Synthesis, structure, and insertion reactivity of zirconium and hafnium amidate benzyl complexes

Article abstract of DOI:10.1021/om100424j

A series of amidate-ligated dibenzyl zirconium and hafnium complexes are accessed through protonolysis reactions of the amide proligands 2,6-dimethylphenylpivaloylamide, [^DMP(NO)^tBu]H (3), and 1,3-bis(1-adamantylamide)-2,2-dimethylpropane, ^Ad[O₂N ₂]H₂ (5), with Zr(CH₂Ph)₄ or Hf(CH₂Ph)₄. The resulting dibenzyl complexes [ ^DMP(NO)^tBu]₂Zr(CH₂Ph)₂ (4), ^Ad[O₂N₂]Zr(CH₂Ph) ₂(THF) (6), and ^Ad[O₂N₂]Hf(CH ₂Ph)₂(THF) (7) are structurally characterized. Insertion reactions of 4 with isocyanides are investigated, resulting in the formation of an η²-iminoacyl species, [^DMP(NO)^tBu] ₂Zr(η²-2,6-Me₂C₆H ₃N=CCH₂Ph)₂ (8), which undergoes thermal C=C coupling to form an enediamido complex, [^DMP(NO)^tBu] ₂Zr(η⁴-ArNC(CH₂Ph)=C(CH₂Ph)NAr) (Ar = 2,6-Me₂C₆H₃) (9). Analogous insertion of ^tBuN≡C into the Zr-C bonds of 4 results in the formation of a vinylamido complex, [^DMP(NO)^tBu]₂Zr(N( ^tBu)CH=CHPh)₂ (10), through a presumed 1,2-hydrogen migration mechanism from an iminoacyl intermediate similar to 8. Complexes 8 and 9 are also structurally characterized.

Full text of DOI:10.1021/om100424j

3546 Organometallics 2010, 29, 3546–3555
DOI: 10.1021/om100424j
Synthesis, Structure, and Insertion Reactivity of Zirconium and Hafnium
Amidate Benzyl Complexes
Robert K. Thomson and Laurel L. Schafer*
Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver,
British Columbia, Canada, V6T 1Z3
Received May 5, 2010
A series of amidate-ligated dibenzyl zirconium and hafnium complexes are accessed through
protonolysis reactions of the amide proligands 2,6-dimethylphenylpivaloylamide, [DMP(NO)tBu]H
(3), and 1,3-bis(1-adamantylamide)-2,2-dimethylpropane, Ad[O2N2]H2 (5), with Zr(CH2Ph)4 or
Hf(CH2Ph)4. The resulting dibenzyl complexes [DMP(NO)tBu]2Zr(CH2Ph)2 (4), Ad[O2N2]Zr(CH2Ph)2-
(THF) (6), and Ad[O2N2]Hf(CH2Ph)2(THF) (7) are structurally characterized. Insertion reactions
of 4 with isocyanides are investigated, resulting in the formation of an η2-iminoacyl species,
[
DMP(NO)tBu]2Zr(η2-2,6-Me2C6H3NdCCH2Ph)2 (8), which undergoes thermal CdC coupling to
form an enediamido complex, [DMP(NO)tBu]2Zr(η4-ArNC(CH2Ph)dC(CH2Ph)NAr) (Ar = 2,6-
Me2C6H3) (9). Analogous insertion of tBuNtC into the Zr-C bonds of 4 results in the formation of a
vinylamido complex, [DMP(NO)tBu]2Zr(N(tBu)CHdCHPh)2 (10), through a presumed 1,2-hydrogen
migration mechanism from an iminoacyl intermediate similar to 8. Complexes 8 and 9 are also
structurally characterized.
Introduction
been investigating amidate complexes of the group 4 metals
for various catalytic applications.2,3 Amidate complexes of a
variety of metals have been prepared and fully charac-
terized.2-4 These amidate ligands can chelate hard early
transition metals as σ-bonded four-electron donors. Thus,
a hallmark of this class of complexes is the generation of very
electropositive, sterically accessible metal centers. This is
due to the nonsymmetric nature of amidate binding and
the tight bite angles (approximately 60°) imposed by the four-
membered metallacycle. Two closely related ligand systems
to amidates are the amidinate5 and guanidinate6 ligands,
which have been widely studied for a broad range of cata-
lytic and stoichiometric organometallic transformations.
Selective C-C bond formation remains a challenging
transformation for the rationally designed synthesis of tar-
geted compounds and/or materials. Organometallic chemis-
try has played an extremely important role in the selective
preparation of C-C bonds, due to the prevalence of transi-
tion metal-carbon bonded species as key intermediates in
such transformations.1 Our research group and others have
*To whom correspondence should be addressed. E-mail: schafer@
chem.ubc.ca.
(1) Selected recent reviews include: (a) Colby, D. A.; Bergman, R. G.;
Ellman, J. A. Chem. Rev. 2010, 110, 624–655. (b) Doyle, M. P.; Duffy, R.;
Ratnikov, M.; Zhou, L. Chem. Rev. 2010, 110, 704–724. (c) Gunay, A.;
Theopold, K. H. Chem. Rev. 2010, 110, 1060–1081. (d) Johansson, C. C. C.;
Colacot, T. J. Angew. Chem., Int. Ed. 2010, 49, 676–707. (e) Ashenhurst,
J. A. Chem. Soc. Rev. 2010, 39, 540–548.
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C.; Thomson, R. K.; Gillon, B.; Patrick, B. O.; Schafer, L. L. Chem.
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B. O.; Schafer, L. L. Chem.;Eur. J. 2007, 13, 2012–2022. (d) Wood, M. C.;
Leitch, D. C.; Yeung, C. S.; Kozak, J. A.; Schafer, L. L. Angew. Chem., Int.
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pubs.acs.org/Organometallics
Published on Web 07/15/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 16, 2010 3547
More recently, ureate ligand systems have also shown com-
plementary reactivity to the amidate-bound complexes.7
Notably, stoichiometric insertion studies of C-E multiple
bonds (E = N, O, S) into amidinate and guanidinate organo-
metallic species have shown interesting reactivity profiles
in comparison to those of other group 4 complexes.5,6,8
These results on related ligand sets, coupled with our ob-
servations of unique catalytic activity that is accessible with
amidate complexes,2,3,9 suggest that complementary reacti-
vity may be observed with amidate-supported group 4
organometallic complexes.
The synthesis of amidate-supported amido complexes and
homoleptic amidate species via protonolysis with homolep-
tic titanium, zirconium, and yttrium amido starting materi-
als is very facile and has been previously reported.2h,3c,10-12
Furthermore, organometallic dibenzyl complexes of zirco-
nium and hafnium can be synthesized through protonolysis
using two equivalents of proligand, from easily prepared
M(CH2Ph)4 starting materials (M = Zr, Hf).13 Notably,
amidate-supported titanium and zirconium benzyl com-
plexes have been prepared by Scott and co-workers using
this protonolysis approach.3e
We communicated the first group 4 amidate alkyl com-
plexes 1 and 2, which are prepared via protonolysis using two
equivalents of the proligand 2,6-dimethyphenylbenzamide
([DMP(NO)Ph]H) and Hf(CH2Ph)4.14 While the THF adduct
1 has been structurally characterized, the unsolvated species
2 (eq 1) could be observed in the solution phase, but could be
obtained only as an amorphous powder in the solid state.14
Figure 1. ORTEP depiction of the solid-state molecular struc-
ture of [DMP(NO)tBu]2Zr(CH2Ph)2, 4 (ellipsoids at 30% probabi-
lity, hydrogens omitted).
amidate ligands in the equatorial plane.14 Interestingly, an
unusual and sterically unfavorable cis-N geometry of the
amidate ligands is observed in the solid-state molecular
structure, presumably due to stabilization by π-stacking
interactions between the 2,6-dimethylphenyl units of the
amidate ligands. In complex 1, the benzyl ligands are arranged
in a trans fashion, in contrast to previously characterized
seven-coordinate amidate-supported bis(amido) complexes,
which have the amido ligands cis to each other.2d As de-
scribed above, the coordinated THF ligand is labile in
1
solution, as observed by H NMR spectroscopy, resulting
in an equilibrium with the unsolvated species 2 (eq 1). This
complex displays solvatochromic behavior and changes
from an orange solution to a yellow solution upon removal
of the THF solvent under vacuum.14
While solid-state molecular structural analysis of the six-
coordinate hafnium complex 2 was not possible, the pro-
posed structure, based upon solution phase behavior, is a
pseudo-octahedral species with a cis arrangement of the
benzyl ligands, exhibiting overall C2 symmetry. Such a C2
symmetric structure can be characterized in the solid state
for the related six-coordinate zirconium dibenzyl complex
Building upon these preliminary results, here we discuss
the synthesis and characterization of new organometallic
zirconium and hafnium amidate complexes and their sub-
sequent insertion reactivity with alkyl and aryl isocyanides,
which leads to both rearrangement and C-C coupling
reactions.
