Oxidatively induced ??-hydrogen abstraction. A mild protocol to generate terminal titanium alkylidenes containing a β-hydrogen

Article abstract of DOI:10.1021/om060308k

One-electron oxidation of the Ti(III) bis-isobutyl complexes (nacnac)Ti(CH₂ⁱPr)₂ (1) (nacnac^- = [ArNC(^tBu)]₂CH, Ar = 2,6-ⁱPr₂C ₆H₃) and (PNP)Ti(CH₂ⁱPr)₂ (4) (PNP^- = N[2-P(CHMe₂)₂-4-methylphenyl] ₂) with AgOTf promotes exclusive α-hydrogen abstraction to provide the first structurally characterized examples of terminal group 4 alkylidenes bearing a β-hydrogen, namely, (nacnac)Ti=CHⁱPr(OTf) (2) and (PNP)Ti=CHⁱPr(OTf) (5). These complexes have been prepared and characterized by means of multinuclear NMR spectroscopy as well as single-crystal X-ray diffraction analysis. In the case of the nacnac framework, the reactive Ti=CHⁱPr motif can readily engage in an intramolecular Wittig-like rearrangement. However, the isobutylidene motif can be stabilized when supported by a more robust ancillary ligand such as PNP, which is demonstrated by the thermal resistance of 5 and the preparation of a rare example of a stable alkylidene methyl complex (PNP)Ti=CHⁱPr(Me) (6).

Full text of DOI:10.1021/om060308k

Organometallics 2006, 25, 3963-3968
3963
Oxidatively Induced r-Hydrogen Abstraction. A Mild Protocol to
Generate Terminal Titanium Alkylidenes Containing a â-Hydrogen
Brad C. Bailey, Falguni Basuli, John C. Huffman, and Daniel J. Mindiola*
Department of Chemistry and Molecular Structure Center, Indiana UniVersity,
Bloomington, Indiana 47405
ReceiVed April 5, 2006
i
One-electron oxidation of the Ti(III) bis-isobutyl complexes (nacnac)Ti(CH2 Pr)2 (1) (nacnac-
)
i
[ArNC(tBu)]2CH, Ar ) 2,6-iPr2C6H3) and (PNP)Ti(CH2 Pr)2 (4) (PNP- ) N[2-P(CHMe2)2-4-methylphe-
nyl]2) with AgOTf promotes exclusive R-hydrogen abstraction to provide the first structurally characterized
examples of terminal group 4 alkylidenes bearing a â-hydrogen, namely, (nacnac)TidCHiPr(OTf) (2)
and (PNP)TidCHiPr(OTf) (5). These complexes have been prepared and characterized by means of
multinuclear NMR spectroscopy as well as single-crystal X-ray diffraction analysis. In the case of the
nacnac framework, the reactive TidCHiPr motif can readily engage in an intramolecular Wittig-like
rearrangement. However, the isobutylidene motif can be stabilized when supported by a more robust
ancillary ligand such as PNP, which is demonstrated by the thermal resistance of 5 and the preparation
of a rare example of a stable alkylidene methyl complex (PNP)TidCHiPr(Me) (6).
might explain why most terminal alkylidenes of group 45,8-15
are restricted only to alkyl groups lacking â-hydrogens.7,16,17
In principle, if an alkylidene with â-hydrogens were to be
assembled, rearrangement of an alkylidene to an olefin would
also be a competitive pathway given the intrinsic instability of
â-hydrogens with respect to the bound olefin. The latter
rearrangement has been recognized as a potentially damaging
side-reaction within the alkene metathesis cycle.18 Despite these
restrictions, the microscopic reverse, olefin to alkylidene, has
been observed with low-valent second- and third-row transition
Introduction
Alkyl lithiums or Grignards containing â-hydrogens are often
sought as efficient reducing reagents in the organotransition
metal chemistry of group 4.1,2 Prototypical among these nu-
cleophiles are the tBu, nBu, and iBu class of alkyls. For example,
“in situ Ti(II)” coupling reagents can be generated in the
i
n
i
presence of nucleophiles such as PrLi, BuLi, BuLi, or the
corresponding Grignard reagents.1-4 However, in some cases
the transient Ti(II) species, generated from a Ti(IV) reduction
using an alkyl reagent such as an isobutyl, can sometimes be
trapped with an inert substrate such as N2.5 One credible reason
for these alkyls being so unstable on the metal could originate
from energetically favorable decomposition pathways such as
â-hydrogen elimination or â-hydrogen abstraction reactions.
Consequently, common reagents such as TiCl4(THF)2 can be
readily converted to “TiCl2(THF)x”, 1-butene, and butane with
2 equiv of nBuLi.6 As a result, promoting R-hydrogen abstraction
as opposed to â-hydrogen elimination or abstraction is a rare
phenomenon in organometallic chemistry, unless â-hydrogen-
free alkyl groups are invoked.7 Therefore, the above arguments
(8) van der Heijden, H.; Hessen, B. J. Chem. Soc., Chem. Commun. 1995,
154-146.
(9) Binger, P.; Mu¨ller, P.; Philipps, P.; Gabor, B.; Mynott, R.; Herrmann,
A. T.; Langhauser, F.; Kru¨ger, C. Chem. Ber. 1992, 125, 2209-2212.
(10) van Doorn, J. A.; van der Heijden, H.; Orpen, A. G. Organometallics
1994, 13, 4271-4277.
(11) van Doorn, J. A.; van der Heijden, H.; Orpen, A. G. Organometallics
1995, 14, 1278-1283.
(12) Sinnema, P.-J.; van der Veen, L.; Spek, A. L.; Veldman, N.; Teuben,
J. H. Organometallics 1997, 16, 4245-4247.
(13) (a) Basuli, F.; Bailey, B. C.; Tomaszewski, J.; Huffman, J. C.;
Mindiola, D. J. J. Am. Chem. Soc. 2003, 125, 6052-6053. (b) Basuli, F.;
Bailey, B. C.; Watson, L. A.; Tomaszewski, J.; Huffman, J. C.; Mindiola,
D. J. Organometallics 2005, 24, 1886-1906. (c) Basuli, F.; Bailey, B. C.;
Huffman, J. C.; Mindiola, D. J. Organometallics 2005, 24, 3321-3334.
(d) Bailey, B. C.; Huffman, J. C.; Mindiola, D. J.; Weng, W.; Ozerov, O.
V. Organometallics 2005, 24, 1390-1393.
(14) (a) Weng, W.; Yang, L.; Foxman, B. M.; Ozerov, O. V. Organo-
metallics 2004, 23, 4700-4705. (b) Fan, L.; Foxman, B. M.; Ozerov, O.
