Preparation of new zirconium benzamidinates: Alkyl derivatives and low-valent chemistry yielding metallacycles via coupling of alkynes and ethylene

Article abstract of DOI:10.1039/a703109b

A wide range of new zirconium(IV) derivatives utilizing the N,N′-bis(trimethylsilyl)benzamidinato ligand are reported. The previously reported dichloride, L₂ZrCl₂ [L = PhC(NSiMe₃)₂], reacted cleanly with 1 equivalent of Me₂Mg in Et₂O to give L₂ZrMe₂ which was isolated as colorless crystals from CH₂Cl₂ or Et₂O. Attempting to prepare the methyl chloride derivative using 0.5 equivalent of Me₂Mg yielded mixtures of dichloride, dimethyl and methyl chloride derivatives. The compound L₂ZrCl₂ reacted cleanly with 1 equivalent of the bulkier alkyl LiCH₂SiMe₃ giving L₂Zr(CH₂SiMe₃)Cl. Reactivity of methyl derivatives with a variety of small molecules (CO, CO₂ or acetone) is reported. The dimethyl compound, L₂ZrMe₂, reacted cleanly with B(C₆F₅)₃ to form the methyltriarylborate complex L₂Zr[MeB(C₆F₅)₃]Me which is moderately active towards ethylene polymerization. Additionally several other derivatives are conveniently prepared by salt-metathesis reactions with the dichloride including: L₂Zr(CH₂Ph)₂, L₂Zr(OSO₂CF₃)₂, L₂Zr[NH(C₆H₃Prⁱ₁-2,6)]Cl, L₂Zr(BH₄)₂, L₂Zr[ESi(SiMe₃)₃]Cl (E = Se or Te). The 1% Na-Hg amalgam reduction of L₂ZrCl₂ in the presence of diphenylacetylene or trimethylsilylacetylene yielded orange zirconacyclopentadienes L₂Zr(C₄Ph₄) and L₂Zr[C₄H₂(SiMe₃)₂-2,4] in moderate yields. The compound L₂Zr(C₄Ph₄) reacted readily with CO to give the dark red η²-cyclopentadienone L₂Zr[η²-C(O)C₄Ph₄]. Analogous to the formation of the zirconacyclopentadienes, reduction in the presence of ethylene gave the zirconacyclopentane, L₂Zr(C₄H₈), in good yield. When the reduction is carried out in the absence of any trapping ligands, however, a benzamidinate ligand is oxidatively cleaved and the dimeric imido-iminoacyl compound, [LZr(η²-PhCNSiMe₃)(μ-NSiMe₃)] ₂, is isolated as orange crystals in moderate yield. Single-crystal X-ray diffraction data are reported for L₂ZrCl₂, L₂ZrMe₂ and L₂Zr(C₄H₈).

Full text of DOI:10.1039/a703109b

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Preparation of new zirconium benzamidinates: alkyl derivatives and
low-valent chemistry yielding metallacycles via coupling of alkynes
and ethylene†
John R. Hagadorn and John Arnold*,‡
Department of Chemistry, University of California, Berkeley, California 94720, USA
A wide range of new zirconium() derivatives utilizing the N,NЈ-bis(trimethylsilyl)benzamidinato ligand are
reported. The previously reported dichloride, L2ZrCl2 [L = PhC(NSiMe3)2], reacted cleanly with 1 equivalent of
Me2Mg in Et2O to give L2ZrMe2 which was isolated as colorless crystals from CH2Cl2 or Et2O. Attempting to
prepare the methyl chloride derivative using 0.5 equivalent of Me2Mg yielded mixtures of dichloride, dimethyl and
methyl chloride derivatives. The compound L2ZrCl2 reacted cleanly with 1 equivalent of the bulkier alkyl
LiCH2SiMe3 giving L2Zr(CH2SiMe3)Cl. Reactivity of methyl derivatives with a variety of small molecules (CO,
CO2 or acetone) is reported. The dimethyl compound, L2ZrMe2, reacted cleanly with B(C6F5)3 to form the
methyltriarylborate complex L2Zr[MeB(C6F5)3]Me which is moderately active towards ethylene polymerization.
Additionally, several other derivatives are conveniently prepared by salt-metathesis reactions with the dichloride
including: L2Zr(CH2Ph)2, L2Zr(OSO2CF3)2, L2Zr[NH(C6H3Pri2-2,6)]Cl, L2Zr(BH4)2, L2Zr[ESi(SiMe3)3]Cl (E = Se
or Te). The 1% Na–Hg amalgam reduction of L2ZrCl2 in the presence of diphenylacetylene or trimethylsilyl-
acetylene yielded orange zirconacyclopentadienes L2Zr(C4Ph4) and L2Zr[C4H2(SiMe3)2-2,4] in moderate yields. The
compound L2Zr(C4Ph4) reacted readily with CO to give the dark red η2-cyclopentadienone L2Zr[η2-C(O)C4Ph4].
Analogous to the formation of the zirconacyclopentadienes, reduction in the presence of ethylene gave the
zirconacyclopentane, L2Zr(C4H8), in good yield. When the reduction is carried out in the absence of any trapping
ligands, however, a benzamidinate ligand is oxidatively cleaved and the dimeric imido-iminoacyl compound,
[LZr(η2-PhCNSiMe3)(µ-NSiMe3)]2, is isolated as orange crystals in moderate yield. Single-crystal X-ray
diffraction data are reported for L2ZrCl2, L2ZrMe2 and L2Zr(C4H8).
Recently, there has been growing interest in the use of
N-donor ligands as Cp (Cp = η-C5H5) alternatives for early-
transition-metal chemistry.1 Driving much of this research is
the tremendous success that metallocenes have enjoyed in
important reactions including olefin polymerization, heterocy-
cle formation and organic transformations.2–4 A number of
workers have explored the use of bulky amido,5–9 porphyrin,10
N4-macrocycles,11–15 and other ligands with much success. We
were attracted to the N,NЈ-bis(trimethylsilyl)benzamidinate
ligand due to its ease of preparation and derivatization and its
proven synthetic utility for transition metal, main group and
f-block element derivatives throughout the periodic table.16–18
We 19 and others20–22 have published results on a variety of
zirconium amidinates; much of the interest has been in their
ability to support electrophilic, olefin polymerization catalysts.
Sterically, the bis(trimethylsilyl)benzamidinate ligand appears
to be intermediate to Cp and Cp* (Cp* = η-C5Me5) ligands,
although the shape of the ligand sphere is quite different.23
Electronically, the hard three-electron donor ligands are
expected to generate a highly Lewis-acidic metal. Indeed,
reactivity differences between bis(amidinate) and bis(cyclo-
pentadienyl) systems have been attributed 23 to the highly polar-
ized nature of the metal–nitrogen bonds leading to increased
metal ionicity. In this paper, we report the full experimental
details of a range of new Zr derivatives and their reaction chem-
istry, as well as details of some previously communicated
work.19
L2Zr(CH2Ph)2
Me2Mg
L2Zr[NH(C6H3Pri2-2,6)]Cl
LiNH(CH3Pri2-2,6)
PhCH2MgCl
L2ZrCl2
LiBH4
L2ZrMe2
L2Zr(BH4)2
LiESi(SiMe3)3
E = Se or Te
LiCH2SiMe3
AgOTf
L2Zr(CH2SiMe3)Cl
L2Zr[ESi(SiMe3)3]Cl
L2Zr(OTf)2
Scheme 1 L = PhC(NSiMe3)2, OTf = OSO2CF3
starting material for the preparation of a wide range of deriv-
atives via salt metathesis. Dimethyl and dibenzyl derivatives
were easily prepared by the addition of Me2Mg or PhCH2MgCl
solutions to the dichloride in Et2O. Typical isolated yields fol-
lowing work-up and crystallization were over 80%. Similarly,
Rausch and co-workers21 have recently reported preparing the
dimethyl compound from L2ZrCl2 and MeLi. The compound
L2ZrMe2 is a high melting, colorless crystalline solid that dis-
plays no sign of decomposition after 1 year in a N2-filled dry-
box. The yellow dibenzyl derivative is likewise thermally stable.
In contrast to the titanium system, attempts to prepare the
methyl chloride derivative, L2Zr(Me)Cl, by the addition of 0.5
equivalent of Me2Mg to an homogeneous tetrahydrofuran (thf)
solution of L2ZrCl2 gave a mixture of dimethyl, methyl chloride
and dichloride derivatives (12, 73 and 15% respectively; based
Results and Discussion
1
on H NMR analysis of the crude solution). Purification by
Salt-metathesis reactions of L2ZrCl2
As shown in Scheme 1, L2ZrCl2 24 has proven to be an excellent
crystallization from Et2O proved impossible due to co-
crystallization of the three species. While Cp2Zr(Me)Cl is
commonly prepared 25,26 by heating an equimolar mixture of
Cp2ZrMe2 and Cp2ZrCl2 in toluene, only ca. 15% conversion to
L2Zr(Me)Cl was observed upon heating a [2H8]toluene solution
† Dedicated to the memory of Professor Sir Geoffrey Wilkinson, FRS.
‡ E-Mail: arnold@socrates.berkeley.edu
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Scheme 2
of the dimethyl and dichloride compounds to 130 ЊC for 3 d.
atm (atm = 101 325 Pa) per h, giving a polymer which melts
Further heating only resulted in slow decomposition of the
dimethyl. Additional attempts using milder reagents (Me2Zn or
Me3Al) led to no reaction with the dichloride. Although pure
L2Zr(Me)Cl could not be obtained, samples of ca. 90% purity
could be obtained by the thermolysis of L2ZrMe2 in CCl4.