[
DMP(NO)tBu]2Zr(CH2Ph)2 (4, Figure 1). This compound is
synthesized in 80% yield using the synthetic protocol pre-
sented in eq 2.
Results and Discussion
Synthesis and Characterization of Dibenzyl Complexes.
Complex 1 has been fully characterized, and this seven-
coordinate pseudo-pentagonal bipyramidal species has the
Dibenzyl complex 4 is isolated as a bright yellow powder
and can be readily recrystallized from pentane. The solid-
state molecular structure is shown in Figure 1. Selected bond
lengths and angles are collected in Table 1, and crystal-
lographic data in Table 2. Solution phase behavior of 4 is
consistent with C2 symmetry, as indicated by single reso-
nances for the amidate tert-butyl and aryl methyl groups at δ
0.91 and 2.05, respectively. This suggests free rotation about
the N-Cipso bonds of the 2,6-dimethylphenyl substituents.
Free rotation of the benzyl groups is also observed by a single
resonance at δ 2.24. Variable-temperature 1H NMR experi-
ments on 4 do not indicate any slow fluxional processes that
can be arrested at low temperature (spectra were recorded as
low as -80 °C). It is important to note that even when THF is
used as the reaction solvent, 4does not form a seven-coordinate
(7) (a) Leitch, D. C.; Beard, J. D.; Thomson, R. K.; Wright, V. A.;
Patrick, B. O.; Schafer, L. L. Eur. J. Inorg. Chem. 2009, 2691–2701.
(b) Leitch, D. C.; Dunbar, C. R.; Payne, P. R.; Schafer, L. L. J. Am. Chem.
Soc. 2009, 131, 18246–18247.
(8) Ong, T.-G.; Wood, D.; Yap, G. P. A.; Richeson, D. S. Organo-
metallics 2002, 21, 1–3.
(9) Bexrud, J. A.; Eisenberger, P.; Leitch, D. C.; Payne, P. R.;
Schafer, L. L. J. Am. Chem. Soc. 2009, 131, 2116–2118.
(10) Bexrud, J. A.; Schafer, L. L. Dalton Trans. 2010, 39, 361–363.
(11) Stanlake, L. J. E.; Beard, J. D.; Schafer, L. L. Inorg. Chem. 2008,
47, 8062–8068.
(12) Thomson, R. K.; Zahariev, F. E.; Zhang, Z.; Patrick, B. O.;
Wang, Y. A.; Schafer, L. L. Inorg. Chem. 2005, 44, 8680–8689.
(13) Zucchini, U.; Albizzati, E.; Giannini, U. J. Organomet. Chem.
1971, 26, 357–372.
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2005, 83, 1037–1042.

3548 Organometallics, Vol. 29, No. 16, 2010
Thomson and Schafer
˚
Table 1. Selected Bond Lengths (A) and Angles (deg) for Dibenzyl Complexes 4, 6, and 7
4
6
7
Zr1-O1
2.099(1)
2.108(1)
2.284(1)
2.288(1)
2.244(2)
2.239(2)
95.75(5)
142.16(5)
82.98(6)
139.85(5)
97.18(8)
103.8(1)
105.1(1)
58.78(5)
112.55(1)
Zr1-O1
2.208(2)
2.196(2)
2.289(2)
2.183(2)
2.187(2)
2.358(3)
2.366(3)
161.62(7)
82.46(6)
81.29(6)
59.84(7)
59.68(7)
77.74(7)
165.6(1)
113.5(2)
116.6(2)
113.2(2)
Hf1-O1
2.193(2)
2.181(2)
2.256(2)
2.166(2)
2.174(2)
2.341(4)
2.357(4)
160.35(8)
81.68(8)
81.14(8)
60.28(9)
60.00(9)
78.13(9)
168.7(1)
115.1(2)
114.2(2)
112.2(3)
Zr1-O2
Zr1-O2
Hf1-O2
Zr1-N1
Zr1-O3
Hf1-O3
Zr1-N2
Zr1-N1
Hf1-N1
Zr1-C27
Zr1-N2
Hf1-N2
Zr1-C34
Zr1-C28
Hf1-C28
O1-Zr1-O2
N1-Zr1-N2
N1-Zr1-C27
O1-Zr1-C27
C27-Zr1-C34
C28-C27-Zr1
C35-C34-Zr1
O1-Zr1-N1
O1-C1-N1
Zr1-C35
Hf1-C35
O1-Zr1-O2
O1-Zr1-O3
O2-Zr1-O3
O2-Zr1-N2
O1-Zr1-N1
N2-Zr1-N1
C28-Zr1-C35
C29-C28-Zr1
C36-C35-Zr1
O1-C1-N1
O1-Hf1-O2
O1-Hf1-O3
O2-Hf1-O3
O2-Hf1-N2
O1-Hf1-N1
N2-Hf1-N1
C28-Hf1-C35
C29-C28-Hf1
C36-C35-Hf1
O1-C1-N1
Table 2. Crystallographic Data for Complexes 4, 6, 7, 8, and 9
4
6
7
8
9
empirical formula
fw
cryst syst
C
682.04
triclinic
P1 (#2)
9.719(2)
12.169(3)
16.612(4)
72.624(10)
85.866(11)
76.118(10)
1820.3(7)
2
40H50N2O2Zr
C45H62N2O3Zr
770.19
triclinic
C45H62N2O3Hf
857.46
triclinic
C58H68N4O2Zr
944.38
monoclinic
P21/c
19.475(5)
12.736(5)
20.838(5)
90
90.379(5)
90
C58H68N4O2Zr
944.38
monoclinic
P21/n
13.036(4)
22.774(7)
16.957(5)
90
94.825(10)
90
space group
˚
P1 (#2)
P1 (#2)
a (A)
8.8174(7)
11.5483(9)
21.155(3)
86.984(10)
82.894(9)
69.810(6)
2006.2(3)
2
11.4687(12)
17.4135(18)
22.171(2)
103.5860(10)
94.322(2)
109.066(3)
4011.6(7)
4
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
5168(3)
4
1.214
5016(3)
4
1.250
Dc (g cm-3
T (K)
)
1.244
173 ( 1
1.275
173 ( 1
1.420
173 ( 1
3
173 ( 1
173 ( 1
solvent/color
(h, k, l)
pentane/yellow
-16 e h e 14
-19 e k e 17
-26 e l e 24
720
1.28-36.55
0.337
52 902
hexanes/yellow
-11 e h e 11
-15 e k e 15
-26 e l e 27
820
2.11-27.88
0.315
17 662
hexanes/yellow
-14 e h e 12
-22 e k e 22
-27 e l e 26
1768
2.27-27.88
0.264
35 599
pentane/colorless
-20 e h e 20
-13 e k e 13
-22 e l e 18
2000
toluene/yellow
-18 e h e 18
-31 e k e 31
-23 e l e 23
2000
F(000)
θ range (deg)
2.14-22.65
0.257
48 486
1.50-30.27
0.265
64 748
linear abs coeff (mm-1
total no. of reflns collected
)
no. of unique reflns (F >4σ(F ))
no. of obsd reflns
11 233
15 411
7282
8114
13 738
16 302
4552
6785
9945
14 747
Rint
R1, wR2 (I >2σ(I))
GoF
0.0458
0.0707, 0.1359
1.044
0.0461
0.0494, 0.1127
1.087
0.0407
0.0368, 0.0749
1.068
0.0708
0.1215, 0.2504
1.055
0.0645
0.0888, 0.1549
1.033
3
peak/hole (e/A )
˚
0.610, -0.515
1.009, -1.023
1.614, -1.557
2.337, -1.216
0.647, -0.901
complex analogous to 1. In comparison to the hafnium
complex 1, 4 is significantly more photochemically and
thermally prone to degradation.
The structure of 4 is C2 symmetric, with the nitrogen
donors of the amidate ligands trans to each other. While
η1-coordination of the benzyl group is obvious for 1,14 the
hapticity of the benzyl group in 4 is less clear. The typical
parameters used to evaluate the hapticity of benzyl ligands
are (1) the bond angle formed by the ipso carbon of the benzyl
group, the benzylic carbon, and the metal center,15 (2) the
chemical shift of the ortho protons of the benzyl group,16 and
(3) the sum of the van der Waals radii of the metal center and
the ipso carbon.17 In this case, the bond angles at the benzylic
carbon atoms in 4 are 103.8(1)° and 105.1(1)° and are
considerably more acute than the 122.3(4)° and 124.3(4)°
bond angles for 1, but still obtuse compared to previously
observed angles near 90°.16b,17b,18 While a wide variation in
this bond angle has been observed to be dependent upon the
steric and electronic requirements of the metal center,19 the
bond angles in 4 are best classified as intermediate between
η1- and η2-hapticity for the benzyl group.16a A similar
“intermediate” hapticity has been reported for a β-diketimi-
nate tribenzyl species, (TTP)Zr(CH2Ph)3 (TTP = p-tolyl-
NC(CH3)CHC(CH3)N-p-tolyl),20 and the Cp complex
(15) Dryden, N. H.; Legzdins, P.; Trotter, J.; Yee, V. C. Organome-
tallics 1991, 10, 2857–2870.
