Synthesis, structure and molecular dynamics of η2-iminoacyl compounds [Cp(ArO)Zr(η2-ButNCCH2Ph) (CH2Ph)] and [Cp(ArO)Zr(η2-ButNCCH2Ph)2]

Article abstract of DOI:10.1039/b202244n

The reaction of the substrate [CpZr(CH₂Ph)₃] with the ligands 2,3,5,6-tetraphenyl-1, 2-phenyl-4,6-di-tert-butyl-2 or 2-(1-naphthyl)-4,6-di-tert-butyl-phenol 3 leads to the corresponding compounds [Cp(ArO)Zr(CH₂Ph)₂

Full text of DOI:10.1039/b202244n

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Synthesis, structure and molecular dynamics of ꢀ2-iminoacyl
compounds [Cp(ArO)Zr(ꢀ2-ButNCCH2Ph)(CH2Ph)] and
[Cp(ArO)Zr(ꢀ2-ButNCCH2Ph)2]
Matthew G. Thorn, Jongtaik Lee, Phillip E. Fanwick and Ian P. Rothwell*
Department of Chemistry, 1393 Brown Building, Purdue University, West Lafayette,
IN 47907-1393, USA
Received 28th January 2002, Accepted 20th June 2002
First published as an Advance Article on the web 7th August 2002
The reaction of the substrate [CpZr(CH2Ph)3] with the ligands 2,3,5,6-tetraphenyl- 1, 2-phenyl-4,6-di-tert-butyl- 2 or
2-(1-naphthyl)-4,6-di-tert-butyl-phenol 3 leads to the corresponding compounds [Cp(ArO)Zr(CH2Ph)2] 4–6. Solution
studies show that naphthyl rotation is slow on the NMR timescale at ambient temperatures within 6 leading to non-
equivalent benzyl groups with diastereotopic methylene protons. The solid-state structure of 5 shows both benzyl
ligands to be η1-bound. Compounds 4–6 react with tert-butylisocyanide in hydrocarbon solvents to initially produce
the mono(iminoacyl) derivatives [Cp(ArO)Zr(η2-ButNCCH2Ph)(CH2Ph)] 7–9 followed by the bis(iminoacyl)
products [Cp(ArO)Zr(η2-ButNCCH2Ph)2] 10–12. In the solution 13C NMR spectra of the iminoacyl derivatives the
Zr–CN carbon atom resonates at δ 242–244 ppm (7–9) and δ 229–234 ppm (10–12) consistent with the η2-C,N
binding. This was confirmed in the solid state by X-ray diffraction studies of 8, 11 and 12. At ambient temperatures
only one set of iminoacyl resonances are observed for 10 and 11, indicating that both iminoacyl rotation and
aryloxide rotation are facile. At lower temperatures the iminoacyl ligands in 11 become non-equivalent in the
1H NMR spectrum consistent with restricted rotation about the Zr–O–Ar bond. The iminoacyl ligands in the
2-(1-naphthyl) derivative 12 are non-equivalent in solution NMR spectra from Ϫ75 to ϩ85 ЊC. The solution
fluxionality of these molecules as determined by NMR studies is discussed in detail.
Zr(CH2Ph)2] towards organic isocyanides. The aryloxides were
Introduction
chosen to give insight into the solution fluxionality of the
One major focus of our research over the last two decades has
generated iminoacyl compounds.
been to explore the chemistry of Group 4 metal organometallic
compounds containing the bis(aryloxide) fragment [(ArO)2M]
(M = Ti, Zr, Hf ).1–3 This was stimulated by the burgeoning
Results and discussion
amount of exciting chemistry being developed for the corre-
sponding metallocenes [Cp2M]4 combined with the isolobal
relationship between O donor ligands such as alkoxides, aryl-
oxides and siloxides and the cyclopentadienyl unit.5,6 With the
correct choice of (typically bulky) aryloxide ligand it is possible
to generate both novel and complimentary stoichiometric and
catalytic reactivity supported by this metal fragment. Although
a number of isostructural motifs are present for stoichio-
metrically related [Cp2MLn] and [(ArO)2MLn] compounds, the
high electronegativity of the aryloxide oxygen combined with
its more flexible donating capabilities often lead to stoichio-
metries (and reactivity) not found for the metallocenes.7 An
important example relates to the reaction of the substrates
[Cp2MR2] and [(ArO)2MR2] (M = Ti, Zr, Hf ) towards carbon
monoxide and isoelectronic organic isocyanides.8 The metal-
locene compounds readily form mono-insertion products, e.g.