Reaction progress was monitored periodically by 1H NMR
spectroscopy. After 17 h at 53 ЊC, a mixture with the com-
position 87% methyl chloride, 8% dimethyl and 5% dichloride
was obtained. Attempts to use a stoichiometric amount of CCl4
in C6D6 only led to 23% conversion to the methyl chloride after
7 d at 53 ЊC. With the use of a bulkier substituent, however, it
was possible to prepare an alkyl chloride derivative. Reaction of
0.5 equivalent of Mg(CH2SiMe3)2 with L2ZrCl2 in Et2O fol-
lowed by crystallization from hexamethyldisiloxane (HMDSO)
yielded analytically pure crystals of L2Zr(CH2SiMe3)Cl in 52%
yield.
just below 140 ЊC.§
Several other derivatives were prepared from L2ZrCl2 by salt-
metathesis reactions. Reaction of the dichloride with AgOTf in
thf gave L2Zr(OTf)2 in good yield. The solubility of the bis-
(triflate) in hexanes and the observation of a single signal in the
19F NMR spectrum (in C6D6) are consistent with covalently
bonded triflates. The compound L2ZrCl2 reacted cleanly with
LiBH4 in Et2O giving L2Zr(BH4)2 in 79% yield following
hexanes work-up. Infrared spectroscopy reveals multiple bands
attributable to B᎐H stretches a factor which complicates
determination of hapticity. One major feature is a strong singlet
at 2511 cmϪ1 assignable30 to the B᎐H (terminal) stretch of an
η3-BH4 ligand. The tetrahydroborate derivative is fairly
unreactive compared to the zirconocene analogue,31–33 failing to
react with diphenylacetylene or CO in C6D6 at room temp-
erature. Also, attempts to generate a terminal Zr hydride by
the addition of Lewis bases (PMe3, pyridine, Ph3PO, Et3N or 4-
dimethylaminopyridine) failed to give any reaction. The seleno-
late and tellurolate derivatives, L2Zr[ESi(SiMe3)3]Cl (E = Se or
Te), were prepared by the reaction of the dichloride with
(thf)2LiESi(SiMe3)3 in hexanes. Both are highly soluble in
hydrocarbon solvents yet can be isolated from HMDSO in ca.
65% yield. By comparison to known zirconocene compounds,34
the failure of L2Zr[ESi(SiMe3)3]Cl to react with a second
equivalent of (thf)2LiESi(SiMe3)3 is consistent with the quali-
tative view of the PhC(NSiMe3)2 ligand as being more sterically
demanding than Cp.35
[2H6]Benzene solutions of L2ZrMe2 were found to react
cleanly and readily (<1 h) with O2, CO2 or acetone (1 equiv-
alent) giving L2Zr(OMe)2, L2Zr(O2CMe)Me and L2Zr-
(OCMe3)Me respectively. Although L2Zr(OMe)2 did not react
with additional equivalents of O2, the acetate and alkoxide
derivatives were found to react with excess CO2 and acetone
within 12 h giving complex mixtures of products. Unlike
Cp2ZrMe2, which reacts with CO to cleanly form Cp2Zr-
[η2-C(O)Me]Me,27,28 L2ZrMe2 rapidly gave forest green solu-
tions from which we were unable to characterize any products.
When CO was reacted with L2Zr(Me)Cl in C6D6, however,
clean conversion to L2Zr[η2-C(O)Me]Cl occurred within 12 h.
The acyl functionality was characterized by 13C-{1H} NMR
spectroscopy which revealed a downfield signal at δ 325 and by
Reduction chemistry of L2ZrCl2
The reductive coupling of alkynes by generated ‘Cp2Zr’ is well
known and has proven to be a useful technique for the prepar-
ation of a wide range of dienes and heterocycles.36–38 Our
exploration of alkyne and ethylene coupling by reduced
zirconium amidinates has likewise shown promising results.
As shown in Scheme 2, reduction of L2ZrCl2 by 1% Na–Hg
in thf in the presence of alkynes and ethylene yielded the
expected zirconacyclopentadiene and zirconacyclopentane
products. Reduction of the dichloride in the presence of 2
equivalents of diphenylacetylene, followed by hexanes work-
up, gave L2Zr(C4Ph4) as orange crystals in 20% yield. When
only 1 equivalent of the alkyne is used, the zirconacyclo-
pentadiene is still formed along with [LZr(η2-PhCNSiMe3)(µ-
IR spectroscopy which showed the CO stretch at 1589 cmϪ1
.
Insertion of acetone into the Zr᎐C bond of L2Zr(Me)Cl
yielding L2Zr(OCMe3)Cl proceeded similarly to that of the
dimethyl, but required longer to go to completion.
Recently, several workers have utilized zirconium amidi-
nates to support olefin polymerization catalysts.20–22 Rausch
and co-workers reported 21 reacting L2ZrMe2 with
Ph3C[B(C6F5)3] to presumably form a cationic zirconium
alkyl, with the loss of Ph3CMe. Surprisingly, this derivative
was found to be inactive for ethylene polymerization, where-
as the L2ZrCl2–methylaluminoxane (MAO) mixture displayed
moderate activity. We found that L2ZrMe2 readily reacts with
B(C6F5)3, which has been shown by Marks and co-workers29
to be an effective co-catalyst, in C6D6 to give a single product
that displays spectroscopic data consistent with L2Zr[MeB-
(C6F5)3]Me. Similar to the aforementioned L2ZrCl2–MAO
system, the ‘cation-like’ derivative readily polymerizes ethyl-
ene, with an activity of ca. 20 kg of polyethylene mol Zr per
§ Full details of polymerization studies will be published separately.
Preliminary studies were carried out in toluene in a Fischer–Porter
apparatus under the following conditions: T = 25 ЊC, 4 atm ethylene,
[catalyst] = 6.7 m.
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Fig. 1 Variable-temperature 1H NMR spectra of L2Zr(C4Ph4) taken in
C6D6 showing the SiMe3 peaks
NSiMe3)]2 (see later) indicating that the zirconacyclopropene
is not likely to be isolated. The zirconacyclopentadiene dis-
1
plays a broadened signal in the H NMR (C6D6) spectrum for
the trimethylsilyl group which at low temperature (Tc = 10 ЊC)
splits into two signals of equal intensity (Fig. 1). The acti-
vation parameter for this fluxional process, which we attribute
to being simple ligand rotation, is calculated to be 13(1) kcal
molϪ1 (cal = 4.184 J). When the asymmetric alkyne
Me3SiCCH was used, the 2,4 substituted zirconacyclopenta-
diene, L2Zr[C4H2(SiMe3)2-2,4], was isolated in 39% yield. No
evidence for the formation of other regioisomers was found
upon 1H NMR analysis of the crude reaction solution.
Hydrolysis of Zr᎐C bonds by the addition of several equiva-
lents of H2O to C6D6 solutions of L2Zr(C4Ph4) and
L2Zr[C4H2(SiMe3)2-2,4] cleanly gave (1E, 3E)-1,2,3,4-tetra-
phenylbuta-1,3-diene and (1E)-1,3-bis(trimethylsilyl)buta-1,3-
diene (along with an uncharacterized white precipitate). Reac-
tion of L2Zr(C4Ph4) with CO in toluene occurs immediately
(Scheme 2) forming the η2-cyclopentadienone, L2Zr[η2-
C(O)C4Ph4], which was isolated in 61% yield. The dark red
zirconacyclopentadienone was characterized analytically and
displays a parent ion in the electron impact (EI) mass spec-
trum. Although indefinitely stable in C6D6, it was found to
decompose rapidly in CDCl3. Similar to its precursor zirco-
Fig. 2 Comparison of structural features of crystallographically char-
acterized derivatives with related zirconocenes42–44
revealed a stretch at 1518 cmϪ1 which is consistent with either a
C᎐N or a C᎐C double bond, and X-ray crystallography showed
the compound to be the dimeric imido-iminoacyl complex,
[LZr(η2-PhCNSiMe3)(µ-NSiMe3)]2, formed via the oxidative
cleavage of an amidinate ligand. Details of the crystal structure
have been communicated 19 and a line drawing is shown in
Scheme 2. The metallacycle reactions imply that the reaction
proceeds via a ‘L2Zr’ intermediate which must undergo C᎐N
cleavage of an amidinate ligand and dimerization to afford the
isolated product. Attempts to trap intermediates formed after
ligand cleavage (with phosphines, CO or thf) failed implying
that ligand cleavage may occur after a bimetallic intermediate is
formed. We have also recently reported similar ligand cleavage
in a related Ti system.39 Additionally, Cotton and co-workers
have reported 40,41 C᎐N bond cleavages of formamidinate
ligands by reduced Ti and Ta systems.
nacyclopentadiene, L2Zr[η2-C(O)C4Ph4] also displays
a
broadened signal in the 1H NMR spectrum (C6D6) for the
trimethylsilyl groups which decoalesce into two singlets of
equal intensity (Tc = Ϫ23 ЊC) giving a calculated activation
parameter [∆G‡ = 12(1) kcal molϪ1] which is slightly lower
than that of the zirconacyclopentadiene.
Crystal structure descriptions
Structural data and collection parameters can be found in Table
1. While this manuscript was in preparation, the structures of
L2ZrCl2 and L2ZrMe2 were reported by Walther et al.,20 so their
descriptions will be appropriately brief. Comparisons will be
made to the related zirconocene derivatives Cp2ZrCl2,42
Cp2ZrMe2,43 and Cp2Zr[C5H8(CH2)2-1,2]44 shown in Fig. 2.
