Activation of an aryl C-H bond converts chelating diphenolate ligands bound to zirconium into trianionic pincer ligands: σ-Donor ligand effects versus thermolysis

Article abstract of DOI:10.1021/om100732d

This report describes the synthesis and characterization of new zirconium benzyl complexes supported by a trianionic pincer ligand. Treating Zr(CH ₂Ph)₄ with the terphenyldiol [^tBuOCO]H ₃ (1) in benzene affords [^tBuOCHO]Zr(CH ₂Ph)₂ (2). Thermolysis of 2 leads to formation of dinuclear {[^tBuOCO]ZrCH₂Ph}₂ (3), which contains a five-coordinate zirconium center in a trigonal-bipyramidal (tbp) geometry. Adding 2 equiv of PMe₃ to 2 affords [^tBuOCO] ZrCH₂Ph(PMe₃)₂ (4-PMe₃). X-ray crystallographic analysis reveals strong agostic interactions for the benzyl ligand in both 3 and 4-PMe₃. Treatment of 2 with 2 equiv of THF results in hydrocarbon-soluble [^tBuOCO]ZrCH₂Ph(THF) ₂ (5). NMR spectroscopic measurements indicate a C _2v-symmetric molecule that is isostructural with 4-PMe₃. Addition of the larger phosphine PMe₂Ph to 2 provides the corresponding mono-PMe₂Ph complex in solution, but a small amount of the bis-diphenolate [^tBuOCHO]₂Zr (6) also forms. Complex 6 was independently synthesized by treating Zr(CH₂Ph)₄ with 2 equiv of 1. When 2 equiv of pyridine (py) is added to 2, the intermediate [^tBuOCHO]ZrCH₂Ph(η²-C₅H ₄N)py (7) results from pyridine o-C-H bond activation. After 48 h, complex 7 releases another 1 equiv of toluene by activation of the pincer C _ipso-H bond to produce the trianionic pincer complex [ ^tBuOCO]Zr(η²-C₅H₄N)(py) ₂ (8). Multinuclear and 2D NMR spectroscopic experiments and combustion analysis support the molecular assignment of 8. Addition of α-picoline to 2 provides different results compared to py. Initially, the α-picoline adduct [^tBuOCHO]Zr(CH₂Ph) ₂(α-picoline) (9) forms. Addition of another 1 equiv of α-picoline provides the mixed η²(N,C)-6-Me-pyridyl)/ η²(N,C-CH₂)-pyrid-2-yl complex [^tBuOCHO] Zr(η²(N,C)-6-Me-pyridyl)(η²(N,C-CH ₂)-pyrid-2-yl) (10).

Full text of DOI:10.1021/om100732d

Organometallics 2010, 29, 6711–6722 6711
DOI: 10.1021/om100732d
Activation of an Aryl C-H Bond Converts Chelating Diphenolate
Ligands Bound to Zirconium into Trianionic Pincer Ligands: σ-Donor
Ligand Effects versus Thermolysis
Subramaniam Kuppuswamy, Ion Ghiviriga, Khalil A. Abboud, and Adam S. Veige*
Center for Catalysis, University of Florida, P.O. Box 117200, Gainesville, Florida 32611, United States
Received August 6, 2010
This report describes the synthesis and characterization of new zirconium benzyl complexes
supported by a trianionic pincer ligand. Treating Zr(CH2Ph)4 with the terphenyldiol [tBuOCO]H3 (1)
in benzene affords [tBuOCHO]Zr(CH2Ph)2 (2). Thermolysis of 2 leads to formation of dinuclear
{[tBuOCO]ZrCH2Ph}2 (3), which contains a five-coordinate zirconium center in a trigonal-bipyr-
amidal (tbp) geometry. Adding 2 equiv of PMe3 to 2 affords [tBuOCO]ZrCH2Ph(PMe3)2 (4-PMe3).
X-ray crystallographic analysis reveals strong agostic interactions for the benzyl ligand in both 3 and
4-PMe3. Treatment of 2 with 2 equiv of THF results in hydrocarbon-soluble [tBuOCO]ZrCH2Ph-
(THF)2 (5). NMR spectroscopic measurements indicate a C2v-symmetric molecule that is isostruc-
tural with 4-PMe3. Addition of the larger phosphine PMe2Ph to 2 provides the corresponding mono-
PMe2Ph complex in solution, but a small amount of the bis-diphenolate [tBuOCHO]2Zr (6) also
forms. Complex 6 was independently synthesized by treating Zr(CH2Ph)4 with 2 equiv of 1. When 2
equiv of pyridine (py) is added to 2, the intermediate [tBuOCHO]ZrCH2Ph(η2-C5H4N)py (7) results
from pyridine o-C-H bond activation. After 48 h, complex 7 releases another 1 equiv of toluene by
activation of the pincer Cipso-H bond to produce the trianionic pincer complex [tBuOCO]Zr(η2-
C5H4N)(py)2 (8). Multinuclear and 2D NMR spectroscopic experiments and combustion analysis
support the molecular assignment of 8. Addition of R-picoline to 2 provides different results
compared to py. Initially, the R-picoline adduct [tBuOCHO]Zr(CH2Ph)2(R-picoline) (9) forms.
Addition of another 1 equiv of R-picoline provides the mixed η2(N,C)-6-Me-pyridyl)/η2(N,C-CH2)-
pyrid-2-yl complex [tBuOCHO]Zr(η2(N,C)-6-Me-pyridyl)(η2(N,C-CH2)-pyrid-2-yl) (10).
Introduction
of alkanes13-16 and polyolefins.12,17 More recently, their appli-
cation was extended to the dehydrocoupling of phosphines18-20
and arsines21 and heterocoupling of phosphines with silanes
and germanes.22,23 Trianionic pincer ligands7,24-32 fuse three
anionic donor groups, providing nearly exclusive meridional
Electronically unsaturated, neutral four-coordinate zirco-
nium monoalkyl or hydride species are important intermediates
in numerous transformations, including hydrozirconation,1-5
hydrosilylation,6 olefin polymerization,7-12 and hydrogenolysis
(14) Corker, J.; Lefebvre, F.; Lecuyer, C.; Dufaud, V.; Quignard, F.;
Choplin, A.; Evans, J.; Basset, J. M. Science 1996, 271, 966.
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(16) Lecuyer, C.; Quignard, F.; Choplin, A.; Olivier, D.; Basset, J. M.
Angew. Chem., Int. Ed. 1991, 30, 1660.
*To whom correspondence should be addressed. E-mail: veige@
chem.ufl.edu.
(1) Wipf, P.; Kendall, C. Top. Organomet. Chem. 2004, 8, 1.
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Ghebreab, M. B.; Donovan, K. L.; Davidson, J. J.; Hughes, R. P.;
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(21) Roering, A. J.; Davidson, J. J.; MacMillan, S. N.; Tanski, J. M.;
Waterman, R. Dalton Trans. 2008, 4488.
(9) For an example of alkene insertion see: Turculet, L.; Tilley, T. D.
Organometallics 2004, 23, 1542.
(10) For an example of isocyanide and alkene insertion see: Turculet,
L.; Tilley, T. D. Organometallics 2002, 21, 3961.
(11) For an example of alkene insertion see: Jia, L.; Ding, E.;
Rheingold, A. L.; Rhatigan, B. Organometallics 2000, 19, 963.
(12) For examples of heterogeneous/surface catalysts see refs 13-17
and: Dufaud, V. R.; Basset, J. M. Angew. Chem., Int. Ed. 1998, 37, 806.
(13) Coperet, C.; Chabanas, M.; Saint-Arroman, R. P.; Basset, J. M.
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(24) Sarkar, S.; McGowan, K. P.; Culver, J. A.; Carlson, A. R.;
Koller, J.; Peloquin, A. J.; Veige, M. K.; Abboud, K. A.; Veige, A. S.
Inorg. Chem. 2010, 49, 5143.
(25) Golisz, S. R.; Labinger, J. A.; Bercaw, J. E. Organometallics
2010, 29, 5026.
r
2010 American Chemical Society
Published on Web 11/24/2010
pubs.acs.org/Organometallics