V. Organometallics 2004, 23, 326-328. A similar ligand framework has
been also reported. (c) Liang, L.-C.; Lin, J.-M.; Hung, C.-H. Organometallics
2003, 22, 3007-3009. (d) Winter, A. M.; Eichele, K.; Mack, H.; Potuznik,
S.; Mayer, H. A.; Kaska, W. C. J. Organomet. Chem. 2003, 682, 149-
154.
* Corresponding author. E-mail: mindiola@indiana.edu.
(1) For some representative examples: (a) Eisch, J. J.; Gitua, J. N.
Organometallics 2003, 22, 24-26. (b) Eisch, J. J.; Shi, X.; Alila, J. R.;
Thiele, S. Chem. Ber./Recl. 1997, 130, 1175-1187. (c) Eisch, J. J.; Alila,
J. R. Organometallics 2000, 19, 1211-1213. (d) Eisch, J. J. J. Organomet.
Chem. 2001, 617-618, 148-157.
(2) (a) Kulinkovich, O. G.; Sviridov, S. V.; Vasilevski, D. A.; Prityckaja,
T. S. Zh. Org. Khim. 1989, 25, 2244-2245. (b) Kulinkovich, O. G.;
Sviridov, S. V.; Vasilevski, D. A. Synthesis 1991, 234. (c) Kulinkovich, O.
G.; de Meijere, A. Chem. ReV. 2000, 100, 2789-2834.
(3) Sato, F.; Urabe, H.; Okamoto, S. Chem. ReV. 2000, 100, 2835-2886.
(4) (a) Knight, K. S.; Wang, D.; Waymouth, R. M.; Ziller, J. J. Am.
Chem. Soc. 1994, 116, 1845-1854. (b) Knight, K. S.; Waymouth, R. M. J.
Am. Chem. Soc. 1991, 113, 6269-6270.
(15) (a) Fryzuk, M. D.; Mao, S. S. H.; Zaworotko, M. J.; MacGillovray,
L. R. J. Am. Chem. Soc. 1993, 115, 5336. (b) Fryzuk, M. D.; Duval, P. B.;
Patrick, B. O.; Rettig, S. J. Organometallics 2001, 20, 1608-1613.
(16) A Lewis acid-stabilized titanium alkylidene complex bearing
â-hydrogens has been reported. Kru¨ger, C.; Mynott, R.; Siedenbiedel, C.;
Stehling, L.; Wilke, G. Angew. Chem., Int. Ed. Engl. 1991, 30, 1666-
1668.
(5) Baumann, R.; Stumpf, R.; Davis, W. M.; Liang, L.-C.; Schrock, R.
R. J. Am. Chem. Soc. 1999, 121, 7822-7836.
(6) Eisch, J. J.; Shi, X.; Lasota, J. Z. Naturforsch. 1995, 50b, 342-350,
and references therein.
(17) d0 Zirconium alkylidenes containing â-hydrogens have been spec-
troscopically characterized. Hartner, F. W., Jr.; Schwartz, J.; Clift, S. M. J.
Am. Chem. Soc. 1983, 105, 640-641.
(7) (a) Schrock, R. R. Acc. Chem. Res. 1979, 12, 98-104. (b) Schrock,
R. R. Acc. Chem. Res. 1990, 23, 158-165. (c) Schrock, R. R. Chem. ReV.
2002, 102, 145-179. (d) Schrock, R. R. Reactions of Coordinated Ligands;
Braterman, P. R., Ed.; Plenum: NY, 1986. (e) Feldman, J.; Schrock, R. R.
Prog. Inorg. Chem. 1991, 39, 1-74.
(18) (a) Roger, C.; Bodner, G. S.; Hatton, W. G.; Gladysz, J. A.
Organometallics 1991, 10, 3266-3274. (b) Hatton, W. G.; Gladysz, J. A.
J. Am. Chem. Soc. 1983, 105, 6157-6158.
10.1021/om060308k CCC: $33.50 © 2006 American Chemical Society
Publication on Web 06/27/2006

3964 Organometallics, Vol. 25, No. 16, 2006
Bailey et al.
Scheme 1. Synthesis of Complexes 1-3
metal centers.19 In fact, Schrock has observed the base-induced
rearrangement of tantalum-olefin complexes to the thermody-
namically more favored â-hydrogen-containing alkylidenes.19f
The energetic favorability of the latter alkylidene was attributed
to a strong R-agostic interaction with the metal center.
In lieu of these limitations, one alternate option to promoting
R-hydrogen abstraction under mild conditions is an oxidatively
induced R-hydrogen abstraction.13 The latter process is facile
at low temperatures and does not depend on external stimulants
such as heat, light, or base to promote the R-hydrogen
abstraction step.20 In addition, the protocol avoids the use of
powerful electrophiles (e.g., AlR3), hence resulting in a terminal,
Lewis acid-free, and low-coordinate alkylidene complex.21
In this article, we wish to report that one-electron oxidation
of titanium complexes bearing alkyl groups with â-hydrogens
promotes, exclusively, R-hydrogen abstraction to afford the first
structural examples of terminal titanium alkylidenes with a
â-hydrogen.17 Synthesis, characterization, and single-crystal
structural studies of this new class of terminal alkylidene,
specifically isobutylidenes, are presented and discussed. De-
pending on the supporting ancillary ligand, the titanium isobu-
tylidene functionality is sufficiently stable for further reaction
chemistry.
â-diketiminate ligand [ArNC(Me)]2CH (Ar ) 2,6-iPr2C6H3).22
In view of that, we concentrated our attention toward the isobutyl
group, which has a bulk size comparable to the neopentyl
fragment, yet possesses both R- and â-hydrogens.
Accordingly, when a pentane solution of (nacnac)TiCl213b is
i
treated with 2 equiv of BuMgCl at -35 °C, the bis-alkyl
titanium(III) complex (nacnac)Ti(iBu)2 (1) is readily obtained
in 79% yield upon workup of the reaction mixture (Scheme 1).
While solution magnetic measurements of 1 are consistent with
a d1 paramagnetic species (µeff ) 1.95 µB), the molecular
structure displays the expected connectivity for a four-coordinate
Ti(III) bis-alkyl (Ti-CR, 2.117(3) and 2.146(3) Å, Figure 1)
complex in a tetrahedral environment.23,24 Although most
nonperipheral hydrogen atoms from the alkyl groups were
located and refined isotropically, no R- or â-hydrogen agostic
interactions were evident from the crystal structure (Figure 1).
