Chiral alkoxide-functionalized guanidinates from ring-opening rearrangement of aminooxazolinate complexes

Article abstract of DOI:10.1021/om0607649

Treatment of Cp*M(NMe₂)₃ (M = Zr, Hf) with both achiral and optically pure chiral aminooxazoline proligands HL yields metastable aminooxazolinate half-sandwich diamide complexes [Cp* ML(NMe₂)₂]. These species undergo clean rearrangement via oxazoline ring-opening to carbodiimides followed by amide migratory insertion. The chiral-at-metal products contain tridentate alkoxide-functionalized guanidinates, as confirmed by X-ray diffraction. In some of the chiral ligand systems, single diastereomer samples can be prepared, either by direct reaction or after recrystallization. As a result of the chelate structure, no thermal conversion between diastereomers is observed. A mechanism leading to the observed diastereoselection involving an intramolecular CH-π interaction in the major product is proposed.

Full text of DOI:10.1021/om0607649

136
Organometallics 2007, 26, 136-142
Chiral Alkoxide-Functionalized Guanidinates from Ring-Opening
Rearrangement of Aminooxazolinate Complexes
Andrew L. Gott, Stuart R. Coles, Adam J. Clarke, Guy J. Clarkson, and Peter Scott*
Department of Chemistry, UniVersity of Warwick, Gibbet Hill Road, CoVentry CV4 7AL, U.K.
ReceiVed August 22, 2006
Treatment of Cp*M(NMe2)3 (M ) Zr, Hf) with both achiral and optically pure chiral aminooxazoline
proligands HL yields metastable aminooxazolinate half-sandwich diamide complexes [Cp*ML(NMe2)2].
These species undergo clean rearrangement via oxazoline ring-opening to carbodiimides followed by
amide migratory insertion. The chiral-at-metal products contain tridentate alkoxide-functionalized
guanidinates, as confirmed by X-ray diffraction. In some of the chiral ligand systems, single diastereomer
samples can be prepared, either by direct reaction or after recrystallization. As a result of the chelate
structure, no thermal conversion between diastereomers is observed. A mechanism leading to the observed
diastereoselection involving an intramolecular CH-π interaction in the major product is proposed.
Introduction
Tetrasubstituted guanidine-derived compounds can bind to
metals in a variety of different modes.1 From the organometallic
chemist’s perspective, it is perhaps the deprotonated η2-form
(Figure 1) that has been of most interest, not least because of
the similarity to the less electron-rich amidinates.2 Guanidinate
complexes of group 4 elements were first synthesized by Lappert
and co-workers in 1970, via the insertion of carbodiimides into
the homoleptic group 4 dialkylamides M(NMe2)4 (M ) Ti/Zr/
Hf).3 Since this time, they have been used as spectator ligands
in a variety of systems in which the electronic and steric
properties can be subtly altered by the correct choice of
substituents in the positions R1-R3. In addition to a series of
synthetic studies into structural chemistry and the reaction of
such complexes with small molecules,4 guanidinate ligands have
recently been applied to a series of group 4 complexes that
catalytically mediate organic transformations including the
metathesis of carbodiimides,5 hydroamination of alkynes,6 and
guanylation of amines.7 Guanidinate ligands have also been used
to support both neutral and cationic zirconium complexes, which
were subsequently employed in R-olefin polymerization8 and
Figure 1. Relationship between guanidinate, amidinate, and
aminooxazolinate.
have also been employed in the synthesis of dinitrogen
complexes of titanium.9 Very recently, Ti guanidinate complexes
were used as precursors for titanium carbonitride via low-
pressure chemical vapor deposition.10
The use of the related amidinate2 ligand set is undoubtedly
more widespread than its guanidinate counterpart, and half-
sandwich complexes containing the general structural unit [(η5-
C5R5)M(η2-amidinate)] (where R ) H, Me and M ) Ti/Zr/Hf)
have been extensively studied. Following early work on silyl
benzamidinates,11 related compounds have been actively em-
ployed as polymerization catalysts by Sita12 and others.13 In
the context of half-sandwich complexes, the amidinate ligand
is also a useful ancillary in related metal-centered reactivity
studies,14 binuclear compounds,15 and complexes containing
imide16 and phosphinimide functionalities.17
* To whom correspondence should be addressed. E-mail: peter.scott@
warwick.ac.uk.
(1) (a) Coles, M. P. Dalton Trans. 2006, 985. (b) Bailey, P. J.; Pace, S.
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ReV. 2005, 105, 67. (d) Best, M. D.; Tobey, S. L.; Anslyn, E. V. Coord.
Chem. ReV. 2003, 240, 3. (e) Hosseni, M. W. Coord. Chem. ReV. 2003,
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Given the successes of the half-sandwich group 4 amidinates
in catalysis, we sought to incorporate our recently developed
chiral diazaallyl ligand system aminooxazolinate18 into similar
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10.1021/om0607649 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 12/01/2006

Chiral Alkoxide-Functionalized Guanidinates
Organometallics, Vol. 26, No. 1, 2007 137
Chart 1. Aminooxazoline Proligands Used in This Work
complexes. The proligands are readily synthesized from isothio-
cyanates and aminoalcohols,19 and the wide range of such
starting materials allows the synthesis of many variants. We
have incorporated this diazaallyl moiety into other chiral organic
ligand frameworks including 2,2′-diamino-6,6′-dimethylbi-
phenyl20 and 1,2-diaminocyclohexyl.21
Results and Discussion
Preliminary Observations. The aminooxazoline proligands
HLn (n ) 1-5, Chart 1) were synthesized by previously
reported methods.18 Deprotonation with NaH and nBuLi readily
gave the compounds NaLn and LiLn. Subsequent reaction of
these materials with Cp*MCl3 (M ) Zr, Hf) gave intractable
mixtures. Reaction between Cp*MMe3 (M ) Zr, Hf) and HL1-5
also failed to yield tractable products. Treatment of the readily
available Cp*M(NMe2)3 (M ) Zr, Hf) with HL1-5 in NMR
tube scale reactions however led to slow consumption of the
poorly soluble proligand and the generation of 1 equiv of
dimethylamine.