6712 Organometallics, Vol. 29, No. 24, 2010
Kuppuswamy et al.
Zr(CH2Ph)4 in benzene at 23 ꢀC affords [tBuOCHO]Zr-
(CH2Ph)2 (2) as a pale yellow crystalline solid (eq 1). Attempts
to grow single crystals of 2 were unsuccessful, but a combina-
tion of 1H and 13C{1H} NMR spectroscopic techniques indi-
cate 2 is a Cs-symmetric dibenzyl complex, with a chelating bis-
phenolate ligand. A gHMQC experiment in C6D6 reveals a
correlation between the pincer Cipso-H proton at 5.17 ppm
and a carbon resonance at 113.0 ppm. The 13C{1H} NMR spec-
trum reveals a distinct downfield signal at 159.5 ppm resulting
from two equivalent benzyl Cipso agostic interactions with the
electronically unsaturated Zr(IV) ion (formally a 12-electron
1
complex without the agostic interaction33,34). The H NMR
spectrum of 2 indicates the tBu groups are also equivalent and
their protons resonate at 1.63 ppm. The central ring of the bis-
phenolate defines two distinct chemical environments for the
methylene protons, appearing at 2.73 and 3.13 ppm. Complex 2
exhibits spectroscopic data and symmetry similar to that of a
crystallographically characterized Ti derivative.7
Figure 1. Target molecules: four-coordinate trianionic pincer
supported Zr-alkyl species.
coordination, and contribute a maximum of 10 electrons, thus
enabling access to coordinatively and electronically unsatu-
rated complexes. Bound to Zr(IV), trianionic pincer ligands
leave only one additional site for an anionic ligand. Depending
on whether the trianionic pincer ligand is OCO (A) or NCN
(B), the four-coordinate complexes depicted in Figure 1 are
potential targets for catalyzing the reactions mentioned
above. Not able to adopt a tetrahedral geometry, these
complexes will add a substrate to form trigonal-bipyramidal
(tbp) or square-pyramidal complexes. As evidence, the pince-
-
rate NCN trianionic pincer complexes [2,6-iPrNCN]HfX2
Synthesis and Characterization of {[tBuOCO]ZrCH2Ph}2
(3). Thermolysis of 2 in benzene for 2 h produces dimeric
{[tBuOCO]ZrCH2Ph}2 (3) as a yellow microcrystalline solid
(eq 2). Slow evaporation of a concentrated ether solution of 3
provides single crystals amenable to X-ray diffraction ex-
periments. Figure 2 depicts the molecular structure of 3 and a
truncated fragment that highlights the coordination sphere
of the Zr(IV) ion. Table 1 gives crystallographic refinement
data. Results from the X-ray diffraction indicate 3 crystal-
lizes in the centrosymmetric monoclinic I2/a space group and
comprises two Zr(IV) ions, two benzyls, and two trianionic
OCO pincer ligands. Dimer 3 is C2-symmetric, and the asym-
metric unit consists of half of the dimer. The trianionic pincer
ligand binds one Zr ion with an aryloxide linkage and a
Zr-Cipso bond, but the second aryloxide bridges to the adja-
(where X =Cl, Me) are only isolable as salts.31 If alkenes are
the substrates, the insertion can ensue, leading to polyolefin
synthesis. However, Bercaw et al. report that bis-phenolate
titanium dibenzyl species are not effective precatalysts for
propylene polymerization in the absence of an activator.7 This
result prompted an examination into catalyst deactivation
and the possibility of isolating or trapping the low-coordinate
species A and B as σ-donor adducts.
This report details the synthesis of [tBuOCHO]Zr(CH2Ph)2
(2) and its subsequent pincer Cipso-H activation by thermo-
lysis or addition of σ-donor ligands. Included are the synthesis
and characterization of dimeric zirconium benzyl {[tBuOCO]-
ZrCH2Ph}2 (3), bis-trimethylphosphine zirconium benzyl
[tBuOCO]ZrCH2Ph(PMe3)2 (4-PMe3), bis-tetrahydrofuran
zirconium benzyl [tBuOCO]ZrCH2Ph(THF)2 (5), bis-diphe-
nolate zirconium [tBuOCHO]2Zr (6), bis-phenolate pyridyl-
pyridine zirconium benzyl [tBuOCHO]ZrCH2Ph(η2-C5H4N)py
(7), pyridinyl bis-pyridine zirconium [tBuOCO]Zr(η2-C5H4N)-
(py)2 (8), R-picoline zirconium dibenzyl [tBuOCHO]Zr-
(CH2Ph)2(R-picoline) (9), and [tBuOCHO]Zr(η2(N,C)-6-Me-
pyridyl)(η2(N,C-CH2)-pyrid-2-yl) (10).
˚
cent zirconium, creating a Zr-Zr distance of 3.4677(8) A.
Zirconium adopts a distorted-trigonal-bipyramidal (tbp)
geometry in which C12, C25, and O2#1 occupy the trigonal
plane (sum of the angles 359.3(1)ꢀ). The axial atoms O1 and
O2 are distorted significantly from linearity by ∼27ꢀ (—O1-
Zr1-O2 = 153.04(9)ꢀ).
Results and Discussion
Synthesis and Characterization of [tBuOCHO]Zr(CH2Ph)2
(2). Alcoholysis between [tBuOCO]H3 (1) and 1 equiv of
(26) O’Reilly, M.; Falkowski, J. M.; Ramachandran, V.; Pati, M.;
Abboud, K. A.; Dalal, N. S.; Gray, T. G.; Veige, A. S. Inorg. Chem. 2009,
48, 10901.
(27) Korobkov, I.; Gorelsky, S.; Gambarotta, S. J. Am. Chem. Soc.
2009, 131, 10406.
(28) Sarkar, S.; Carlson, A. R.; Veige, M. K.; Falkowski, J. M.;
Abboud, K. A.; Veige, A. S. J. Am. Chem. Soc. 2008, 130, 1116.
(29) Sarkar, S.; Abboud, K. A.; Veige, A. S. J. Am. Chem. Soc. 2008,
130, 16128.
Reflecting the difference between a η1-aryloxide and bridg-
˚
ing μ2-aryloxide, the Zr1-O1 bond distance (1.928(2) A) is
˚
considerably shorter than Zr1-O2 (2.185(2) A) and Zr1-O-
2
˚
˚
(2)#1 (2.176(2) A). Zr-C1(sp ) (Zr1-C12 = 2.240(3) A) and
(30) Agapie, T.; Day, M. W.; Bercaw, J. E. Organometallics 2008, 27,
6123.
(31) Koller, J.; Sarkar, S.; Abboud, K. A.; Veige, A. S. Organome-
tallics 2007, 26, 5438.
(32) Agapie, T.; Bercaw, J. E. Organometallics 2007, 26, 2957.
(33) Hartwig, J. F. In Organotransition Metal Chemistry: From
Bonding to Catalysis; University Science Books: Sausalito, CA, 2010; p 64.
(34) Brookhart, M.; Green, M. L. H.; Wong, L. L. Prog. Inorg. Chem.
1988, 36, 1.

Article
Organometallics, Vol. 29, No. 24, 2010 6713
Figure 2. Molecular structure of 3 (left) with tBu groups and hydrogen atoms removed for clarity and a truncated drawing of 3 (right)
˚
that highlights the Zr coordination sphere with ellipsoids drawn at the 50% probability level. Selected bond distances (A): Zr1-O1 =
1.928(2), Zr1-O2 = 2.185(2), Zr1-O(2)#1 = 2.176(2), Zr1-C12 = 2.240(3), Zr1-C19 = 2.651(3), Zr1-C25 = 2.277(3), Zr1-Zr1#1 =
3.4677(8). Bond angles (deg): O1-Zr1-O2 = 153.04(9), O1-Zr1-O2#1 = 92.92(9), O1-Zr1-C12 = 83.95(12), O1-Zr1-C25 =
100.72(12), O2-Zr1-O2#1 = 69.61(10), O2-Zr1-C12 = 84.61(11), O2-Zr1-C25 = 106.04(11), O2#1-Zr1-C12 = 113.54(10),
O2#1-Zr1-C25 = 123.55(10), C12-Zr1-C25 = 122.18(12).
Table 1. X-ray Crystallographic Structure Parameters and Refinement Data
3
4-PMe3
6
empirical formula
formula wt
cryst syst
C
66H68O4Zr2
C39H52O2P2Zr
705.97
monoclinic
P21/c
C58H62O4Zr
914.3
monoclinic
C2/c
1107.64
monoclinic
I2/a
space group
dimens (mm)
0.33 ꢀ 0.25 ꢀ 0.05
0.30 ꢀ 0.22 ꢀ 0.07
0.25 ꢀ 0.19 ꢀ 0.18
˚
a (A)
12.9165(17)
26.630(3)
11.1851(9)
18.2273(15)
19.250(2)
15.606(2)
˚
b (A)
˚
c (A)
18.979(4)
90
94.480(3)
90
6508.0(17)
4
0.361
2304
1.130
18.0111(14)
90
101.790(2)
90
3594.5(5)
4
0.427
1488
1.305
18.149(3)
90
119.316(4)
90
4754.0(11)
8
0.278
21928
1.277
R (deg)
β (deg)
γ (deg)
3
˚
˚
V (A )
Z (A)
abs coeff (mm-1
F(000)
)
Dcalcd (g/cm3)
˚
γ(Mo KR) (A)
temp (K)
0.710 73
100(2)
0.710 73
100(2)
0.710 73
100(2)
θ range (deg)
completeness to θmax, %
no. of rflns collected
1.53-27.50
99.1
28 038
7430 (0.1350)
7430/0/331
1.86-27.50
99.8
31 270
8241 (0.0193)
8241/0/409
1.78-27.50
99.9
23 052
5457 (0.0244)
5457/0/289
indep reflections (Rint
)
no. of data/restraints/params
final R indices (I > 2σ(I))
R indices (all data)
largest diff peak/hole, e/A
goodness of fit on F2
R1 = 0.0501, wR2 = 0.1033 (4560)
R1 = 0.0862, wR2 = 0.1106
0.721/-0.684
R1 = 0.0227, wR2 = 0.0564 (7474)
R1 = 0.0263, wR2 = 0.0583
0.403/-0.421
R1 = 0.0251, wR2 = 0.0647 (5147)
R1 = 0.0271, wR2 = 0.0661
0.358/-0.323
3
˚
0.906
1.032
1.064
3
˚
˚
Zr-C(sp ) (Zr-C25 = 2.277(3) A) differ by 0.037(3) A,
indicative of the variation in hybridization at each carbon.
The benzyl forms an agostic interaction by coordination
interaction, and the angle, 84ꢀ, is more acute.35 According to
Tonks and Bercaw et al., when the metal ion is electronically
unsaturated the ligand will distort to maximize pπ-dπ dona-
tion from the aryloxides.36 Formally a 12-electron complex
without aryloxide pπ-dπ donation, the OCO ligand distorts,
evidenced by the twisted central ring of the terphenyl frame.
The central rings twist by ∼28 and ∼46ꢀ relative to the two
outer ring planes of the pincer. The severe 46ꢀ distortion
occurs because that ring contains the bridging alkoxide. An
isostructural Ti derivative exhibits similar distortions.25
˚
between C19ipso and the zirconium (Zr1-C19 = 2.651(3) A).
The Zr-Cipso agostic interaction is comparable to that in other
electronically unsaturated monobenzyl complexes, such as
˚
2.648(2) A for CH[(CH3)2SiNAr]3ZrCH2Ph (where Ar = p-
fluorophenyl, I), and 2.753(7) and 2.795(8) A for CH[(CH3)2-
SiNAr0]3ZrCH2Ph (where Ar0 = p-tolyl, II; two crystallo-
graphically independent molecules).6 Similar Zr-C-Cipso
bond angles are found for this set of monobenzyl complexes
(3, 87.31(1)ꢀ; I, 88.24(14)ꢀ; II, 91.4(5) and 93.1(5)ꢀ), though in
II the angle is larger to complement the slightly weaker agostic
bond.6 The related complex Zr(OAr)(CH2Ph)3 (OAr = 2,6-
di-tert-butylphenoxide) exhibits a much stronger agostic
˚
(35) Latesky, S. L.; Mcmullen, A. K.; Niccolai, G. P.; Rothwell, I. P.;
Huffman, J. C. Organometallics 1985, 4, 902.
(36) Tonks, I. A.; Henling, L. M.; Day, M. W.; Bercaw, J. E. Inorg.
Chem. 2009, 48, 5096.