Synthesis, characterization and solution fluxionality of
compounds
The aryloxide precursors 2,3,5,6-tetraphenyl- 1,20 2-phenyl-4,6-
di-tert-butyl- 2,21 and 2-(1-naphthyl)-4,6-di-tert-butyl-phenol 3
(Scheme 1),22 have been applied to this study. Metallation resist-
ant 1 contains a symmetrically substituted phenoxide nucleus
whereas 2 contains non-equivalent ortho-substituents. The
symmetry is broken down further with the 1-naphthyl ligand, 3.
Restricted rotation about the phenoxy–(1-naphthyl) bond leads
[Cp2Ti(η2-MeCO)(Me)],9
[Cp2Zr(OAr)(η2-ButNCCH2Ph)]10
and [Cp2Zr(η2-RCN-p-tol)] {R = CH(SiMe3)2}11 which have a
diverse reactivity.12–15 Further carbonylation can occur but the
products do not arise via bis(acyl) intermediates.16 Carbonyl-
ation of the aryloxide compounds is complicated by the high
reactivity of the ensuing acyl groups, e.g. facile acylation of
pyridine.17 However, insertion into both of the metal–alkyl
bonds occurs with isocyanides to produce bis(iminoacyls).18
Subsequent reactivity can include coupling of iminoacyl groups
to produce ene-diamide ligands.19 In the context of these
differences we have investigated the reactivity of recently iso-
lated mixed cyclopentadienyl, aryloxide compounds [Cp(ArO)-
Scheme 1
3398
J. Chem. Soc., Dalton Trans., 2002, 3398–3405
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b202244n

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Table 1 Selected bond distances (Å) and angles (Њ) for [CpZr(OC6H2-
Ph-2-But2-4,6)(CH2Ph)2] (5)
Table 2 Selected bond distances (Å) and angles (Њ) for [CpZr(OC6H2-
Ph-2-But2-4,6)(η2-ButNCCH2Ph)(CH2Ph)] (8)
Zr–O(10)
Zr–C(20)
1.954(2)
2.276(3)
Zr–C(30)
Zr–Cp
2.262(3)
2.192(4)
Molecule 1
Zr(1)–O(110)
Zr(1)–N(17)
N(17)–C(18)
2.009(5)
2.213(7)
1.259(9)
Zr(1)–C(18)
Zr(1)–C(19)
2.186(8)
2.319(8)
Zr–O(10)–C(11)
O(10)–Zr–C(20)
O(10)–Zr–C(30)
O(10)–Zr–Cp
159.0(2)
106.29(9)
108.41(9)
115.2(1)
108.3(1)
C(20)–Zr–Cp
C(30)–Zr–Cp
Zr–C(20)–C(21)
Zr–C(30)–C(31)
110.6(1)
107.9(1)
128.8(2)
97.4(2)
Zr(1)–O(110)–C(111) 157.3(5)
N(17)–Zr(1)–C(19)
C(18)–Zr(1)–C(19)
Zr(1)–N(17)–C(18)
N(17)–C(18)–Zr(1)
91.0(3)
106.2(3)
72.2(5)
74.6(5)
C(20)–Zr–C(30)
O(110)–Zr(1)–N(17)
O(110)–Zr(1)–C(18)
O(110)–Zr(1)–C(19)
N(17)–Zr(1)–C(18)
93.9(2)
118.4(3)
101.2(2)
33.3(2)
to a chiral ligand. Previous work has shown that the barrier
to this rotation is 18.0(5) kcal molϪ1 at 67 ЊC in 2,6-di(1-
naphthyl)phenol (meso–dl exchange by NMR).22 This barrier is
higher in metal derivatives such as [CpTi(OC6H3Np2-2,6)Me2]
where the methyl groups appear as two sharp singlets at 90 ЊC in
the 1H NMR spectrum.23 The simple addition of these phenols
(1 equiv.) to the precursor [CpZr(CH2Ph)3]24 in hydrocarbon
solvents leads to the mono(aryloxides) 4–6 respectively (Scheme
2). The solution spectroscopic properties of 4–6 are interesting.