Complex 1 is thermally stable in solution, but one-electron
oxidation with AgOTf in pentane at -35 °C promotes only
R-hydrogen abstraction concomitant with Ag0 and isobutane
formation to afford a rare example of the isobutylidene23,26
complex (nacnac)TidCHiPr(OTf) (2) as dark red blocks in 73%
yield (Scheme 1). Diagnostic features for 2 include four
diasteriotopic methyl groups for the nacnac-isopropyls and one
tBu environment for the nacnac- backbone. A CR resonance
centered at δ 258.9 ppm with a JC-H coupling constant of 86
Hz is representative of 2 having a terminal alkylidene func-
tionality.7,13 The JC-H coupling from the 13C NMR spectral data
Results and Discussion
Recently, our group reported that (nacnac)Ti(CH2tBu)2 (nacnac-
) [ArNC(tBu)]2CH, Ar ) 2,6-iPr2C6H3), when oxidized by one
electron, afforded alkylidene species of the type (nacnac)Tid
CHtBu(X) (X- ) OTf, I) in excellent yields. The anion present
in the oxidant determines the nature of X.13b However, the alkyl
groups must be sterically imposing in order to promote the
R-hydrogen abstraction since complexes such as (nacnac)Ti-
(CH3)2 (nacnac- ) [ArNC(tBu)]2CH, Ar ) 2,6-iPr6H2), when
oxidized by AgOTf, do not afford the corresponding meth-
ylidene (nacnac)TidCH2(OTf), but the five-coordinate titanium
complex (nacnac)Ti(CH3)2(OTf).13b For this reason we turned
our attention to bulky alkylating groups that contain â-hydro-
gens. Unfortunately, attempts to alkylate (nacnac)TiCl213b with
2 equiv of RMgCl (R ) iPr or tBu) proved difficult, presumably
due to excess crowding imposed by the alkyl groups. Contrary
n
to sterics, efforts to incorporate the less crowded Bu group
onto Ti(III) were also unsuccessful for reasons that we currently
do not understand. The latter result was also surprising, since
Budzelaar and co-workers have reported exceedingly stable bis
nBu complexes of Ti(III) supported by the less crowded
(22) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485-1494.
(23) See Experimental Section for complete details.
i
(24) Crystallographic details for (nacnac)Ti(CH2 Pr)2 (1): A green crystal
(19) (a) Hirsekorn, K. F.; Veige, A. S.; Marshak, M. P.; Koldobskaya,
Y.; Wolczanski, P. T.; Cundari, T. R.; Lobkovsky, E. B. J. Am. Chem.
Soc. 2005, 127, 4809-4830. (b) Freundlich, J. S.; Schrock, R. R.; Davis,
W. M. J. Am. Chem. Soc. 1996, 118, 3643-3655. (c) Miller, G. A.; Cooper,
N. J. J. Am. Chem. Soc. 1985, 107, 709-711. (d) Hughes, R. P.; Maddock,
S. M.; Rheingold, A. L.; Guzei, I. A. Polyhedron 1998, 17, 1037-1043.
(e) Giannini, L.; Guillemot, G.; Solari, E.; Floriani, C.; Re, N.; Chiesi-
Villa, A.; Rizzoli, C. J. Am. Chem. Soc. 1999, 121, 2797-2807. (f) Schrock,
R. R.; Seidel, S. W.; Mosch-Zanetti, N. C.; Shih, K.-Y.; O’Donoghue, M.
B.; Davis, W. M.; Reiff, W. M. J. Am. Chem. Soc. 1997, 119, 11876-
11893. (g) Schrock, R. R.; Seidel, S. W.; Mosch-Zanetti, N. C.; Dobbs, D.
A.; Shih, K.-Y.; Davis, W. M. Organometallics 1997, 16, 5195-5208. (h)
Ozerov, O. V.; Watson, L. A.; Pink, M.; Caulton, K. G. J. Am. Chem. Soc.
2003, 125, 9604-9605.
(20) (a) Schrock, R. R. Acc. Chem. Res. 1979, 12, 98. (b) Schrock, R.
R. Acc. Chem. Res. 1990, 23, 158. (c) Schrock, R. R. Chem. ReV. 2002,
102, 145. (d) Schrock, R. R. In Reactions of Coordinated Ligands;
Braterman, P. R., Ed.; Plenum: New York, 1989. (e) Beckhaus, R. Angew.
Chem., Int. Ed. Engl. 1997, 36, 686. (f) Baumann, R.; Stumpf, R.; Davis,
W. M.; Liang, L.-C.; Schrock, R. R. J. Am. Chem. Soc. 1999, 121, 7823.
(21) (a) Tebbe, F. N.; Parshall, G. W.; Reddy, G. S. J. Am. Chem. Soc.
1978, 100, 3611-3613. (b) Hartner, F. M.; Clift, S. M.; Schwartz, J.; Tulip,
T. H. Organometallics 1987, 6, 1346-1350.
of approximate dimensions 0.35 × 0.35 × 0.35 mm3 was selected and
mounted on a glass fiber. A total of 183 625 reflections (-39 e h e 39,
-17 e k < 17, -35 e l e 35) were collected at T ) 123(2) K in the range
2.76-30.01°, of which 17 852 were unique (Rint ) 0.0517), Mo KR radiation
(λ ) 0.71073 Å). A direct-methods solution was calculated, which provided
most non-hydrogen atoms from the E-map. There is a disorder in some of
the peripheral groups of one of the two independent molecules in the
asymmetric unit. All hydrogen atoms not associated with the disordered
atoms were located in subsequent Fourier maps and included as isotropic
contributors in the final cycles of refinement. All hydrogen atoms associated
with the disorder were placed in ideal positions and refined as riding atoms
with relative isotropic displacement parameters. All non-hydrogen atoms
were refined with anisotropic displacement parameters. The residual peak
and hole electron densities were 0.601 and -0.296 e A-3. The absorption
coefficient was 0.240 mm-1. The least squares refinement converged
normally with residuals of R(F) ) 0.0387, wR(F2) ) 0.1123 and a GoF )
1.012 (I > 2σ(I)). C43H71N2Ti, space group P2(1)/c, monoclinic, a ) 28.380-
(1) Å, b ) 12.6335(7) Å, c ) 24.976(1) Å, â ) 114.676(1)°, V ) 8137.0-
(7) Å3, Z ) 8, Dcalcd ) 1.084 mg/m3, F(000) ) 2920.