6714 Organometallics, Vol. 29, No. 24, 2010
Kuppuswamy et al.
The 1H and 13C{1H} NMR spectra of 3 are consistent with
the solid-state observations. The benzyl methylene protons
are diastereotopic (J = 10 Hz) and resonate as two doublets
at 2.57 and 2.87 ppm. The corresponding carbon resonates
slightly downfield compared with that in 2 (65.5 and 66.5 ppm)
at 67.0 ppm. Reflecting the different binding modes of the
alkoxides, two resonances appear for the tBu proton at 1.23
and 1.78 ppm. The pincer Zr-Cipso appears well downfield at
190.9 ppm, easily distinguishable from the unactivated bis-
phenolate form in 2 (113.0 ppm).
Synthesis and Characterization of [tBuOCO]ZrCH2Ph(PMe3)2
(4-PMe3), [tBuOCO]ZrCH2Ph(THF)2 (5), and [tBuOCHO]2Zr
(6). Thermolysis of 2 leads to the formation of dimer 3. The tBu
groups on the OCO ligand are not sufficiently bulky to prevent
dimerization, since they adopt bridging positions between the
two Zr ions. Stabilizing mononuclear alkyl species is possible
by addition of PMe3. Treating 2 with 2 equiv of PMe3 yields
the bis-trimethylphopshine adduct [tBuOCO]ZrCH2Ph(PMe3)2
(4-PMe3) as yellow crystalline blocks upon precipitation from
benzene (eq 3). Once precipitated, the complex does not redis-
solve and is insoluble in common solvents, including the haloge-
nated solvents dichloromethane and chloroform. The reaction
mixture was amenable to multinuclear (1H, 13C{1H}, and 31P-
{1H}) NMR experiments prior to precipitation.
Figure 3. Molecular structure of 4-PMe3 with ellipsoids drawn
at the 50% probability level and hydrogen atoms removed for
clarity. Selected bond distances (A): Zr1-O1 = 2.0032(9), Zr1-
˚
O2 = 2.0063(9), Zr1-C1 = 2.3065(12), Zr1-C33 = 2.3330(13),
Zr1-C34=2.7976(13), Zr1-P1=2.8108(4), Zr1-P2=2.7696(4).
Bond angles [(deg): O1-Zr1-O2 = 164.32(4), O1-Zr1-C1 =
83.65(4), O1-Zr1-P1 = 86.48(3), O1-Zr1-P1 = 89.07(3), O1-
Zr1-C33 = 98.63(4), O2-Zr1-P1 = 86.03(3), O2-Zr1-P2 =
93.18(3), O2-Zr1-C1=82.01(4), O2-Zr1-C33 = 96.96(4), C1-
Zr1-P1 = 85.19(3), C1-Zr1-P2 = 74.54(3), C1-Zr1-C33 =
149.79(5), C33-Zr1-P1 = 124.96(3), C33-Zr1-P2 = 75.38(3),
P1-Zr1-P2 = 159.6(1).
˚
and Zr1-P2 = 2.7696(4) A). These bond lengths are some-
what longer than typically observed for Zr-phosphine
complexes.40-46 Short bonds appear in the complexes [Cp2Zr-
þ
47
˚
(Et)(PMe3)] (Zr-P = 2.691(4) A), Cp2Zr(cyclohexyne)PMe3
The 1H NMR spectrum of 4-PMe3 in C6D6 reveals symmetric
48
˚
(Zr-P = 2.689(3) A), and [Cp2Zr(benzdiyne)PMe3]2 (Zr-
tBu groups with protons that resonate at 1.67 ppm. In the
P = 2.667(2) A).49 In contrast, Cp2Zr(CH2CH2B(C6F5)3)-
˚
t
13C{1H} spectrum, the corresponding Bu carbons appear at
(PPh2Me) features a longer bond due to the larger diphenyl-
50
methylphosphine ligand (Zr-P = 2.828(1) A).
30.8 and 35.7 ppm. The chemically equivalent benzyl methylene
protons appear as a singlet at 2.77 ppm, whereas in complex 3
the protons are diastereotopic. Resonating upfield from free
PMe3 (0.86 ppm), the equivalent PMe3 protons appear at
0.33 ppm. The PMe3 methyl carbons couple to phosphorus
as a pseudotriplet as a consequence of virtual coupling at
13.0 ppm (JPC=13 Hz).37-39 The 31P{1H} NMR spectrum
of 4-PMe3 exhibits a single resonance at 31.5 ppm.
The yellow blocks that deposit from the reaction medium
are single crystals, and an X-ray diffraction experiment pro-
vides the solid-state structure of 4-PMe3. Figure 3 depicts the
monomeric molecular structure of 4-PMe3, which comprises
one trianionic pincer, two PMe3 ligands, and one benzyl. Table 1
gives refinement data. Including the agostic interaction, the co-
ordination geometry of 4-PMe3 is best described as a distorted
monocapped octahedron. The trans-PMe3 ligands are bent to-
ward the pincer ligand by 20ꢀ (—P1-Zr1-P2 = 159.611(11)ꢀ),
and the Zr-P bond lengths differ slightly (Zr1-P1 = 2.8108(4)
˚
Another distortion appears for the benzyl ligand, which is
bent toward one of the PMe3 ligands by 30ꢀ to accommodate
an agostic interaction (—C1-Zr1-C33 = 149.79(5)ꢀ). Inter-
estingly, C34ipso of the benzyl is nearly linearly aligned with the
C1 carbon of the pincer, creating the angle —C1-Zr1-C34 =
178.10(4)ꢀ. The agostic interaction is weaker in 4-PMe3 (Zr1-
C34ipso = 2.7976(13) A) than in 3 (Zr1-C19ipso = 2.651(3) A),
but a correspondingly shorter trans Zr1-C1pincer bond in 4-
PMe3 is not observed. Instead, the Zr1-C1pincer bond is longer
˚
˚
˚
in 4-PMe3 (Zr1-C1=2.3065(12) A) than in 3 (Zr1-C12=
2.240(3) A). More impressive is the acute 74.54(3)ꢀ angle
between P2 and C1 on the pincer ligand, which must be forced
˚
(42) Ramakrishna, T. V. V.; Lushnikova, S.; Sharp, P. R. Organo-
metallics 2002, 21, 5685.
(43) Lee, H.; Desrosiers, P. J.; Guzei, I.; Rheingold, A. L.; Parkin, G.
J. Am. Chem. Soc. 1998, 120, 3255.
(44) Procopio, L. J.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc.
1991, 113, 1870.
(45) Vandenhende, J. R.; Hessen, B.; Meetsma, A.; Teuben, J. H.
(37) For a discussion of virtual coupling see ref 38 and: Drago, R. S.
In Physical Methods in Chemistry; Saunders: Philadelphia, 1977; p 222.
(38) Jordan, R. F.; Bajgur, C. S.; Dasher, W. E.; Rheingold, A. L.
Organometallics 1987, 6, 1041.
Organometallics 1990, 9, 537.
(46) Cotton, F. A.; Diebold, M. P.; Kibala, P. A. Inorg. Chem. 1988,
27, 799.
(47) Jordan, R. F.; Bradley, P. K.; Baenziger, N. C.; Lapointe, R. E.
(39) Mann, B. E.; Shaw, B. L.; Stainban, Re J. Chem. Soc., Chem.
J. Am. Chem. Soc. 1990, 112, 1289.
Commun. 1972, 151.
(48) Buchwald, S. L.; Lum, R. T.; Dewan, J. C. J. Am. Chem. Soc.
1986, 108, 7441.
(49) Buchwald, S. L.; Lucas, E. A.; Dewan, J. C. J. Am. Chem. Soc.
(40) Basta, R.; Harvey, B. G.; Arif, A. M.; Ernst, R. D. Inorg. Chim.
Acta 2004, 357, 3883.
(41) Pikies, J.; Baum, E.; Matern, E.; Chojnacki, J.; Grubba, R.;
1987, 109, 4396.
Robaszkiewicz, A. Chem. Commun. 2004, 2478.
(50) Sun, Y. M.; Piers, W. E.; Rettig, S. J. Chem. Commun. 1998, 127.

Article
Organometallics, Vol. 29, No. 24, 2010 6715
Figure 4. Molecular structure of 6 (left) with ellipsoids drawn at the 50% probability level and hydrogen atoms and the solvent of
crystallization molecule (benzene) removed for clarity and the truncated structure of 6 (right) highlighting the Zr(IV) coordination
˚
sphere. Selected bond distances (A): Zr1-O1 = 1.9733(9), Zr1-O2 = 1.9835(9), Zr1-C12 = 2.8162(13). Bond angles (deg): O1-Zr1-
O1#1 = 105.89(5), O1-Zr1-O2 = 107.01(4), O1-Zr1-O2#1 = 96.32(4), O1#1-Zr1-O2 = 96.32(4), O1#1-Zr1-O2#1 = 107.01(4),
O2-Zr1-O2#1 = 140.97(5).
into this position by the benzyl ligand; the P1-Zr-C1 angle is
larger (85.19(3)ꢀ). Addition of 1 equiv of PPh3 to 2 in C6D6
does not produce the corresponding mono- or bis-PPh3 com-
plex. Instead, no reaction occurs at 23 ꢀC, and refluxing the
solution results in formation of dimer 3.
at 189.9 ppm is typical for the pincer carbon bound to Zr
and compares favorably with 3 (190.9 ppm) and 4-PMe3
(194.5 ppm). The additional 14 aromatic protons resonate
between 6.46 and 7.70 ppm, and the corresponding carbons
are located between 119.8 and 157.6 ppm.
Inducing the pincer Cipso-H bond activation by addition of
a σ-donor ligand provides compelling evidence for a general
approach to installing the trianionic form of the pincer ligand.
For example, treating 2 with 2 equiv of THF in C6D6 results in
the bis-THF adduct [tBuOCO]ZrCH2Ph(THF)2 (5; eq 4). An
alternative synthesis of compound 5 is possible by stirring an
equimolar ratio of 1 and Zr(CH2Ph)4 at 23 ꢀC in THF.
Spatially cumbersome σ-donor ligands such as PPh3 do
not promote the aryl C-H bond activation. Treating 2 with 2
equiv of the smaller PMe2Ph, however, results in the formation
of the mono-PMe2Ph complex [tBuOCO]ZrCH2Ph(PMe2Ph2)
(4-PMe2Ph; see the Supporting Information). Attempts to
recrystallize and purify 4-PMe2Ph lead to precipitation of a
minor amount of the bis-diphenolate complex [tBuOCHO]2Zr
(6). Only present as a minor product, an alternative synthesis
that provides analytically pure 6 in 68% yield involves adding
2 equiv of 1 directly to Zr(CH2Ph)4 in benzene (eq 5).
[tBuOCHO]2Zr (6) is insoluble in hydrocarbon, ethereal, and
halogenated solvents; moreover, DMF and DMSO do not
dissolve 6.
1H and 13C{1H} NMR spectroscopy and combustion anal-
ysis confirm the composition and purity of 5. The 1H NMR
spectrum of 5 exhibits two broad resonances at 0.96 and
3.48 ppm that integrate to eight protons each and are attrib-
utable to the THF ligands. In comparison with free THF
(1.40 and 3.57 ppm), the coordinated THF protons are
shifted upfield.51,52 In the 13C{1H} spectrum, the corre-
sponding THF carbon resonances appear at 25.4 and 72.3
ppm. Characteristic benzyl protons resonate at 2.89 ppm,
and the corresponding methylene 13C resonance appears at
58.8 ppm. The 18 protons of the tBu resonate as a singlet at
1.76 ppm, and the corresponding quaternary and primary
carbons appear at 31.1and 35.7 ppm, respectively. A singlet
As 6 was not amenable to solution-phase characterization,
its molecular structure was determined by subjecting single
crystals that deposit from the reaction medium to an X-ray
diffraction experiment. Figure 4 depicts the molecular struc-
ture of 6, the figure caption contains pertinent bond lengths
and angles, and Table 1 gives crystal refinement data. Two
diphenolate ligands bond to one Zr(IV) ion, rendering the
complex C2 symmetric. The zirconium ion sits on a 2-fold
rotation axis, and the asymmetric unit comprises half of the
complex and a half-molecule of solvent (benzene). Within
the asymmetric unit, the two Zr-O distances differ slightly
(51) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.;
Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. Organome-
tallics 2010, 29, 2176.
(52) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997,
62, 7512.
˚
˚
(Zr1-O1 = 1.9733(9) A and Zr1-O2 = 1.9835(9) A). One
large angle between opposing ligand alkoxides imparts