Zr(1)–C(19)–C(191) 122.2(5)
Molecule 2
Zr(2)–O(210)
Zr(2)–N(27)
N(27)–C(28)
1.998(4)
2.207(7)
1.293(9)
Zr(2)–C(28)
Zr(2)–C(29)
2.223(8)
2.317(8)
Zr(2)–O(210)–C(211) 158.5(5)
N(27)–Zr(2)–C(29)
C(28)–Zr(2)–C(29)
Zr(2)–N(27)–C(28)
N(27)–C(28)–Zr(2)
89.9(3)
106.0(3)
73.9(5)
72.1(5)
O(210)–Zr(2)–N(27)
O(210)–Zr(2)–C(28)
O(210)–Zr(2)–C(29)
N(27)–Zr(2)–C(28)
94.2(2)
119.1(3)
100.5(2)
34.0(2)
Zr(2)–C(29)–C(291) 123.0(5)
2
protons exhibiting a significantly larger J coupling than the
Zr–CH2Ph protons. However, two diastereoisomers of 9
(restricted naphthyl rotation on the NMR timescale, Scheme 3)
are clearly present in the solution spectra. Integration of the
C5H5 resonances at δ 4.88 and 5.15 ppm show a 53/47 mixture
of the two isomers in solution. Each isomer gives rise to two
separate AB patterns for the benzyl methylene protons. In the
solution 13C NMR spectra of the mono-iminoacyl derivatives
7–9 the Zr–CN carbon atom resonates at δ 242–244 ppm. Two
well resolved resonances are observed for the two isomers of 9.
The chemical shift of these iminoacyl carbon atoms is consist-
ent with an η2-C,N binding of this function in solution,8 as
confirmed in the solid state by a single crystal diffraction study
of 8 (Fig. 2, Table 2).
Scheme 2
All show a single set of Cp and aryloxide resonances in the 1H
NMR spectrum. In compound 4 the benzyl ligands are equiv-
alent, but diastereotopic methylene protons confirm the lack
of a plane of symmetry through this group. A similar pattern
is observed for 5 implying that restricted rotation about the
Zr–O–Ar bond does not occur on the NMR timescale. In con-
trast the 1-naphthyl derivative 6 shows non-equivalent benzyl
ligands in both the 1H (two AB patterns) and 13C NMR spectra.
This clearly shows that restricted rotation about the phenoxy–
naphthyl bond occurs on the NMR timescale. The solid-state
structure of 5 (Fig. 1, Table 1) shows a three-legged piano stool
Fig. 2 ORTEP (50% thermal ellipsoids) view of [CpZr(OC6H2Ph-2-
But2-4,6)(η2-ButNCCH2Ph)(CH2Ph)] (8) (molecule 2).
The spectroscopic properties of the bis-iminoacyl derivatives
10–12 are particularly interesting and in some aspects puzzling.
In the solid state both 11 and 12 contain both iminoacyl groups
η2-C,N bound as shown (Fig. 3 and 4, Tables 3 and 4). The CN
vectors of the iminoacyl groups are arranged in a head-to-tail
fashion, one nitrogen atom is towards the aryloxide oxygen
while the other is closer to the Cp group (as represented in
Scheme 3). Again the aryloxide wedge lies approximately
coplanar with the Cp ring. If this static structure were
maintained in solution then one would predict non-equivalent
iminoacyl groups for the symmetric 2,3,5,6-tetraphenyl-
phenoxide complex 10. In the 1H NMR spectrum of 10 at
Ϫ55 ЊC in toluene-d8 solution, a single, Me3CNCH2Ph singlet
and Me3CNCH2Ph AB pattern show that the iminoacyl ligands
are equivalent on the NMR timescale at this temperature
(Fig. 5). The pattern remains essentially unchanged up to
Fig. 1 ORTEP35 (50% thermal ellipsoids) view of [CpZr(OC6H2Ph-2-
But2-4,6)(CH2Ph)2] (5).
geometry about the metal center. The aryloxide ligand is
oriented so that the phenoxy wedge lies close to coplanar with
the Cp group as shown in Scheme 2. Important parameters for
the structurally characterized compounds are discussed in a
later section.