(25) To our knowledge only one example of a terminal isobutylidene
complex has been reported. Hansen, S. M.; Volland, M. A. O.; Rominger,
F.; Eisentrager, F.; Hofmann, P. Angew. Chem., Int. Ed. Engl. 1999, 38,
1273-1276.

OxidatiVely Induced R-Hydrogen Abstraction
Organometallics, Vol. 25, No. 16, 2006 3965
Figure 1. Molecular structures of 1 and 2. All H atoms and solvent
molecules have been omitted for clarity. The SO2CF3 group of 2
has also been removed. For 1: Ti(1)-C(43), 2.146(3); Ti(1)-C(39),
2.117(3); Ti(1)-N(2), 2.0154(9); Ti(1)-N(6), 2.020(1); Ti(1)-
C(43)-C(44), 127.69(9); N(2)-Ti(1)-N(6), 96.76(4); Ti(1)-
C(39)-C(40), 131.2(1); C(43)-Ti(1)-C(39), 104.40(5); N(2)-
Ti(1)-C(39),; N(2)-Ti(1)-C(43),; N(6)-Ti(1)-C(39),; N(6)-
Ti(1)-C(43),. For 2: Ti(1)-C(39), 1.86(1); Ti(1)-N(2), 2.054(8);
Ti(1)-N(6), 2.023(8); Ti(1)-O(43), 2.007(7); Ti(1)-C(39)-C(40),
167(1); N(2)-Ti(1)-N(6), 95.6(3); C(39)-Ti(1)-O(43), 110.1-
(4); N(2)-Ti(1)-C(39), 105.3(4); N(2)-Ti(1)-O(43), 110.8(3);
N(6)-Ti(1)-C(39), 116.2(5); N(6)-Ti(1)-O(43), 117.1(3).
Figure 2. Molecular structures of 3 and 5. All H atoms and solvent
molecules have been omitted for clarity. The SO2CF3 group of 3
has also been removed. For 3: Ti(1)-C(6), 2.203(6); Ti(1)-N(2),
2.005(2); Ti(1)-N(30), 1.714(2); Ti(1)-C(3), 2.588(5); Ti(1)-
O(43), 2.009(2); N(2)-C(3), 1.340(6); C(6)-C(5), 1.394(2); C(5)-
C(4), 1.415(2); C(4)-C(3), 1.425(2); Ti(1)-N(30)-C(31), 173.2-
(1); O(43)-Ti(1)-N(30), 106.41(5); N(2)-Ti(1)-N(30), 109.98(5);
C(6)-Ti(1)-N(30), 105.35(6). For 5: Ti(1)-C(31), 1.858(5); Ti-
(1)-N(10), 2.036(4); Ti(1)-O(35), 1.986(3); Ti(1)-P(2), 2.579-
(4); Ti(1)-P(18), 2.596(4); P(18)-Ti(1)-P(2), 151.13(5); N(10)-
Ti(1)-C(31), 113.2(2); Ti(1)-C(31)-C(32), 162.1(5); N(10)-
Ti(1)-P(2), 76.80(11); N(10)-Ti(1)-P(18), 75.62(11); O(35)-
Ti(1)-C(31), 113.3(2).
suggests a strong R-hydrogen agostic interaction taking place
1
with the metal center.5,7 Most notably, the H NMR spectrum
of 2 reveals a doublet of septets for the isobutylidene â-hydro-
gen, while the R-hydrogen on the alkylidene resolves as a
doublet. As a result, all NMR spectroscopic data are consistent
with complex 2 retaining Cs symmetry in solution and containing
a distorted, terminal alkylidene functionality possessing R- and
â-hydrogens.
complex 2 having tBu groups to block the intramolecular [2+2]-
cycloaddition,13a,b the alkylidene functionality is apparently far
less crowded and hitherto more prone to the intramolecular
group-transfer process (Scheme 1). Complex 3 was characterized
1
by a combination of H and 13C NMR spectroscopy as well
Large red-brown crystals of 2 were grown from pentane at
-35 °C, and the single-crystal molecular structure confirmed a
four-coordinate titanium complex having Cs symmetry and a
short TidC bond length (Ti(1)-C(39) ) 1.87(1) Å, Figure
1).23,26 It should be emphasized that the data quality for the
crystal is poor, presumably due to decomposition of the crystal
prior to transferring it to the cold stream of N2.26 Despite this,
the molecular structure unarguably depicts an alkylidene iso-
propyl group that lies along the σ-plane bisecting N-Ti-N and
is oriented along the same side with respect to the triflato ligand.
The obtuse Ti(1)-C(39)-C(40) angle of 167(1)° provides
strong crystallographic credence for an R-agostic interaction
taking place with the four-coordinate Ti(IV) center. No â-hy-
drogen agostic interaction was evident from the orientation of
the â-H in the molecular structure of complex 2.
single-crystal X-ray diffraction analysis (Figure 2).23,27 Salient
metrical parameters for the olefin imide moieties in complex 3
are depicted with the molecular structure in Figure 2. Complex
3 is a close analogue of other titanium imide complexes reported
by our group, namely, the Wittig-rearranged complexes (η2-Ht-
BuCdC(tBu)CHC(tBu)N[Ar])TidNAr(X) (X- ) OTf, Cl, Br,
I, BH4, CH2SiMe3).13a-c
To prepare more kinetically stable alkylidene complexes of
titanium, we resorted to the robust pincer framework N[2-
-
P(CHMe2)2-4-methylphenyl]2 (PNP) previously reported by
Ozerov and co-workers.14 Following a protocol analogous to
that of 1, the d1 complex (PNP)Ti(iBu)223 (4) was prepared, and
subsequent oxidation with AgOTf afforded the five-coordinate
isobutylidene (PNP)TidCHiPr(OTf) (5) in 73% yield (Scheme
2).28 The alkylidene motif in 5 displays spectroscopic features
Although isolable at cold temperatures (-35 °C) under an
inert atmosphere, complex 2 is a kinetic product since solutions
cleanly decompose over 24 h at 25 °C to afford (η2-HiPrCd
C(tBu)CHC(tBu)N[Ar])TidNAr(OTf) (3), a compound resulting
from an intramolecular Wittig-like rearrangement.13,27 Despite
1
similar to 2 in both the H and 13C NMR spectra (13C NMR,
TidC ) 296.9 ppm; 1H NMR, TidCH ) 8.46 ppm, Tid
CHCHMe2 ) 2.55 ppm). In addition, the 31P NMR spectrum
(27) Crystallographic details for (η2-HiPrCdC(tBu)CHC(tBu)N[Ar])Tid
NAr(OTf) (3): A brown-red prism of approximate dimensions 0.35 × 0.35
× 0.30 mm3 was selected and mounted on a glass fiber. A total of 52 328
reflections (-19 e h e 19, -26 e k e 26, -23 < l e 23) were collected
at T ) 128(2) K in the range 2.49-26.46°, of which 5200 were unique
(Rint ) 0.1027), Mo KR radiation (λ ) 0.71073 Å). A direct-methods
solution was calculated, which provided most non-hydrogen atoms from
(26) Crystallographic details for (nacnac)TidCHiPr(OTf) (2): An orange-
brown plate of approximate dimensions 0.20 × 0.20 × 0.05 mm3 was
selected and mounted on a glass fiber. A total of 19 325 reflections (-12
e h e 9, -20 e k e 21, -21 e l e 22) were collected at T ) 125(2) K
in the range 2.32-22.32°, of which 1536 were unique (Rint ) 0.3258), 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. All
hydrogen atoms were placed in ideal positions and refined as riding atoms
with relative isotropic displacement parameters. The residual peak and hole
electron densities were 0.476 and -0.273 e A-3. The largest residuals were
in the vicinity of the triflate group. The absorption coefficient was 0.309
mm-1. The least squares refinement converged normally with residuals of
R(F) ) 0.0570, wR(F2) ) 0.1416 and a GoF ) 0.641 (I > 2σ(I)).