Scheme 1. Synthesis of Half-Sandwich Aminooxazolinate
Complexes
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J. C.; Sita, L. R. Organometallics 2006, 25, 531. (c) Kissounko, D. A.;
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Synthesis of [Cp*MLn(NMe2)2]. In the case of the reaction
between Cp*Zr(NMe2)3 and the least sterically demanding
proligand HL1 a ca. 1:1 mixture of unreacted metal precursor
and a species assigned as the (bis)ligand complex [Cp*ZrL1 -
2
(NMe2)] was observed (Scheme 1); the use of this ligand was
not explored further. In contrast, treatment of Cp*M(NMe3)3
with HL2-5 cleanly yielded the metastable complexes [Cp*ZrLn-
(NMe2)2] (n ) 2-5) and [Cp*HfLn(NMe2)2] (n ) 2, 3) (1a-
f). No reaction was observed with Cp*Ti(NMe2)3, even after
heating to elevated temperatures for 3 days.
1
In the H NMR spectrum of [Cp*ZrL2(NMe2)2] (1a) thus
synthesized in situ, the two inequivalent oxazoline methyl groups
give rise to broad singlets, and a broad resonance is observed
for the oxazoline OCH2 unit at δ 3.52 ppm. Cooling the sample
to 213 K resulted in sharpening of resonances and decoalescence
of the latter into a pair of AB doublets at 3.37 and 3.45 ppm.
This behavior is consistent with the presence of a chiral-at-
metal system undergoing racemization on the NMR chemical
shift time scale.18
For the complexes 1c-f, the presence of elements of chirality
centered at both the ligand and the metal gives rise to the
possibility of diastereoisomerism. The 1H NMR spectra of
[Cp*ZrL3(NMe2)2] (1c) are typical; at 233 K two diastereomers
are observed (diastereomeric ratio (d.r.) 2.5:1), as demonstrated
by two sets of two resonances for the inequivalent dimethyl-
amido ligands (major δ 2.58 and 3.12 ppm, minor δ 3.02 and
3.04 ppm). A series of overlapping multiplets was observed in
the oxazoline region. By 293 K the diastereomers are rapidly
interconverting on this time scale; the mutually coupled protons
of the oxazoline ring give resonances at 3.86, 4.08, and 4.72
ppm, and two amido NMe2 group resonances are observed at
2.69 and 3.05 ppm. Coalescence of these two amido unit
resonances was not observed up to 323 K, whereupon the rate
of an irreversible isomerization reaction (vide infra) became too
rapid to allow further study. These observations are consistent
with epimerization either by N-dissociation or in-place rotation
(ring flipping) of the diazaallyl unit. The latter would fail to
equilibrate the two amido units, and the former would have to
(16) (a) Guiducci, A. E.; Boyd, C. L.; Mountford, P. Organometallics
2006, 25, 1167. (b) Boyd, C. L.; Clot, E.; Guiducci, A. E.; Mountford, P.
Organometallics 2005, 24, 2347. (c) Guiducci, A. E.; Cowley, A. R.;
Skinner, M. E. G.; Mountford, P. J. Chem. Soc., Dalton Trans. 2001, 1392.
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W. Organometallics 2005, 24, 1091. (b) Hollink, E.; Wei, P. R.; Stephan,
D. W. Organometallics 2004, 23, 1562.
(18) Munslow, I. J.; Wade, A. R.; Deeth, R. J.; Scott, P. Chem. Commun.
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690, 3373.

138 Organometallics, Vol. 26, No. 1, 2007
Gott et al.
Table 1. Key to Complexes 2 with Associated
Diastereoselectivities
Scheme 2. Mechanism of the Conversion 1a f 2a
2
R1
R2
M
d.r. of 2 a
a
b
c
d
e
f
Me
Me
H
H
H
Me
Me
Ph
Zr
Hf
Zr
Hf
Zr
Zr
n/a
n/a
6:1b
Ph
>20:1c
1.7:1
2.3:1
iPr
H
tBu
1
b
a Determined by H NMR spectroscopy on crude products. Improved
c
to >20:1 after recrystallization. Structure determined by X-ray diffraction.
coordinated carbodiimide of III. While the ring-opening of
oxazolines in polymerization is well documented,23 few ex-
amples of such a process occurring in transition metal complexes
have been observed; it has recently been demonstrated that
acetate counter-anions in Pd(II) complexes supported by pyridyl
bisoxazoline ligands promote ring-opening, although the manner
in which the ring-opened ligand binds to the metal is entirely
different.24 Molecular modeling suggests that the seven-
membered-ring species III is not susceptible to migratory
insertion of one of the zirconium amide ligands at the carbo-
diimide unit, but N-dissociative rearrangement to the more stable
chelate IV would lead eventually to the guanidinate complex
2a. The latter insertion process is analogous to the intermolecular
reaction of M(NMe2)4 with diimides3 (vide supra). Intramo-
lecular migration of amide co-ligands to coordinated CdN bonds
is nevertheless rare, a recent (first) example being reversible
attack of dimethylamide co-ligands at the imine carbon atom
of Schiff-base tin complexes.25
The formally tridentate, dianionic ligand formed in this
process is best described as a guanidinate functionalized by an
alkoxide pendent arm. Such functionalization is known for
amidinate ligands bound to transition metals;13a,16b,26 however
these compounds are, to our knowledge, the first such guanidi-
nate complexes of either the main group or transition metal
elements.
Diastereoselective Syntheses of 2c-f. For the chiral ligand
complexes there arises the possibility of formation of diaster-
eomers with opposite configurations at the metal. The zirconium
compound 2c was formed with d.r. 6:1, on both the NMR tube
and preparative scales. Crystallization from pentane yielded the
major diastereomer as the single product (d.r. >100) in 21%
yield, the low yield once again a reflection of the high solubility
of the complex. Given these results, we were somewhat
surprised to find that only one diastereomer of the Hf analogue
2d was observed. The remaining compounds 2e and 2f gave
lower selectivities, and their solubility precluded attempts to
improve the d.r. via crystallization (Table 1).
be accompanied by site exchange in the three-legged piano stool
intermediate.14j While it is thus difficult to exclude either
possibility, compounds 1a-f certainly undergo an N-dissociative
exchange process (vide infra), and we thus we favor the former
mechanism.
Ring-Opening Reactions of [Cp*MLn(NMe2)2]. Compounds
1a-f cleanly isomerized at room temperature to new chiral
species 2a-f (Scheme 1), as confirmed by NMR spectroscopy,
the X-ray structure of one example (vide infra), and other data.
Preparative-scale reactions in toluene yielded the compounds
in near quantitative yield. Crystallization from pentane at -30
°C yielded analytically pure materials in the case of 2a-d, albeit
in low/moderate yields due to the high solubility of the
complexes. Purification of the highly pentane soluble semisolids
2e and 2f was achieved by sublimation under high vacuum (10-6
mmHg).