Reaction of 4–6 with tert-butylisocyanide proceeds initially
to produce mono-insertion products 7–9 followed by formation
of bis(iminoacyl) derivatives 10–12 (Scheme 3). The mono-
iminoacyl derivatives 7 and 8 contain a single set of Cp and
aryloxide ligand signals. The diastereotopic benzyl protons
appear as well resolved AB patterns with the iminoacyl PhCH2
J. Chem. Soc., Dalton Trans., 2002, 3398–3405
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Scheme 3
Table 3 Selected bond distances (Å) and angles (Њ) for [CpZr(OC6H2-
Ph-2-But2-4,6)(η2-ButNCCH2Ph)2] (11)
Zr–O(10)
Zr–N(5)
Zr–N(7)
Zr–C(6)
2.056(2)
2.245(2)
2.267(2)
2.245(2)
Zr–C(8)
Zr–Cp
N(5)–C(6)
N(7)–C(8)
2.257(2)
2.281(2)
1.275(3)
1.275(3)
Zr–O(10)–C(11)
O(10)–Zr–N(5)
O(10)–Zr–N(7)
O(10)–Zr–C(6)
O(10)–Zr–C(8)
O(10)–Zr–Cp
N(5)–Zr–N(7)
N(5)–Zr–C(6)
N(5)–Zr–C(8)
N(5)–Zr–Cp
147.6(1)
86.50(6)
138.19(6)
102.94(7)
108.79(7)
106.4(1)
83.84(6)
32.99(7)
95.41(7)
149.91(9)
N(7)–Zr–C(6)
N(7)–Zr–C(8)
N(7)–Zr–Cp
C(6)–Zr–C(8)
C(6)–Zr–Cp
C(8)–Zr–Cp
Zr–N(5)–C(6)
N(5)–C(6)–Zr
Zr–N(7)–C(8)
N(7)–C(8)–Zr
90.40(8)
32.75(7)
102.06(8)
115.77(8)
117.0(1)
105.45(8)
73.5(1)
73.5(1)
73.2(1)
74.0(1)
Fig. 3 ORTEP (50% thermal ellipsoids) view of [CpZr(OC6H2Ph-2-
But2-4,6)(η2-ButNCCH2Ph)2] (11).
Table 4 Selected bond distances (Å) and angles (Њ) for [CpZr(OC6H2-
Np-2-But2-4,6)(η2-ButNCCH2Ph)2] (12)
Zr–O(50)
Zr–N(10)
Zr–N(30)
Zr–C(20)
Zr–C(40)
Zr–C(1)
2.048(2)
2.253(2)
2.297(3)
2.221(3)
2.254(3)
2.532(3)
Zr–C(2)
Zr–C(3)
Zr–C(4)
Zr–C(5)
N(10)–C(20)
N(30)–C(40)
2.584(3)
2.582(3)
2.552(3)
2.496(3)
1.271(4)
1.273(4)
Zr–O(50)–C(51)
O(50)–Zr–N(10)
O(50)–Zr–N(30)
O(50)–Zr–C(20)
O(50)–Zr–C(40)
N(10)–Zr–N(30)
N(10)–Zr–C(20)
N(10)–Zr–C(40)
152.1(2)
87.20(9)
136.12(9)
107.7(1)
106.9(1)
86.48(9)
33.0(1)
N(30)–Zr–C(20)
N(30)–Zr–C(40)
C(20)–Zr–C(40)
Zr–N(10)–C(20)
N(10)–C(20)–Zr
Zr–N(30)–C(40)
N(30)–C(40)–Zr
89.3(1)
32.5(1)
116.0(1)
72.1(2)
74.9(2)
71.9(2)
75.6(2)
99.4(1)
Fig. 4 ORTEP (50% thermal ellipsoids) view of [CpZr(OC6H2Np-2-
But2-4,6)(η2-ButNCCH2Ph)2] (12).