Carrying out the reduction under ethylene (100 psi, 1
psi = 6894.76 Pa) gave the zirconacyclopentane product,
L2Zr(C4H8), which was isolated as orange crystals from hexanes
in 67% yield. This improved yield relative to the zirconacyclo-
pentadienes is possibly due to a higher concentration of alkene
(compared to alkyne) in solution or possibly just better crystal-
lization properties. The compound L2Zr(C4H8) is remarkably
L2ZrCl2. An ORTEP 45 view is shown in Fig. 3 with selected
bond lengths and angles in Table 2. The solid-state structure
contains a crystallographically imposed two-fold axis which
splits the Cl᎐Zr᎐Cl angle. As expected, the amidinates are co-
ordinated to the Zr center cis to one another. The Zr᎐N bond
lengths are similar [2.251(4), 2.208(4) Å], with a slight elong-
ation of the Zr᎐N bond trans to N. The Zr᎐Cl bond length of
1
stable, showing no decomposition (by H NMR spectroscopy)
after 1 year in a fluorescent-lit dry box. Unlike the hindered
zirconacyclopentadienes, reactivity with CO (in C6D6) is messy,
apparently forming multiple products.
43
Carrying out the Na–Hg reduction in the absence of trapping
ligands afforded a new orange product which displayed
2.403(1) Å is relatively short compared to those in Cp2ZrCl2
[2.436(5), 2.446(5) Å] perhaps reflecting the ionic bonding of
the amidinate ligands relative to the soft Cp ligands. The broad
Cl᎐Zr᎐Cl angle [103.95(9)Њ] compared to that in Cp2ZrCl2
[97.1(2)Њ] implies a sterically unhindered Zr center in the solid
state.
1
four trimethylsilyl signals of equal intensity in the H NMR
spectrum (in C6D6). At elevated temperatures (Tc = 75 ЊC), two
of the signals coalesced [∆G‡ = 17(1) kcal molϪ1] revealing a
very sterically hindered metal center(s). Infrared spectroscopy
J. Chem. Soc., Dalton Trans., 1997, Pages 3087–3096
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Table 1 Crystal data and collection parameters
L2ZrCl2
L2ZrMe2
L2Zr(C4H8)
Formula
M
C26H46Cl2N4Si4Zr
689.15
C28H52N4Si4Zr
648.31
C30H54N4Si4Zr
674.35
Space group
T/ЊC
C2/c (no. 15)
Ϫ105
C2/c (no. 15)
Ϫ104
P21/n (no. 14)
Ϫ160
a/Å
b/Å
20.941(3)
9.2798(15)
17.867(3)
3453.3(17)
95.963(15)
4
1.28
21.416(6)
9.312(2)
17.670(3)
3506(2)
95.77(2)
4
1.23
10.5075(1)
12.6696(1)
28.2416(3)
3706.33(7)
99.665(1)
4
c/Å
U/Å3
β/Њ
Z
D/g cmϪ3
1.208
Diffractometer
Radiation (λ/Å)
Monochromator
Detector
Enraf-Nonius CAD-4
Mo-Kα (0.71 073)
Graphite
Enraf-Nonius CAD-4
Mo-Kα (0.71 073)
Graphite
Siemens SMART
Mo-Kα (0.71 073)
Graphite
CCD area detector
ω, 0.3Њ
30 s per frame
Hemisphere
3–46.5
Crystal scintillation counter
θ–2θ, ∆θ = 0.70 ϩ 0.35 tanθ
Crystal scintillation counter
θ–2θ, ∆θ = 0.70 ϩ 0.35 tanθ
Scan type, width
Scan speed
Reflections measured
2θ range/Њ
5.49 (θ, Њ minϪ1
ϩh, ϩk, ±l
3–45
)
5.49 (θ, Њ minϪ1
ϩh, ±k, ±l
3–45
)
µ/cmϪ1
6.20
4.64
4.49
Tmin, Tmax
0.91, 1.35
0.17 × 0.28 × 0.35
2420
2250
1897
0.94, 1.00
0.30 × 0.40 × 0.40
4945
2278
1917
0.910, 0.997
0.20 × 0.15 × 0.15
15 242
5614
3752
568
0.0376
0.0405
1.51
Crystal dimensions/mm
Reflections measured
Unique reflections
Observations (I > 3σ)
Parameters
R
168
168
0.0443
0.0537
2.397
0.0267
0.0363
1.501
RЈ
S
Table 2 Selected bond lengths (Å) and angles (Њ) for L2ZrCl2
Zr᎐Cl
2.403(1)
2.208(4)
2.251(4)
1.765(4)
N(2)᎐Si(2)
N(1)᎐C(1)
N(2)᎐C(1)
C(1)᎐C(2)
1.763(4)
1.315(6)
1.326(6)
1.518(7)
Zr᎐N(1)
Zr᎐N(2)
N(1)᎐Si(1)
Cl᎐Zr᎐Cl
103.95(9)
91.22(10)
147.82(11)
60.58(14)
N(1)᎐Zr᎐N(1Ј)
N(1)᎐Zr᎐N(2Ј) 111.54(14)
N(2)᎐Zr᎐N(2Ј) 169.9(2)
90.5(2)
N(1)᎐Zr᎐Cl
N(1)᎐Zr᎐ClЈ
N(1)᎐Zr᎐N(2)
Table 3 Selected bond lengths (Å) and angles (Њ) for L2ZrMe2
Zr᎐C(1)
Zr᎐N(1)
Zr᎐N(2)
N(1)᎐Si(1)
2.241(4)
2.319(2)
2.237(2)
1.752(2)
N(2)᎐Si(2)
N(1)᎐C(2)
N(2)᎐C(2)
C(2)᎐C(3)
1.744(2)
1.320(4)
1.340(4)
1.507(4)
Fig. 3 An ORTEP view of L2ZrCl2 down the C2 axis drawn with 50%
thermal ellipsoids. Hydrogens omitted for clarity
C(1)᎐Zr᎐C(1)
N(1)᎐Zr᎐C(1)
N(1)᎐Zr᎐C(1Ј)
N(1)᎐Zr᎐N(2)
105.36(22)
96.33(11)
87.71(11)
59.39(9)
N(1)᎐Zr᎐N(1Ј) 176.15(13)
N(1)᎐Zr᎐N(2Ј) 117.57(9)
N(2)᎐Zr᎐N(2Ј)
92.84(13)
L2ZrMe2. An ORTEP view is shown in Fig. 4 with selected
bond lengths and angles in Table 3. Like the dichloride, the
isomorphous dimethyl contains a crystallographically imposed
two-fold axis splitting the Me᎐Zr᎐Me angle. The Zr᎐N bond
lengths [2.319(2), 2.237(2) Å] show an elongation of the Zr᎐N
bond trans to N. Sharing the trends observed for the dichloride,
the Zr᎐Me bond length of 2.241(4) Å is short compared to
44
those in Cp2ZrMe2 (2.273, 2.280 Å), and the Me᎐Zr᎐Me
bond angle of 105.4(2)Њ is large relative to that of Cp2ZrMe2
(95.6Њ).