(16) (a) Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell,
I. P.; Huffman, J. C. Organometallics 1985, 4, 902–908. (b) Dryden, N. H.;
Legzdins, P.; Phillips, E. C.; Trotter, J.; Yee, V. C. Organometallics 1990, 9,
882–884.
(17) (a) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M.
Advanced Inorganic Chemistry, 6th ed.; John Wiley & Sons, Inc.: Toronto,
1999. (b) Legzdins, P.; Phillips, E. C.; Trotter, J.; Yee, V. C.; Einstein, F. W. B.;
Jones, R. H. Organometallics 1991, 10, 986–1002.
(18) Warren, T. H.; Schrock, R. R.; Davis, W. M. Organometallics
1996, 15, 562–569.
(19) Carmona, E.; Marin, J. M.; Paneque, M.; Poveda, M. L. Orga-
nometallics 1987, 6, 1757–1765.
(20) Qian, B.; Scanlon, W. J.; Smith, M. R. Organometallics 1999, 18,
1693–1698.

Article
Organometallics, Vol. 29, No. 16, 2010 3549
CpZr(CH2Ph)3, which has a benzyl ligand with a bond angle
of 94.5°.21
performing these protonolysis reactions with proligand 5.
The extra entropic driving force provided by the chelate
effect of the tetradentate ligand set can result in the forma-
tion of homoleptic species as byproducts in these reactions,
even when performed in a strict 1:1 stoichiometry. The
extremely low solubility of 5 in nearly all common solvents
makes the slow addition of a solution of 5 to a solution of
M(CH2Ph)4 unfeasible, and addition of cold solvent to an
intimate mixture of 5 and M(CH2Ph)4 still results in the
formation of large quantities of homoleptic byproducts. To
circumvent this problem, the slow addition of 5 to a THF
solution of M(CH2Ph)4 via solid addition funnel is required.
This results in high yields of the desired dibenzyl species as
bright yellow (Ad[O2N2]Zr(CH2Ph)2(THF), 6) and pale yel-
low (Ad[O2N2]Hf(CH2Ph)2(THF), 7) powders.
Given the acute angles formed at the benzylic carbon
atoms and the overall C2 symmetry of 4, it is surprising that
the diastereotopic benzylic protons do not manifest as two
different signals. Fluxional processes are likely responsible
for this observation. Interconversion between η1- and η2-
coordination modes of the benzyl ligands is possible; how-
ever, variable-temperature 1H NMR experiments do not
indicate any observable changes at low temperature. With
η2-benzyl ligands, it is often seen that the ortho protons are
shifted to higher field, which can be attributed to significant
π-donation to the metal center.16a For 4, no arene resonances
are observedupfield of approximatelyδ 6.8, which is generally
considered the cutoff for η2-behavior,16a supporting average
η1-binding in the solution phase. It is also possible that the
amidate ligands undergo isomerization in solution through a
κ1-O-bound amidate intermediate that cannot be observed,
As illustrated in eq 3, these complexes are stabilized by
THF in solution, with signals for coordinated THF appear-
ing at δ 1.33 and 3.99 for 7. The 1H NMR spectra for 6 and 7
are nearly identical, suggesting that they are isostructural.
Solution phase C2v geometry is supported by the high sym-
1
even when using low-temperature H NMR spectroscopic
experiments. However, this isomerization process seems less
probable for these dibenzyl complexes, as the benzyl ligands
offer less electronic stabilization than the amido ligands in the
bis(amidate) bis(amido) complexes reported previously.12
Inspection of the distances between Zr1 and the ipso
1
metry of the H NMR spectra of 6 and 7, with a single
resonance observed for the amidate ligand tether methyl
groups of 7 at δ 0.86, suggesting a tether ring-flipping process
on the NMR time scale. Likewise, single resonances for the
benzylic and tether methylene protons are observed at δ 1.73
and 3.19, respectively. The protons of the bulky adamantyl
groups appear as three resonances in a 2:1:2 ratio at δ 1.66,
1.95, and 2.09.
˚
˚
carbon atoms (C28-2.97 A and C35-2.98 A) shows that
they fall well outside the distance expected for formal Zr-C
16a,22
˚
bonds, which are usually approximately 2.2-2.4 A.
However, weak noncovalent interactions between zirconium
and the ipso benzyl carbons are present, since the Zr1-C28
and Zr1-C35 distances fall within the sum of the van der
Similar to complexes 1, 2, and 4, complexes 6 and 7 do not
exhibit any solution behavior suggestive of η2-coordination
of the benzyl groups. Free rotation of the benzyl groups
about their M-C bonds in solution is facile and cannot be
arrested during low-temperature 1H NMR experiments.
Interestingly, unlike 1, the coordinated THF ligand in 6
and 7 is not labile in solution. Since these THF adducts are
formally 14-electron species, the coordination of THF helps
satisfy the electronic requirements of the metal centers in
these species. The lack of THF lability may be due to the fact
that this tethered bis(amidate) ligand does not offer sufficient
flexibility to assume a more traditional pseudo-octahedral
geometry upon loss of THF. Verification of the planar bind-
ing geometry of the bis(amidate) ligand in complexes 6 and 7
is given in their solid-state molecular structures in Figure 2,
with selected bond lengths and angles presented in Table 1.
The metrical parameters given in Table 1 are unexcep-
tional and show that 6 demonstrates very similar bond
lengths and angles to 1 and 4, where the amidate unit bite
angle in all of these complexes is approximately 60°. The
bond angle between the trans benzyl groups is 165.6(1)°,
which is slightly contracted in comparison to 1, where this
angle is 169.8(2)°.14 The highly exposed nature of the zirco-
nium center in 6 is apparent in Figure 2, where the bulky
adamantyl groups effectively shield the metal center from the
sides, but leave the metal center accessible from the top,
bottom, and front. As observed previously for 1, the THF
coordinates in the equatorial position between the two
benzyl groups, generating a pentagonal bipyramidal struc-
ture. The bond angles at the benzylic carbon atoms are
obtuse, indicating η1-binding of the benzyl ligands to Zr
(C(29)-C(28)-Zr(1)=113.5(2)° and C(36)-C(35)-Zr(1)=
116.6(2)°). The overall symmetry of 6 is Cs; however, rapid
ring-flipping of the amidate tether and free rotation of the
23
˚
Waals radii of Zr and C (∼3.7 A). These data taken
together suggest a degree of η2-character for the benzyl
ligands in 4 in the solid state, which may be due to crystal
packing, especially considering that, in the solution phase,
data are indicative of η1-hapticity.
Tethered Tetradentate Amidate Dibenzyl Complexes. In
contrast to the titanium bis(amidate) bis(amido) complexes
described previously, the dibenzyl complexes 1, 2, and 4 do
not appear to undergo amidate ligand isomerization as
readily.12 This reduces the need for a tethered bis(amidate)
ligand to control geometric isomerization. However, the
ability to access a trans-type pentagonal bipyramidal geo-
metry for the hafnium dibenzyl complex 1 indicates that the
tethered proligand 1,3-bis(1-adamantylamide)-2,2-dimethyl-
propane, Ad[O2N2]H2 (5), should be suitable for stabilizing
bis(alkyl) complexes of zirconium and hafnium, as this
ligand should preferentially bind in a planar fashion.2d,7a
Synthesis of the zirconium (6) and hafnium (7) dibenzyl com-
plexes of proligand 5 can be accomplished as shown in eq 3.
While this reaction is completely analogous to the synthe-
sis of 1, 2, and 4, additional care must be taken when
(21) Scholz, J.; Rehbaum, F.; Thiele, K.-H.; Goddard, R.; Betz, P.;
Krueger, C. J. Organomet. Chem. 1993, 443, 93–99.
(22) Jordan, R. F.; LaPointe, R. E.; Bajgur, C. S.; Echols, S. F.;
Willett, R. J. Am. Chem. Soc. 1987, 109, 4111–4113.
(23) Bondi, A. J. Phys. Chem. 1964, 68, 441–451.

3550 Organometallics, Vol. 29, No. 16, 2010
Thomson and Schafer
Figure 2. ORTEP depictions of solid-state molecular structures of Ad[O2N2]M(CH2Ph)2(THF), M = Zr (6), Hf (7) (ellipsoids at 30%
probability).
benzyl groups about the Zr-C linkages give rise to the
observed C2v solution phase structure.