C40H60F3N2O3STi, space group P2(1)2(1)2(1), orthorhombic, a ) 10.912-
(9) Å, b ) 18.99(1) Å, c ) 19.84(1) Å, R ) â ) γ ) 90°, V ) 4112(6)
Å3, Z ) 4, Dcalcd ) 1.218 mg/m3, F(000) ) 1612.
i
the E-map. There is a slight disorder in one of the Pr groups. All non-
hydrogen atoms were refined with anisotropic displacement parameters. All
hydrogen atoms not associated with the disorder were located in subsequent
Fourier maps and included as isotropic contributors in the final cycles of
refinement, and the remaining hydrogen atoms were placed in idealized
positions and refined as riding atoms with relative isotropic displacement
parameters. The residual peak and hole electron densities were 1.025 and
-0.473 e A-3. The absorption coefficient was 0.439 mm-1. The least squares
refinement converged normally with residuals of R(F) ) 0.0545, wR(F2)
) 0.1569 and a GoF ) 0.851 (I > 2σ(I)). C45H73F3N2O3STi, space group
P2(1)/c, monoclinic, a ) 15.245(1) Å, b ) 20.245(2) Å, c ) 17.852(2) Å,
â ) 115.068(3)°, V ) 4991(1) Å3, Z ) 4, Dcalcd ) 1.101 mg/m3, F(000) )
1784.

3966 Organometallics, Vol. 25, No. 16, 2006
Scheme 2. Synthesis of Complexes 4-6
Bailey et al.
Conclusions
In summary, we have prepared and structurally characterized
two unique examples of group 4 terminal alkylidene complexes
containing a â-hydrogen. The following work presented here
demonstrates that isobutyl groups bound to titanium can
selectively undergo R-hydrogen abstraction over the more
common â-hydrogen elimination and R-hydrogen abstraction
themes, when promoted by a one-electron oxidation step. We
also fail to observe other rare but reported rearrangements
involving the decomposition of d0 complexes bearing two
isobutyl ligands. For example, γ-H abstraction processes have
been shown to ultimately generate σ2,π-butadiene Zr derivatives
(eq 1),29 while multiple intra- and intermolecular C-H bond
activation steps can produce a µ-[σ2,η3-C4H5] ligand bridged
between two Zr centers (eq 2).30 On the basis of our work, Md
CHR functionalities of the early-transition metal series are no
longer restricted to R groups where â-hydrogens are excluded.
We are currently exploring what other â-hydrogen alkylidene
fragments can be incorporated onto titanium and whether
systems similar to 5 and 6 can undergo reductive elimination
of the alkylidene to the olefin.
manifests two sets of doublets with a low JP-P coupling constant
(54 Hz), which is in accord with the phosphines being
significantly slanted from a trans geometry.
Single-crystal X-ray diffraction analysis of 528 depicts the
expected connectivity with a short TidC (1.858(5) Å) bond and
an obtuse TidC-C angle of 162.1(5)° (Figure 2). The orienta-
tion of the iPr group places the â-hydrogen away from the metal
and orthogonal to the R-hydrogen, the latter of which is
interacting with the metal via an R-hydrogen agostic interaction
(JC-H ) 98 Hz).
Unlike 2, complex 5 is kinetically stable under N2 both as a
solid and in solution despite possessing a terminal and nucleo-
philic alkylidene with a â-hydrogen. In fact, thermolysis of 5
in C6D6 (3 days, 80 °C) does not result in any observable
decomposition when assayed by 1H and 31P NMR spectroscopy.
As a result, the OTf- functionality in 5 can be readily displaced
via treatment with MeMgCl in pentane to afford a rare example
of a titanium alkylidene methyl complex, (PNP)TidCHiPr(CH3)
(6) (82% yield, Scheme 2).13c,23 Complex 6 is also remarkably
stable both in solution and as a solid. However, thermolysis of
6 (C6D6, 80 °C) leads to a myriad of products, which we have
not identified. The downfield R-C alkylidene resonance (279.4
ppm) and the downfield doublet observed for the isobutylidene
hydrogen (8.38 ppm) of 6 are a clear manifestation of a terminal
isobutlyidene motif being present. A doublet of septets and a
set of diastereotopic doublets resulting from the methine and
methyl groups of the isobutylidene isopropyl, respectively,
illustrate that the isobutylidene fragment remains intact upon
Experimental Section
General Considerations. Unless otherwise stated, all operations
were performed in an M.Braun Lab Master double-drybox under
an atmosphere of purified nitrogen or using high-vacuum standard
Schlenk techniques under an argon atmosphere.31 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.32
Diethyl ether was dried by passage through a column of activated
alumina.32 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 and C7D8 were purchased from Cambridge
Isotope Laboratory (CIL), degassed, and vacuum transferred to 4
Å molecular sieves. THF-d8 was purchased from CIL and used as
received. Celite, alumina, and 4 Å molecular sieves were activated
under vacuum overnight at 200 °C. Li(nacnac)22 (nacnac-
[ArNC(tBu)]2CH, Ar ) 2,6-iPr2C6H3), (nacnac)TiCl2,13b and Li-
(PNP) (PNP ) N[2-P(CHMe2)2-4-methylphenyl]2
- 14 were prepared
according to the literature. All other chemical were used as received.