L2Zr(C4H8). The ORTEP views are shown in Figs. 5 and 6
with selected bond lengths and angles in Table 4. Geometry at
the Zr center is pseudo-octahedral, with the amidinate ligands
bonded cis in typical fashion. The Zr᎐N bond lengths [2.215(3),
2.317(3), 2.250(3), 2.315(3) Å] display the same trans influence
observed in the aforementioned dichloride and dimethyl struc-
Fig. 4 An ORTEP view of L2ZrMe2 drawn with 50% thermal
ellipsoids. Hydrogens omitted for clarity
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C᎐Zr᎐C angle of 76.4(2)Њ is exceptionally acute relative to
Table 4 Selected bond lengths (Å) and angles (Њ) for L2Zr(η2-C4H8)
that of the dimethyl [105.4(2)Њ] and compared to the related
parameter of Cp2Zr[C5H8(CH2)2-1,2] [89.2(1)Њ]. The high
quality of the data set allowed for the location of the metalla-
cycle hydrogens in a Fourier-difference map and their sub-
sequent isotropic refinement. This revealed close contacts
between Zr᎐H(2) and Zr᎐H(7) at distances of 2.41(4) and
2.48(4) Å respectively. In addition, the acute Zr᎐C(1)᎐H(2)
and Zr᎐C(4)᎐H(7) angles of 88(3) and 93(2)Њ respectively lend
additional support to the presence of agostic interactions with
the formally 12-electron metal center.46
Zr᎐N(1)
Zr᎐N(2)
Zr᎐N(3)
Zr᎐N(4)
Zr᎐C(1)
Zr᎐C(4)
Zr᎐H(2)
Zr᎐H(7)
C(1)᎐C(2)
C(2)᎐C(3)
2.215(3)
2.317(3)
2.250(3)
2.315(3)
2.252(4)
2.244(5)
2.41(4)
2.48(4)
1.526(7)
1.528(7)
C(3)᎐C(4)
C(1)᎐H(1)
C(1)᎐H(2)
C(2)᎐H(3)
C(2)᎐H(4)
C(3)᎐H(5)
C(3)᎐H(6)
C(4)᎐H(7)
C(4)᎐H(8)
1.525(6)
1.09(4)
0.95(4)
0.97(4)
0.94(4)
0.93(4)
1.03(4)
0.96(4)
0.96(4)
N(1)᎐Zr᎐N(2)
N(1)᎐Zr᎐N(3) 102.4(1)
N(1)᎐Zr᎐N(4) 111.6(1)
N(1)᎐Zr᎐C(1)
N(1)᎐Zr᎐C(4)
N(2)᎐Zr᎐N(3) 102.4(1)
N(2)᎐Zr᎐N(4) 159.8(1)
N(2)᎐Zr᎐C(1)
N(2)᎐Zr᎐C(4)
N(3)᎐Zr᎐N(4)
N(3)᎐Zr᎐C(1)
60.1(1)
N(3)᎐Zr᎐C(4)
N(4)᎐Zr᎐C(1)
N(4)᎐Zr᎐C(4)
C(1)᎐Zr᎐C(4)
Zr᎐C(1)᎐H(2)
Zr᎐C(4)᎐H(7)
Zr᎐C(1)᎐C(2)
Zr᎐C(4)᎐C(3)
100.0(2)
94.9(1)
103.0(1)
76.4(2)
88(3)
93(2)
113.7(3)
112.9(3)
Experimental
General considerations
94.3(1)
144.8(2)
Standard Schlenk-line and glove box techniques were used
throughout the preparative procedures. Tetrahydrofuran,
diethyl ether, hexamethyldisiloxane and hexanes were distilled
from sodium–benzophenone under nitrogen. Dichloro-
methane was distilled from CaH2 under nitrogen; CDCl3 was
predried over 4 Å molecular sieves, degassed with three freeze–
pump–thaw cycles, and vacuum transferred from CaH2; C6D6
and [2H8]toluene were predried over 4 Å molecular sieves,
degassed with three freeze–pump–thaw cycles, and vacuum
transferred from sodium–benzophenone; CO, CO2 (bone
dry) and H2 were used directly from gas cylinders without
purification. The dichloride L2ZrCl2 was prepared by reac-
tion of ZrCl4(thf)2 with (tmen)Li[PhC(NSiMe3)2] (tmen =
N,N,NЈ,NЈ-tetramethylethylenediamine) in thf following a pro-
cedure similar to that reported for the Ti analogue.47 The com-
pounds Me2Mg,48,49 (thf)2LiSeSi(SiMe3)3,50 (thf)2LiTeSi-
103.8(1)
88.9(1)
59.9(1)
153.4(1)
C(1)᎐C(2)᎐C(3) 109.4(4)
C(2)᎐C(3)᎐C(4) 108.7(4)
50
51,52
(SiMe3)3 and B(C6F5)3
were prepared according to litera-
ture procedures. The compound LiCH2SiMe3 was prepared by
the addition of Me3SiCH2Cl to a Li dispersion in Et2O. Methyl-
lithium (halide free) and PhCH2MgCl solutions were used as
purchased from Aldrich. Lithium tetrahydroborate and AgOTf
were purchased from Strem and used as received. The com-
pound LiNHC6H3Pri2-2,6 was prepared by addition of the pri-
mary amine to n-butyllithium in hexanes–diethyl ether. Melting
points were determined in sealed capillary tubes under nitrogen
and are uncorrected. Proton and 13C-{1H} NMR spectra were
recorded at ambient temperatures. Chemical shifts (δ) are given
relative to residual protium in the deuteriated solvent at δ 7.24,
7.15, 2.09 for CDCl3, C6D6 and [2H8]toluene (methyl) respect-
ively. Selenium-77 spectra were indirectly referenced to Me2Se
at δ 0 by direct reference to KSeCN in ethanol at δ Ϫ322.
Fluorine-19 spectra were referenced to PhCF3 at δ 0.0. Infrared
samples were prepared as Nujol mulls and spectra taken using
KBr plates. Elemental analyses and mass spectral data were
determined within the College of Chemistry, University of
California, Berkeley. Single crystal X-ray structure determin-
ation was performed at CHEXRAY, University of California,
Berkeley.
Fig. 5 An ORTEP view of L2Zr(C4H8) drawn with 50% thermal
ellipsoids. Hydrogens omitted for clarity
L2ZrMe2
A diethyl ether solution of Me2Mg (42.7 cm3, 14.5 mmol) was
added dropwise to L2ZrCl2 (10.0 g, 14.5 mmol) in diethyl ether
(200 cm3) forming a cloudy, light beige solution. After stirring
overnight, the ether was removed under reduced pressure
affording a light beige solid. The solid was extracted with
CH2Cl2 (150 cm3) and filtered through a Celite pad on a fritted
disc. Concentration to 100 cm3 followed by cooling to Ϫ40 ЊC
gave the product as analytically pure, colorless crystals (7.7 g,
Fig. 6 An ORTEP view of the core of L2Zr(C4H8) drawn with 50%
thermal ellipsoids
1
82%). M.p. 190–201 ЊC. H NMR (C6D6, 300 MHz): δ 7.22–
tures. The zirconacyclopentane moiety is twisted. The Zr᎐C
bond distances [2.252(4), 2.244(5) Å] are virtually identical to
that of the dimethyl derivative [2.241(4) Å] but are shorter than
those of Cp2Zr[C5H8(CH2)2-1,2]44 [2.275(2), 2.286(2) Å]. The
7.17 (m, 4 H), 7.03–6.97 (m, 6 H), 1.02 (s 6 H), 0.12 (s, 36 H).
13C-{1H} NMR (C6D6, 75.5 MHz): δ 184.4, 140.9, 128.8, 126.2,
44.8, 2.2. IR (KBr): 1391s, 1261m, 1247m, 1167w, 1113w, 980m,
920w, 841s, 787m, 759m, 720m, 702m, 494m cmϪ1 (Found: C,
J. Chem. Soc., Dalton Trans., 1997, Pages 3087–3096
3091

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51.76; H, 7.77; N, 8.87. Calc. for C28H52N4Si4Zr: C, 51.87; H,
8.08; H, 8.64%).
hexanes gave analytically pure product. M.p. 200 ЊC (decomp.).
1H NMR (C6D6, 300 MHz): δ 7.44 (d, J = 8.1, 4 H), 7.30 (t,
J = 7.4 Hz, 4 H), 7.05–6.95 (m, 12 H), 2.85 (s, 4 H), 0.02 (s,
36 H). 13C-{1H} NMR (C6D6, 75.5 MHz): δ 187.4, 150.0,
140.5, 129.0, 128.8, 128.2, 127.6, 126.2, 121.2, 78.3, 2.8. IR
(KBr): 1594m, 1391s, 1260 (sh), 1248m, 1203m, 1178w,
1075w, 1028w, 1006m, 982s, 920w, 837s (br), 787m, 765m,
743m, 714m, 699m, 552w, 529w, 501m cmϪ1 (Found: C,
59.93; H, 7.49; N, 6.96. Calc. for C40H60N4Si4Zr: C, 60.02; H,
7.55; H, 7.00%).
Reaction of L2ZrCl2 with Me2Mg
Tetrahydrofuran (30 cm3) was added to L2ZrCl2 (0.50 g, 0.72
mmol) forming a clear, colorless solution. A diethyl ether
solution of Me2Mg (1.5 cm3, 0.36 mmol) was added dropwise
over 15 min. After stirring overnight, the volatile materials were
removed under reduced pressure producing a white solid. The
solid was extracted with CH2Cl2 (20 cm3) and filtered. Removal
of the CH2Cl2 under reduced pressure produced a white solid
which was found to be composed of 73% L2Zr(Me)Cl, 15%
L2ZrCl2 and 12% L2ZrMe2 by 1H NMR spectroscopy. Attempts
to isolate pure L2Zr(Me)Cl by crystallization have been unsuc-
cessful. 1H NMR (C6D6, 300 MHz): δ 7.2–7.1 (m, 6 H), 7.0–6.9
(m, 8 H), 1.31 [s, 3 H, L2Zr(Me)Cl], 1.02 (s, 1 H, L2ZrMe2), 0.18
(s, 7 H, L2ZrCl2), 0.15 [s, 36 H, L2Zr(Me)Cl], 0.12 (s, 6 H,
L2ZrMe2).
L2Zr[SeSi(SiMe3)3]Cl
At Ϫ10 ЊC, hexanes (40 cm3) were added to L2ZrCl2 (0.35 g,
0.50 mmol) and (thf)2LiSeSi(SiMe3)3 (0.25 g, 0.53 mmol) form-
ing a cloudy yellow solution. After stirring overnight at room
temperature, the volatile materials were removed under reduced
pressure affording a light yellow solid. Extraction of the solid
with HMDSO (25 cm3) followed by filtration gave a clear,
yellow solution. Concentration of the solution to 10 cm3 and
cooling to Ϫ40 ЊC gave 0.21 g of product as small yellow
crystals. A second crop (0.11 g) was isolated from the mother-
Reaction of L2ZrMe2 with CCl4
A solution of L2ZrMe2 (2.00 g, 3.08 mmol) in CCl4 (30 cm3) was
heated to 53 ЊC for 17 h. At this time, 1H NMR analysis of the
reaction mixture indicated a mixture with the composition 87%
L2Zr(Me)Cl, 8% L2ZrMe2 and 5% L2ZrCl2. The volatiles were
removed under reduced pressure, and the residue crystallized
from Et2O. The resulting colorless crystals (1.6 g, 78%) had
similar composition to the crude solution and were used in
subsequent reaction studies.
1
liquor. Total yield: 0.32 g, 65%. M.p. 179–184 ЊC. H NMR
(C6D6, 300 MHz): δ 7.32–7.28 (m, 4 H), 7.01–6.96 (m, 6 H),
0.54 (s, 27 H), 0.23 (s, 36 H). 13C-{1H} NMR (C6D6, 75.5 MHz):
δ 183.7, 140.3, 129.3, 128.2, 126.5, 2.9, 1.8. 77Se NMR (C6D6,
57.2 MHz): δ Ϫ2.92. IR (KBr): 1378s (br), 1243m, 1002m,
979m, 841s (br), 765m, 706m, 494m cmϪ1 (Found: C, 43.05;
H, 7.22; N, 6.01. Calc. for C35H73ClN4SeSi8Zr: C, 42.88; H,
7.51; N, 5.72%).