The 1H NMR spectrum of 2a is sharp and essentially invariant
with temperature between 213 and 363 K. At room temperature,
inequivalent methyl groups are observed at δ 1.20 and 1.24 ppm.
A pair of AB doublets at δ 3.87 and 4.37 ppm correspond to
the OCH2 unit. Elsewhere in the spectrum, the major feature of
interest is the presence of two singlets (6H each) for Me2N
groups at δ 3.17 and 2.21 ppm. The former is in the expected
chemical shift region for a Zr-bound amide,22 and the latter
corresponds to the uncoordinated guanidinate NMe2 moiety.8
In the 13C{1H} NMR spectrum the central C atom of the
guanidinate appears at δ 163.5 ppm, cf. δ 171.0 ppm for [Cp-
{(Me2N)C(NiPr)2}ZrCl2].8
A single-crystal X-ray diffraction study was performed on a
crystal of 2d grown from a saturated pentane solution of the
pure material at room temperature. The molecular structure is
(23) (a) Kobayashi, S.; Uyama, H. J. Polym. Sci., Part A; Polym. Chem.
2002, 40, 192. (b) Culbertson, B. M. Prog. Polym. Sci. 2002, 27, 579. (c)
Aoi, K.; Okada, M. Prog. Polym. Sci. 1996, 21, 151.
(24) Kazi, A. B.; Jones, G. D.; Vicic, D. A. Organometallics 2005, 24,
6051.
(25) Nimitsiriwat, N.; Marshall, E. L.; Gibson, V. C.; Elsegood, M. R.
J.; Dale, S. H. J. Am. Chem. Soc. 2004, 126, 13598.
(26) (a) Boyd, C. L.; Guiducci, A. E.; Dubberley, S. R.; Tyrell, B. R.;
Mountford, P. J. Chem. Soc., Dalton Trans. 2002, 4175. (b) Doyle, D.;
Gun’ko, Y. K.; Hitchcock, P. B.; Lappert, M. F. J. Chem. Soc., Dalton
Trans. 2000, 4093. (c) Bambirra, S.; Brandsma, M. J. R.; Brussee, E. A.
C.; Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics 2000, 19, 3197.
(d) Kincaid, K.; Gerlach, C. P.; Giesbrecht, G. R.; Hagadorn, J. R.; Whitener,
G. D.; Shafir, A.; Arnold, J. Organometallics 1999, 18, 5360. (e) Brandsma,
M. J. R.; Brussee, E. A. C.; Meetsma, A.; Hessen, B.; Teuben, J. H. Eur.
J. Inorg. Chem. 1998, 1867.
A mechanism for the formation of 2a is shown in Scheme 2.
1
It is evident from H NMR spectra described above that 1a is
undergoing structural exchange with respect to the amino-
oxazolinato unit, and the presence at equilibrium of intermediate
II (Scheme 2) featuring the [N,O] coordination mode is feasible.
Ring-opening of II as shown, promoted by coordination of the
O atom to the Lewis acid forms the alkoxide unit and
(22) Irigoyen, A. M.; Martin, A.; Mena, M.; Palacios, F.; Yelamos, C.
J. Organomet. Chem. 1995, 494, 255.

Chiral Alkoxide-Functionalized Guanidinates
Organometallics, Vol. 26, No. 1, 2007 139
Table 3. Bond Lengths (Å) for 2d (estimated standard
deviations are given in parentheses)
Hf(1)-O(101)
Hf(1)-N(300)
Hf(1)-N(104)
Hf(1)-N(106)
Hf(1)-C(201)
Hf(1)-C(205)
Hf(1)-C(202)
Hf(1)-C(204)
Hf(1)-C(203)
1.999(3)
2.067(4)
2.203(4)
2.267(4)
2.481(5)
2.509(5)
2.531(5)
2.549(5)
2.554(5)
2.225
N(104)-C(105)
C(105)-N(106)
C(105)-N(105)
N(105)-C(113)
N(105)-C(114)
N(106)-C(107)
C(201)-C(205)
C(201)-C(202)
C(202)-C(203)
C(103)-C(115)
C(203)-C(204)
C(204)-C(205)
N(300)-C(301)
N(300)-C(302)
1.326(5)
1.355(5)
1.358(6)
1.456(6)
1.462(6)
1.429(6)
1.401(9)
1.415(8)
1.401(7)
1.507(7)
1.402(7)
1.405(8)
1.449(7)
1.460(7)
Hf(1)-Cpcent
*
Hf(1)-C(105)
O(101)-C(102)
C(102)-C(103)
C(103)-N(104)
2.694(4)
1.400(6)
1.557(7)
1.465(6)
from planarity with the diazaallyl unit due to steric crowding
from the two adjacent phenyl groups. There appears to be some
donation of the lone pair of the guanidinate nitrogen toward
the metal center as the C(105)-N(105) bond distance of 1.358-
(6) Å demonstrates: this connectivity is shorter than the bond
length observed in the typical C-N single bonds N(105)-
C(114) (1.462(6) Å) and N(105)-C(113) (1.456(6) Å).
The Hf(1)-N(300) distance in the terminal dimethylamide
unit at 2.067(4) Å is at the shorter end of the range of Hf amides
(2.04-2.24 Å).27 In the alkoxide the Hf(1)-O(101) bond
distance of 1.999(3) Å is comparable with the only other
reported hafnium alkoxide (1.969 Å) supported by a Cp*
ligand,28 and the bond angle Hf(1)-O(101)-C(102) of 123.1-
(3)° is indicative of sp3 hybridization at oxygen, and thus
formally a one-electron donor. The distance between the central
hafnium and the centroid of the Cp* ligand is 2.223 Å. This
falls within the range of values reported (2.188-2.230 Å) for
related hafnium amidinate complexes supported by a Cp*
ancillary.14e All other bond lengths and angles are unremarkable.
The 1H-1H NOESY and nOe difference spectra of the major
isomers of 2c and 2d are analogous, suggesting that both
compounds have the same diastereomeric structure as deter-
mined by X-ray diffraction for the latter.
Origin of Diastereoselection. Variable-temperature 1H NMR
spectroscopy on the diastereomeric mixtures of 2e and 2f
revealed no exchange between isomers on this time scale.
Storage of an NMR sample containing diastereomerically pure
2c at 60 °C for weeks led to no appearance of the minor
diastereomer observed earlier. Thus, the thermal interconversion
between diastereomers of 2a is severely restricted, and the
diastereomeric ratios reported in Table 1 are of the kinetic
products. These ratios then reflect the ratio between diastere-
omers of the immediate precursor to 2c, i.e., IVa and IVb
(Scheme 3).