Scheme 4
ϩ85 ЊC although the chemical shifts do vary gradually with
temperature. Hence we can conclude that iminoacyl
rotation (possibly via an η1-intermediate) is facile on the NMR
timescale, but chemical exchange of iminoacyl environ-
ments (which would result in the benzyl protons becoming
non-diastereotopic) is not occurring (Scheme 4). A similar situ-
ation has been reported for the compound [Zr(OC6H3But2-
2,6)(η2-xyNCCH2Ph)2(CH2Ph)].18 However, at intermediate
temperatures there is selective broadening of some of the
resonances in the 1H NMR spectrum of 10. This is particularly
true at Ϫ40 ЊC where the downfield methylene proton of the
benzyl group is broader than the upfield one (Fig. 5). Also the
Cp proton signal is broadened at this temperature. At Ϫ10 ЊC
the signals are much sharper again and remain so up to ϩ85 ЊC.
The 1H NMR spectrum of 2-phenyl-4,6-di-tert-butyl-
phenoxide 11 at Ϫ45 ЊC in toluene-d8 solution shows non-
equivalent iminoacyl groups as evidenced by two sharp
Me3CNCH2Ph singlets and two well resolved Me3CNCH2Ph
AB patterns in the 1H NMR spectrum. Only one set of Cp and
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J. Chem. Soc., Dalton Trans., 2002, 3398–3405

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signals we estimate the barrier to aryloxide rotation to be
14.0(5) kcal molϪ1 at ϩ25 ЊC. However, as with 10, although
the Cp resonance is a sharp singlet at Ϫ45 and ϩ85 ЊC, at
intermediate temperatures there is some broadening.
The Ϫ45 ЊC 1H NMR spectrum of the 1-naphthylphenoxide
derivative 12 shows a single set of Cp (sharp singlet) and aryl-
oxide resonances (Fig. 6). Two sharp Me3CNCH2Ph singlets
Fig. 5 1H NMR spectrum (300 MHz, C6D5CD3; * protio impurity) of
10 at three different temperatures.
OAr resonances are observed. Hence we can conclude that at
this temperature restricted rotation about the Zr–O–Ar bond is
occurring leading to the non-equivalence of the iminoacyl
groups (Scheme 5). We assume, based upon the data obtained
Fig. 6 1H NMR spectrum (300 MHz, C6D5CD3; * protio impurity) of
12 at three different temperatures.
and two well resolved Me3CNCH2Ph AB patterns are also
present. The solid-state structure of 12 (Fig. 4) shows that the
aryloxide wedge is oriented so that the naphthyl group is point-
ing away from the iminoacyl group (major isomers shown in
Scheme 6). It therefore appears that only one enantiomeric pair
of the two possible aryloxide rotamers that can be envisaged are
detectable by NMR in solution. It seems reasonable that the
naphthyl group strongly favors the rotamer with the naphthyl
group oriented away from the iminoacyl ligand (Scheme 6) as
observed in the solid state. As the temperature of the solution is
raised, there is a broadening and then sharpening of some of
1
the H signals. The Cp and one of the Me3CNCH2Ph reson-
ances broaden in the Ϫ5 to ϩ45 ЊC region but then become
sharp singlets in essentially the same position at ϩ85 ЊC
(Fig. 6). The two Me3CNCH2Ph AB patterns also broaden,
change chemical shifts slightly and then sharpen up as two
Me3CNCH2Ph AB patterns (one pair appearing close to a sing-
let due to almost identical chemical shifts). The low and high
temperature limiting spectra of 12 therefore are consistent with
the proposed solution structure and dynamics outlined. What is
puzzling is the sometimes selective broadening of resonances at
intermediate temperatures for all three of the bis-iminoacyl
compounds 10–12.