6716 Organometallics, Vol. 29, No. 24, 2010
Kuppuswamy et al.
Scheme 1. Synthetic Details for the Synthesis of [tBuOCHO]Zr(CH2Ph)(η-C5H4N)py (7) and [tBuOCO]Zr(η-C5H4N)(py)2 (8)
a quasi-sawhorse geometry to the complex (—O2-Zr1-
O2#1 = 140.97(5)ꢀ; see the right-hand side of Figure 4). As
a consequence of having to span the terphenyl framework,
the angle between alkoxides within one diphenolate splays to
—O1-Zr1-O2 = 107.01(4)ꢀ. The most notable feature of
complex 6 is that the two diphenolates are oriented face to
face but are rotated such that one pincer central ring π-stacks
with a pincer external ring of the opposite ligand. This subtle
twist allows one of the tBu groups to slip in between two tBu
groups from the opposite diphenolate.
pyridine and ortho-metalated pyridine occupy the remaining
basal sites, and the benzyl sits in the apical position. In con-
trast to 3 and 4-PMe3, no agostic interaction forms between
the Zr(IV) ion and the benzyl Cipso atom; the Zr1-C12 dis-
˚
tance is 2.862(3) A. In fact, the benzyl arene ring leans toward
one side of the molecule (O2), causing one of the Zr-O bonds
˚
to elongate; the experimental values are Zr1-O1 = 1.988(2) A
˚
and Zr1-O2 = 2.012(2) A. In the solid state, the N-bound
pyridine twists relative to the ortho-metalated ring by ∼88ꢀ.
The Zr1-N1 and Zr1-N2 bond distances vary significantly
Synthesis and Characterization of [tBuOCHO]Zr(CH2Ph)-
(η-C5H4N)py (7) and [tBuOCO]Zr(η-C5H4N)(py)2 (8). Treat-
ment of 2 with 2 equiv of pyridine (py) leads to the formation
of [tBuOCHO]Zr(CH2Ph)(η-C5H4N)py (7). Unlike the case
when PMe3 and THF add to 2, the bis-py adduct [tBuOCO]-
Zr(CH2Ph)py2 is not isolable; instead, immediate activation
of the o-C-H bond on one py occurs, with concomitant libera-
tion of toluene (Scheme 1). Pentamethylcyclopentadienyl (Cp*)
zirconium alkyl cationic complexes exhibit similar pyridine
o-CH metalation.53-61 Complex 7 is not stable in solution at
ambient temperature; however, the reaction end point can
be determined by monitoring the reaction periodically by 1H
NMR spectroscopy. Typically the reaction takes 2 h to com-
plete. Removal of all volatiles and washing the residual solid
with pentane provides 7 as a crystalline yellow powder in 69%
yield. Once isolated in the solid state, complex 7 is stable, but
redissolving 7 for the purpose of spectroscopic analysis results
in further reactivity. Fortunately, single crystals amenable to
an X-ray diffraction study provide the molecular structure of 7.
Figure 5 depicts the results of the structural refinement as
well as pertinent bond lengths and angles, and Table 2 gives
refinement data.
by 0.201(2) A, reflecting the different binding modes (η vs η ).
Interestingly, the η-pyridinyl group orients in two distinct ways
by situating the N atom exo (0.75(2) site occupancy) versus
endo (0.25(2) site occupancy) relative to the apical benzyl. In
solution, the η-pyridinyl isomerizes between the two positions
fasterthanthe1H NMR time scale, thus exhibiting only one set
of resonances (vide infra).
1
2
˚
An appropriately shorter Zr-C bond results for the ortho-
˚
metalated pyridine (Zr1-C39 = 2.254(2) A) versus the Zr-
˚
benzyl bond (Zr1-C27 = 2.327(3) A). Cipso of the central ring
in the diphenolate ligand is aligned with the Zr-CH2 axis with
an angle of —C12-Zr1-C27 = 154.07(3)ꢀ, but it is unrea-
˚
sonably distant (Zr-C12 = 2.862(3) A) to form a strong
interaction. Instead, Cipso most likely resides in that position
naturally due to the chelate.
Analytically pure 7 will precipitate from C6D6 upon its
formation, but forcing 7 to redissolve with heat promotes
subsequent reactivity (∼17% conversion to compound 8,
Scheme 1). To circumvent these problems, it is necessary to
complete 1H NMR and 13C{1H} NMR spectroscopic analysis
on 7 generated in situ, prior to complete deposition. The 1H
NMR spectrum of 7 reveals a broad singlet at 2.79ppm for the
t
Complex 7 comprises one chelating dianionic bis-pheno-
late ligand, one benzyl group, one pyridine, and one ortho-
metalated pyridine. The Zr(IV) ion adopts a square-pyrami-
dal coordination environment. The diphenolate aryloxides
bind trans to each other in the basal plane, the N-bound
benzyl CH2 protons and a singlet at 1.30 ppm for the Bu
protons. For the benzyl CH2 protons to be equivalent, it must
invert and rotate freely in solution. Broad resonances attrib-
utable to the η1-pyridine ligand appear at 9.30, 8.83, and 7.61
ppm. In the 13C{1H} NMR spectrum of 7 a resonance appears
at 201.1 ppm, attributable to the Zr-Cpyridinyl carbon.57,59-61
Other resonances consistent with the solid-state structure
include a benzyl CH2 at 57.8 ppm and C(CH3)3 and C(CH3)3
resonances at 35.5 and 30.4 ppm, respectively.
(53) For examples of Zr-pyridinyl and Zr-pyridyl complexes see
refs 54-61 and: Jordan, R. F.; Taylor, D. F.; Baenziger, N. C. Organo-
metallics 1990, 9, 1546.
(54) Guram, A. S.; Swenson, D. C.; Jordan, R. F. J. Am. Chem. Soc.
With an extra 1 equiv of pyridine present, complex 7converts
to the trianionic pincer complex [tBuOCO]Zr(η-C5H4N)(py)2
(8) in 93% yield (Scheme 1). A suite of NMR spectroscopic
techniques permits the identification of complex 8. Obtained
at -60 ꢀC in toluene-d8, the 1H-1H and 1H-13C (one-bond
and long-range) couplings within the DQCOSY, gHMQC,
and gHMBC spectra permit the absolute assignment of each
1H and 13C{1H} NMR resonance (see Table S1 in the Support-
ing Information for the complete assignment). At 25 ꢀC, the
pyridines self-exchange and as a consequence exhibit broad
1992, 114, 8991.
(55) Guram, A. S.; Jordan, R. F.; Taylor, D. F. J. Am. Chem. Soc.
1991, 113, 1833.
(56) Guram, A. S.; Jordan, R. F. Organometallics 1991, 10, 3470.
(57) Jordan, R. F.; Guram, A. S. Organometallics 1990, 9, 2116.
(58) Jordan, R. F.; Taylor, D. F. J. Am. Chem. Soc. 1989, 111, 778.
(59) Oishi, M.; Kato, T.; Nakagawa, M.; Suzuki, H. Organometallics
2008, 27, 6046.
(60) Krut’ko, D. P.; Kirsanov, R. S.; Belov, S. A.; Borzov, M. V.;
Churakov, A. V.; Howard, J. A. K. Polyhedron 2007, 26, 2864.
(61) Bradley, C. A.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem. Soc.
2003, 125, 8110.