Figure 2. Molecular structure of 2d. Displacement ellipsoids are
at the 50% probability level. Hydrogen atoms have been omitted
for clarity.
Table 2. Selected Data Collection and Refinement
Parameters for [Cp*HfL3′(NMe2)], 2d
formula
M
C29H40HfN4O
639.14
cryst morphology
cryst dimens (mm)
cryst syst
space group
a (Å)
colorless block
0.20 × 0.12 × 0.10
orthorhombic
P212121
9.0546(11)
15.272(2)
20.203(3)
2793.8(7)
4
b (Å)
c (Å)
V (Å3)
Z
d(calc) (g/cm3)
1.520
7.106
180(2)
µ(Mo KR) (mm-1
T (K)
)
F(000)
1288
no. of reflns measd
no. of unique reflns
R1 [I > 2σ(I)]
15 518
4885 [R(int) ) 0.0389]
0.0261
wR2
0.0588
no. of data/restraints/params
goodness of fit
4885/18/325
1.017
0.716 and -0.662
largest diff peak and hole (e‚Å-3
)
given in Figure 2, with crystallographic data and selected bond
lengths and angles in Tables 2, 3, and 4. The complex
crystallized in the orthorhombic space group P212121, with one
molecule in the asymmetric unit. The guanidinate is bound in
an η2-fashion through both nitrogen atoms. The two bond
lengths C(105)-N(104) and C(105)-N(106) of 1.355(5) and
1.326(5) Å, respectively, are significantly different and indicate
a contribution from a more localized RN(106)dC-N(104)R
resonance form. This is borne out in that Hf-N(106) at 2.267-
(4) Å is shorter than Hf-N(104) at 2.203 Å and that N(104) is
significantly pyramidalized (sum of angles ) 340.0°). Although
the latter is certainly not a requirement for assignment of amido
character at that atom, this distortion does serve to reduce ring
strain in the bicyclic chelate structure.
An explanation of the observed diastereoselection in the
formation of 2c is immediately apparent from examination of
molecular models of the diastereomers IV. (The MM2 package
of Chem3D Ultra was used to compute structures based on
standard bond lengths and angles taken from the molecular
structure of 2d and related compounds.) For IVa there is minor
steric pressure between the Cp* ligand and the phenyl group
attached to the stereogenic C center (Scheme 3). In IVb the
(27) (a) Yasumoto, T.; Yamagata, T.; Mashima, K. Organometallics
2005, 24, 3375. (b) Castillo, I.; Tilley, T. D. J. Organomet. Chem. 2002,
431, 643-644. (c) Kloppenburg, L.; Petersen, J. L. Polyhedron 1995, 14,
69. (d) Chivers, T.; Gao, X.; Parvez, M. Inorg. Chem. 1995, 34, 1681. (e)
Bol, J. E.; Hessen, B.; Teuben, J. H.; Smeets, W. J. J.; Spek, A. L.
Organometallics 1992, 11, 1981. (f) Bai, H.; Roesky, H. W.; Noltemeyer,
M.; Witt, M. Chem. Ber. 1992, 125, 825.
The angle of the mean least-squares planes between the NMe2
of the guanidinate ligand and the diazaallyl moiety, defined by
the planes N(106)-C(105)-N(105) and C(113)-N(105)-
C(114), is 27.4°. The guanidinate amine group is distorted away
(28) Arnold, J.; Woo, H.-G.; Tilley, T. D.; Rheingold, A. L.; Geib, S. J.
Organometallics 1988, 7, 2045.

140 Organometallics, Vol. 26, No. 1, 2007
Table 4. Selected Bond Angles (deg) for 2d (estimated standard deviations are given in parentheses)
Gott et al.
O(101)-Hf(1)-N(300)
O(101)-Hf(1)-N(104)
N(300)-Hf(1)-N(104)
91.69(16)
73.53(13)
121.39(14)
109.8
111.8
123.1(3)
102.3(4)
O(101)-Hf(1)-N(106)
N(300)-Hf(1)-N(106)
N(104)-Hf(1)-N(106)
127.95(13)
95.12(15)
59.08(14)
120.3
118.2
110.9(4)
110.6(4)
O(101)-Hf(1)-Cpcent
N(106)-Hf(1)-Cpcent
*
*
N(104)-Hf(1)-Cpcent
*
*
N(300)-Hf(1)-Cpcent
C(102)-O(101)-Hf(1)
C(102)-C(103)-N(104)
O(101)-C(102)-C(103)
N(104)-C(105)-N(106)
Scheme 3. Origin of Diastereoselection in the Formation of
2c
argon/vacuum Schlenk line or an MBraun LabStar glovebox. All
glassware and cannulae were stored in an oven at >373 K. Solvents
were predried and then refluxed under nitrogen from an appropriate
drying agentstoluene from sodium; pentane from NaK alloysand
were stored in glass ampules and rigorously degassed before use.
C6D6 and C6D5CD3 were freeze-thaw-degassed and refluxed in
vacuo for 3 days over potassium metal and vacuum transferred
before use. The aminooxazoline proligands HL1-5 18
Cp*Zr-
,
(NMe2)3,22 and Cp*HfCl3 were prepared according to published
procedures. LiNMe2 (99.9% grade) was obtained from Chemat
Technology and used as received. NMR spectra were recorded on
29
1
Bruker DPX300, DPX400, and DRX 500 spectrometers. H and
13C NMR spectra were referenced internally using residual protio-
solvent resonances relative to tetramethylsilane (δ ) 0 ppm).
Elemental analyses were obtained by Warwick Analytical Services
and MEDAC Ltd, Surrey, U.K. Mass spectra were obtained on a
VG Autospec mass spectrometer by the Department of Chemistry
Mass Spectrometry Service. Attempts to purify 2f by sublimation
led to partial decomposition, reflected in a less than satisfactory
microanalysis.
Synthesis of Cp*Hf(NMe2)3. A Schlenk tube was charged with
Cp*HfCl3 (2.64 g, 6.3 mmol) and LiNMe2 (1.00 g, 19.5 mmol, 3.1
equiv). The reaction vessel was cooled to -78 °C (dry ice/acetone
slush bath), and cold toluene (50 mL) was added with stirring. The
reaction was left to stir at -78 °C for 30 min and then allowed to
slowly warm to ambient temperature overnight. The resulting pale
yellow suspension was filtered through a frit packed with Celite,
and the solvent was removed in vacuo to yield an oily yellow
residue, which was redissolved in pentane. The volatiles were then
removed to yield the title compound as a waxy, pale yellow solid
(some of which could not be removed from the reaction vessel).