Scheme 5
for 10, that iminoacyl rotation is facile. As the temperature of
the solution is raised the Me3CNCH2Ph tert-butyl proton
resonances broaden and coalesce at ϩ25 ЊC (300 MHz). By
ϩ85 ЊC a single, sharp resonance is observed. Similarly the
two non-equivalent, diastereotopic Me3CNCH2Ph AB patterns
coalesce to form a single AB pattern at the higher temperature.
From the temperature of the coalescence of the tert-butyl
Solid state structures
Selected structural parameters for compounds 5, 8 (pentane
solvate, two independent molecules), 11 and 12 are given in
Tables 1–4 while Table 5 contains crystal data and data collec-
tion parameters. The Zr–OAr distance of 1.954(2) Å in 5 is
J. Chem. Soc., Dalton Trans., 2002, 3398–3405
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Table 5 Crystal data and data collection parameters
Compound
5
8
11
12
Formula
Formula weight
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
C39H44OZr
620.01
C2/c (no. 15)
27.9412(6)
13.9072(3)
20.6729(4)
C44H53NOZrؒ1/3C5H12
727.09
P21/n (no. 14)
16.5371(8)
17.372(1)
31.204(1)
C49H62N2OZr
786.27
P1 (no. 2)
C53H64N2OZr
836.33
P1 (no. 2)
¯
¯
12.1678(4)
12.3408(4)
15.8545(3)
82.153(2)
88.504(2)
63.853(1)
2115.5(2)
2
11.9950(7)
13.3697(9)
14.9039(5)
99.974(3)
99.813(3)
97.689(2)
2286.5(4)
2
124.493(1)
100.265(3)
γ/Њ
V/Å3
6620.9(5)
8
1.244
8821(1)
8
1.095
Z
ρcalc/g cmϪ3
1.234
1.215
Temperature/K
Radiation (wavelength)
R
RW
203
203
203
193
Mo-Kα (0.71073 Å)
0.048
0.122
Mo-Kα (0.71073 Å)
0.084
0.207
Mo-Kα (0.71073 Å)
0.044
0.101
Mo-Kα (0.71073 Å)
0.052
0.109
Scheme 6
slightly longer than the values of 1.903(4) and 1.936(4) Å
found in the bis(aryloxide) [Zr(OC6H3But2-2,6)(OC6H2But2-2,6-
OMe-4)(CH2Ph)2]25 indicating a less electron deficient metal
center upon replacing OAr with Cp. This interatomic distance
also increases slightly as the benzyl ligands are replaced by
iminoacyl groups; cf. 2.004(5) Å (av.) in 8 and 2.056(2),
2.048(2) Å in 11 and 12, respectively. As expected, the Zr–O–Ar
angles are all large and do not correlate at all with the Zr–OAr
distance.26 A feature of highly electron deficient metal benzyl
compounds is the presence of unexpectedly low M–CH2–Ph
angles (sometimes less than 90Њ) observed in many solid state
derivatives. These acute angles have been interpreted in terms
of ηn-interactions between the metal center and the benzyl
ligand.27 There is also spectroscopic evidence for some of these
ηn-interactions being maintained in solution.25 However, the
observation of M–CH2–Ph angles lower than 100Њ in the solid
state structures of early transition metal benzyl compounds
should not be over interpreted in terms of bonding/reactivity.
This is highlighted by a recent study showing dramatically dif-
ferent angles can be observed for different solvates of the same
molecule, i.e. packing forces may dominate what is apparently a
flexible bond angle.28 Hence, the Zr–C(30)–C(31) angle of
97.4(2)Њ for one of the benzyl ligands in 5 is not particu-
larly noteworthy. The other benzyl ligands in 5 and 8 have
corresponding angles of 128.8(2), 122.2(5) and 123.0(5)Њ.