Single crystals of the hafnium congener 7 were also grown
from pentane (Figure 2). Aside from a slight contraction of
the bond distances between the ligand donor atoms and the
metal center, 7 is completely isostructural to 6. These bond
length reductions can be attributed to hafnium relativistic
Figure 3. Common geometric isomers of bis(η2-iminoacyl)
complexes.
effects, giving rise to slightly decreased bond lengths in the 5d
congener when compared to the 4d complex.17a
Insertion Reactions of Isocyanides. Insertion of isocyanides
into metal-carbon bonds is a well-known process that has
been extensively studied; therefore, it is an attractive place to
begin fundamental investigations of amidate-supported
group 4 organometallic species.24 The insertion of isocya-
nides into group 4 metal-carbon bonds is known to proceed
through initial coordination of the carbon lone pair, fol-
lowed by rapid insertion into the adjacent M-C bond.24,25
This results in the formation of an iminoacyl complex, where
the NdC bond is usually coordinated to the metal center in
an η2-fashion.26 Unlike the reversible insertion of CO to
form acyl species, the formation of iminoacyl complexes is
irreversible, resulting in complexes that are stable to ther-
mally induced deinsertion processes.24
groups, each experiencing hindered rotation about the
N-Cipso bond. This is possible in a C2 symmetric species,
where the amidate ligand aryl groups and the inserted iso-
cyanide aryl groups experience hindered rotation on the NMR
time scale. Also, the notable upfield chemical shift of δ 0.95 for
an aryl methyl substituent may be due to significant arene ring
current induced deshielding from the adjacent group. Thus, on
the basis of these spectroscopic data the insertion product 8 is
proposed to have the structure shown in eq 4.
The insertion of 2,6-dimethylphenyl isocyanide was in-
vestigated with zirconium dibenzyl complex 4. Upon addi-
tion of two equivalents of isocyanide to a solution of 4 in
C6D6 in a J-Young NMR tube, the solution is observed to
immediately change from bright yellow to colorless. The 1H
NMR spectrum of the reaction mixture indicates formation
of a single product in quantitative yield; however on a
preparative scale the white powdery material can be isolated
only in 52% yield. Successful insertion of the isocyanide
moieties is suggested by the appearance of doublets at δ 3.35
and 3.59 corresponding to diastereotopic benzylic protons.
The bis(iminoacyl) complex 8 ([DMP(NO)tBu]2Zr(η2-2,6-
Me2C6H3NdCCH2Ph)2) is nonfluxional in solution, where
the presence of four singlets of equal intensity at δ 0.95, 1.92,
2.12, and 2.62 is suggestive of two unique 2,6-dimethylphenyl
The η2-binding mode in eq 4 is also suggested by 13C NMR
spectroscopic data, where the resonance at δ 250.6 is char-
acteristic of η2-coordinated iminoacyl carbons.24,25 The
most commonly observed geometric isomers of bis η2-imi-
noacyls are best described as pseudo-tetrahedral in either a
head-to-head (A) or head-to-tail (B) arrangement, as shown
in Figure 3.24,26b Interconversion between these two forms
can occur, and in some cases has been observed spectros-
copically.26d The solution phase structure of 8 appears static
at room temperature, as observed by 1H NMR spectroscopy.
Due to the observed C2 symmetry, 8 is consistent with geo-
metric isomer B, where the ancillary ligands (L) are κ2-
amidate groups. Variable-temperature 1H NMR experi-
ments suggest that interconversion between forms A and B
is not particularly facile, as no change in the spectrum is
observed over the range of temperatures (-40 to 90 °C).
The solid-state molecular structure of 8 is shown in Figure 4.
Selected bond distances and angles are presented in Table 3.
The presence of η2-ligation is confirmed by Zr-N and Zr-C
bond lengths that are nearly identical for each of the imi-
(24) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059–1079.
(25) Scott, M. J.; Lippard, S. J. Organometallics 1997, 16, 5857–5868.
(26) (a) Spencer, L. P.; Fryzuk, M. D. J. Organomet. Chem. 2005, 690,
5788–5803. (b) Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.; Kobriger,
L.; Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Folting, K.; Huffman,
J. C. J. Am. Chem. Soc. 1987, 109, 390–402. (c) Giannini, L.; Caselli, A.;
Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.; Re, N.; Sgamellotti, A.
J. Am. Chem. Soc. 1997, 119, 9198–9210. (d) Thorn, M. G.; Lee, J.;
Fanwick, P. E.; Rothwell, I. P. J. Chem. Soc., Dalton Trans. 2002, 3398–
3405. (e) Sebastian, A.; Royo, P.; Gomez-Sal, P.; Ramirez de Arellano, C.
Eur. J. Inorg. Chem. 2004, 3814–3821.
˚
˚
noacyl groups (Zr1-N3=2.243(6) A, Zr1-C3=2.252(7) A

Article
Organometallics, Vol. 29, No. 16, 2010 3551
˚
˚
and Zr1-N4 = 2.246(6) A, Zr1-C4 = 2.249(8) A). As
expected, the iminoacyl NdC bond lengths are consistent
energy of the π*CN orbital.29 Furthermore, coupling in this
case is possible only if the iminoacyl ligands rearrange to the
“head-to-head isomer A (Figure 3). Accordingly, C-C
coupling is more readily achieved with electron-withdrawing
groups on the iminoacyl moiety, such as aryl substituents,
and less readily achieved with electron-donating alkyl groups
on the iminoacyl unit.29 The xylyl groups in 8 are slightly
activating and, thus, fit this pattern of reactivity. Formation
of a new CdC bond to generate the enediamido com-
plex [DMP(NO)tBu]2Zr(η4-ArNC(CH2Ph)dC(CH2Ph)NAr),
9 (Ar = 2,6-Me2C6H3), is confirmed by the solid-state
molecular structure illustrated in Figure 5, with relevant
bond lengths and angles given in Table 3.
˚
with double bonds (C3-N3 = 1.27(1) A and C4-N4 =
1.282(9) A), matching the structure shown in eq 4. The
27
˚
head-to-tail arrangement of the iminoacyl ligands is also
verified in the solid state, where the overall structure matches
that for isomer B from Figure 3. In many cases where two η2-
iminoacyl ligands are bound to a group 4 metal, the L-M-L
plane is not parallel to the iminoacyl NdC bonds and is twisted
substantially from the CfN vectors (Figure 3).24,26b In the
solid-state structure of 8, the twist angle between the iminoacyl
CfN vectors and the plane defined by C1-Zr1-C2 is ap-
proximately 26°, thereby allowing the bulky amidate N-sub-
stituents to be spatially removed from the bulky iminoacyl
substituents. This is more easily viewed in Figure 4B, which
shows 8 as viewed down its C2 axis of symmetry. This twist
angle is similar to the value seen for the bulky bis(aryloxy)
zirconium complex (Zr(O-2,6-tBu2C6H3)2(η2-tBuNdCCH2-
Ph)2), which exhibits a twist angle of 21.5°.26b
Figure 5 shows that 9 is not Cs symmetric in the solid state,
indicating that solution fluxionality must be occurring to
˚
Table 3. Selected Bond Lengths (A) and Angles (deg) for Insertion
Products 8 and 9
8
9
While 8 is stable in solution at room temperature, heating
this complex to 110 °C for 24 h results in the formation of a
new bright yellow species having Cs symmetry in solution. 1H
NMR spectroscopy of the product of this reaction shows the
presence of two resonances for the aryl methyl groups, indi-
cating free rotation about the N-Cipso bonds of the 2,6-
dimethylphenyl groups of the inserted isocyanides and the
amidate ligands. Additionally, the 13C NMR spectroscopic
signal at δ 250.6 is absent, while a new signal at δ 115.6 is
observed, indicative of an sp2-hybridized carbon center.
These results are consistent with a well-established coupling
transformation (eq 5).24,25,28
Zr1-O1
2.214(5)
2.217(5)
2.339(6)
2.335(6)
2.243(6)
2.246(6)
2.252(7)
2.249(8)
1.27(1)
1.282(9)
79.3(2)
129.2(2)
110.2(3)
108.0(2)
32.9(2)
Zr1-O1
2.134(2)
2.164(2)
2.470(2)
2.346(2)
2.033(2)
2.069(2)
2.560(2)
2.548(2)
1.381(3)
1.406(3)
1.410(3)
56.04(7)
57.69(7)
142.2(2)
121.0(2)
93.8(1)
117.1(2)
123.4(2)
118.9(2)
146.0(2)
120.7(2)
92.8(1)
117.5(2)
123.8(2)
118.6(2)
116.11(7)
93.72(7)
Zr1-O2
Zr1-O2
Zr1-N1
Zr1-N1
Zr1-N2
Zr1-N2
Zr1-N3
Zr1-N3
Zr1-N4
Zr1-N4
Zr1-C3
Zr1-C27
Zr1-C4
Zr1-C28
N3-C3
C27-C28
N4-C4
N3-C28
O1-Zr1-O2
N1-Zr1-N2
C3-Zr1-C4
N3-Zr1-N4
N3-Zr1-C3
N4-Zr1-C4
C29-N3-C3
C29-N3-Zr1
C3-N3-Zr1
C37-C3-Zr1
C37-C3-N3
N3-C3-Zr1
C52-C4-Zr1
C52-C4-N4
N4-C4-Zr1
C4-N4-Zr1
C44-N4-C4
C44-N4-Zr1
N4-C27
O1-Zr1-N1
O2-Zr1-N2
C37-N3-Zr1
C37-N3-C28
C28-N3-Zr1
C52-C28-N3
C52-C28-C27
C27-C28-N3
C29-N4-Zr1
C29-N4-C27
C27-N4-Zr1
C45-C27-N4
C45-C27-C28
C28-C27-N4
O1-Zr1-O2
N1-Zr1-N2
33.2(2)
127.3(6)
158.0(5)
73.9(4)
162.2(6)
123.2(7)
73.1(4)
161.0(4)
124.4(7)
73.3(4)
73.5(4)
125.6(6)
159.8(5)
The formation of new C-C bonds by the coupling of
isocyanides in the presence of early transition metals is
dependent upon the steric and electronic properties of both
the metal center and the isocyanides.24 This process is gene-
rally intramolecular in nature and is dictated largely by the
Figure 4. (A) ORTEP depiction (ellipsoids at 30% probability) of solid-state molecular structure of [DMP(NO)tBu]2Zr(η2-2,6-
Me2C6H3NdCCH2Ph)2, 8 (hydrogens omitted), (B) viewed down the C2 axis of symmetry (amidate substituents and hydrogens
omitted).