Isolated yield: 2.24 g (5.0 mmol, 80%). While the above material
was spectroscopically pure, 1.15 g (82%) of analytically pure
material could be obtained by sublimation of 1.40 g of crude
material at 120 °C and 10-3 mmHg. Anal. Calcd for C16H33N3Hf:
carbodiimide spacer orients the two phenyl groups very well
for formation of a CH-π interaction, thus favoring the formation
of this diastereomer and perhaps increasing its reactivity with
respect to the migratory insertion reaction. An explanation for
the still higher d.r. observed in the synthesis of the otherwise
identical hafnium analogue 2d would require a more detailed
analysis. The mechanism of diastereoselection shown in Scheme
3 is however consistent with the observation of relatively low
d.r. for 2e and 2f. In these alkyl-substituted compounds we
would rely solely on steric effects for stereoselection, and while
this distinguishes relatively poorly between isomers of IV, it is
encouraging that the tert-butyl compound 2f displays signifi-
cantly higher selectivity than the isopropyl species 2e.
1
C 43.09; H 7.46; N 9.42. Found: C 43.26; H 7.42; N 9.25. H
NMR (300 MHz, C6D6, 298 K): δ 1.99 ppm (s, 15H, C5Me5), 2.96
(s, 18H, 3 × Hf-NMe2). 13C{1H} NMR (75.5 MHz, C6D6, 298
K): δ 10.9 ppm (C5Me5), 43.6 (Hf-NMe2), 117.2 (C5Me5). MS
(EI +ve) m/z: 447 (33, M+), 399 (37, M+ - NMe2), 354 (29, M+
- 2NMe2).
General NMR-Scale Synthesis of Aminooxazoline Complexes.
An NMR tube fitted with J. Young concentric stopcock was charged
with an appropriate amount of proligand (ca. 0.05 mmol) and taken
into the glovebox, whereupon it was slurried in C6D6. Addition of
1 equiv of Cp*M(NMe2)3 (M ) Zr, Hf) in C6D6 led to slow
dissolution of the proligand. The sample was then transferred to
an NMR spectrometer for analysis. All 1H NMR spectra were
recorded at 300 MHz in C6D6 at 298 K. The subsequent rearrange-
ments were monitored by running further spectra at regular intervals.
Conclusions
For this half-sandwich group 4 system (and unlike our earlier
examples18,20,21) the aminooxazolinato ligand is unstable with
respect to a fascinating ring-opening/amido migratory insertion
process. The product alkoxide-functionalized guanidinates are
also very interesting since they provide a chiral-at-metal system
whichsunusually for early transition metalssis configuration-
ally stable. Also, diastereoselection in the synthesis of certain
of these compounds arises unexpectedly from an intramolecular
CH-π interaction; steric effects play a minor role.
With regard to the potential uses of this type of chiral system
in early metal catalysis, we might look to the readily available
aminothiazolinyl analogues21 or indeed the pyrrolyl compounds
to reduce susceptibility to ring opening, but the problems of
diastereoselection and epimerization are likely to be solved only
through the use of multidentate chelates.20
[Cp*ZrL2(NMe2)2], 1a. 1H NMR: δ 1.10 ppm (m, v br, 6H, 2
× NCMe2 oxazoline), 1.95 (s, 15H, C5Me5), 2.95 (s, 12H, 2 ×
Zr-NMe2), 3.52 (m, v br, 2H, OCH2 oxazoline), 6.91 (t, 1H, p-Ar
C-H, 3JHH ) 8 Hz), 7.14 (d, 2H, o-Ar C-H, 3JHH ) 7 Hz), 7.26 (t,
3
2H, m-Ar C-H, JHH ) 8 Hz).
[Cp*HfL2(NMe2)2], 1b. 1H NMR: δ 1.03 ppm (s, br, 3H,
NCMe2 oxazoline), 1.13 (s, br, 3H, NCMe2 oxazoline), 1.99 (s,
Experimental Section
General Considerations. All manipulations were conducted
using standard inert-atmosphere techniques using a dual-manifold
(29) Wolczanski, P. T.; Bercaw, J. E. Organometallics 1982, 1, 793.

Chiral Alkoxide-Functionalized Guanidinates
Organometallics, Vol. 26, No. 1, 2007 141
3
15H, C5Me5), 3.01 (s, br, 12H, Hf-NMe2), 3.49 (d of d, v br, 2H,
8 Hz), 6.91 (t, 1H, p-Ar C-H, JHH ) 7 Hz), 7.20 (t, 2H, m-Ar
3
OCH2 oxazoline), 6.93 (t, 1H, p-Ar C-H, JHH ) 8 Hz), 7.21 (d,
C-H, 3JHH ) 7 Hz). 13C{1H} NMR (75.5 MHz, C6D6, 298 K): δ
11.2 ppm (C5Me5), 24.2, 25.8 (2 × Hf-OCH2CMe2), 39.7 (NMe2
guanidinate), 44.5 (Hf-NMe2), 60.9 (Hf-OCH2CMe2), 83.0 (Hf-
OCH2CMe2N), 117.4 (C5Me5), 121.6, 123.2, 128.8 (all Ar C-H),
147.5 (Ar Cq), 164.9 (guanidinate Cq). MS (EI +ve) m/z: 592 (60,
M+), 547 (100, M+ - NMe2).
3
3
2H, o-Ar C-H, JHH ) 8 Hz), 7.29 (t, 2H, m-Ar C-H, JHH ) 8
Hz).
[Cp*ZrL3(NMe2)2], 1c. 1H NMR: δ 1.92 ppm (s, 15H, C5Me5),
2.69 (s, br, 6H, Zr-NMe2), 3.05 (s, 6H, Zr-NMe2), 3.86 (d of d,
1H, OCH2 oxazoline, 2JHH ) 8 Hz, 3JHH ) 5 Hz), 4.08 (d of d, 1H
OCH2 oxazoline, 2JHH ) 8 Hz), 4.72 (d of d, 1H, NCHPh oxazoline,
[Cp*ZrL3′(NMe2)], 2c. A J. Young ampule was charged with
(S)-HL3 (0.266 g, 1.12 mmol) and Cp*Zr(NMe2)3 (0.400 g, 1.12
mmol). Toluene (10 mL) was added, and the reaction vessel was
evacuated and heated to 60 °C for 48 h. After this time, the solvent
was removed in vacuo, and the oily yellow residue was redissolved
in pentane and evaporated to dryness to remove residual toluene.