Article
Organometallics, Vol. 29, No. 24, 2010 6717
resonances at 8.73 (o-CH, 4H), 6.20 (m-CH), and 6.60 ppm
(p-CH). Figure 6 depicts the results of a variable-temperature
1H NMR study from -60 to 50 ꢀC in toluene-d8. Line-shape
analysis provides the activation energy of ΔGq(298 K) =
12.0(3) kcal/mol for the self-exchange (ΔSq = -5.5(6) cal/
(mol K), ΔHq = 10.4(1) kcal/mol). At -60 ꢀC, the exchange
process slows and the resonances at 8.73 and 6.20 ppm split
into two at 9.01 and 8.64 ppm and at 6.40 and 6.31 ppm,
respectively. The resonance at 6.60 ppm sharpens as the tem-
perature decreases but does not resolve into two signals. Rapid
exchange between the pyridines, even at -60 ꢀC, prevents
assignment of cis versus trans pyridines. Though the pyridines
self-exchange, they do not exchange with the η-pyridinyl, even at
55 ꢀC. The 15N NMR spectrum of 8 at -60 ꢀC reveals three
resonances at 290.1 (η-pyridinyl), 280.0 (py), and 278.3 ppm
(py). Important 13C{1H} NMR assignments include the
Zr-Cpincer carbon at 188.0 ppm and the Zr-Cpyridinyl carbon
at 207.2 ppm, which is downfield from 7 but is within the
range for other reported Zr-pyridinyls.57,59-61
Synthesis and Characterization of [tBuOCHO]Zr(CH2Ph)2-
(r-picoline) (9) and [tBuOCHO]Zr(η2(N,C)-6-Me-pyridyl)(η2-
(N,C-CH2)-pyrid-2-yl) (10). Addition of THF, PMe3, or py
to 2 induces rapid toluene elimination and aromatic C-H bond
activation. Coordination of the substrate must initiate the C-H
bond activation, because no reaction occurs upon addition of
2,6-lutidine. In contrast, R-picoline easily binds upon the addi-
tion of 2 equiv. Adduct 9 forms prior to any C-H bond activa-
tion or toluene elimination event (Scheme 2), providing
insight into the mechanism. Yellow blocks of [tBuOCHO]Zr-
(CH2Ph)2(R-picoline) (9; 88%), which are single crystals,
deposit as the reaction mixture is slowly warmed to ambient
temperature.
An X-ray diffraction experiment provides satisfactory
data to solve the molecular structure of 9. Figure 7 depicts
the molecular structure of 9, the figure caption gives perti-
nent bond lengths and angles, and Table 2 gives refinement
data. The structural refinement indicates that the asym-
metric unit contains 9 and two benzene solvent molecules.
The Zr(IV) ion adopts a C1-symmetric square-pyramidal
geometry in which one benzyl, the R-picoline, and the diphe-
nolate comprise the basal plane. The second benzyl group
occupies the apical position, and its phenyl ring leans to
one side of the complex. The most striking feature is that the
R-picoline resides in two sites with occupancy factors refined
at 0.738(4) for the major isomer and 0.264(4) for the minor
isomer. A consequence of the apical benzyl lean and sterics,
Figure 5. Molecular structure of 7 with ellipsoids drawn at the
50% probability level and hydrogen atoms removed for clarity.
Selected bond distances (A): Zr1-O1 = 1.988(2), Zr1-O2 =
˚
2.012(2), Zr1-N1 = 2.403(2), Zr1-N2 = 2.202(2), Zr1-C27 =
2.327(3), Zr1-C39 = 2.254(2), Zr1-C12 = 2.863(0), Zr1-C28 =
3.230(0). Bond angles (deg): O1-Zr1-O2 = 148.64(7), O1-Zr1-
N1 = 83.72(7), O1-Zr1-N2 = 98.50(7), O1-Zr1-C27 =
97.52(9), O1-Zr1-C39 = 87.87(8), O2-Zr1-N1 = 87.82(7),
O2-Zr1-N2 = 98.20(7), O2-Zr1-C27 = 110.54(9), O2-Zr1-
C39 = 90.92(8), N2-Zr1-N1 = 163.25(8), N2-Zr1-C27 =
83.77(10), N2-Zr1-C39 = 34.77(8), C27-Zr1-N1 = 79.48(9),
C39-Zr1-N1 = 161.54(8), C39-Zr1-C27 = 118.02(10).
Table 2. X-ray Crystallographic Structure Parameters and Refinement Data
7
9
10
empirical formula
formula wt
cryst syst
C
90H90N4O4Zr2
C55H58NO2Zr
856.24
triclinic
P1
C38H40N2O2Zr
647.94
monoclinic
P21/c
1474.10
monoclinic
C2/c
space group
dimens (mm)
0.16 ꢀ 0.13 ꢀ 0.03
0.14 ꢀ 0.07 ꢀ 0.04
0.12 ꢀ 0.11 ꢀ 0.04
˚
a (A)
29.1174(9)
16.0255(5)
12.1545(7)
14.6482(9)
11.4471(10)
17.0000(15)
˚
b (A)
˚
c (A)
19.8750(6)
90
118.469(1)
90
8152.6(4)
4
0.306
3080
1.201
14.7222(9)
63.211(3)
74.803(3)
84.545(4)
2257.2(2)
2
2.309
902
1.260
16.9534(14)
90
97.364(5)
90
3271.9(5)
4
0.371
1352
1.315
R (deg)
β (deg)
γ (deg)
3
˚
˚
V (A )
Z (A)
abs coeff (mm-1
F(000)
)
Dcalcd (g/cm3)
˚
γ(Mo KR) (A)
temp (K)
0.71073
100(2)
1.54178
100(2)
0.71073
100(2)
θ range (deg)
completeness to θmax (%)
no. of rflns collected
1.59-27.50
100.0
40 404
9356 (0.0652)
9356/0/447
3.38-66.18
96.2
40 219
7611 (0.0720)
7611/0/530
1.70-27.50
100.0
46 655
7507 (0.0844)
7507/0/407
no. of indep rflns (Rint
)
no. of data/restraints/params
final R indices (I > 2σ(I))
R indices (all data)
largest diff peak/hole (e A )
goodness of fit on F2
R1 = 0.0456, wR2 = 0.1032 (6583)
R1 = 0.0719, wR2 = 0.1095
0.478/-0.304
R1 = 0.0325, wR2 = 0.0763 (6494)
R1 = 0.0410, wR2 = 0.0799
0.882/-0.627
R1 = 0.0365, wR2 = 0.0701 (5084)
R1 = 0.0680, wR2 = 0.0769
0.425/-0.421
3
˚
1.114
0.985
0.914

6718 Organometallics, Vol. 29, No. 24, 2010
Kuppuswamy et al.
1
Figure 6. Stacked spectra from a variable-temperature H NMR experiment of [tBuOCO]Zr(η-C5H4N)(py)2 (8) in toluene-d8 from
-60 to 50 ꢀC.
Scheme 2. Synthetic Details for the Synthesis of [tBuOCHO]Zr(CH2Ph)2(r-picoline) (9) and [tBuOCHO]Zr(η2(N,C)-6-Me-pyridyl)-
(η2(N,C-CH2)-pyrid-2-yl) (10)
the major isomer places the methyl group of the R-picoline
on the opposite side. The two benzyl ligands are cis (—C27-
Zr1-C34 = 88.33(9)ꢀ), and the angle at the benzyl methy-
lenes differ, with the more acute angle providing a slightly
longer Zr-C bond (—Zr1-C27-C28 = 98.82(1)ꢀ corre-
5% of complex 10 forms). Complementary to the solid state
R-picoline disorder, resonances attributable to the two iso-
mers appear in the H NMR spectrum, though some are
1
indistinguishable due to overlap. Distinct resonances for the
isomers include two sets of benzyl methylenes at 1.83 and 2.56
ppm (major) and at 2.63 and 2.73 ppm (minor) in a 6.7:1 ratio.
The corresponding 13C{1H} resonances for the benzyl methy-
lenes appear at 68.1 and 68.9 ppm, but the minor isomer reso-
nances are undetectable due to the lower concentration. Both
isomer tBu protons must overlap, as only a single resonance
˚
sponds to Zr-C27 = 2.302(2) A and —Zr1-C34-C35 =
˚
116.45(0)ꢀ corresponds to 2.289(2) A).
Complex 9 is insoluble in hydrocarbon solvents but will
dissolve in chlorinated solvents. Once in solution, subsequent
reactivity ensues (vide infra). In fact, the 2 equiv of R-picoline
used in the synthesis are necessary to promote the exclusive
formation of 9; otherwise, a mixture of products forms.
Conducting the NMR experiments at -25 ꢀC slows the
reactivity and provides sufficient time to complete the solu-
tion-phase spectroscopic characterization (an unavoidable
t
appears at 1.75 ppm. The observation of one Bu resonance
also indicates the complex is Cs symmetric in solution, imply-
ing fast rotation around the Zr-benzyl bonds. A broad reso-
nance integrating to three protons appears at 2.19 ppm, which
is shifted from free R-picoline (2.38 ppm). Dramatically

Article
Organometallics, Vol. 29, No. 24, 2010 6719
Figure 7. Molecular structure of 9 (left) with ellipsoids drawn at the 50% probability level and hydrogen atoms removed for clarity
˚
and the truncated structure of 9 (right) highlighting the Zr(IV) coordination sphere. Selected bond distances (A): Zr1-O1 =
1.9759(16), Zr1-O2 = 1.9987(15), Zr1-N1 = 2.4941(13), Zr1-N10 = 2.525(4), Zr1-C27 = 2.302(2), Zr1-C34 = 2.289(2), Zr1-
C12 = 2.812(2). Bond angles (deg): O1-Zr1-O2 = 150.51(6), O1-Zr1-C34 = 98.16(8), O2-Zr1-C34 = 111.20(8), O1-Zr1-
C27 = 93.29(8), O2-Zr1-C27 = 90.35(8), C34-Zr1-C27 = 88.33(9), O1-Zr1-N1 = 99.42(6), O2-Zr1-N1 = 83.65(6), C34-
Zr1-N1 = 79.80(8), C27-Zr1-N1 = 163.68(8), O1-Zr1-N10 = 88.93(14), O2-Zr1-N10 = 92.65(14), C34-Zr1-N10 = 81.43(15),
C27-Zr1-N10 = 169.74(14), N1-Zr1-N10 = 10.49(13).
upfield, the pincer Cipso-H proton appears at 4.40 ppm, which
corresponds to an aromatic carbon at 113.5 ppm. Adjacent to
this proton is the minor isomer resonance at 4.52 ppm. The
dibenzyl complex 2 also exhibits an unusual upfield resonance
for the Cipso-H proton at 5.17 ppm. Normally this proton
resides downfield in the 7.5-8.5 ppm region of the 1H NMR
spectrum. Close inspection of the solid-state structure of 9
provides an explanation for the dramatic shift, and Figure 7
depicts a truncated section of 9 that highlights this interaction.
The calculated Cipso-H proton points into the center of a
benzyl aromatic ring, thus shielding it from the external field
and causing the upfield resonance.
If, instead of isolating 9 upon precipitation, the reaction
mixture is stirred for 12 h, the second R-picoline equivalent
binds and reacts to form the dipyridyl complex [tBuOCHO]-
Zr(η2-(N,C)-6-Me-pyridyl)(η2-(N,C-CH2)-pyrid-2-yl) (10)
(Scheme 2). Multinuclear NMR spectroscopy and single-
crystal X-ray crystallography support the structural assign-
ment. Complex 10 is not stable at ambient temperature in the
solid state; the colorless microcrystalline powder turns pink
within 2 days. A 1H NMR spectrum of a sample left at ambi-
ent temperature in the solid state reveals the presence of the
protonated ligand precursor [tBuOCO]H3 (1) and R-picoline.
A pentane/diethyl ether solution of 10 cooled to -35 ꢀC in a
glovebox freezer results in the formation of an unidentifiable
red impurity. However, dissolving 10 in hot pentane and
cooling the solution slowly produces crystals suitable for a
single-crystal X-ray diffraction experiment as well as some
decomposition products. Figure 8 depicts the result of the
structural refinement, the figure caption contains pertinent
bond lengths and angles, and Table 2 gives the crystal refine-
ment data. Complex 10 contains three unique metallacycles in
a C1-symmetric arrangement: (1) the chelating diphenolate,
(2) the η2-(N,C)-6-Me-pyridyl, and (3) the η2-(N,C-CH2)-
pyrid-2-yl.54,62-65 The inclusion of three metallacycles results
in a highly distorted six-coordinate Zr(IV) ion. The highly
distorted geometry does not conform to any regular polyhe-
dron. Thebestdescriptionof the geometry isa square pyramid
in which the C-N bond of the η2-(N,C)-6-Me-pyridyl, the
diphenolate alkoxides, and the N atom of the η2-(N,C-CH2)-
pyrid-2-yl occupy the square plane. The CH2 group from the
η2-(N,C-CH2)-pyrid-2-yl occupies the apical position, though
due to the chelate its position deiviates significantly. Possibly to
avoid opposing strong Zr-C trans bonds, the N atoms orient
linearly opposite each other (—N1-Zr-N2 = 172.05(7)ꢀ) and
force the Zr-C bonds cis (—C27-Zr1-C38 = 91.06(9)ꢀ). In
the η2-(N,C)-6-Me-pyridyl three-membered ring the Zr1-N2
˚
and Zr1-C38 distances are 2.2425(18) and 2.230(2) A, respec-
tively, and the N2-Zr1-C38 angle is 34.82(7)ꢀ. These metrics
˚
comparewelltothoseof7(Zr1-N2 = 2.203(2) A, Zr1-C39 =
˚
2.253(2) A, and N1-Zr1-C2 = 34.78(8)ꢀ) and the reported
[Cp2Zr(η2-(N,C)-6-Me-pyridyl)(PMe3)]þ complex53 (where
˚
˚
Zr-N = 2.21(1) A, Zr-C = 2.29(2) A, and N-Zr-C =
34.2(7)ꢀ). In the η2-(N,C-CH2)-pyrid-2-yl four-membered
ring, a larger N-Zr-C angle appears and the Zr-C bond is
˚
˚
appropriately 0.087(3) A longer (Zr1-C27 = 2.317(3) A).
˚
For comparison, the Zr1-N1 (2.3199(19) A) distance is
significantly shorter than in [Cp2Zr(η2(N,C-CH2)-6-Me-
pyridyl)] (2.407(4) A)63 and slightly longer than in [Cp2Zr-
þ
˚
(η2(N,C-CH2CH2)-6-Me-pyridyl)]þ (2.303(2) A).
53
˚
Retaining Cs symmetry in solution (C6D6), the 1H NMR
spectrum of 10 reveals a single resonance for the tBu protons
at 1.05 ppm. A distinct singlet appears at 2.82 ppm for the
η2-(N,C-CH2)-pyrid-2-yl methylene protons, and in the 13C-
{1H} NMR spectrum, the corresponding carbon resonates at
43.2 ppm. The methyl group protons on the η2-(N,C)-6-Me-
pyridyl ligand resonate as a broad singlet at 1.88 ppm, which
is significantly shifted upfield from those of free R-picoline
(64) Beshouri, S. M.; Chebi, D. E.; Fanwick, P. E.; Rothwell, I. P.;
Huffman, J. C. Organometallics 1990, 9, 2375.
(65) Bailey, S. I.; Colgan, D.; Engelhardt, L. M.; Leung, W. P.;
Papasergio, R. I.; Raston, C. L.; White, A. H. J. Chem. Soc., Dalton
Trans. 1986, 603.
(62) Kim, Y. H.; Kim, T. H.; Kim, N. Y.; Cho, E. S.; Lee, B. Y.; Shin,
D. M.; Chung, Y. K. Organometallics 2003, 22, 1503.
(63) Beshouri, S. M.; Fanwick, P. E.; Rothwell, I. P.; Huffman, J. C.
Organometallics 1987, 6, 891.