CHN analyses were performed by Desert Analytics, Tucson, AZ.
1H, 13C, 19F, and 31P NMR spectra were recorded on Varian 400 or
300 MHz NMR spectrometers. 1H and 13C NMR are reported with
1
alkylation. In addition, the H NMR spectrum of 5 displays a
triplet at 0.80 ppm for the titanium-methyl group (JH-P ) 2.8
Hz) and a broad resonance in the 13C NMR at 50.0 ppm, which
resolves into a quartet in the 1H-coupled 13C (JC-H ) 113 Hz).
)
1
Both H and 31P NMR spectra are consistent with complex 6
)
retaining C1 symmetry in solution.
(28) Crystallographic details for (PNP)TidCHiPr(OTf) (5): A dark red
crystal of approximate dimensions 0.25 × 0.25 × 0.20 mm3 was selected
and mounted on a glass fiber. A total of 22 328 reflections (-12 e h e 10,
-25 e k < 25, -19 e l e 23) were collected at T ) 128(2) K in the range
2.11-27.55°, of which 9642 were unique (Rint ) 0.0508), 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. The residual peak and
hole electron densities were 1.025 and -0.473 e A-3. The absorption
coefficient was 0.439 mm-1. The least squares refinement converged
normally with residuals of R(F) ) 0.0576, wR(F2) ) 0.1249 and a GoF )
0.869 (I > 2σ(I)). C31H48F3NO3P2STi, space group P2(1), monoclinic, a )
9.9065(9) Å, b ) 20.034(7) Å, c ) 18.234(7) Å, â ) 103.196(3)°, V )
3523.4(5) Å3, Z ) 4, Dcalcd ) 1.285 mg/m3, F(000) ) 1440.
(29) Keaton, R. J.; Koterwas, L. A.; Fettinger, J. C.; Sita, L. R. J. Am.
Chem. Soc. 2002, 124, 5932-5933.
(30) Keaton, R. J.; Sita, L. R. Organometallics 2002, 21, 4315-4317.
(31) 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 D.C.,
1987; pp 79-98.
(32) Pangborn; A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518-1520.

OxidatiVely Induced R-Hydrogen Abstraction
Organometallics, Vol. 25, No. 16, 2006 3967
reference to solvent resonances (residual C6D5H in C6D6, 7.16 and
128.0 ppm). 19F NMR chemical shifts are reported with respect to
external HOCOCF3 (-78.5 ppm). 31P NMR chemical shifts are
reported with respect to external H3PO4 (aqueous solution, δ 0.0
ppm). Solution magnetization measurements were determined by
the method of Evans.33 X-ray diffraction data were collected on a
SMART6000 (Bruker) system under a stream of N2 (g) at low
temperatures.34,35
(HiPrCdC(tBu)CHC(tBu)N[Ar]), 161.5 (HiPrCdC(tBu)CHC(tBu)N-
[Ar]), 157.7 (C6H3), 147.4 (C6H3), 146.9 (C6H3), 143.0 (C6H3),
142.6 (C6H3), 138.2 (C6H3), 136.0 (HiPrCdC(tBu)CHC(tBu)N[Ar],
JC-H ) 122 Hz), 127.3 (C6H3), 125.6 (C6H3), 123.5 (C6H3), 122.7
(C6H3), 122.6 (C6H3), 122.5 (C6H3), 90.25 (HiPrCdC(tBu)CHC-
(tBu)N[Ar], JC-H ) 151 Hz), 43.47 (HiPrCdC(CMe3)CHC-
(CMe3)N[Ar]), 40.47 (HiPrCdC(CMe3)CHC(CMe3)N[Ar]), 33.43
(CHMe2), 31.41 (HiPrCdC(CMe3)CHC(CMe3)N[Ar]), 30.61 (HiPr-
CdC(CMe3)CHC(CMe3)N[Ar]), 30.20 (CHMe2), 28.90 (CHMe2),
28.05 (CHMe2), 27.29 (CHMe2), 26.79 (Me), 26.68 (Me), 25.36
(Me), 24.62 (two Me groups), 24.41 (Me), 24.27 (Me), 24.10 (Me),
23.49 (Me), 23.22 (Me). 19F NMR (23 °C, 282.3 MHz, C6D6): δ
-77.30 (s, Ti-O3SCF3). Anal. Calcd for C40H61N2O3SF3Ti: C,
63.65; H, 8.14; N, 3.71. Found: C, 63.03; H, 7.99; N, 3.65.
Preparation of (nacnac)Ti(iBu)2 (1). To a stirring pentane
suspension of (nacnac)TiCl2 [462 mg, 0.74 mmol] at -35 °C was
added dropwise a solution of ClMgiBu2 [2 M in ether, 0.76 mL,
1.53 mmol]. The solution was allowed to warm to room temperature
and was stirred for 20 min. The solution was filtered, and the
resulting green solution was reduced in volume in vacuo and cooled
to -35 °C for 24 h to afford green crystals of 1 [392 mg, 0.59
mmol, 79% yield].
Preparation of (PNP)Ti(CH2CHMe2)2 (4). In a vial was added
TiCl3(THF)3 [153 mg, 0.413 mmol] in toluene (5 mL), and the
solution was cooled to -35 °C. To the green-blue solution was
added a cold (-35 °C) yellow toluene (6 mL) solution of Li(PNP)
[171 mg, 0.393 mmol]. The solution changed from blue-green to
red then finally to a purple color. The solution was stirred for 1 h
and then cooled to -35 °C. To the purple solution was added
ClMgCH2CHMe2 [2 M in ether, 423 µL, 0.847 mmol] diluted in
toluene (3 mL). The solution changed from purple to brown-red
and was stirred for 1 h. The solution was dried in vacuo and was
redissolved in pentane. The solution was filtered through a bed of
Celite, and the resulting brown solution was reduced in volume in
vacuo and cooled to -35 °C to give 4 as a brown powder [141
mg, 0.239 mmol, 58% yield].
For 1: 1H NMR (C6D6, 300.1 MHz, 25 °C): δ 7.66 (∆ν1/2
)
224 Hz), 5.59 (∆ν1/2 ) 41 Hz), 4.27 (∆ν1/2 ) 51 Hz), 3.73 (∆ν1/2
) 126 Hz), 3.31 (∆ν1/2 ) 358 Hz), 3.01 (∆ν1/2 ) 55 Hz), 0.58
(∆ν1/2 ) 120 Hz). Evans magnetic moment (C6D6, 298 K): µeff
)
1.95 µB. Anal. Calcd for C43H71N2Ti: C, 77.79; H, 10.78; N, 4.22.