Reaction of L2ZrMe2 with B(C6F5)3
L2Zr[TeSi(SiMe3)3]Cl
[2H6]Benzene was added to L2ZrMe2 (2.4 mg, 3.7 µmol) and
B(C6F5)3 (1.9 mg, 3.7 µmol) forming a clear colorless solution.
Within 30 min, a single product {L2Zr[MeB(C6F5)3]Me} had
formed. 1H NMR (C6D6, 400 MHz): δ 7.1–7.0 (m, 4 H), 7.0–6.8
(m, 6 H), 2.06 (br, 3 H), 1.07 (s, 3 H), Ϫ0.15 (s, 36 H). 19F NMR
(C6D6, 57.2 MHz): δ Ϫ132.0 (d, J = 23, 6 F ), Ϫ160.9 (t, J = 21,
3 F ), Ϫ165.1 (t, J = 19 Hz, 6 F ).
At Ϫ10 ЊC, toluene (40 cm3) was added to [PhC(NSiMe3)2]2-
ZrCl2 (0.50 g, 0.73 mmol) and (thf)2LiTeSi(SiMe3)3 (0.38 g, 0.73
mmol) forming a cloudy yellow-orange solution. After warm-
ing to ambient temperature, the solution became dark orange.
After stirring overnight, the volatile materials were removed
under reduced pressure. Extraction with HMDSO (40 cm3)
followed by filtration gave a clear orange solution. Concentra-
tion of the solution to 5 cm3 and cooling to Ϫ40 ЊC gave 0.10
g of product as orange crystals. A second crop (0.40 g) was
isolated from the mother-liquor. Total yield: 0.50 g, 67%.
M.p. 144–149 ЊC. 1H NMR (C6D6, 300 MHz): δ 7.31–7.27
(m, 4 H), 6.99–6.94 (m, 6 H), 0.57 (s, 27 H), 0.22 (s, 36 H).
13C-{1H} NMR (C6D6, 75.5 MHz): δ 183.2, 140.0, 129.4,
128.3, 126.4, 3.0, 2.3. IR (KBr): 1378s (br), 1243m, 1008m,
979m, 838s (br), 761m, 709m, 626m cmϪ1 (Found: C, 41.22;
H, 7.05; N, 5.73. Calc. for C35H73ClN4Si8TcZr: C, 40.86; H,
7.15; N, 5.45%).
L2Zr(CH2SiMe3)Cl
Diethyl ether (40 cm3) was added to L2ZrCl2 (2.00 g, 2.90 mmol)
and Mg(CH2SiMe3)2 (0.303 g, 1.52 mmol) forming a cloudy
colorless solution. After stirring overnight, the volatile
materials were removed under reduced pressure affording an
oily residue. The residue was extracted with hexanes (50 cm3)
and filtered through a pad of Celite on a fritted disc. The
hexanes were removed in vacuo and the white residue taken up
in HMDSO. Concentration of this solution to 5 cm3 followed
by cooling to Ϫ40 ЊC afforded the analytically pure product as
large colorless crystals (1.1 g, 52%). M.p. 105–108 ЊC. 1H NMR
(C6D6, 300 MHz): δ 7.33–7.28 (m, 4 H), 7.00–6.95 (m, 6 H),
1.52 (s, 2 H), 0.51 (s, 9 H), 0.17 (s, 36 H). 13C-{1H} NMR (C6D6,
75.5 MHz): δ 185.1, 140.1, 129.3, 126.4, 68.7, 3.9, 2.7. IR
(KBr): 1400s (br), 1262m, 1248s, 1160w, 1074w, 1010w, 982s,
915m, 836s (br), 786m, 763m, 743m, 714m, 499m cmϪ1 (Found:
C, 48.93; H, 7.67; N, 7.96. Calc. for C30H57ClN4Si5Zr: C, 48.63;
H, 7.75; N, 7.56%).
L2Zr(NHC6H3Pri2-2,6)Cl
At Ϫ10 ЊC, toluene (110 cm3) was added to L2ZrCl2 (2.00 g,
2.90 mmol) and LiNHC6H3Pri2-2,6 (0.55 g, 3.0 mmol) forming
a cloudy, dull yellow solution. The mixture was warmed to
room temperature over 2 h. After stirring overnight, the toluene
was removed under reduced pressure affording a light yellow
solid. The solid was extracted with hexanes (75 cm3) and
filtered. Concentration of the clear yellow solution to 20 cm3
followed by cooling to Ϫ40 ЊC produced 1.25 g of product as
yellow crystals. A second crop (0.12 g) was isolated from the
mother-liquor. Total yield: 1.37 g, 58%. Analytically pure
crystals were obtained by recrystallization in hexanes. M.p.
L2Zr(CH2Ph)2
To a colorless slurry of L2ZrCl2 (3.00 g, 4.35 mmol) and Et2O
(45 cm3) was added an ether solution of PhCH2MgCl (5.00 cm3,
8.71 mmol) forming a cloudy yellow solution. After stirring
overnight, the volatiles were removed under reduced pressure
and the yellow solid was extracted with CH2Cl2 (60 cm3). The
extract was filtered through a pad of Celite on a fritted disc and
concentrated to 30 cm3. Pentane (20 cm3) was added and the
solution was filtered again. Cooling to Ϫ40 ЊC yielded the
product as yellow crystals (2.7 g, 78%). Recrystallization from
1
197–200 ЊC. H NMR (C6D6, 300 MHz): δ 7.37–7.31 (m, 4 H),
7.22 (d, J = 7.6, 2 H), 7.18 (s, 1 H), 7.07 (t, J = 7.6, 1 H), 7.01–
6.96 (m, 6 H), 4.07 (br, 2 H), 1.52 (d, J = 6.7 Hz, 6 H), 0.11 (s, 36
H). 13C-{1H} NMR (C6D6, 75.5 MHz): δ 184.6, 140.3, 129.3,
128.2, 127.8, 126.7, 122.9, 28.6, 25.1, 2.5. IR (KBr): 1400s (br),
1248s, 1189s, 1161w, 1114w, 1075w, 1032w, 1009m, 984s, 927w,
843s (br), 788m, 762m, 742m, 716m, 499m cmϪ1 (Found: C,
3092
J. Chem. Soc., Dalton Trans., 1997, Pages 3087–3096

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1
54.96; H, 7.89; N, 8.60. Calc. for C38H64ClN5Si4Zr: C, 54.99; H,
7.77; N, 8.44%).
overnight (0.61 g, 79%). H NMR (CDCl3, 400 MHz): δ 7.34–
7.29 (m, 6 H), 7.21–7.16 (m, 4 H), 1.45 (s, 9 H), 0.19 (s, 3 H),
Ϫ0.11 (s, 36 H). 13C-{1H} NMR (CDCl3, 75.5 MHz): δ 182.7,
141.6, 128.3, 128.0, 125.9, 77.8, 32.5, 32.1, 2.2.
L2Zr(OTf)2
To a 100 cm3 round-bottomed flask containing [PhC(N-
SiMe3)2]2ZrCl2 (0.50 g, 0.73 mmol) and AgOTf (0.41 g, 1.6
mmol) was added thf (30 cm3) forming a milky white slurry.
After stirring overnight, the volatiles were removed under
reduced pressure and the residue was extracted with Et2O (40
cm3). The extract was filtered through Celite on a fritted disc
and concentrated to 10 cm3. The addition of hexanes (10 cm3)
followed by concentration to 10 cm3 and cooling to Ϫ40 ЊC
yielded 0.24 g of product as large colorless crystals. A second
crop of crystals yielded 0.17 g of product. Total yield: 0.41 g,
62%. M.p. 195–198 ЊC. 1H NMR (C6D6, 300 MHz): δ 7.40
(br, 4 H), 7.00–6.86 (m, 6 H), 0.11 (s, 36 H). 13C-{1H} NMR
(C6D6, 75.5 MHz): δ 189.0, 138.0, 130.4, 128.2, 1.7. 19F NMR
(C6D6, 57.2 MHz): δ Ϫ13.7. IR (KBr): 1364s, 1255m, 1240m,
1201s, 1154m, 981s (br), 836s (br), 788w, 765m, 745w, 708w,
691w, 632m, 594w, 508m cmϪ1 (Found: C, 36.89; H, 5.02; N,
6.02. Calc. for C28H46F6N4O6S2Si4Zr: C, 36.70; H, 5.06; N,
6.11%.
Reaction of L2Zr(Me)Cl with acetone
A procedure similar to that for the reaction of L2ZrMe2 with
acetone was followed excepting that the reaction was carried
out overnight and 5 equivalents of acetone were added to
L2Zr(Me)Cl giving the product L2Zr(OCMe3)Cl in 75% yield.
1H NMR (C6D6, 300 MHz): δ 7.28–7.20 (m, 4 H), 7.00–6.90
(m, 6 H), 1.57 (s, 9 H), 0.17 (s, 36 H). 13C-{1H} NMR
(CDCl3, 75.5 MHz): δ 182.5, 140.8, 128.7, 128.0, 126.1, 79.4,
32.1, 2.2.