3552 Organometallics, Vol. 29, No. 16, 2010
Thomson and Schafer
Figure 5. ORTEP depiction (ellipsoids at 30% probability) of [DMP(NO)tBu]2Zr(η4-ArNC(CH2Ph)dC(CH2Ph)NAr), 9 (Ar = 2,6-
Me2C6H3): (A) hydrogens omitted; (B) hydrogens and amidate substituents omitted.
give rise to the observed 1H NMR spectrum. Solution phase
amidate fluxionality has been observed previously, and a
proposed κ2-κ1-κ2 mechanism for this process must be
considered.12 The new C-C bond formed falls within the
With the knowledge that literature precedent for C-C
coupling of iminoacyls is favored with electron-withdrawing
groups, such as 2,6-dimethylphenyl, and disfavored with
electron-donating groups, the possibility of divergent beha-
vior was investigated by studying the insertion of tert-
butyl isocyanide.24,29 Upon addition of two equivalents of
tBuNtC to 4, the solution immediately deepens in color
from pale yellow to an intense golden yellow. The 1H NMR
spectrum of the insertion product 10 is consistent with a C2
symmetric complex: there is one signal for the aryl methyl
groups and two signals for the tert-butyl groups of the
amidate ligands and inserted isocyanide units. Splitting of
the signal for the benzylic protons in 10 into two canted
doublets is suggestive of isocyanide insertion; however, the
chemical shift of these signals is shifted far downfield at δ
5.84 and 7.28. These chemical shifts instead suggest the
presence of vinyl amido ligands as shown in eq 6.6c,24,31
˚
range expected for a double bond (C27-C28 = 1.381(3) A),
and the C-N distances of the enediamido backbone are
˚
consistent with single bonds (N3-C28 = 1.406(3) A and
27
˚
N4-C27 = 1.410(3) A).
A significant fold angle of approximately 55° exists
between the planes defined by N4-C27-C28-N3 and
N4-Zr1-N3. Fold angles of this size are commonly seen
for complexes of this type. One related example is a bis-
(guanidinate) enediamido complex, which has a fold angle of
44.8°.8 The deviation from planarity has been rationalized by
the need to relieve steric interactions, as well as the additional
electronic stabilization offered by the η4-interaction with
the metal center.8,28b,d,29 While the Zr1-C27 and Zr1-C28
3
˚
bond distances (2.560(2) and 2.548(2) A, respectively) lie
The JHH coupling constants of 14 Hz for these signals
indicate a trans geometry about the double bond.27
outside the range generally observed for Zr-C σ-bonds, they
are similar to the distances observed in Cp complexes of Zr
5
30
˚
(average Zr-η -C5H5 distances are ∼2.48-2.55 A).
Although it would be desirable to couple different isocyanide
units to generate novel diamido ligands, the high reactivity of 4
results in rapid insertion of two equivalents of isocyanide per
zirconium center, even with strict 1:1 stoichiometry. The rapid
insertion of two equivalents of isocyanide into Zr-C bonds in
the presence of only one equivalent of isocyanide is not generally
seen. In most cases, insertion of a single isocyanide results in
stable mixed alkyl η2-iminoacyl complexes.24 However, the
observed reactivity reported here is consistent with both the
greater steric access and enhanced electrophilic character of
zirconium afforded by the amidate ligands in 4.
Vinylamido insertion products such as [DMP(NO)tBu]2-
Zr(N(tBu)CHdCHPh)2 (10) have been reported in the lit-
erature, but are relatively rare for group 4 metals.6e,31b,c
Rothwell and co-workers reported a vinylamido hafnocene
complex that resulted from the insertion of 2,6-dimethylphe-
nyl isocyanide into the Hf-C bonds of Cp2Hf(CH2-py-6-
Me)2.31b In that case, the solid-state molecular structure of
the insertion product clearly established the trans geometry
of the vinyl group, and doublets for the trans vinyl protons
(27) Smith, M. B.; March, J. March’s Advanced Organic Chemistry:
Reactions, Mechanisms, and Structure, 5th ed.; Wiley: Toronto, 2001.
(28) (a) McMullen, A. K.; Rothwell, I. P.; Huffman, J. C. J. Am.
Chem. Soc. 1985, 107, 1072–1073. (b) Chamberlain, L. R.; Durfee, L. D.;
Fanwick, P. E.; Kobriger, L. M.; Latesky, S. L.; McMullen, A. K.; Steffey,
B. D.; Rothwell, I. P.; Foltin, K.; Huffman, J. C. J. Am. Chem. Soc. 1987,
109, 6068–6076. (c) Ramos, C.; Royo, P.; Lanfranchi, M.; Pellinghelli,
M. A.; Tiripicchio, A. Eur. J. Inorg. Chem. 2005, 3962–3970. (d) Giannini,
L.; Caselli, A.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.; Re, N.;
Sgamellotti, A. J. Am. Chem. Soc. 1997, 119, 9709–9719.
(29) Durfee, L. D.; McMullen, A. K.; Rothwell, I. P. J. Am. Chem.
Soc. 1988, 110, 1463–1467.
(30) Barger, P. T.; Santarsiero, B. D.; Armantrout, J.; Bercaw, J. E.
J. Am. Chem. Soc. 1984, 106, 5178–5186.
1
were observed in the H NMR spectrum at δ 4.6-4.8 and
3
8.5-9.5, with JHH coupling constants of 12-13 Hz.31b
(31) (a) Beshouri, S. M.; Chebi, D. E.; Fanwick, P. E.; Rothwell, I. P.;
Huffman, J. C. Organometallics 1990, 9, 2375–2385. (b) Beshouri, S. M.;
Fanwick, P. E.; Rothwell, I. P.; Huffman, J. C. Organometallics 1987, 6, 891–
893. (c) Lee, L.; Berg, D. J.; Bushnell, G. W. Organometallics 1997, 16,
2556–2561.

Article
Organometallics, Vol. 29, No. 16, 2010 3553
A related bis(guanidinate) dibenzyl Zr complex was shown
to insert two equivalents of xylyl isocyanide, resulting in the
formation of a bis(guanidinate) bis(vinylamido) product,
analogous to 10.6e The close similarity in the diagnostic
NMR spectroscopic signals between these complexes and
those of 10 lend further support to the proposed structure in
through protonolysis of tetrabenzyl zirconium and hafnium
starting materials with organic amide proligands. Both
bidentate and tetradentate amidate ligands are successful
at stabilizing these complexes. The zirconium complex 4 was
less stable to heat and light than the previously reported
hafnium complex 1 and exhibited intermediate η1/η2-hapti-
city of the benzyl ligands in the solid state, while behaving as
an η1-benzyl species in solution. Seven-coordinate species
can be observed for both bidentate and tetradentate ami-
date-supported dibenzyl complexes, consistent with the re-
duced steric encumbrance of this asymmetric ligand set in
comparison with related amidinate and guanidinate systems.
Migratory insertion of aryl isocyanides was observed for 4,
resulting in the η2-iminoacyl complex 8, which can undergo
thermal coupling to form enediamido complex 9. Insertion
of tBuNtC resulted in the formation of a vinylamido com-
plex, 10, which is presumably generated from a transient
η2-iminoacyl intermediate via a 1,2-hydrogen migration. The
inability to controllably insert one equivalent of isocyanide is
indicative of the extremely electrophilic nature of 4. All of the
fundamental organometallic chemistry reported here is con-
sistent with the unique coordination environment supported
by the ionic character of the amidate bonding interactions in
this family of complexes.12
1
eq 6.6e,31b In addition to the H NMR spectroscopic data,
13C NMR spectroscopy supports the presence of a vinyl
group, with signals at δ 106.2 and 134.4, consistent with sp2-
hybridized carbon centers. It has also been reported that
vinylamido ligands can be accessed through primary amine
additions to alkynes coordinated to tungsten pyrazolyl
1
borate complexes.32 In these cases, the H NMR spectro-
scopic data are very similar to those obtained for 10,
supporting the formulation in eq 6. Finally, mass spectro-
metry data of 10, which is isolated as a bright yellow powder
in 86% yield, confirm the insertion of two equivalents of
tBuNtC into 4, to give a parent ion of m/z = 846. While
X-ray crystallographic verification of this structure was not
possible, the data presented are strongly supportive of the
designation given in eq 6.