6720 Organometallics, Vol. 29, No. 24, 2010
Kuppuswamy et al.
Figure 8. Molecular structure of 10 (left) with ellipsoids drawn at the 50% probability level and hydrogen atoms and solvent molecules
(benzene) removed for clarity and the truncated structure of 10 (right) highlighting the Zr(IV) coordination sphere. Selected bond
˚
distances (A): Zr1-O1 = 1.9760(15), Zr1-O2 = 1.9866(15), Zr1-N1 = 2.3199(19), Zr1-N2 = 2.2425(18), Zr1-C27 = 2.317(3),
Zr1-C38 = 2.230(2), Zr1-C1 = 2.842(2). Bond angles (deg: O1-Zr1-O2 = 147.18(6), O1-Zr1-C38 = 100.30(7), O2-Zr1-C38 =
98.31(7), O1-Zr1-N2 = 93.92(6), O2-Zr1-N2 = 86.18(6), C38-Zr1-N2 = 34.82(7), O1-Zr1-C27 = 103.08(9), O2-Zr1-
C27 = 103.36(9), C38-Zr1-C27 = 91.06(9), N2-Zr1-C27 = 125.70(8), O1-Zr1-N1 = 90.44(6), O2-Zr1-N1 = 86.55(6),
C38-Zr1-N1 = 150.26(8), N2-Zr1-N1 = 172.05(7), C27-Zr1-N1 = 59.38(8).
(2.39 ppm) and of 9 (2.19 ppm). With the benzyl groups
removed and no aromatic ring to shield it, the diphenolate
Cipso-H proton appears in a typical position at 8.98 ppm,
though somewhat downfield from 7 (7.11 ppm). Thermolysis
of 10 for 12 h in C6D6 at 100 ꢀC does not activate the Cipso-H
proton to provide the trianionic pincer form of the ligand;
instead, the solution turns red. Above 100 ꢀC 10 decomposes
rapidly.
dialkyl complexes promotes R-abstraction resulting in alkyl-
idene formation.30,66-70 If this occurs, then the pincer Cipso-H
bond can add across the resulting MdC double bond. Alter-
natively, addition of the nucleophile may assist by forcing the
benzyl group into a cis position that maximizes orbital align-
ment for metathesis with the pincer Cipso-H bond. The crystal-
lographically characterized R-picoline complex [tBuOCHO]-
Zr(CH2Ph)2(R-picoline) (9) features this precise arrangement.
In fact, a recent study by Bercaw et al. indicates both mecha-
nisms are competitive during formation of a titanium dimer
analogous to 3.25
Conclusions
In the absence of a σ-donor, the diphenolate complex
[tBuOCHO]Zr(CH2Ph)2 (2) converts to the dimer {[tBuOCO]-
ZrCH2Ph}2 (3) upon heating. Complex 3 contains a bridging
aryloxide ligand from the OCO trianionic pincer, rendering it
inert to further derivatization, including no reaction with H2,
CO, or ethylene. The bridging aryloxide indicates the tBu group
is not bulky enough to prevent dimerization, which is undesir-
able, especially if this occurs during catalytic processes such as
polymerization of alkenes.7,25 Supporting this contention is the
observation that two ligands can bind one Zr ion, exemplified
in the synthesis of the bis-diphenolate complex [tBuOCO]2Zr
(6). The dimerization reaction requires some thermal input
(80 ꢀC, 2 h), in contrast to events when σ-donor ligands are
present. Addition of THF or PMe3 promotes the facile loss of
toluene and C-H activation of the pincer Cipso-H bond to
create the trianionic pincer form of the ligand and the corre-
sponding mononuclear complexes [tBuOCO]ZrCH2Ph(L)2
(L=PMe3, 4-PMe3; L=THF, 5). What role does the σ-donor
play? It is well-known that addition of external nucleophiles to
The presence of an o-C-H bond on py shunts the pincer
Cipso-H bond activation, leading to the η2-pyridinyl com-
plex [tBuOCHO]Zr(CH2Ph)(η-C5H4N)py (7). This chemis-
try can be extended to primary C-H bond activation when
R-picoline is the substrate, leading to [tBuOCHO]Zr(η2(N,
C)-6-Me-pyridyl)(η2(N,C-CH2)-pyrid-2-yl) (10). Regardless
of the mechanism, addition of a σ donor prevents deleterious
dimerization and provides a method to convert terphenyl
diphenolate ligands into their trianionic form. The σ donors
also enable the isolation of monoalkyl complexes supported
by trianionic pincer ligands. Exhibition of facile aryl and pri-
mary C-H bond activation reactions are compelling; the
challenge remains to exploit them in catalytic reactions.
Synthetic Procedures
General Considerations. Unless specified otherwise, all ma-
nipulations were performed under an inert atmosphere using
standard Schlenk or glovebox techniques. Glassware was oven-
dried before use. Pentane, toluene, diethyl ether (Et2O), tetrahy-
drofuran (THF), and 1,2-dimethoxyethane (DME) were dried
using a GlassContours drying column. Benzene-d6 and THF-d8
(Cambridge Isotopes) were dried over sodium-benzophenone
(66) Morton, L. A.; Chen, S. J.; Qiu, H.; Xue, Z. L. J. Am. Chem. Soc.
2007, 129, 7277.
(67) Schrock, R. R. Acc. Chem. Res. 1979, 12, 98.
(68) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978, 100,
3359.
(69) Mclain, S. J.; Wood, C. D.; Messerle, L. W.; Schrock, R. R.;
Hollander, F. J.; Youngs, W. J.; Churchill, M. R. J. Am. Chem. Soc.
1978, 100, 5962.
ꢀ
˚
ketyl, distilled or vacuum-transferred, and stored over 4 A molec-
ular sieves. Pyridine was dried over KOH and distilled and stored
ꢀ
˚
over 4 A molecular sieves. Commercially available Zr(CH2Ph)4
and PMe3 were used without further purification. [tBuOCO]H3
28
was prepared according to the literature procedures. NMR spectra
were obtained on Varian Mercury Broad Band 300 MHz or
Varian Mercury 300 MHz spectrometers. Chemical shifts are
(70) Fellmann, J. D.; Rupprecht, G. A.; Wood, C. D.; Schrock, R. R.
J. Am. Chem. Soc. 1978, 100, 5964.