Reaction of LЈ2Zr(Me)Cl with CO [LЈ = 4-MeC6H4C(NSiMe3)2]
A C6D6 (ca. 0.5 cm3) solution of LЈ2Zr(Me)Cl (ca. 5 mg) was
transferred into a Teflon-capped NMR tube. The solution was
freeze–pump–thawed and charged with CO (20 psi). After a few
minutes, the solution became yellow and within 12 h, complete
conversion to a single product [LЈ2Zr(η2-C(O)Me)Cl] had
1
occurred. H NMR (C6D6, 300 MHz); δ 7.17 (d, J = 8.4, 4 H),
6.85 (d, J = 7.8 Hz, 4 H), 2.75 (s, 3 H), 1.99 (s, 6 H), 0.17 (s, 36
H). 13C-{1H} NMR (C6D6, 75.5 MHz): δ 325.3, 183.3, 138.8,
138.5, 128.9, 126.5, 33.1, 21.2, 2.5. IR (KBr, neat film): 3061w,
2954m, 2897w, 1589w, 1577w, 1499m, 1446s, 1393s (br), 1247s,
1167w, 1008 (sh), 984s, 920w, 838s (br), 762m, 703m, 496m
L2Zr(BH4)2
Diethyl ether (50 cm3) was added to a 100 cm3 round-bottomed
flask containing L2ZrCl2 (4.00 g, 5.80 mmol) and LiBH4 (0.320
g, 14.5 mmol). After stirring overnight, the volatiles were
removed under reduced pressure giving a white solid. The solid
was extracted with warm hexanes (130 cm3) and filtered
through a pad of Celite on a fritted disc giving a clear colorless
solution. Concentration to 90 cm3 followed by cooling to
Ϫ40 ЊC afforded analytically pure product as long colorless
needles. Total yield from two crops: 3.0 g, 79%. M.p. 226–
228 ЊC. 1H NMR (C6D6, 400 MHz): δ 7.13–7.08 (m, 4 H), 6.98–
6.82 (m, 6 H), 2.14 (br, 8 H), 0.10 (s, 36 H). 13C-{1H} NMR
(C6D6, 75.5 MHz): δ 183.9, 140.0, 129.2, 126.5, 2.5. IR (KBr):
2511m, 2441w, 2400w, 2362m, 2340w, 2199w (br), 2144m (br),
1249s, 1163w, 1116w, 1075w, 1031w, 1008m, 984s, 924w, 838s
(br), 784w, 764m, 718m, 498m cmϪ1 (Found: C, 47.88; H, 8.33;
N, 8.55. Calc. for C26H54B2N4Si4Zr: C, 48.20; H, 8.40; N,
8.65%).
cmϪ1
.
L2Zr(ç2-C4Ph4)
To a 250 cm3 round-bottomed flask containing L2ZrCl2 (2.50 g,
3.63 mmol), 1% Na–Hg amalgam (0.33 g Na, 15 mmol Na),
and Ph2C2 (1.36 g, 7.62 mmol) was added thf (100 cm3) cooled
to Ϫ78 ЊC. The mixture was stirred at Ϫ10 ЊC for 4 h, then
allowed to warm to ambient temperature. After stirring
overnight, the volatile materials were removed under reduced
pressure leaving an orange residue. This residue was extracted
with hexanes (120 cm3) and filtered, giving a clear orange solu-
tion. Concentration of the solution to 30 cm3, warming to ca.
50 ЊC, and cooling to room temperature resulted in small
orange crystals of the product forming within 2 h (0.70 g, 20%).
M.p. 215–218 ЊC (decomp.). 1H NMR (CDCl3, 300 MHz):
δ 7.32–7.20 (m, 6 H), 7.11 (t, J = 7.6, 4 H), 6.94 (d, J = 7.4, 4 H),
6.89 (t, J = 7.3 Hz, 4 H), 6.82–6.70 (m, 12 H), Ϫ0.09 (br, 36 H).
13C-{1H} NMR (CDCl3, 75.5 MHz): δ 205.8, 189.0, 153.2,
149.5, 141.0, 139.9, 130.6, 128.9, 127.7, 127.6, 127.2, 126.4,
124.5, 122.7, 2.5 (br). EI mass spectrum: m/z (relative inten-
sity) 973 (Mϩ, 36), 796 (Mϩ Ϫ Ph2C2, 4), 647 (4), 616 (L2Zrϩ,
4), 382 (26), 305 (8), 249 (8), 180 (100), 165 (26), 146 (14). IR
(KBr): 1588w, 1387s (br), 1248m, 1164w, 1075w, 1006w,
981m, 843s (br), 768m, 698m, 500m cmϪ1 (Found: C, 66.88;
H, 6.96; N, 5.71. Calc. for C54H66N4Si4Zr: C, 66.54; H, 6.82;
N, 5.75%).
Reaction of L2ZrMe2 with O2
A Teflon-capped NMR tube containing L2ZrMe2 (ca. 5 mg)
and C6D6 was degassed by freeze–pump–thaw techniques then
backfilled with O2 (5 psi). Within 1.5 h, the reaction had
reached completion with only a single product [L2Zr(OMe)2]
observed by 1H NMR spectroscopy. 1H NMR (C6D6, 400
MHz): δ 7.25–7.20 (m, 4 H), 7.05–7.00 (m, 6 H), 4.08 (s, 6 H),
0.13 (s, 36 H).
Reaction of L2ZrMe2 with CO2
Reaction carried out similarly to that of L2ZrMe2 with O2.
The only differences are that 15 psi of CO2 were used and the
L2Zr[ç2-C4H2(SiMe3)2-2,4]
1
1
reaction time was 1 h. L2Zr(OAc)Me, 100% by H NMR. H
NMR (C6D6, 400 MHz): δ 7.32–7.25 (m, 4 H), 6.05–6.97 (m,
6 H), 1.98 (s, 3 H), 1.09 (s, 3 H), 0.16 (36 H). 13C-{1H} NMR
(C6D6, 75.5 MHz): δ 183.9, 140.7, 128.8, 138.1, 126.5, 124.7,
47.7, 23.5, 2.8. IR (CsI, neat): 2953m, 2898w, 1554m
(br), 1498w, 1400s (br), 1247s, 1170w, 1124w, 1074w, 1032w,
985s, 945w, 920w, 839s (br), 761m, 721m, 702m, 610w, 496m
To a 100 cm3 round-bottomed flask containing L2ZrCl2 (0.75 g,
1.1 mmol) and 1% Na–Hg amalgam (0.053 g Na, 2.3 mmol Na)
was added thf (30 cm3) and trimethylsilylacetylene (0.46 cm3,
3.3 mmol) cooled to Ϫ50 ЊC. The mixture was stirred at Ϫ10 ЊC
for 3 h, then allowed to warm to ambient temperature. After
stirring overnight, the volatile materials were removed under
reduced pressure. The oily residue was extracted with hexanes
(40 cm3) and filtered. The hexanes were removed under reduced
pressure and the orange oil was taken up in HMDSO. Con-
centration of the solution to 5 cm3 and cooling to Ϫ40 ЊC gave
the product as an orange solid (0.32 g, 39%). Recrystallization
from HMDSO gave analytically pure product. M.p. 115 ЊC
cmϪ1
.
Reaction of L2ZrMe2 with acetone
To a toluene (20 cm3) solution of L2ZrMe2 (0.71 g, 1.1 mmol)
was added acetone (84 µl, 1.1 mmol). After 45 min, the volatiles
were removed under reduced pressure producing the product
L2Zr(OCMe3)Me as a colorless oil that solidified upon standing
1
(decomp.). H NMR (CDCl3, 400 MHz): δ 8.94 (d, J = 2.1, 1
J. Chem. Soc., Dalton Trans., 1997, Pages 3087–3096
3093

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H), 8.49 (d, J = 2.1 Hz, 1 H), 7.36–7.30 (m, 6 H), 7.21–7.15 (m,
4 H), 0.14 (s, 9 H), 0.13 (s, 9 H), Ϫ0.16 (s, 36 H). 13C-{1H}
NMR (CDCl3, 75.5 MHz): δ 213.9, 209.2, 185.4, 155.4, 150.6,
140.9, 128.5, 127.9, 125.9, 2.1, 0.9, Ϫ1.6. IR (KBr): 1410s (br),
1246s, 1168w, 1074w, 1031w, 1008w, 983s, 913m, 843s (br),
7.69; N, 8.65. Calc. for C55H99N8Si8Zr2: C, 51.63; H, 7.80; N,
8.76%).
X-Ray crystallography
786m, 758m, 719m, 700m, 615w, 555w, 498m cmϪ1
.
Table 1 lists a summary of crystallographic data for all struc-
turally characterized compounds.
L2Zr[ç2-C(O)C4Ph4]
L2ZrCl2. Crystals suitable for X-ray diffraction studies were
grown from Et2O at Ϫ15 ЊC. A small crystal was mounted 53 on
a glass fiber using Paratone-N hydrocarbon oil. The crystal was
then transferred to an Enraf-Nonius CAD-4 diffractometer
and centered in the beam. It was cooled to Ϫ105 ЊC by a nitro-
gen flow low-temperature apparatus which had been previously
calibrated by a thermocouple placed at the sample position.
Crystal quality was evaluated via measurement of intensities
and inspection of peak scans. Automatic peak search and
indexing procedures yielded a triclinic reduced primitive cell.
Inspection of the Niggli values revealed a C-centered mono-
clinic cell. The final cell parameters and specific data collection
parameters for this data set are given in Table 1.
The 2420 raw intensity data were converted to structure fac-
tor amplitudes and their estimated standard deviations (e.s.d.s)
by correction for scan speed, background and Lorentz and
polarization effects. Inspection of intensity standards revealed a
reduction of 10% of the original intensity. The data were cor-
rected for this decay. Inspection of the azimuthal scan data¶
showed variations which did not agree from reflection to reflec-
tion, indicating possible orientation problems during collection
of the azimuthal scans. An empirical correction was made to
the data based on the combined differences of Fo and Fc follow-
ing refinement of all atoms with isotropic thermal parameters
(Tmax = 1.35, Tmin = 0.91, no θ dependence). Inspection of the
systematic absences indicated possible space groups Cc and C2/
c. The choice of the centric group was confirmed by the success-
ful solution and refinement of the structure. Removal of the
systematically absent data left 2250 unique data in the final data
set.