The most important structural parameters are those for the
zirconium C,N-bound iminoacyl ligands. A large number of
simple η2-RNCRЈ ligands attached to transition metal centers
are now known.8 It is interesting to compare the structural
parameters for the compounds obtained in this study with
other related zirconium iminoacyl derivatives. One measure of
the extent of η2-binding which has been applied to both acyl
and iminoacyl ligands is the value of the parameter [d(M–E)
Ϫ d(M–C)] (E = O, N). This parameter can be used as a meas-
ure of the electron deficiency of the metal, with negative values
occurring for highly electrophilic metal centers. However, it is
important to realize that iminoacyl substituents will undoubt-
edly influence these parameters. In the bis(aryloxide) com-
pound [Zr(OC6H3But2-2,6)2(η2-ButNCCH2Ph)2] the Zr–C and
Zr–N distances are 2.228(3) and 2.221(3) Å, respectively. The
corresponding distances in the Cp derivatives 11 and 12 (which
have the same iminoacyl substituents, Tables 3 and 4) are very
slightly longer. However, in all three compounds [d(M–N)
Ϫ d(M–C)] are close to zero. Analysis of the Cambridge Struc-
tural Database shows 14 different compounds containing
zirconium–iminoacyl groups.29 A plot of the values of d(Zr–N)
vs. d(Zr–C) for these compounds is shown in Fig. 7. It can be
seen that there is an approximately even distribution about the
x = y relationship. The compounds obtained in this study can be
seen to be very similar to previously isolated iminoacyls of
3402
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[CpZr(OC6H2Np-2-But-4,6)(CH2Ph)2] (6).
A
sample of
[CpZr(CH2Ph)3] (1.0 g, 2.3 mmol) was dissolved in benzene.
This solution was stirred as 2-(1-naphthyl)-4,6-di-tert-
butylphenol (493 mg, 1.75 mmol) 3, was slowly added. The
yellow mixture was stirred for thirty minutes and evacuated
to dryness affording a yellow solid (1.3 g, 80%). 1H NMR
(C6D6, 30 ЊC): δ 6.59–7.82 (aromatics); 5.35 (s, Cp); 2.04 (d),
1.80 [d, 2J(1H–1H) = 10 Hz, Zr–CH2]; 0.97 (d), 0.58 (d,
2J(1H–1H) = 11 Hz, Zr–CH2) 1.65 (s), 1.30 (s, CMe3); 0.97 (d),
0.58 [d, 2J(1H–1H) = 10.7 Hz, Zr–CH2]. Selected 13C NMR
(C6D6, 30 ЊC): δ 159.3 (Zr–O–C); 114.6 (Cp); 65.0, 64.4
(Zr–CH2); 36.2, 35.0 (CMe3); 32.2, 31.3 (CMe3).
[CpZr(OC6HPh4-2,3,5,6)(ꢀ2-ButNCCH2Ph)(CH2Ph)] (7). A
sample of 4 was placed in a NMR tube and dissolved in
d6-benzene. This solution was titrated with tert-butylisocyanide
forming initially the mono-iminoacyl product 7. 1H NMR
(C6D6, 30 ЊC): δ 6.51–7.24 (aromatics); 5.02 (s, Cp); 3.62 (d),
3.51 [d, 2J(1H–1H) = 17 Hz, NCCH2Ph]; 2.52 (d), 1.57 [d,
2J(1H–1H) = 10 Hz, Zr–CH2Ph]; 1.12 (s, NCMe3). 13C NMR
(C6D6, 30 ЊC): δ 244.2 (NCCH2Ph); 159.1 (Zr–O–C); 111.2
(Cp); 62.5 (Zr–CH2); 50.7 (NCMe3); 43.4 (NCCH2Ph); 30.4
(NCMe3).
Fig. 7 Plot of d(Zr–N) (Å) vs. d(Zr–C) (Å) for simple η2-iminoacyl
derivatives of zirconium (᭹, ref. 29). Compounds obtained in this study
(ᮀ).
zirconium. The most negative value for [d(M–N) Ϫ d(M–C)]
occurs for the compound [(methoxycalix[4]arene)Zr(η2-But-
NCPh)]29g (three electron withdrawing phenoxides and a
methoxy donor group around the metal) while the most positive
value is for the compound [Cp2Zr(SC4N2Me2)(η2-xyNCMe)]29h
(18-electron compound).
[CpZr(OC6H2Ph-2-But2-4,6)(ꢀ2-ButNCCH2Ph)(CH2Ph)] (8).