Article
Organometallics, Vol. 29, No. 24, 2010 6721
reported in δ (ppm). For 1H and 13C{1H} NMR spectra the
solvent resonance was referenced as an internal standard, and for
31P{1H} NMR spectra the 85% H3PO4 resonance was referenced
as an external standard. Elemental analyses were performed at
Complete Analysis Laboratory Inc., Parsippany, NJ.
frozen again, THF (18 mg, 0.246 mmol, 2 equiv) was added,
and the mixture was slowly warmed to 23 ꢀC. All volatiles were
removed in vacuo to yield 5 as a pale yellow crystalline solid
1
(80 mg, 93%). H NMR (300 MHz, C6D6; δ (ppm)): 7.70 (m,
4H, Ar H), 7.43 (d, J = 7.6 Hz, 2H, Ar H), 7.31 (dd, J = 7.8 Hz,
2H, Ar H), 7.05 (t, J = 7.8 Hz, 1H, Ar H), 6.93 (m, 3H, Ar H),
6.72 (bm, 2H, Ar H), 6.46 (t, J = 6.7 Hz, 1H, Ar H), 3.48 (bs,
8H, -OCH2), 2.89(s, 2H, -CH2Ph), 1.76(s, 18H, -C(CH3)3), 0.96
(s, 8H, -CH2). 13C{1H} NMR (75.4 Hz, C6D6; δ (ppm)): 189.9 (s,
Zr-Cpincer), 157.6, 144.1, 138.4, 135.7, 130.5, 130.1, 130.1, 129.7,
127.5, 126.5, 126.0, 125.3, 123.8, 119.8 (aryl), 72.3 (s, -OCH2),
58.8 (s, -CH2Ph), 35.7 (s, -C(CH3)3), 31.1 (s, -C(CH3)3), 25.4 (s,
-CH2). Anal. Calcd for C41H50O4Zr: C, 70.54; H, 7.22. Found: C,
70.46; H, 7.06.
Synthesis of [tBuOCHO]Zr(CH2Ph)2 (2). A sealable NMR
tube was charged with [tBuOCO]H3 (1; 46 mg, 0.123 mmol)
and benzene-d6 (0.3 mL) and then frozen (-35 ꢀC). Zr(CH2Ph)4
(56 mg, 0.123 mmol) was dissolved in benzene-d6 (0.3 mL) and
then added to the frozen solution of 1. The resulting mixture was
warmed to 23 ꢀC and then filtered. All volatiles were removed in
vacuo to yield 2 as a yellow crystalline solid (70 mg, 88%). 1H
NMR (300 MHz, C6D6; δ (ppm)): 7.38 (dd, J = 6.1 Hz, 2H, Ar
H), 7.00-7.02 (m, 3H, Ar H), 6.88 (dd, J = 7.6 Hz, 4H, Ar H),
6.79 (dd, J = 6.1 Hz, 4H, Ar H), 6.66-6.76 (m, 5H, Ar H),
6.57-6.59 (m, 1H, Ar H), 5.17 (s, 1H, Ar H), 3.13 (s, 2H,
-CH2Ph), 2.72 (s, 2H, -CH2Ph), 1.63 (s, 18H, -C(CH3)3).
13C{1H} NMR (75.36 Hz, C6D6; δ (ppm)): 159.5, 146.7, 138.0,
137.1, 135.7, 133.3, 133.3, 131.6, 131.1, 130.9, 129.7, 129.7, 129.4,
128.9, 128.9, 128.8, 128.0, 126.0, 124.4, 124.2, 121.0, 113.0 (aryl),
66.5 (s, -CH2Ph), 65.5 (s, -CH2Ph), 35.9 (s, -C(CH3)3), 31.5 (s,
-C(CH3)3). Anal. Calcd for C40H42O2Zr: C, 74.37; H, 6.55.
Found: C, 74.35; H, 6.37.
Synthesis of [tBuOCHO]2Zr (6). A sealable NMR tube or a
vial was charged with [tBuOCO]H3 (1; 46 mg, 0.123 mmol) and
benzene (0.3 mL) and then frozen (-35 ꢀC). Zr(CH2Ph)4 (28 mg,
0.062 mmol) was dissolved in benzene (0.3 mL) and then added to
the frozen solution of 1. The resulting mixture was slowly warmed
to 23 ꢀC. Analytically pure colorless crystalline solid or single crys-
tals of 6 were obtained from the reaction mixture (35 mg, 68%,
based on Zr starting material). Anal. Calcd for C52H56O4Zr: C,
74.69; H, 6.75. Found: C, 74.89; H, 6.60.
Synthesis of [tBuOCHO]ZrCH2Ph(η2-C5H4N)py (7). A seal-
able NMR tube was charged with [tBuOCO]H3 (1; 46 mg, 0.123
mmol) and benzene-d6 (0.3 mL) and then frozen (-35 ꢀC).
Zr(CH2Ph)4 (56 mg, 0.123 mmol) was dissolved in benzene-d6
(0.3 mL) and then added to the frozen solution of 1. The result-
ing mixture was warmed to 23 ꢀC to form 2 in situ. The reaction
solution was frozen again, pyridine (20 mg, 0.246 mmol, 2 equiv)
was added, and the mixture was slowly warmed to 23 ꢀC. The
progress of the reaction was monitored periodically by 1H NMR
spectroscopy to determine the end point. Typically the reaction
was complete after 1-2 h. All volatiles were removed in vacuo,
and the crude product was washed with cold pentanes (3 ꢀ
2 mL) to yield 7 as a colorless crystalline solid (60 mg, 69%). 1H
NMR (300 MHz, C6D6, 10 ꢀC; δ (ppm)): 9.30 (bs, 1H, Ar H),
8.83 (bs, 1H, Ar H), 8.30 (d, J = 5.2 Hz, 2H, Ar H), 7.80 (dd, J =
6.4 Hz, J = 7.3 Hz, 2H, Ar H), 7.61 (bs, 1H, Ar H), 7.39 (d, J =
7.9 Hz, 2H, Ar H), 7.31 (d, J = 2.2 Hz, 2H, Ar H), 7.11 (s, 1H, Ar
H), 7.06 (d, J = 6.4 Hz, 2H, Ar H), 7.00 (s, 1H, Ar H), 6.95 (t,
J = 7.9 Hz, 2H, Ar H), 6.87-6.90 (m, 2H, Ar H), 6.84 (s, 1H,
Ar H), 6.63 (dd, J = 7.6 Hz, J = 7.9 Hz, 2H, Ar H), 6.19 (t, J =
6.4 Hz, 2H, Ar H), 2.79 (bs, 2H, -CH2Ph), 1.30 (s, 18H,
-C(CH3)3). 13C{1H} NMR (75.36 Hz, C6D6, 10 ꢀC; δ (ppm)):
201.1 (s, Zr-Cpincer), 160.0, 155.2, 150.8, 149.9, 146.9, 142.4,
137.7, 137.3, 136.9, 136.5, 133.6, 132.2, 130.5, 129.8, 129.6, 127.5,
126.5, 125.0, 124.7, 123.8, 120.1, 119.8, 117.4 (aryl), 57.8 (s,
-CH2Ph), 35.5 (s, -C(CH3)3), 30.4 (s, -C(CH3)3). Anal. Calcd
for C43H44N2O2Zr: C, 72.53; H, 6.23; N, 3.93. Found: C, 72.42; H,
6.18; N, 3.82.
Synthesis of {tBuOCO]ZrCH2Ph}2 (3). A sealable NMR tube
was charged with [tBuOCO]H3 (1) (46 mg, 0.123 mmol) and
benzene-d6 (0.3 mL) and then frozen (-35 ꢀC). Zr(CH2Ph)4
(56 mg, 0.123 mmol) was dissolved in benzene-d6 (0.3 mL) and
then added to the frozen solution of 1. The resulting mixture was
warmed to 23 ꢀC and then placed in an 80 ꢀC oil bath for 2 h. The
reaction mixture was cooled to room temperature, and all vola-
tiles were removed in vacuo. The crude product was washed two
times with cold pentanes, to yield 3 as a pale yellow crystalline
solid (40 mg, 59%). 1H NMR (300 MHz, C6D6; δ (ppm)): 7.40 (d,
J = 7.0 Hz, 1H, Ar H), 7.12-7.24 (m, 3H, Ar H), 6.79-6.90 (m,
3H, ArH), 6.63 (t, J =7.8 Hz, 1H, ArH), 6.48 (d, J = 7.3Hz, 1H,
Ar H), 6.30 (t, J = 7.5 Hz, 2H, Ar H), 6.20 (t, J = 7.3 Hz, 1H, Ar
H), 6.07 (d, J = 7.0 Hz, 1H, Ar H), 2.87 (d, J = 10.1 Hz, 1H,
-CH2Ph), 2.58 (d, J = 10.1 Hz, 1H, -CH2Ph), 1.78 (s, 9H,
-C(CH3)3), 1.23 (s, 9H, -C(CH3)3). 13C{1H} NMR (75.4 Hz,
C6D6; δ (ppm)): 190.9 (Zr-Cpincer, 158.0, 151.4, 140.3, 140.2,
140.0, 138.7, 137.5, 136.9, 133.1, 132.9, 131.2, 129.4, 129.1, 126.7,
126.8, 125.6, 125.3, 124.7, 121.1 (aryl), 67.0 (s, -CH2Ph), 35.9 (s,
-C(CH3)3), 35.4 (s, -C(CH3)3), 33.5 (s, -C(CH3)3), 30.6 (s,
-C(CH3)3). Anal. Calcd for C33H34O2Zr: C, 71.56; H, 6.19.
Found: C, 71.29; H, 6.10.
Synthesis of [tBuOCO]ZrCH2Ph(PMe3)2 (4-PMe3). A seal-
able NMR tube was charged with [tBuOCO]H3 (1; 46 mg, 0.123
mmol) and benzene-d6 (0.3 mL) and then frozen (-35 ꢀC). Zr-
(CH2Ph)4 (56 mg, 0.123 mmol) was dissolved in benzene-d6
(0.3 mL) and then added to the frozen solution of 1. The result-
ing mixture was warmed to 23 ꢀC, and then PMe3 (13 μL, 0.246
mmol) was added. The reaction mixture was allowed to stand at
23 ꢀC for 3 h to yield yellow blocks of 4-PMe3 (45 mg, 52%). 1H
NMR (300 MHz, C6D6; δ (ppm)): 7.60-7.71 (m, 7H, Ar H), 7.34
(m, J = 7.6 Hz, 3H, Ar H), 7.26 (t, J = 7.6 Hz, 2H, Ar H), 6.96
(t, J = 7.8 Hz, 1H, Ar H), 6.81 (t, J = 7.3 Hz, 1H, Ar H), 2.77 (s,
2H, -CH2Ph), 1.67 (s, 18H, -C(CH3)3), 0.33 (bs, 18H, -P(CH3)3).
13C{1H} NMR (75.36 Hz, C6D6; δ (ppm)): 194.8 (s, Zr-Cpincer),
158.8, 145.2, 142.2, 138.2, 136.1, 130.9, 130.5, 130.1, 128.2, 127.4,
126.0, 124.3, 121.0, 119.9 (aryl), 52.6 (s, -CH2Ph), 35.7 (s,
-C(CH3)3), 30.8 (s, -C(CH3)3), 13.0 (dd, JPC = 13.0 Hz,
-P(CH3)3). 31P{1H} NMR (121 Hz, C6D6; δ (ppm)): 31.54 (bs).
Anal. Calcd for C39H52O2P2Zr: C, 66.35; H, 7.42. Found: C, 66.28;
H, 7.25.
Synthesis of [tBuOCO]Zr(η2-C5H4N)(py)2 (8). A sealable
NMR tube was charged with [tBuOCO]H3 (1; 46 mg, 0.123 mmol)
and benzene-d6 (0.3 mL) and then frozen (-35 ꢀC). Zr(CH2Ph)4
(56 mg, 0.123 mmol) was dissolved in benzene-d6 (0.3 mL) and
then added to the frozen solution of 1. The resulting mixture
was warmed to 23 ꢀC to form 2 in situ. The reaction solution was
frozen again, pyridine (30 mg, 0.369 mmol, 3 equiv) was added,
and the mixture was warmed to 23 ꢀC. The resulting solution was
heated to 50 ꢀC for 1 h. All volatiles were removed in vacuo to
provide a light brown solid that was washed with cold pentanes
(3 ꢀ 2 mL) to yield 8 as a colorless crystalline solid (80 mg, 93%).
1H NMR (300 MHz, C7D8; δ (ppm)): 8.73 (bs, 4H, Ar H), 7.83 (d,
J = 4.9 Hz, 1H, Ar H), 7.73 (t, J = 1.2 Hz, 1H, Ar H), 7.71 (t, J =
1.2 Hz, 1H, Ar H), 7.68 (d, J = 7.6 Hz, 3H, Ar H), 7.27 (dd, J =
1.5 Hz, J = 7.6 Hz, 2H, Ar H), 7.24 (s, 1H, Ar H), 7.19 (dd, J =
7.9 Hz, J = 7.6 Hz, 1H, Ar H), 6.89 (dd, J = 7.9 Hz, J = 7.6 Hz,
2H, Ar H), 6.72 (bs, 1H, Ar H), 6.60 (bs, 2H, Ar H), 6.30 (bs, 4H,
Ar H), 1.37 (s, 18H, -C(CH3)3). 13C{1H} NMR (75.36 Hz, C7D8;
δ (ppm)): 207.9 (s, Zr-Cpy), 188.2 (s, Zr-Cpincer), 157.4, 150.3,
Synthesis of [tBuOCO]ZrCH2Ph(THF)2 (5). A sealable NMR
tube was charged with [tBuOCO]H3 (1; 46 mg, 0.123 mmol)
and benzene-d6 (0.3 mL) and then frozen (-35 ꢀC). Zr(CH2Ph)4
(56 mg, 0.123 mmol) was dissolved in benzene-d6 (0.3 mL) and
then added to the frozen solution of 1. The resulting mixture was
warmed to 23 ꢀC to form 2 in situ. The reaction solution was