In a Schlenk tube, toluene (10 cm3) was added to L2Zr(η2-
C4Ph4) (0.19 g, 0.20 mmol) forming a clear orange solution. The
tube was briefly evacuated and then backfilled with CO (2 psi).
Almost immediately, the solution became dark red. After 20
min, the volatiles were removed under reduced pressure, and to
the oily residue was added pentane (15 cm3) causing dark red
microcrystals to form (0.12 g, 61%). M.p. 220–222 ЊC. 1H NMR
(C6D6, 300 MHz): δ 7.67 (d, J = 7.0, 4 H), 7.49 (d, J = 7.0, 4
H), 7.17 (t, J = 7.7, 4 H), 7.09 (t, J = 7.5 Hz, 4 H), 6.99 (m,
14 H), 0.05 (s, 36 H). 13C-{1H} NMR (C6D6, 75.5 MHz):
δ 185.4, 140.2, 139.0, 137.9, 132.5, 130.9, 129.6, 129.0, 127.5,
124.6, 120.4, 3.0. EI mass spectrum: m/z (relative intensity)
1001 (Mϩ, 12), 986 (10), 916 (13), 898 (100), 882 (13), 808 (10),
723 (10), 704 (10), 635 (10), 546 (10), 531 (25), 458 (80), 442
(15), 305 (22), 289 (15), 176 (20), 146 (20). IR (KBr): 1592m,
1248m, 1168w, 984m, 835s (br), 763m, 740m, 712m, 702m,
656w, 638w, 606w, 542w, 500m cmϪ1 (Found: C, 65.56; H,
6.82; N, 5.49. Calc. for C55H66N4OSi4Zr: C, 65.88; H, 6.63; N,
5.59%).
L2Zr(ç2-C4H8)
Tetrahydrofuran (30 cm3) cooled to Ϫ78 ЊC was added to
L2ZrCl2 (2.00 g, 2.90 mmol) and 1% Na–Hg amalgam (0.267 g
Na, 11.6 mmol Na) in a Fischer–Porter bottle. Immediately,
ethene (100 psi) was added and the reaction mixture was slowly
allowed to warm to ambient temperature while stirring rapidly.
After stirring for 2 d, the volatiles were removed under reduced
pressure and the orange-gray residue was extracted with
hexanes (50 cm3). Filtration followed by concentration to 4 cm3
afforded the product as orange crystals overnight (1.3 g, 67%).
Recrystallization from hexanes gave analytically pure product.
M.p. 115 ЊC (decomp.). 1H NMR (C6D6, 300 MHz): δ 7.24–7.18
(m, 4 H), 7.03–6.97 (m, 6 H), 2.89 (qnt, J = 3.4 Hz, 4 H), 1.73
(m, 4 H), 0.11 (s, 36 H). 13C-{1H} NMR (C6D6, 75.5 MHz):
δ 185.9, 140.7, 128.8, 126.5, 73.3, 33.8, 2.5. IR (KBr): 1425s,
1399s, 1248s, 1167w, 1074w, 1031w, 1008w, 982s, 920w, 842s
(br), 785w, 761m, 744w, 719m, 686w, 500m cmϪ1 (Found: C,
53.21; H, 8.12; N, 8.20. Calc. for C30H54N4Si4Zr: C, 53.43; H,
8.07; N, 8.31%).
The structure was solved by comparison to the isomorphous
Ti structure and refined via standard least-squares and Fourier
techniques. Hydrogen atoms were assigned idealized locations
and values of Biso approximately 1.3 times the Beq of the calcu-
lations, but not refined. The final residuals (R = [Σ Fo| Ϫ |Fc ]/
¹
¹
2
2
²
²
Σ|Fo|, RЈ = [Σw(|Fo| Ϫ |Fc|) ] , S = {[Σw(|Fo| Ϫ |Fc|) ]/(no Ϫ nv)} ,
where no is the number of observations, nv the number of
variable parameters, and the weights w were given by: w = 1/
¹
2
2
2
2
2
2
2
²
σ (Fo), σ(Fo ) = [σo (Fo ) ϩ (pFo ) ] , where σ (Fo) is calculated
as above from σ(Fo)2 and where p is the factor used to lower
the weight of intense reflections) for 168 variables refined
against the 1897 data for which F2 > 3σ(F2) were R = 0.0443,
RЈ = 0.0537 and S = 2.397. The R value for all 2250 data was
0.0541.
[LZr(ç2-PhCNSiMe3)(ì-NSiMe3)]2ؒ0.5C6H4
To a 100 cm3 round-bottomed flask charged with L2ZrCl2 (1.00
g, 1.45 mmol) and 1% Na–Hg amalgam (0.13 g Na, 5.8 mmol
Na) was added thf (45 cm3) cooled to Ϫ78 ЊC. The mixture was
stirred at Ϫ10 ЊC for 4 h, then allowed to warm to ambient
temperature. After stirring overnight, the volatile materials
were removed under reduced pressure leaving a brown residue.
Extraction with hexanes (50 cm3) followed by filtration gave a
clear red-orange solution. Concentration of the solution to
5 cm3 and cooling to Ϫ40 ЊC produced the product as
small, orange crystals (0.23 g, 26%). M.p. 220–223 ЊC. 1H
NMR (C6D6, 300 MHz): δ 7.42 (d, J = 7.7, 4 H), 7.32–
7.20 (m, 8 H), 7.18–7.07 (m, 4 H), 6.99 (t, J = 7.4 Hz, 4 H),
1.25 (m, hexane, 4 H), 0.86 (m, hexane, 3 H), 0.42 (s, 18 H),
0.18 (s, 18 H), 0.06 (s, 18 H), Ϫ0.48 (s, 18 H). 13C-{1H}
NMR (C6D6, 75.5 MHz): δ 279.5, 184.6, 141.7, 140.6, 129.6,
128.8, 128.3, 127.5, 127.4, 127.3, 126.3, 31.6 (hexane), 22.7
(hexane), 14.1 (hexane), 7.1, 4.2, 3.3, 2.7. IR (KBr): 1518m,
1440s (br), 1244s, 1004m, 989m, 884s, 842s (br), 752m, 722m,
690w, 604w, 584s, 507w, 486m cmϪ1 (Found: C, 51.20; H,
The quantity minimized by the least-squares program was
Σw(|Fo| Ϫ |Fo|)2, where w is the weight of a given observation.
The p factor, used to reduce the weight of intense reflections,
was set to 0.03 throughout the refinement. The analytical forms
of the scattering factor tables for the neutral atoms were used 54
and all scattering factors were corrected for both the real and
imaginary components of anomalous dispersion.55
L2ZrMe2. Crystals suitable for X-ray diffractions studies were
grown from Et2O at Ϫ15 ЊC. Data collection was performed
analogously to that for L2ZrCl2.
The 4945 raw intensity data were converted to structure fac-
tor amplitudes and their e.s.d.s by correction for scan speed,
background and Lorentz and polarization effects. Inspection of
¶ Reflections used for azimuthal scans were located near χ = 90Њ and the
intensities measured at 10Њ increments of rotation of the crystal about
the diffraction vector.
3094
J. Chem. Soc., Dalton Trans., 1997, Pages 3087–3096

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4 J. P. Collman, L. S. Hegedus, J. R. Norton and R. G. Finke,
Principles and Applications of Organotransition Metal Chemistry,
University Science Books, Mill Valley, 1987.
5 C. P. Schaller, C. C. Cummins and P. T. Wolczanski, J. Am. Chem.
Soc., 1996, 118, 591.
6 R. R. Schrock, C. C. Cummins, T. Wilhelm, S. Lin, S. M. Reid,
M. Kol and W. M. Davis, Organometallics, 1996, 15, 1470.
7 J. D. Scollard and D. H., McConville, J. Am. Chem. Soc., 1996, 118,
10 008.
8 P. J. Shapiro, W. D. Cotter, W. P. Schaefer, J. A. Labinger and
J. E. Bercaw, J. Am. Chem. Soc., 1994, 116, 4623.
9 R. A. Andersen, Inorg. Chem., 1979, 18, 2928.
10 H. Brand and J. Arnold, Coord. Chem. Rev., 1995, 140, 137.
11 D. Jacoby, S. Isoz, C. Floriani, A. Chiesi-Villa and C. Rizzoli, J. Am.
Chem. Soc., 1995, 117, 2793.
12 L. Giannini, E. Solari, S. De Angelis, T. R. Ward, C. Floriani,
A. Chiesi-Villa and C. Rizzoli, J. Am. Chem. Soc., 1995, 117, 5801.
13 R. Uhrhammer, D. G. Black, T. G. Gardner, J. D. Olsen and
R. F. Jordan, J. Am. Chem. Soc., 1993, 115, 8493.
14 C. E. Housmekerides, D. L. Ramage, C. M. Kretz, J. T. Shontz,
R. S. Pilato, G. L. Geoffroy, A. L. Rheingold and B. S. Haggerty,
Inorg. Chem., 1992, 31, 4453.
intensity standards revealed negligible reduction in intensities
(0.8%) over data collection. Inspection of the azimuthal scan
data¶ showed a variation Imin/Imax = 0.94 for the average curve.
An empirical correction based on the observed variation was
applied to the data.
Inspection of the systematic absences indicated possible
space groups Cc and C2/c. The choice of the centric group was
confirmed by the successful solution and refinement of the
structure. Removal of the systematically absent data left 2278
unique data in the final data set.