The resulting white solid was dissolved in the minimum amount
of pentane and allowed to stand at 4 °C until crystalline material
was deposited. Yield: 0.131 g (0.24 mmol, 21%). Anal. Calcd for
C29H40N4OZr: C, 63.11; H, 7.31; N, 10.15. Found: C, 63.29; H,
7.44; N, 10.12. 1H NMR (300 MHz, C6D6, 298 K): δ 1.84 ppm (s,
6H, NMe2 guanidinate), 2.03 (s, 15H, C5Me5), 3.29 (s, 6H, Zr-
3
2JHH ) 8 Hz, JHH ) 5 Hz), 6.94 (m, 1H, Ar C-H), 7.05-7.14
(m, 5H, Ar C-H), 7.30 (m, 4H, Ar C-H).
[Cp*HfL3(NMe2)2], 1d. 1H NMR: δ 1.96 ppm (s, 15H, C5Me5),
2.72 (s, br, 6H, Hf-NMe2), 3.10 (s, 6H, Hf-NMe2), 3.85 (d of d,
2
3
1H, OCH2 oxazoline, JHH ) 8 Hz, JHH ) 4 Hz), 4.06 (d, 1H
OCH2 oxazoline, 2JHH ) 8 Hz), 4.68 (d of d, 1H, NCHPh oxazoline,
2JHH ) 8 Hz ,3JHH ) 4 Hz), 6.95 (m, 1H, Ar C-H), 7.07-7.13
(m, 5H, Ar C-H), 7.33 (m, 4H, Ar C-H).
[Cp*ZrL4(NMe2)2], 1e. 1H NMR: δ 0.61 ppm (d, 3H, (CH3)2-
CH, 3JHH ) 7 Hz), 0.76 (d, br, 3H, (CH3)2CH, 3JHH ) 8 Hz), 1.96
(s, 15H, C5Me5), 2.05 (m, 1H, (CH3)2CH), 2.96 (s, 6H, Zr-NMe2),
3.03 (s, 6H, Zr-NMe2), 3.71 (m, 2H, OCH2 oxazoline), 3.94 (m,
2
NMe2), 4.27 (d, 1H, Zr-OCHCHPh, JHH ) 10 Hz), 4.51 (d, 1H,
Zr-OCH2CHPh, 3JHH ) 6 Hz), 4.98 (d of d, 1H, Zr-OCH2CHPh,
3JHH ) 10 Hz, 2JHH ) 6 Hz), 6.91 (t, 1H, Ar C-H, 3JHH ) 8 Hz),
7.03 (m, 3H, Ar C-H), 7.17-7.23 (m, 4H, Ar C-H), 7.32 (d, 2H,
Ar C-H, 3JHH ) 8 Hz). 13C{1H} NMR (75.5 MHz, C6D6, 298 K):
δ 11.5 (C5Me5), 38.2 (NMe2 guanidinate), 46.8 (Zr-NMe2), 68.3
(N-CHPh), 79.6 (Zr-OCH2), 118.9 (C5Me5), 121.6, 122.1, 124.3,
127.0, 128.3, 129.3 (all Ar C-H), 147.5, 149.4 (both Ar Cq), 165.6
(guanidinate Cq). MS (EI +ve) m/z: 550 (24, M+), 506 (100, M+
- NMe2).
3
1H, NCHiPr oxazoline), 6.90 (t, 1H, p-Ar C-H, JHH ) 7 Hz),
7.21 (d, br, 2H, o-Ar C-H, 3JHH ) 7 Hz), 7.27 (t, 2H, m-Ar C-H,
3JHH ) 7 Hz).
1
[Cp*ZrL5(NMe2)2], 1f. H NMR: δ 0.80 ppm (s, 9H, NCHtBu
oxazoline), 1.95 (s, br, 15H, C5Me5), 2.92 (s, 6H, Zr-NMe2), 3.03
(s, 6H, Zr-NMe2), 3.36 (m, 1H, OCH2 oxazoline), 3.75 (m, br,
1H, OCH2 oxazoline), 4.03 (m, 1H, br, NCHtBu oxazoline), 6.92
(m, 1H, p-Ar C-H), 7.26 (m, br, 4H, o- and p-Ar C-H).
Preparative-Scale Reactions of Ring-Opened Guanidinate
Complexes. [Cp*ZrL2′(NMe2)], 2a. A Schlenk tube was charged
with HL2 (0.159 g, 0.84 mmol) and Cp*Zr(NMe2)3 (0.300 g, 0.84
mmol). Toluene (10 mL) was added, and the reaction vessel
evacuated and left to stir at room temperature for 24 h. After this
time, the solvent was removed in vacuo, and the oily yellow residue
was redissolved in pentane and evaporated to dryness to remove
residual toluene. The resulting white solid was dissolved in the
minimum amount of pentane and allowed to stand at room
temperature until crystalline material was deposited. Yield: 0.172
g (0.34 mmol, 41%). Anal. Calcd for C25H40N4OZr: C, 59.60; H,
8.00; N, 11.12. Found: C, 59.14; H, 8.07; N, 11.07. 1H NMR (300
MHz, C6D6, 298 K): δ 1.20 ppm (s, 3H, Zr-OCH2CMe2), 1.24
(s, 3H, Zr-OCH2CMe2N), 1.99 (s, 15H, C5Me5), 2.21 (s, 6H, NMe2
guanidinate), 3.17 (s, 6H, Zr-NMe2), 3.87 (d, 1H, Zr-OCH2CMe2,
2JHH ) 10 Hz), 4.37 (d, 1H, Zr-OCH2CMe2, 2JHH ) 10 Hz), 6.69
[Cp*HfL3′(NMe2)], 2d. A J. Young ampule was charged with
(S)-HL3 (0.300 g, 1.20 mmol) and Cp*Hf(NMe2)3 (0.535 g, 1.20
mmol). Toluene (10 mL) was added, and the reaction vessel was
evacuated and heated to 60 °C for 48 h. After this time, the solvent
was removed in vacuo, and the oily yellow residue was redissolved
in pentane and evaporated to dryness to remove residual toluene.