Found: C, 77.79; H, 10.64; N, 3.99.
Preparation of (nacnac)TidCHiPr(OTf) (2). In a vial was
dissolved 1 [197 mg, 0.30 mmol] in pentane (15 mL), and the
solution was cooled to -35 °C. To the cold green solution was
added solid AgOTf [83.9 mg, 0.33 mmol], and the mixture was
stirred for 20 min. The solution changed from green to a dark red
color with precipitation of silver. The solution was filtered, reduced
in volume in vacuo, and cooled to -35 °C to afford 2 as dark red
crystals [168 mg, 0.22 mmol, 73% yield].
1
For 4: H NMR (23 °C, 399.8 MHz, C6D6): δ 9.19 (ν1/2 ) 50
Hz), 6.56 (ν1/2 ) 57 Hz), 5.35 (ν1/2 ) 91 Hz), 5.21 (ν1/2 ) 90 Hz),
3.89 (ν1/2 ) 47 Hz), 2.52 (ν1/2 ) 8 Hz), 2.12 (ν1/2 ) 5 Hz), 1.97
(ν1/2 ) 187 Hz), 0.32 (ν1/2 ) 94 Hz), -0.27 (ν1/2 ) 54 Hz), -4.83
(ν1/2 ) 52 Hz), -5.34 (ν1/2 ) 93 Hz), -23.80 (ν1/2 ) 369 Hz). µeff
) 1.91 µB (C6D6, 298 K, Evans’ method). Multiple attempts to
obtain satisfactory elemental analysis were unsuccessful.
For 2: 1H NMR (23 °C, 399.8 MHz, C6D6): δ 7.10-7.00 (m,
6H, Ar-H), 5.48 (s, 1H, ArN(tBu)CCHC(tBu)NAr), 4.27 (d, 1H,
TidCHCHMe2), 3.28 (septet, 2H, CHMe2), 3.08 (septet, 2H,
CHMe2), 2.16 (doublet of septet, 1H, TidCHCHMe2), 1.80 (d, 6H,
CHMe2), 1.47 (d, 6H, CHMe2), 1.33 (d, 6H, CHMe2), 1.25 (d, 6H,
CHMe2), 1.01 (s, 18H, ArN(tBu)CCHC(tBu)NAr), 0.29 (d, 6H,
CHMe2). 13C NMR (23 °C, 100.6 MHz, C6D6): δ 258.9 (Tid
CHCHMe2, JC-H ) 86 Hz), 175.8 (ArN(tBu)CCHC(tBu)NAr),
147.4 (C6H3), 143.1 (C6H3), 139.0 (C6H3), 127.0 (C6H3), 124.4
(C6H3), 123.9 (C6H3), 92.08 (ArN(tBu)CCHC(tBu)NAr, JC-H ) 154
Hz), 46.52 (TidCHCHMe2, JC-H ) 128.1 Hz), 44.38 (ArN(CMe3)-
CCHC(CMe3)NAr), 31.88 ((ArN(CMe3)CCHC(CMe3)NAr), 30.27
(CHMe2), 28.87 (CHMe2), 26.88 (Me), 26.27 (Me), 24.47 (Me),
24.28 (Me), 23.0 (Me). 19F NMR (23 °C, 282.3 MHz, C6D6): δ
-77.75 (s, Ti-O3SCF3). Anal. Calcd for C40H61N2O3SF3Ti: C,
63.65; H, 8.14; N, 3.71. Found: C, 63.68; H, 8.00; N, 3.64.
Preparation of (η2-HiPrCdC(tBu)CHC(tBu)N[Ar])TidNAr-
(OTf) (3). In a vial was dissolved 2 [75 mg, 0.30 mmol] in pentane
(15 mL), and the solution was kept at glovebox temperature for 24
h. The solution was reduced in volume in vacuo and cooled to -35
°C to afford 3 as dark brown crystals [71 mg, 0.094 mmol, 94%
yield].
For 3: 1H NMR (23 °C, 399.8 MHz, C6D6): δ 7.04-6.08 (m,
6H, Ar-H), 5.67 (s, 1H, HiPrCdC(tBu)CHC(tBu)N[Ar]), 4.48 (sep-
tet, 1H, CHMe2), 3.93 (septet, 1H, CHMe2), 3.28 (septet, 1H, CH-
Me2), 3.04 (septet, 1H, CHMe2), 2.08 (m, 1H, Me2CHCHdC(tBu)-
CHC(tBu)N[Ar]), 1.59-1.56 (overlap of doublets, 6H, CHMe2),
1.53 (d, 3H, CHMe2), 1.40-1.35 (overlap of doublets, 7H, HiPrCd
C(tBu)CHC(tBu)N[Ar] and CHMe2), 1.29 (s, 9H, HiPrCdC(tBu)-
CHC(tBu)N[Ar]), 1.10-1.04 (m, 15H, CHMe2 and HiPrCdC(tBu)-
CHC(tBu)N[Ar]), 0.88 (overlap of doublets, 6H, CHMe2), 0.46 (d,
3H, CHMe2). 13C NMR (23 °C, 100.6 MHz, C6D6): δ 171.8
Preparation of (PNP)TidCHiPr(OTf) (5). In a vial was added
4 [660 mg, 1.117 mmol] in pentane (15 mL), and the solution was
cooled to -35 °C. To the solution was added solid AgOTf [301
mg, 1.171 mmol], and the solution was stirred for 1 h. The solution
quickly changed from brown to a dark red color with formation of
a silver mirror. The solution was filtered, reduced in volume in
vacuo, and cooled to -35 °C to give 5 as dark red crystals [556
mg, 0.816 mmol, 73% yield].
