett. 1990, 167, 575-582. (b) Solution: Van Wazer, J. R.;
Callis, C. F.; Shoolery, J. N.; Jones, R. C. J. Am. Chem. Soc. 1956, 78,
5715-5726.
(31) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-SensitiVe
Compounds, 2nd ed.; Wiley: New York, 1986.
(32) Quin, L. D.; Mesch, K. A.; Orton, W. L. Phosphorus Sulfur Relat.
Elem. 1982, 12, 161-177.

Chiral Mono(phospholyl)titanium Complexes
Organometallics, Vol. 25, No. 5, 2006 1083
0.32 mmol) was added to a solution of (3,4-dimethylphospholyl)-
titanium trichloride (17; 70 mg, 0.30 mmol) in THF (5 mL) at room
temperature. After the mixture was stirred for 10 min, all volatiles
dimer [C36H52N6P2Ti2 + NMe2H + 2H]+). Anal. Calcd for
C18H26N3PTi: C, 59.51; H, 7.21. Found: C, 59.28; H, 7.04.
1
Acknowledgment is made for partial support of this work
to the NSF (Grant No. CHE-0317089), to the donors of the
Petroleum Research Fund, administered by the American
Chemical Society, and to the University of California, Cancer
Research Coordinating Committee. Y.J.A. and R.J.R. acknowl-
edge a Department of Education GAANN fellowship. We thank
Dr. Dan Borchardt for assistance with NMR spectroscopy. We
also thank Professor Franc¸ois Mathey for helpful suggestions
regarding the computational studies and Dr. Rich Kondrat and
Mr. Ron New for assistance with mass spectral analyses.
were removed under vacuum. H NMR (C6D6, 300.052 MHz): δ
2
6.60 (d, JPP ) 37.7 Hz, 2H, PCHC(CH3)), 2.38 (s, 6H, PCHC-
(CH3)), 1.52 (d, 2JPP ) 10.9 Hz, 6H, P(CH3)2), 1.29 (d, 2JPP ) 9.4
Hz, 6H, P(CH3)2). 31P{1H} NMR (C6D6, 121.469 MHz): δ 64.7
2
2
2
(dd, JPP ) 9.4 Hz, Pphospholyl), 34.6 (dd, JPP ) 52.3 Hz, JPP
)
10.2 Hz, Ppseudo-equatorial), 27.4 (dd, 2JPP ) 52.3 Hz, 2JPP ) 8.6 Hz,
P
pseudo-axial).
(η1-Dibenzophospholyl)tris(dimethylamido)titanium (9). 9H-
dibenzophosphole24 (0.27 g, 1.5 mmol) in benzene (5 mL) was
added dropwise to a solution of Ti(NMe2)4 (340 µL, 1.5 mmol) in
benzene (5 mL). After the mixture was stirred for 2 h at room
temperature, volatiles were removed under vacuum at 70 °C for 1
h. After evaporation of the solvent a brown solid was obtained (0.22
g, 41%). The resulting dark brown solid was extracted with toluene
and crystallized in benzene. 1H NMR (C6H6): δ 8.12 (d, J ) 7.41
Hz, 2H), 7.92 (t, J ) 12 Hz, 2H), 7.32 (m, 4H), 2.80 (s, 18H).
13C{1H} NMR (75 MHz): δ 148.2 (d, J ) 23.6 Hz), 141.1, 125.5
(d, J ) 9 Hz), 123.7, 121.6, 121.4, 43.5. 31P{1H} NMR (C6D6,
121.469 MHz): δ 16.8 (s). MS (LDIMS): m/z 771, 772, 773
(100%), 774, 775 (with the expected isotope distribution for the
Supporting Information Available: Text giving further ex-
perimental details of the compounds prepared in this paper, figures
giving spectroscopic data for compounds 3-7 and 9 (1H, 13C, and
31P NMR and MS spectra), tables giving computational details for
9 and 10, including Cartesian coordinates for the minimized
structures, and CIF files giving crystallographic data for 3 and 4.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM050357H