The structure was solved by comparison to the isomorphous
Ti structure and refined via standard least-squares and Fourier
techniques. Hydrogen atoms were assigned idealized locations
and values of Biso approximately 1.3 times the Beq of the calcu-
lations, but not refined. The final residuals (as for L2ZrCl2) for
168 variables refined against the 1917 data for which
F2 > 3σ(F2) were R = 0.0267, RЈ = 0.0363 and S = 1.501. The R
value for all 2278 data was 0.0333.
L2Zr(ç2-C4H8). Crystals suitable for X-ray diffraction studies
were grown from hexanes at Ϫ40 ЊC. A large crystal was cut to
appropriate size and mounted 53 on a glass capillary using
Paratone-N hydrocarbon oil. The crystal was transferred to a
Siemens SMART diffractometer/CCD area detector,56 centered
in the beam, and cooled to Ϫ160 ЊC by nitrogen-flow low-
temperature apparatus which had been previously calibrated by
a thermocouple placed at the same position as the crystal. Pre-
liminary orientation matrix and cell constants were determined
by collection of 60 10-second frames, followed by spot integ-
ration and least-squares refinement. A hemisphere of data was
collected using 0.3Њ ω scans at 30-seconds per frame. The raw
15 M. J. Scott and S. J. Lippard, J. Am. Chem. Soc., 1997, 119, 3411.
16 F. T. Edelmann, Coord. Chem. Rev., 1994, 137, 403.
17 K. Dehnicke, Chem.-Ztg., 1990, 114, 295.
18 J. Barker and M. Kilner, Coord. Chem. Rev., 1994, 133, 219.
19 J. R. Hagadorn and J. Arnold, Organometallics, 1994, 13, 4670.
20 D. Walther, R. Fischer, H. Gorls, J. Koch and B. Schweder,
J. Organomet. Chem., 1996, 508, 13.
21 J. C. Flores, J. C. W. Chien and M. D. Rausch, Organometallics,
1995, 14, 1827.
22 R. Gomez, R. Duchateau, A. N. Chernega, J. H. Teuben,
F. T. Edelmann and M. L. H. Green, J. Organomet. Chem., 1995,
491, 153.
23 R. Duchateau, C. T. van Wee, A. Meetsma, P. T. van Duijnen and
J. H. Teuben, Organometallics, 1996, 15, 2279.
24 H. W. Roesky, B. Meller, M. Noltemeyer, H. G. Schmidt, U. Scholz
and G. M. Sheldrick, Chem. Ber., 1988, 121, 1403.
25 R. F. Jordan, J. Organomet. Chem., 1985, 294, 321.
26 P. J. Walsh, F. J. Hollander and R. G. Bergman, J. Am. Chem. Soc.,
1988, 110, 8729.
27 G. Fachinetti, G. Fochi and C. Floriani, J. Chem. Soc., Dalton
Trans., 1977, 1946.
28 G. Fachinetti, C. Floriani, F. Marchetti and S. Merlino, J. Chem.
Soc., Chem. Commun., 1976, 522.
data were integrated (XY spot spread = 1.60Њ;
Z spot
spread = 0.60Њ) and the unit cell parameters refined (7373 reflec-
tions with I > 5σ) using SAINT.57 Data analysis and absorption
correction (Tmin = 0.910, Tmax = 0.997) were performed using
Siemens XPREP.58 The unit-cell parameters indicated a primi-
tive monoclinic cell and systematic absences indicated space
group P21/c (no. 14). The data were corrected for Lorentz and
polarization effects, but no correction for crystal decay was
applied.
29 X. Yang, C. L. Stern and T. J. Marks, J. Am. Chem. Soc., 1991, 113,
3623.
The 15 242 reflections measured were averaged (Rint = 0.0578)
yielding 5614 unique reflections. The structure was solved and
refined with the TEXSAN 59 software package using direct
methods60 and expanded using Fourier techniques.61 All non-
hydrogen atoms were refined anisotropically. Hydrogens were
located in a Fourier-difference map and were refined isotropic-
ally. The final residuals (as for L2ZrCl2) for the 568 variables
refined against the 3752 data for which F2 > 3σ(F2) were
R = 0.0376, RЈ = 0.0405 and S = 1.51. The quantity minimized
by the least-squares program was Σw(|Fo| Ϫ |Fc|)2, where w is
the weight of a given observation. The p factor was set to 0.03
throughout the refinement. The analytical forms of the scatter-
ing factor tables for the neutral atoms were used 54 and all scat-
tering factors were corrected for both the real and imaginary
components of anomalous dispersion.55
30 T. J. Marks and J. R. Kolb, Chem. Rev., 1977, 77, 263.
31 G. Fachinetti,, G. Fochi and C. Floriani, J. Chem. Soc., Chem.
Commun., 1976, 230.
32 B. D. James, R. K. Nanda and M. G. H. Wallbridge, Chem.
Commun., 1966, 849.
33 P. C. Wailes and H. Weigold, J. Organomet. Chem., 1970, 24, 405.
34 V. Christou, S. P. Wuller and J. Arnold, J. Am. Chem. Soc., 1993,
115, 10 545.
35 M. Wedler, F. Knosel, M. Noltemeyer and F. T. Edelmann,
J. Organomet. Chem., 1990, 388, 21.
36 T. Takahashi, M. Kagdyama, V. Denisov, R. Hara and E. Negishi,
Tetrahedron Lett., 1993, 34, 687.
37 P. J. Fagan, W. A. Nugent and J. C. Calabrese, J. Am. Chem. Soc.,
1994, 116, 1880.
38 S. L. Buchwald, R. T. Lum and J. C. Dewan, J. Am. Chem. Soc.,
1986, 108, 7441.
39 J. R. Hagadorn and J. Arnold, J. Am. Chem. Soc., 1996, 118,
893.
CCDC reference number 186/640.
40 F. A. Cotton, L. M. Daniels, C. A. Murillo and X Wang, Inorg.
Chem., 1997, 36, 896.
41 F. A. Cotton and W. A. Wojtczak, Polyhedron, 1994, 13, 1337.
42 K. Prout, T. S. Cameron, R. A. Forder, S. R. Critchley, B. Denton
and G. V. Rees, Acta Crystallogr., Sect. B, 1974, 30, 2290.
43 W. E. Hunter, D. C. Hrncir, R. V. Bynum, R. A. Pentilla and
J. L. Atwood, Organometallics, 1983, 2, 750.
44 D. F. Taber, J. P. Louley, Y. Wang, W. A. Nugent, D. A. Dixon and
R. L. Harlow, J. Am. Chem. Soc., 1994, 116, 9457.
45 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National
Laboratory, Oak Ridge, TN, 1976.
Acknowledgements
We thank the Petroleum Research Fund, administered by the
ACS, for funding and the Sloan Foundation for the award of a
fellowship (to J. A.).
References
1 A. Togne and L. M. Venanzi, Angew. Chem., Int. Ed. Engl., 1994, 33,
497 and refs. therein.
46 M. Brookhart, M. L. H. Green and L.-L. Wong, Prog. Inorg. Chem.,
1988, 36, 1.
2 R. H. Crabtree, The Organometallic Chemistry of the Transition
Metals, Wiley Interscience, New York, 2nd edn., 1994.
47 D. G. Dick, R. Duchateau, J. H. Edema and S. Gambarotta, Inorg.
Chem., 1993, 32, 1959.
3 C. Elschenbroich and A. Salzer, Organometallics:
Introduction, VCH, New York, 2nd edn., 1992.
A
Concise
48 R. A. Andersen and G. Wilkinson, J. Chem. Soc., Dalton Trans.,
1977, 809.
J. Chem. Soc., Dalton Trans., 1997, Pages 3087–3096
3095

View Article Online
49 G. E. Coates and J. A. Heslop, J. Chem. Soc. A, 1968, 514.
50 P. J. Bonasia, D. E. Gindelberger, B. O. Dabbousi and J. Arnold,
J. Am. Chem. Soc., 1992, 114, 5209.
58 XPREP: Part of the SHELXTL Crystal-Structure Determination
Package, version 5.03, Siemens Industrial Automation Inc.,
Madison, WI, 1994.
51 A. G. Massey and A. J. Park, J. Organomet. Chem., 1966, 5, 218.
52 A. G. Massey and A. J. Park, J. Organomet. Chem., 1964, 2, 245.
53 H. Hope, in Experimental Organometallic Chemistry, eds.
A. L. Wayda and M. Y. Darensbourg, American Chemical Society,
Washington, DC, 1987, p. 257.
54 D. T. Cromer and J. T. Waber, in International Tables for X-Ray
Crystallography, Kynoch Press, Birmingham, 1974, vol. 4, Table
2.2B.
59 TEXSAN: Crystal Structure Analysis Package, Molecular Structure
Corporation, 1992.
60 F. Hai-Fu, SAPI 91, Structure Analysis Programs with Intelligent
Control, Rigaku Corp., Tokyo, 1991.
61 P. T. Beurskens, G. Admiraal, G. Beuskens, W. P. Bosman,
S. Garcia-Granda, R. O. Gould, J. M. M. Smits and C. Smkalla,
DIRDIF 92, The DIRDIF Program System, Technical report of the
Crystallography Laboratory, University of Nijmegen, 1992.
55 D. T. Cromer and J. T. Waber, ibid, Table 2.3.1.
56 SMART Area-Detector Software Package, Siemens Industrial
Automation, Inc., Madison, WI, 1993.
57 SAINT: SAX Area-Detector Integration Program, version 4.024,
Siemens Industrial Automation, Inc., Madison, WI, 1995.
Received 5th May 1997; Paper 7/03109B
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J. Chem. Soc., Dalton Trans., 1997, Pages 3087–3096