The isomerization of η2-iminoacyl groups to vinylamides
can be rationalized by a 1,2-hydrogen migration.31a,b The
difference in reactivity seen for insertion of tBuNtC versus
2,6-Me2C6H3NtC can be explained by two factors. First,
the presence of the electron-donating tert-butyl group in-
creases the energy of the π*CN orbital, making the C-C
coupling of the η2-iminoacyl groups much less favorable.24
Second, steric bulk has been noted as a factor that can reduce
1,2-hydrogen migration in Cp complexes of Hf, where the
insertion of 2,6-Me2C6H3NtC into the R-phenyl-substi-
tuted pyridyl benzyl complex Cp2Hf(CHPh-py-6-Me)2 re-
sults in the generation of the bis(η2-iminoacyl) complex, and
1,2-hydrogen atom migration to the bis(vinylamido) com-
plex cannot be induced.31a This is in contrast to the less
sterically demanding pyridyl benzyl system Cp2Hf(CH2-py-
6-Me)2, which isomerizes to a vinylamido species upon
insertion of 2,6-dimethylphenyl isocyanide.31a It is possible
that the steric bulk of the amidate ligands in 4 prevents this
rearrangement from occurring with 2,6-Me2C6H3NtC.
Experimental Section
Except where stated otherwise, all manipulations were per-
formed under an inert atmosphere of dry, oxygen-free dinitro-
gen using either standard Schlenk or drybox techniques.
Anhydrous hexanes and toluene were purchased from Aldrich,
sparged with dry, degassed dinitrogen, and passed through a
column of activated alumina and Ridox (or Q-5) catalyst prior
to use. Anhydrous benzene, diethyl ether, tetrahydrofuran, and
pentane were purchased from Aldrich, sparged with dry, de-
gassed dinitrogen, and purified by passage through an Innova-
tive Technologies SPS-PureSolv-400-4 apparatus.
Deuterated NMR solvents were purchased from Cambridge
Isotopes Ltd. Deuterated benzene (C6D6) and deuterated to-
luene (C7D8) were degassed by successive freeze-pump-thaw
˚
cycles and stored overnight over activated 4 A molecular sieves
t
However, the BuNtC group is less bulky by comparison
under an atmosphere of dry dinitrogen prior to use. Deuterated
chloroform (CDCl3) was stored in a darkened flask over acti-
and can rearrange to form the bis(vinylamido) complex 10.
While observation of the expected intermediate η2-iminoacyl
species was not possible for this reaction with 4, an NMR
tube scale reaction of Hf complex 1 with two equivalents of
tBuNtC resulted in the formation of the η2-iminoacyl
complex [DMP(NO)Ph]2Hf(η2-tBuNdCCH2Ph)2 (11), as evi-
˚
vated 4 A molecular sieves prior to use with organic molecules.
1H, 13C, and two-dimensional spectra were collected on three
different Bruker instruments: AV-300 with a 5 mm BBI probe
1
operating at 300.0 MHz for H NMR spectroscopy; AV-400
with a 5 mm inverse BBI probe operating at 400.0 MHz for 1H
NMR spectroscopy; AV-400 with a 5 mm BBI probe operating
at 400.0 MHz for 1H NMR spectroscopy. All three instruments
were capable of variable-temperature experiments, ranging
between -150 and þ180 °C. 1H NMR spectra were referenced
to residual protons in deuterated solvents as follows: C6D5H
(δ 7.15), C7D7H (δ 2.09), CHCl3 (δ 7.24) with respect to TMS
(δ 0.00). 13C NMR spectra were referenced to δ 128.39 in
deuterated benzene or δ 77.44 in deuterated chloroform with
respect to TMS (δ 0.00).
1
denced by H NMR spectroscopic data, with diastereotopic
benzylic resonances at δ 2.88 and 3.68. When the NMR tube is
heated to 80 °C over 24 h, the solution changes color from
yellow-orange to emerald green, showing diagnostic reso-
nances at δ 6.02 and 7.74 for the trans vinyl group, indicating
formation of the bis(vinylamido) complex [DMP(NO)Ph]2Hf-
(N(tBu)CHdCHPh)2 (12). Unfortunately, there are also other
side products observed in the reaction mixture, as evidenced by
a number of other signals in the 1H NMR spectrum.
Mass spectra were either collected on an Agilent Technologies
GCMS equipped with a 6890N GC column and a 5793 mass
selective detector operating with an electron impact source and
quadrupolar detector or were collected by Mr. M. Lapawa at the
University of British Columbia, Department of Chemistry
(EIMS on a Kratos MS 50 using a 70 eV electron impact source,
unless otherwise stated). Assigned mass clusters for specific ions
in the mass spectra show the appropriate isotopic patterns as
calculated for the atomic composition of the species. Elemental
analyses were performed by Mr. M. Lakha at the University of
Summary and Conclusions
In summary, amidate-supported zirconium and hafnium
dibenzyl species can be reliably accessed in high yields
(32) Feng, S. G.; White, P. S.; Templeton, J. L. Organometallics 1995,
14, 5184–5192.

3554 Organometallics, Vol. 29, No. 16, 2010
Thomson and Schafer
British Columbia, Department of Chemistry. Due to the air and
moisture sensitivity of the metal complexes analyzed, these
compounds were handled using glovebox or glovebag techni-
ques during analysis. In this class of complexes satisfactory
carbon analyses were problematic and repeated attempts typi-
cally resulted in satisfactory H and N analyses but low C. We
suggest this may be due to incomplete combustion through
carbide formation. To further support the characterization data
presented in the Experimental Section, 1H and 13C NMR
spectral data are included in the Supporting Information.
Crystallographic measurements were made on either Rigaku
ADSC, Rigaku AFC7, or Bruker X8 Apex CCD area detectors
with graphite-monochromated Mo KR radiation. The data were
processed33 and corrected for Lorentz and polarization effects.
The structures were solved by direct methods34 and expanded
using Fourier techniques.35 All non-hydrogen atoms were re-
fined with anisotropic thermal parameters. Neutral atom scat-
tering factors and anomalous dispersion corrections were taken
from the International Tables for X-ray Crystallography.36a All
structures are visualized as ORTEP-3 depictions.37
care was taken to ensure reaction occurred in the absence of
ambient light, and the reaction was not allowed to exceed 10 °C.
The clear bright yellow solution was then concentrated to
dryness in vacuo to give a bright yellow solid residue. The crude
material was dissolved in 30 mL of pentane and filtered through
Celite to remove impurities. The pentane solution was concen-
trated to approximately 10 mL and cooled to -37 °C. The
yellow precipitate was isolated in 57% yield (0.85 g) by filtration
and dried in vacuo. Successive concentration/filtration cycles
allow access to >80% yield of pure 4. Single crystals suitable for
X-ray crystallographic analysis were grown in the dark from a
saturated pentane solution at -37 °C. 1H NMR (C6D6, 25 °C,
300 MHz): δ 0.91 (s, 18H, C(CH3)3), 2.05 (s, 12H, Ph(CH3)2),
2.24 (s, 4H, Zr(CH2Ph)2), 6.86-6.89 (m, 8H, Ar-H), 7.11-7.15
(m, 8H, Ar-H). 13C{1H} NMR (C6D6, 25 °C, 75 MHz): δ 19.4,
27.5, 41.2, 75.8, 123.1, 125.5, 128.6, 129.4, 129.9, 132.1, 142.9,
143.2, 190.7. EIMS (m/z): 589 ([Mþ] - CH2Ph), 497 ([Mþ] - 2
CH2Ph). Anal. Calcd for C40H50N2O2Zr (%): C, 70.44; H, 7.39;
N, 4.11. Found: C, 69.71; H, 7.60; N, 4.67.