The resulting white solid was dissolved in the minimum amount
of pentane and allowed to stand at room temperature, yielding the
title compound as a colorless crystalline solid. Yield: 0.348 g (0.54
mmol, 45%). Anal. Calcd for C29H40N4OHf: C, 54.50; H, 6.31;
1
N, 8.77. Found: C, 54.75; H, 6.28; N, 8.61. H NMR (300 MHz,
C6D6, 298 K): δ 1.88 ppm (s, br, 6H, NMe2 guanidinate), 2.05 (s,
15H, C5Me5), 3.34 (s, 6H, Hf-NMe2), 4.39 (d, 1H, Hf-OCH2-
CHPh, 2JHH ) 10 Hz), 4.50 (d, 1H, Hf-OCH2CHPh,3JHH ) 6 Hz),
2
3
4.85 (d of d, 1H, Hf-OCH2CHPh, JHH ) 10 Hz, JHH ) 6 Hz),
6.90 (t, 1H, Ar C-H, 3JHH ) 7 Hz), 7.04 (m, 3H, Ar C-H), 7.12-
7.19 (m, 4H, Ar C-H), 7.31 (d, 2H, Ar C-H, 3JHH ) 7 Hz). 13C-
{1H} NMR (75.5 MHz, C6D6, 298 K): δ 11.3 ppm (C5Me5), 37.8
(NMe2 guanidinate), 46.6 (Hf-NMe2), 67.8 (Hf-OCH2CHPh), 77.8
(Hf-OCH2CHPh), 117.6 (C5Me5), 122.0, 124.4, 126.6, 128.9 (Ar
C-H), 147.2, 148.7 (Ar Cq), 165.0 (guanidinate Cq). MS (EI +ve)
m/z: 640 (66, M+), 595 (100, M+ - NMe2).
(d, 2H, o-Ar C-H, 3JHH ) 8 Hz), 6.88 (t, 1H, p-Ar C-H, 3JHH
)
8 Hz), 7.20 (t, 2H, m-Ar C-H, 3JHH ) 8 Hz). 13C{1H} NMR (75.5
MHz, C6D6, 298 K): δ 9.8 ppm (C5Me5), 22.7, 24.4 (2 × Zr-
OCH2CMe2), 38.3 (NMe2 guanidinate), 42.5 (Zr-NMe2), 59.7 (Zr-
OCH2CMe2), 82.9 (Zr-OCH2CMe2), 116.9 (C5Me5), 119.9 (p-Ar
C-H), 121.3 (m-Ar C-H), 127.4 (o-Ar C-H), 146.4 (Ar Cq), 163.5
(Cq guanidinate). MS (EI +ve) m/z: 458 (100, M+ - NMe2).
[Cp*ZrL4′(NMe2)], 2e. A J. Young ampule was charged with
(S)-HL4 (0.756 g, 3.70 mmol) and Cp*Zr(NMe2)3 (1.32 g, 3.70
mmol). Toluene (10 mL) was added, and the reaction vessel was
evacuated and heated to 60 °C for 48 h. After this time, the solvent
was removed in vacuo, and the residue redissolved in pentane and
evaporated to dryness to remove residual toluene. The resulting
yellow oily residue was transferred to a sublimation tube via pentane
solution and sublimated at 185 °C/10-6 mmHg to yield the title
compound as a yellow semisolid. Isolated yield: 0.358 g, (0.70
mmol, 19%). Anal. Calcd for C26H42N4OZr: C, 60.30; H, 8.17; N,
[Cp*HfL2′(NMe2)], 2b. A Schlenk tube was charged with HL2
(0.213 g, 1.12 mmol) and Cp*Hf(NMe2)3 (0.500 g, 1.12 mmol).
Toluene (10 mL) was added, and the reaction vessel evacuated and
left to stir at room temperature for 48 h. After this time, the solvent
was removed in vacuo, and the oily yellow residue was redissolved
in pentane and evaporated to dryness to remove residual toluene.
The resulting white solid was dissolved in the minimum amount
of pentane and cooled to -30 °C until crystalline material was
deposited. Cooling of the supernatant to -30 °C yielded further
crystalline material. Total yield: 0.332 g (0.56 mmol, 50%). Anal.
Calcd for C25H40N4OHf: C, 50.80; H, 6.82; N, 9.48. Found: C,
1
10.82. Found: C, 60.38; H, 8.20; N, 10.59. H NMR (300 MHz,
C6D6, 298 K) major diastereomer: δ 0.85 ppm (d, 3H, CH3 of iPr,
3JHH ) 7 Hz), 1.17 (d, 3H, CH3 of iPr, 3JHH ) 7 Hz), 1.77 (m, 1H,
CH of iPr), 1.98 (s, 15H, C5Me5), 2.10 (s, 6H, NMe2 guanidinate),
3.20 (s, 6H, Zr-NMe2), 3.45 (m, 1H, NCHiPr oxazoline), 4.44 (d
of d, 1H, Zr-OCH2, 2JHH ) 11 Hz), 4.57 (m, 1H, Zr-OCH2), 6.93
1
50.44; H, 6.84; N, 9.16. H NMR (300 MHz, C6D6, 298 K): δ
1.17 (s, 3H, Hf-OCH2CMee2), 1.21 (3H, Hf-OCH2CMe2), 2.01
(s, 15H, C5Me5), 2.19 (s, 6H, NMe2 guanidinate), 3.26 (s, 6H, Hf-
NMe2), 4.03 (d, 1H, Hf-OCH2CMe2, 2JHH ) 10 Hz), 4.21 (d, 1H,
2
3
Hf-OCH2CMe2, JHH ) 10 Hz), 6.75 (d, 2H, o-Ar C-H, JHH
)

142 Organometallics, Vol. 26, No. 1, 2007
Gott et al.
(t, 1H, p-Ar C-H, 3JHH ) 8 Hz), 7.00 (d, 2H, o-Ar C-H, 3JHH
)
X-ray Crystallography. Single crystals of [Cp*HfL3′(NMe2)]
(2d) were obtained from a saturated pentane solution at room
temperature as colorless blocks. The crystal was coated in an inert
oil prior to transfer to a cold nitrogen gas stream on a Bruker-AXS
SMART three-circle CCD area detector diffractometer equipped
with Mo KR radiation (λ ) 0.71073 Å). Data were collected using
narrow (0.3° in ω) frame exposures, and intensities corrected using
SADABS.30 The structure was solved using direct methods via
SHELXS and refined using SHELXL. All non-hydrogen atoms were
refined anisotropically, and hydrogen atoms placed in calculated
positions using a riding model (with free rotation for methyl groups).