6722 Organometallics, Vol. 29, No. 24, 2010
Kuppuswamy et al.
144.1, 142.0, 137.1, 136.8, 136.5, 136.1, 129.4, 129.2, 128.5, 128.4,
126.8, 125.8, 125.6, 124.5, 123.7, 123.5, 119.0 (aryl), 35.0 (s,
-C(CH3)3), 30.2 (s, -C(CH3)3). Anal. Calcd for C41H41N3O2Zr:
C, 70.45; H, 5.91; N, 6.01. Found: C, 70.64; H, 6.09; N, 5.87.
Synthesis of [tBuOCHO]Zr(CH2Ph)2(r-picoline) (9). A seal-
able NMR tube or a vial was charged with [tBuOCO]H3 (1; 46 mg,
0.123 mmol) and benzene-d6 (0.3 mL) and then frozen (-35 ꢀC).
Zr(CH2Ph)4 (56 mg, 0.123 mmol) was dissolved in benzene-d6
(0.3 mL) and then added to the frozen solution of 1. The resulting
mixture was warmed to 23 ꢀC to form 2 in situ. The reaction
solution was frozen again, R-picoline (24 μL, 0.246 mmol, 2 equiv)
was added, and the mixture was warmed to 23 ꢀC. Analytically
pure, dark yellow blocks of 9 precipitated after 10 min from the
reaction mixture, and all volatiles were removed in vacuo for 12 h
to provide a yellow powder (80 mg, 88%). There are two isomers
of 9 (9A, 87% and 9B, 13%) at -25 ꢀC. Data for 9A are as follows.
1H NMR (300 MHz, CDCl3 at -25 ꢀC; δ (ppm)): 8.31 (bs, 1H, Ar
H), 7.50 (dd, J = 4.6 Hz, J = 4.9 Hz, 2H, Ar H), 7.40 (s, 5H, Ar
H), 6.96-7.01 (m, 5H, Ar H), 6.73 (t, J = 8.6 Hz, 3H, Ar H), 6.65
(d, J = 7.0 Hz, 4H, Ar H), 6.41 (dd, J = 6.4 Hz, J = 7.0 Hz, 1H,
Ar H), 6.31 (t, J = 7.3 Hz, 2H, Ar H), 4.40 (s, 1H, Ar H), 2.97 (s,
2H, -CH2Ph), 2.56 (s, 2H, -CH2Ph), 2.19 (bs, 3H, -CH3), 1.75
(s, 18H, -C(CH3)3). 13C{1H} NMR (75.36 Hz, CDCl3 at -25 ꢀC;
δ (ppm)): 158.5, 145.3, 139.7, 136.9, 133.0, 131.5, 129.9, 129.2,
128.8, 128.5, 128.4, 128.0, 127.4, 127.3, 125.8, 125.4, 121.2, 120.7,
120.6, 120.1, 113.5 (aryl), 68.9 (s, -CH2Ph), 68.1 (s, -CH2Ph),
35.6 (s, -C(CH3)3), 31.2 (s, -C(CH3)3), 24.6 (s, -CH3). Data
for 9B are as follows. 1H NMR (300 MHz, CDCl3 at -25 ꢀC; δ
(ppm)): 4.52 (s, 1H, Ar H), 3.12 (bs, 3H, -CH3), 2.73 (s, 2H,
-CH2Ph), 2.63 (s, 2H, -CH2Ph), 1.75 (s, 18H, -C(CH3)3). Anal.
Calcd for C46H49NO2Zr: C, 74.75; H, 6.68; N, 1.90. Found: C,
74.59; H, 6.57; N, 1.92.
1H NMR (300 MHz, benzene-d6; δ (ppm)): 8.98 (bs, 1H, Ar H),
7.89 (bs, 1H, Ar H), 7.41 (d, J = 5.8 Hz, 1H, Ar H), 7.38 (d, J =
5.8 Hz, 1H, Ar H), 7.34 (t, J = 1.8 Hz, 2H, Ar H), 7.32 (d, J =
1.8 Hz, 1H, Ar H), 7.22 (dd, J = 1.5 Hz, J = 1.8 Hz, 2H, Ar H),
7.14 (dd, J = 6.7 Hz, J = 7.3 Hz, 1H, Ar H), 6.81-6.91 (m, 5H,
Ar H), 6.47 (d, J = 7.3 Hz, 1H, Ar H), 6.15 (dd, J = 6.7 Hz, J =
7.0 Hz, 1H, Ar H), 2.82 (s, 2H, -CH2), 1.88 (bs, 3H, -CH3),
1.05 (s, 18H, -C(CH3)3). 13C{1H} NMR (75.36 Hz, benzene-d6;
δ (ppm)): 199.8 (s, Zr-CR-picoline), 167.4, 160.6, 154.4, 153.7,
147.2, 146.4, 139.0, 138.0, 137.8, 133.4, 133.3, 132.2, 132.1,
129.4, 129.3, 128.9, 128.5, 128.2, 127.6, 127.5, 127.4, 125.5,
124.3, 123.0, 119.3, 117.2, 115.3 (aryl), 43.2(s, -CH2), 35.3 (s,
-C(CH3)3), 30.2 (s, -C(CH3)3), 21.8 (s, -CH3).
NMR Tube Reaction: Formation of [tBuOCO]ZrCH2Ph(PMe2Ph)
(4-PMe2Ph). A sealable NMR tube was charged with [tBuOCO]H3
(1; 23 mg, 0.062 mmol) and benzene-d6 (0.3 mL) and then frozen
(-35 ꢀC). Zr(CH2Ph)4 (28 mg, 0.062 mmol) was dissolved in
benzene-d6 (0.3 mL) and then added to the frozen solution of 1.
The resulting mixture was warmed to 23 ꢀC, and PMe2Ph (17.5 μL,
0.123 mmol) was then added, and the mixture was allowed to stand
at 23 ꢀC for 10 min. 1H NMR (300 MHz, C6D6; δ (ppm)): 7.75 (d,
J = 7.6 Hz, 2H, Ar H), 7.66 (dd, J = 4.5 Hz, J = 1.5 Hz, 2H, Ar
H), 7.37 (overlapping doublets, J = 7.5 Hz, 4H, Ar H), 7.1 - 6.7 (m,
Ar H), 6.53 (t, J = 7.3 Hz, 1H, Ar H), 2.55 (s, 2H, -CH2Ph), 1.52
(s, 18H, -C(CH3)3), 0.60 (bs, 6H, -P(CH3)2Ph). 13C{1H} NMR
(75.36 Hz, C6D6; δ (ppm)): 194.6 (s, Zr-Cpincer), 158.7, 145.2,
141.3, 137.8, 136.4, 131.1, 129.7, 129.2, 128.9, 127.3, 125.8, 124.4,
120.0 (aryl), 53.9 (s, -CH2Ph), 35.6 (s, -C(CH3)3), 30.9 (s,
-C(CH3)3), 12.2 (bs, -P(CH3)2Ph). Note: the aromatic carbons of
the Zr-PMe2Ph group are broadened due to exchange with free
PMe2Ph and could not be assigned. 31P{1H} NMR (121 Hz, C6D6;
δ (ppm)): -18.6 (bs).
Synthesis of [tBuOCHO]Zr(η2(N,C)-6-Me-pyridyl)(η2(N,C-
CH2)-pyrid-2-yl) (10). A sealable NMR tube or a vial was
charged with [tBuOCO]H3 (1; 46 mg, 0.123 mmol) and ben-
zene-d6 (0.3 mL) and then frozen (-35 ꢀC). Zr(CH2Ph)4 (56 mg,
0.123 mmol) was dissolved in benzene-d6 (0.3 mL) and then
added to the frozen solution of 1. The resulting mixture was
warmed to 23 ꢀC to form 2 in situ. The reaction solution was
frozen again, R-picoline (24 μL, 0.246 mmol, 2 equiv) was added,
and the mixture was warmed to 23 ꢀC. The reaction mixture was
allowed to stand or was stirred at room temperature for 12 h to
form 10. All volatiles were removed in vacuo, and the crude
compound was recrystallized from hot pentanes (50 mg, 65%).
Acknowledgment. A.S.V. thanks UF, NSF CAREER
(No. CHE-0748408), the Camille and Henry Dreyfus Foun-
dation, and The Alfred P. Sloan Foundation for financial
support of this work. K.A.A. thanks UF and the NSF (No.
CHE-0821346) for funding the purchase of X-ray equipment.
Supporting Information Available: Text, figures, tables, and
CIF files giving full experimental procedures, NMR spectra,
and X-ray crystallographic details. This material is available
free of charge via the Internet at http://pubs.acs.org.