Synthesis of Ad[O2N2]H2 (5). A solution of 1,3-diamino-2,2-
dimethylpropane (2.4 mL, 20.1 mmol) and triethylamine (5.6
mL, 40.3 mmol) in 100 mL of CH2Cl2 was cooled to -78 °C
prior to dropwise addition of a CH2Cl2 solution of 1-adaman-
tane carbonyl chloride (7.98 g, 40.3 mmol). The clear, colorless
solution was allowed to warm to room temperature while
stirring overnight. The cloudy white suspension was then ex-
tracted with three portions of 1 M HCl (3 ꢀ 25 mL) until the
aqueous washings were acidic. The organic fraction was then
extracted with a single 25 mL portion of 1 M NaOH. Finally, the
organic fraction was washed with 25 mL of brine, and the
organic fraction was dried over anhydrous MgSO4. Gravity
filtration of the solution to remove MgSO4 was performed, and
excess CH2Cl2 was removed by rotary evaporation to give a
white powder. The product was purified by recrystallization
from a supersaturated toluene solution that was cooled to
-15 °C. A white solid was isolated by filtration, ground with
a mortar and pestle to a fine white powder, and dried while
heating to 120 °C under vacuum overnight in a Schlenk flask to
remove air and moisture. Due to the increased ability of 5 to
hydrogen bond with water, the elevated temperature was used
to remove traces of moisture. The purified product was isolated
in 67% yield (5.75 g). 1H NMR (CDCl3, 25 °C, 300 MHz): δ 0.80
(s, 6H, HNCH2C(CH3)2CH2NH), 1.70 (br, 12H, Ad-(CH-
The following reagents were purchased from Aldrich and
purified by distillation: 2,6-dimethylaniline; H2NCH2CMe2-
CH2NH2; benzoyl chloride; trimethylacetyl chloride; triethyl-
amine; 1-adamantoyl chloride; tertbutylisocyanide. Benzyl
magnesium chloride was purchased from Aldrich and used
as received. ZrCl4, HfCl4, and 2,6-dimethylphenylisocyanide
were purchased from Strem Chemicals and used without fur-
ther purification. Compounds Zr(CH2Ph)4,13 Hf(CH2Ph)4,13
[
[
DMP(NO)Ph]H,14 DMP(NO)Ph]2Hf(CH2Ph)2(THF) (1),14 and
[
DMP(NO)tBu]H (3)11 were prepared via literature methods.
Synthesis of [DMP(NO)Ph]2Hf(CH2Ph)2 (2). This complex was
communicated previously, but full synthetic details and char-
acterization data are presented here.14 In a foil-wrapped Schlenk
flask, 0.93 g (1.7 mmol) of Hf(CH2Ph)4 and 0.77 g (3.4 mmol)
of [DMP(NO)Ph]H were combined. To this mixture of solids was
added approximately 75 mL of toluene at -78 °C via cannula.
The reaction mixture was allowed to warm to room temperature
while stirring for approximately 4 h. Excess toluene was re-
moved, resulting in the isolation of a bright yellow solid residue.
The crude product was dissolved in approximately 25 mL of
hexanes at room temperature and concentrated until a yellow
powder precipitated out of solution. This powder was isolated in
62% yield (0.86 g) by filtration through a fritted disk and dried
1
3
in vacuo. H NMR (C6D6, 25 °C, 300 MHz): δ 2.10 (s, 12H,
(CH2)CH)3), 1.86 (d, 12H, JHH = 3 Hz, Ad-C(CH2)3), 2.02
3
Ph(CH3)2), 2.30 (s, 4H, Hf(CH2Ph)2), 6.78-6.94 (m, 14H total,
(br, 6H, Ad-(CH)3), 2.91 (d, 4H, JHH = 7 Hz, HNCH2C-
3
(CH3)2CH2NH), 6.54 (t, 2H, 3JHH = 6 Hz, NH). 13C{1H} NMR
(CDCl3, 25 °C, 75 MHz): δ 23.5, 28.2, 36.5, 39.3, 40.8, 44.9,
178.7 (no signal observed for quaternary C of adamantyl
group). CIMS (m/z): 427 ([M þ 1þ]). Anal. Calcd for C27H42-
N2O2 (%): C, 76.01; H, 9.92; N, 6.57. Found: C, 75.69; H, 9.96;
N, 6.70.
Ar-H), 7.10-7.24 (m, 8H total, Ar-H), 7.61 (d, 4H, JHH = 7
Hz, Ar-H). 13C{1H} NMR (C6D6, 25 °C, 75 MHz): δ 19.0, 82.9,
122.1, 126.4, 129.0, 128.7, 129.3, 129.5, 130.1, 132.3, 132.7,
133.5, 142.5, 144.7, 179.6. EIMS (m/z): 719 ([Mþ] - CH2Ph),
627 ([Mþ] - 2 CH2Ph). Anal. Calcd for C44H42N2O2Hf (%): C,
65.30; H, 5.23; N, 3.46. Found: C, 64.41; H, 5.36; N, 3.81.
Synthesis of [DMP(NO)tBu]2Zr(CH2Ph)2 (4). In a foil-wrapped
250 mL round-bottomed Schlenk flask equipped with a stir bar,
0.90 g (4.4 mmol) of [DMP(NO)tBu]H (3) was combined with
1.00 g (2.2 mmol) of Zr(CH2Ph)4. To this flask was added 75 mL
of toluene, which had been cooled to -78 °C. The reaction
mixture was then stirred for 3.5 h while allowing to warm to
∼10 °C. Given the thermal and photosensitivity of Zr(CH2Ph)4,
Synthesis of Ad[O2N2]Zr(CH2Ph)2(THF) (6). A foil-wrapped
250 mL round-bottomed Schlenk flask equipped with a stir bar
was loaded with 0.75 g (1.7 mmol) of Zr(CH2Ph)4. To this flask
was added 50 mL of THF via cannula, and the resulting solution
was cooled to -78 °C. Using a solid addition funnel, 0.70 g
(1.7 mmol) of 5 was added to the THF solution of Zr(CH2Ph)4
over a period of 5 min. The cloudy yellow reaction mixture was
then stirred while warming to 0 °C over the course of 4 h. The
clear, bright yellow-orange solution was concentrated to dry-
ness in vacuo to give a bright yellow solid residue, while ensuring
that the reaction temperature did not exceed ∼10 °C. The crude
material was washed with 25 mL of pentane and dried under
vacuum to give a bright yellow powder in 73% yield (0.92 g).
Single crystals suitable for X-ray crystallographic analysis were
grown in the dark from a saturated hexanes solution at -37 °C.
1H NMR (C6D6, 25 °C, 400 MHz): δ 0.72 (s, 6H, C(CH3)2), 1.38
(m, 4H, O(CH2CH2)2), 1.61 (br, 12H, Ad-(CH(CH2)CH)3), 1.90
(br, 6H, Ad-(CH)3), 2.04 (br, 12H, Ad-C(CH2)3), 2.25 (s, 4H,
Zr(CH2Ph)2), 3.08 (s, 4H, NCH2C(CH3)2CH2N), 3.66 (m, 4H,
(33) teXan; Molecular Structure Corp.: The Woodlands, TX, 1996.
(34) Altomane, A.; Burla, M. C.; Cammali, G.; Cascarano, M.;
Giacovazzo, C.; Gagliardi, A.; Moliterni, A. G. G.; Polidoi, G.; Spagna,
A. SIR-97; CNR-IRMEC: Bari, Italy, 1999.
(35) Beurkens, P. T.; Admiraal, G.; Baurskens, G.; Bosman, W. P.;
de Gelder, R.; Israel, R.; Smits, J. M. M. DIRDIF94; University of
Njmegen: Njmegen, The Netherlands, 1994.
(36) (a) International Union of Crystallography. International Tables
for X-ray Crystallography; Kynoch Press: Birmingham, UK, 1974.
(b) International Union of Crystallography. International Tables for
X-ray Crystallography; Kluwer Academic: Boston, MA, 1992.
(37) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.

Article
Organometallics, Vol. 29, No. 16, 2010 3555
O(CH2CH2)2), 6.86 (m, 2H, Ar-H), 7.19-7.24 (m, 8H, Ar-H).
13C{1H} NMR (C6D6, 25 °C, 100 MHz): δ 24.9, 26.0, 28.9, 35.8,
37.2, 38.5, 43.0, 56.3, 62.4, 68.8, 120.2, 127.9, 128.5, 148.2, 192.3.
EIMS (m/z): 605 ([Mþ] - THF - CH2Ph). Anal. Calcd for
C45H62N2O3Zr (%): C, 70.17; H, 8.11; N, 3.64. Found: C, 65.01;
H, 7.99; N, 4.14.
Excess toluene was removed in vacuo to give a yellow-orange
solid. This material was dissolved in 10 mL of pentane and
filtered through Celite to remove 8. Excess pentane was removed
in vacuo, resulting in 81% yield (0.403 g) of 9 as a yellow-orange
solid. This complex can also be synthesized by heating 8 to
110 °C overnight. Single crystals for X-ray analysis were grown
from a saturated toluene solution at room temperature. 1H
NMR (C6D6, 25 °C, 400 MHz): δ 0.82 (s, 18H, C(CH3)3), 1.95
(s, 12H, Ph(CH3)2), 2.19 (s, 12H, Ph(CH3)2), 3.99 (s, 4H,
CH2Ph), 6.65-7.08 (m, 22H, Ar-H). 13C{1H} NMR (C6D6,
25 °C, 100 MHz): δ 20.2, 21.2, 28.1, 37.8, 41.4, 115.6, 124.1,
124.8, 126.3, 128.0, 128.3, 128.6, 130.5, 132.1, 133.3, 140.4,
143.9, 147.3, 187.6.