All H atoms were assigned isotropic thermal parameters 1.2× (1.5×
for methyl groups) the equivalent isotropic displacement parameter
of the parent atom. The absolute structure of the crystal was
confirmed by a Flack parameter of x ) -0.020(11). Programs used
were Bruker AXS SMART (control), SAINT (integration),31 and
SHELXTL32 for structure solution, refinement, and molecular
graphics.
8 Hz), 7.22 (t, 2H, m-Ar C-H, 3JHH ) 8 Hz); minor diastereomer:
δ 1.04 ppm (d, 3H, CH3 of iPr, 3JHH ) 7 Hz), 1.08 (d, 3H, CH3 of
3
i
iPr, JHH ) 7 Hz), 2.04 (s, 15H, C5Me5), 2.18 (m, 1H, CH of Pr),
2.25 (s, 6H, NMe2 guanidinate), 3.11 (s, 6H, Zr-NMe2), 3.26 (m,
1H, NCHiPr), 4.48 (m, 2H, Zr-OCH2), 6.74 (d, 2H, o-Ar C-H,
3JHH ) 8 Hz), 6.89 (t, 1H, p-Ar C-H, JHH ) 8 Hz), 7.22 (t, 2H,
3
m-Ar C-H, JHH ) 8 Hz). 13C{1H} NMR (75.5 MHz, C6D6, 298
3
K) major diastereomer: δ 11.4 ppm (C5Me5), 17.2, 21.6 (both CH3
of iPr), 30.1 (CH of iPr), 38.3 (NMe2 guanidinate), 46.3 (Zr-NMe2),
67.2 (NCHiPr), 71.2 (Zr-OCH2), 118.4 (C5Me5), 122.7, 124.7,
129.5 (all Ar C-H), 149.6 (Ar Cq), 165.2 (guanidinate Cq); minor
i
diastereomer: δ 11.7 ppm (C5Me5), 20.2, 21.7 (both CH3 of Pr),
31.6 (CH of iPr), 40.2 (NMe2 guanidinate), 45.0 (Zr-NMe2), 68.0
(NCHiPr), 73.2 (Zr-OCH2), 119.0 (C5Me5), 121.6, 122.1, 129.7
(all Ar C-H), 149.0 (Ar Cq), 165.2 (guanidinate Cq). MS (EI +ve)
m/z: 472 (100, M+ - NMe2).
[Cp*ZrL5′(NMe2)], 2f. A J. Young ampule was charged with
(S)-HL5 (0.200 g, 0.91 mmol) and Cp*Zr(NMe2)3 (0.328 g, 0.91
mmol). Toluene (10 mL) was added, and the reaction vessel
evacuated and heated to 60 °C for 48 h. After this time, the solvent
was removed in vacuo, and the oily yellow residue was redissolved
in pentane and evaporated to dryness to remove residual toluene.
The process was repeated to yield the title compound as a white
semisolid. Isolated yield: 0.192 g (0.36 mmol, 40%). Anal. Calcd
for C27H44N4OZr: C, 60.97; H, 8.34; N, 10.53. Found: C, 60.05;
H, 8.29; N, 9.84. 1H NMR (300 MHz, C6D6, 298 K) major
diastereomer: δ 1.13 ppm (s, 9H, tBu), 2.04 (s, 15H, C5Me5), 2.28
(s, 6H, NMe2 guanidinate), 3.12 (s, 6H, Zr-NMe2), 3,34 (d, 1H,
Acknowledgment. We acknowledge the EPSRC for finan-
cial support (to A.L.G.). We are extremely grateful to Dr.
Benson M. Kariuki and the Department of Chemistry, University
of Birmingham, U.K., for assistance in the collection of the
X-ray data.
Note Added in Proof. During the processing of this
manuscript a report by Gade and co-workers appeared which
describes a similar ring-opening reaction of bis(aminooxazo-
linates), although a different mechanistic hypothesis was
presented. Ward, B. D.; Risler, H.; Weitershaus, K.; Bellemin-
Laponnaz, S.; Wadepohl, H.; Gade, L. H. Inorg. Chem. 2006,
45, 7777.
3
NCHtBu, JHH ) 6 Hz), 4.52 (m, 1H, Zr-OCH2), 4.72 (d, 1H,
3
3
Zr-OCH2, JHH ) 6 Hz) 6.80 (d, 2H, o-Ar C-H, JHH ) 8 Hz),
3
6.91 (t, 1H, p-Ar C-H, JHH ) 8 Hz), 7.22 (t, 2H, m-Ar C-H);
minor diastereomer: δ 1.02 ppm (s, 9H, tBu), 1.94 (s, 15H, C5Me5),
2.12 (s, 6H, guanidinate NMe2), 3.11 (s, 6H, Zr-NMe2), 3.39 (d,
1H, NCHtBu, 3JHH ) 6 Hz), 4.43 (m, 1H, Zr-OCH2), 4.75 (d, 1H,
Zr-OCH2, 3JHH ) 6 Hz), 6.95-7.03 (m, 3H, m- and p-Ar C-H),
7.08 (d, 2H, o-Ar C-H, 3JHH ) 8 Hz). 13C{1H} NMR (75.5 MHz,
C6D6, 298 K): major diastereomer: δ 11.3 ppm (C5Me5), 28.4 (CH3
of tBu), 36.6 (Cq of tBu), 40.5 (NMe2 guanidinate), 45.0 (Zr-NMe2),
70.2 (NCHtBu), 74.8 (Zr-OCH2), 118.2 (C5Me5), 122.7, 125.8,
129.1 (Ar C-H), 150.1 (Ar Cq), 164.9 (guanidinate Cq); minor
diastereomer: δ 11.7 ppm (C5Me5), 29.3 (CH3 of tBu), 35.3 (Cq of
tBu), 39.3 (NMe2 guanidinate), 46.3 (Zr-NMe2), 68.6 (NCHtBu),
73.9 (Zr-OCH2), 119.2 (C5Me5), 121.6, 122.5, 129.5 (Ar C-H),
149.5 (Ar Cq), 166.0 (guanidinate Cq). MS (EI +ve) m/z: 486 (100,
M+ - NMe2).
Supporting Information Available: CIF file for the structural
determination of 2d. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM0607649
(30) Sheldrick, G. M. SADABS, Program for Area Detector Absorption
Correction; Institute for Inorganic Chemistry, University of Gottingen:
Germany, 1996.
(31) SMART and SAINT; Bruker Analytical X-Ray Systems Inc.:
Madison, WI, 1998.
(32) Sheldrick, G. M. SHELXTL, Version 5.1; Bruker Analytical X-ray
Systems: Madison, WI, 1997.