For 5: 1H NMR (23 °C, 399.8 MHz, C6D6): δ 8.46 (d, 1H, Tid
CHCHMe2), 7.11-7.14 (m, 1H, C6H3), 6.86-6.96 (m, 3H, C6H3),
6.74-6.75 (m, 2H, C6H3), 2.51-2.59 (m, 1H, CHMe2), 2.27-2.47
(m, 4H, CHMe2), 2.15 (s, 3H, C6H3-Me), 2.07 (s, 3H, C6H3-Me),
1.54 (dd, 3H, CHMe2), 1.24-1.39 (m, 9H, CHMe2), 1.02-1.15
(m, 6H, CHMe2), 0.96 (d, 3H, TidCHCHMe2), 0.74-0.90 (m, 6H,
CHMe2), 0.70 (d, 3H, TidCHCHMe2). 13C NMR (23 °C, 100.6
MHz, C6D6): δ 296.9 (TidCHCHMe2, JC-H ) 98 Hz), 158.8 (d,
C6H3), 153.3 (d, C6H3), 133.4 (C6H3), 133.0 (C6H3), 132.7 (C6H3),
132.0 (C6H3), 131.8 (d, C6H3), 122.6 (C6H3), 121.1 (d, C6H3), 120.5
(d, C6H3), 118.1 (d, C6H3), 115.9 (d, C6H3), 47.0 (TidCHCHMe2),
25.4 (TidCHCHMe2), 25.2 (d, CHMe2), 24.7 (TidCHCMe2), 24.0
(d, CHMe2), 22.3 (d, CHMe2), 21.1 (C6H3-Me), 21.0 (d, CHMe2),
20.7 (C6H3-Me), 20.6 (d, CHMe2), 20.4 (d, CHMe2), 19.5 (d,
CHMe2), 18.9 (d, CHMe2), 18.6 (d, CHMe2), 18.1 (d, CHMe2),
17.6 (d, CHMe2), 16.9 (d, CHMe2). 31P NMR (23 °C, 121.5 MHz,
C6D6): δ 34.3 (d, JP-P ) 54 Hz), 24.8 (d, JP-P ) 54 Hz). 19F NMR
(23 °C, 282.3 MHz, C6D6): δ -77.0 (s, Ti-O3SCF3). Anal. Calcd
for C31H48NP2TiO3F3S: C, 54.63; H, 7.10; N, 2.06. Found: C,
54.57; H, 7.28; N, 2.12.
Preparation of (PNP)TidCHiPr(Me) (6). In a vial was added
5 [124 mg, 0.182 mmol] in pentane (4 mL), and the solution was
cooled to -35 °C. To the solution was added MeMgCl [3 M in
THF, 64 µL, 0.191 mmol] diluted in pentane (4 mL). The solution
(33) (a) Sur, S. K. J. Magn. Reson. 1989, 82, 169-173. (b) Evans, D.
F. J. Chem. Soc. 1959, 2003-2005.
(34) SAINT 6.1; Bruker Analytical X-Ray Systems: Madison, WI.
(35) SHELXTL-Plus V5.10; Bruker Analytical X-Ray Systems: Madison,
WI.

3968 Organometallics, Vol. 25, No. 16, 2006
Bailey et al.
changed from dark red to a yellow-brown color. The solution was
allowed to stir for 1 h then was dried in vacuo. The solution was
redissolved in pentane and filtered. The solution was reduced in
volume in vacuo and cooled to -35 °C to give 6 as a yellow-
brown powder [81 mg, 0.148 mmol, 82% yield].
frames. The data collection was carried out using graphite-
monochromated Mo KR radiation with a frame time of 10-60 s
and 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).31 The structure was
solved using SHELXS-97 and refined with SHELXL-97.32 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 (unless otherwise
mentioned). All hydrogen atoms were refined with isotropic
displacement parameters (unless otherwise mentioned).
For 6: 1H NMR (23 °C, 399.8 MHz, C6D6): δ 8.38 (d, 1H, Tid
CHCHMe2), 7.23 (dd, 1H, C6H3), 7.05 (dd, 1H, C6H3), 6.89-6.96
(m, 3H, C6H3), 6.83 (d, 1H, C6H3), 2.73 (m, 1H, TidCHCHMe2),
2.30-2.45 (m, 3H, CHMe2), 2.17 (s, 3H, C6H3-Me), 2.144 (s, 3H,
C6H3-Me), 1.90 (sept, 1H, CHMe2), 1.31-1.40 (m, 9H, CHMe2),
1.23-1.29 (m, 6H, CHMe2), 1.10 (d, 3H, TidCHCHMe2), 1.01-
1.08 (m, 6H, CHMe2), 0.98 (d, 3H, TidCHCHMe2), 0.93 (dd, 3H,
CHMe2), 0.80 (t, JP-H ) 2.75 Hz, 3H, Ti-CH3). 13C NMR (23 °C,
100.6 MHz, C6D6): δ 279.4 (TidCHCHMe2), 160.0 (dd, C6H3),
156.3 (dd, C6H3), 133.1 (C6H3), 132.8 (d, C6H3), 132.7 (C6H3),
132.4 (C6H3), 128.9 (d, C6H3), 126.3 (d, C6H3), 120.8 (d, C6H3),
119.6 (d, C6H3), 118.2 (d, C6H3), 116.5 (d, C6H3), 50.0 (br, Ti-
CH3), 44.8 (TidCHCHMe2), 26.6 (TidCHCHMe2), 25.8 (Tid
CHCHMe2), 25.4 (d, CHMe2), 24.0 (d, CHMe2), 20.9 (d, CHMe2),
20.8 (C6H3-Me), 20.6 (C6H3-Me), 20.2 (d, CHMe2), 19.9 (d,
CHMe2), 19.8 (d, CHMe2), 19.6 (d, CHMe2), 18.9 (d, CHMe2),
18.6 (d, CHMe2), 18.5 (d, CHMe2), 16.9 (d, CHMe2), 16.7 (d,
Acknowledgment. We thank Indiana University-Bloom-
ington, the Dreyfus Foundation, the Sloan Foundation, and the
U.S. NSF (CHE-0348941, PECASE Award) for financial
support of this research. B.C.B acknowledges the Lubrizol
Foundation for a Graduate Fellowship.
CHMe2). 31P NMR (23 °C, 121.5 MHz, C6D6): δ 32.6 (d, JP-P
)
44 Hz), 22.7 (d, JP-P ) 44 Hz). Multiple attempts to obtain
satisfactory elemental analysis were unsuccessful.
Supporting Information Available: CIF files giving complete
details for data sets, including tables with atomic coordinates, bond
lengths and angles, anisotropic displacement parameters, hydrogen
coordinates, and structural diagrams, for complexes 1-3 and 5.
1H NMR spectra for 4 and 6, as well as 13C, 31P, and 19F NMR
spectra for 6 are included. This material is available free of charge
via the Internet at http://pubs.acs.org.
General Parameters for Data Collection and Refinement.
Single crystals of 1 (pentane), 2 (hexane), 3 (hexane), and 5
(pentane) were grown at -35 °C. Inert atmosphere techniques were
used to place the crystal onto the tip of a glass capillary (0.1 mm
diameter) and mounted on a SMART6000 (Bruker) at 112-128-
(2) K. A preliminary set of cell constants was calculated from
reflections obtained from three nearly orthogonal sets of 20-30
OM060308K