Synthesis of Ad[O2N2]Hf(CH2Ph)2(THF) (7). A foil-wrapped
250 mL round-bottomed Schlenk flask equipped with a stir bar
was loaded with 3.00 g (5.5 mmol) of Hf(CH2Ph)4. To this flask
was added 100 mL of THF via cannula, and the resulting
solution was cooled to -78 °C. Using a solid addition funnel,
2.36 g (5.5 mmol) of 5 was added to the THF solution of
Hf(CH2Ph)4 over a period of 5 min. The cloudy yellow reaction
mixture was then stirred while warming to room temperature
overnight. The clear yellow solution was then concentrated to
dryness in vacuo to give a light yellow solid residue. The crude
material was triturated with ∼30 mL of pentane and filtered
over a fritted disk to give 2.75 g (58% yield) of 7 as a pale yellow
powder. The pentane washings were concentrated until product
began to precipitate. After cooling to aid precipitation, an
additional 0.50 g (12% yield) of 7 was isolated by filtration,
resulting in an overall isolated yield of 70%. Single crystals
suitable for X-ray crystallographic analysis were grown in the
Synthesis of [DMP(NO)tBu]2Zr(NtBuCHdCHPh)2 (10). In a
100 mL Schlenk flask, 0.360 g (0.5 mmol) of 4 was dissolved in
approximately 30 mL of toluene at room temperature. To this
solution was added 0.088 g (1.0 mmol) of tBuNtC dissolved in
5 mL of toluene at room temperature. The solution immediately
became an intense yellow color. Excess toluene was removed
in vacuo to give a vibrant yellow solid. This material was
triturated with 10 mL of pentane and isolated by filtration in
86% yield (0.385 g). 1H NMR (C6D6, 25 °C, 300 MHz): δ 1.02
(s, 18H, OdCC(CH3)3), 1.35 (s, 18H, NC(CH3)3), 2.31 (s, 12H,
1
3
dark from a saturated hexanes solution at -37 °C. H NMR
Ph(CH3)2), 5.84 (d, 2H, JHH = 14 Hz, NCHdCHPh), 6.91-
(C6D6, 25 °C, 400 MHz): δ 0.83 (s, 6H, C(CH3)2), 1.33 (m, 4H,
O(CH2CH2)2), 1.66 (br, 12H, Ad-(CH(CH2)CH)3), 1.73 (s, 4H,
Hf(CH2Ph)2), 1.95 (br, 6H, Ad-(CH)3), 2.09 (br, 12H, Ad-
C(CH2)3), 3.19 (s, 4H, NCH2C(CH3)2CH2N), 3.99 (m, 4H,
O(CH2CH2)2), 6.76 (m, 2H, Ar-H), 7.04 (d, 4H, 3JHH = 8 Hz,
Ar-H), 7.19 (m, 4H, Ar-H). 13C{1H} NMR (C6D6, 25 °C, 75
MHz): δ 24.9, 25.0, 28.2, 35.8, 36.5, 37.8, 42.8, 55.3, 57.3, 70.0,
117.9, 125.4, 127.4, 153.9, 190.9. EIMS (m/z): 695 ([Mþ] - THF -
CH2Ph). Anal. Calcd for C45H62N2O3Hf (%): C, 63.03; H, 7.29;
N, 3.27. Found: C, 61.96; H, 7.64; N, 3.50.
7.12 (m, 16H, Ar-H), 7.28 (d, 2H, 3JHH = 14 Hz, NCHdCHPh).
13C{1H} NMR (C6D6, 25 °C, 75 MHz): δ 20.9, 28.3, 30.4, 41.3,
58.4, 106.2, 124.7, 125.2, 125.9, 128.1, 129.0, 132.1, 134.4, 139.5,
144.7 (no signal seen for CdO). EIMS (m/z): 846 ([Mþ]). Anal.
Calcd for C50H68N4O2Zr1 (%): C, 70.79; H, 8.08; N, 6.60.
Found: C, 69.42; H, 7.73; N, 6.16.
NMR Tube Reaction of 1 and tBuNtC to Generate
[
DMP(NO)Ph]2Hf(η2-tBuNdCCH2Ph)2 (11) and [DMP(NO)Ph]2-
Hf(NtBuCHdCHPh)2 (12). In a 20 mL scintillation vial, 0.100 g
(0.1 mmol) of 1 was dissolved in approximately 0.5 mL of C6D6
and transferred into a J-Young NMR tube. In another vial
0.019 g (0.2 mmol) of tBuNtC was dissolved in approximately
0.5 mL of C6D6 and added to the NMR tube. An immediate
color change from orange to yellow-orange occurred upon
Synthesis of [DMP(NO)tBu]2Zr(η2-ArNdCCH2Ph)2 (Ar = 2,6-
Me2C6H3) (8). In a 50 mL Schlenk flask, 0.15 g (0.2 mmol) of 4
was dissolved in approximately 5 mL of toluene at room
temperature. To this solution was added 0.058 g (0.4 mmol) of
2,6-Me2C6H3NtC dissolved in 5 mL of toluene. The bright
yellow solution was stirred at room temperature and became
colorless within minutes. Excess toluene was removed in vacuo
to give a white residue. This material was triturated with 5 mL of
pentane, and the insoluble white powder was isolated by filtra-
tion in 52% yield (0.108 g). Higher yields are possible, but due to
static electricity, the product sticks to glass very well, and small-
scale reactions suffer from this. Single crystals were grown from
a saturated pentane solution at -37 °C. 1H NMR (C6D6, 25 °C,
300 MHz): δ 0.95 (s, 6H, Ph(CH3)2), 1.11 (s, 18H, C(CH3)3), 1.92
(s, 6H, Ph(CH3)2), 2.12 (s, 6H, Ph(CH3)2), 2.62 (s, 6H, Ph-
1
mixing the two solutions. While the H NMR spectrum was
complicated and indicated a mixture of products, signals char-
acteristic of an η2-iminoacyl (11) were observed. 1H NMR
2
(C6D6, 25 °C, 300 MHz): δ 2.88 (d, 2H, JHH = 13 Hz,
tBuNdCCH2Ph), 3.68 (d, 2H, 2JHH = 14 Hz, tBuNdCCH2Ph).
Heating the NMR tube to 80 °C for 24 h resulted in a gradual
color change from yellow-orange to red-brown and finally to
emerald green. Again, the 1H NMR spectrum was complicated
with signals for multiple products, and signals characteristic of a
trans vinylamido complex (12) analogous to 10 were observed.
1H NMR (C6D6, 25 °C, 300 MHz): δ 6.02 (d, 2H, 3JHHt = 13 Hz,
2
3
(CH3)2), 3.35 (d, 2H, JHH = 12 Hz, CH2Ph), 3.59 (d, 2H,
tBuNCHdCHPh), 7.74 (d, 2H, JHH = 12 Hz, BuNCHd
3
2JHH = 12 Hz, CH2Ph), 6.19 (d, 4H, JHH = 7 Hz, Ar-H),
CHPh).
6.83-7.09 (m, 18H, Ar-H). 13C{1H} NMR (C6D6, 25 °C, 75
MHz): δ 18.2, 19.1, 19.4, 20.6, 28.5, 41.3, 44.3, 125.7, 125.8,
126.6, 129.0, 130.0, 130.2, 130.8, 133.5, 133.9, 135.8, 147.8,
149.1, 187.3, 250.6. EIMS (m/z): 942 ([Mþ]), 720 ([Mþ] -
PhCH2CdN(2,6-Me2C6H3)). Anal. Calcd for C58H68N4O2Zr1
(%): C, 73.76; H, 7.26; N, 5.93. Found: C, 70.62; H, 7.25;
N, 5.63.
Acknowledgment. The authors wish to thank B. O.
Patrick for assistance with X-ray crystallography, and
UBC, CFI, BCKDF, and NSERC for financial support
of this work. R.K.T. thanks NSERC for a postgraduate
scholarship.
Synthesis of [DMP(NO)tBu]2Zr(η4-ArNC(CH2Ph)dC(CH2Ph)-
NAr) (Ar = 2,6-Me2C6H3) (9). Ina 100mL Schlenk flask, 0.360 g
(0.5 mmol) of 4 and 0.139 g (1.0 mmol) of 2,6-Me2C6H3NtC
were dissolved in approximately 35 mL of toluene at room
temperature. The bright yellow solution was stirred and heated
to 110 °C overnight, resulting in a yellow-orange solution.
Supporting Information Available: Crystallographic informa-
tion files (CIFs) of complexes 4, 6, 7, 8, and 9 are available,
as well as selected NMR spectra for the complexes reported.
This material is available free of charge via the Internet at
http://pubs.acs.org.