A sample of 5 (220 mg, 0.36 mmol) was dissolved in hexane.
One equivalent of tert-butylisocyanide was added (40.2 µL,
0.36 mmol) and the mixture stirred overnight and then evacu-
ated to dryness. A minimal amount of pentane was added to
this crude solid and upon standing yellow crystals formed.
Anal. calc. for C44H53NOZr: C, 75.16; H, 7.60. Found: C, 74.31;
H, 7.72%. 1H NMR (C6D6, 30 ЊC): δ 6.81–7.53 (aromatics); 5.32
(s, Cp); 3.95 (d), 3.51 [d, 2J(1H–1H) = 16.5 Hz, NCCH2Ph]; 2.69
Experimental
General details
All operations were carried out under a dry nitrogen atmos-
phere using standard Schlenk techniques. The hydrocarbon
solvents were distilled from sodium/benzophenone and stored
over sodium ribbons under nitrogen until use. All organic
reagents were purchased from Aldrich Chemical Co., [CpZrCl3]
from Strem, and used without further purification. The prepar-
ation of phenols 1, 2, 3 and [CpZr(CH2Ph)3] have previously
been reported.20–22,24 The 1H and 13C NMR spectra were
recorded on a Varian Associates Gemini-200, Inova-300, or
General Electric QE-300 spectrometer and referenced to protio
impurities of commercial benzene-d6 or deuterated chloroform
as internal standards. Elemental analyses and molecular
structures were obtained through Purdue in-house facilities.
2
(d), 2.19 [d, J(1H–1H) = 10 Hz, Zr–CH2Ph]; 1.59 (s), 1.30 (s),
1.29 (s, CMe3). 13C NMR (C6D6, 30 ЊC): δ 243.9 (NCCH2Ph);
158.9 (Zr–O–C); 111.3 (Cp); 61.6 (Zr–CH2); 51.5 (NCMe3);
43.1 (NCCH2Ph); 35.4, 34.1 (CMe3); 31.6, 31.0, 29.8 (CMe3).
[CpZr(OC6H2Ph-2-But2-4,6)(ꢀ2-ButNCCH2Ph)(CH2Ph)] (9).
A sample of 6 was placed in a NMR tube and dissolved in d6-
benzene. This solution was titrated with tert-butylisocyanide
forming initially the mono-iminoacyl product 9. 1H NMR
(C6D6, 30 ЊC): δ 6.73–8.02 (aromatics); 4.88 (s), 5.15 (s, Cp);
3.91 (d), 3.86 (d), 3.65 (d), 3.41 (d) [2J(1H–1H) = 16 Hz,
NCCH2Ph]; 2.59 (d), 2.40 (d), 2.06 (d), 1.68 (d) [2J(1H–1H) =
11 Hz, Zr–CH2Ph]; 1.61 (s), 1.52 (s), 1.28 (b), 1.13 (s, CMe3).
13C NMR (C6D6, 30 ЊC): δ 242.9, 242.5 (NCCH2Ph); 159.8,
158.4 (Zr–O–C); 111.5, 110.5 (Cp); 62.2, 61.8 (Zr–CH2); 51.3,
48.9 (NCMe3); 43.3, 43.2 (NCCH2Ph); 35.6, 35.4, 34.3, 34.2,
32.2, 31.9 (CMe3); 31.7, 31.3, 31.2, 30.1, 29.9, 29.8 (CMe3).
Syntheses
[CpZr(OC6HPh4-2,3,5,6)(CH2Ph)2] (4). A sample of [CpZr-
(CH2Ph)3] (1.0 g, 2.32 mmol) was dissolved in benzene. One
equivalent of 2,3,5,6-tetraphenylphenol (930 mg, 2.33 mmol)
1 was added and the mixture stirred overnight and evacuated
to dryness. The resulting crude solid was washed with pentane
and dried in vacuo to give a yellow solid (1.4 g, 82%). Anal.
calc. for C49H40OZr: C, 79.96; H, 5.48. Found: C, 79.69; H,
5.48%. 1H NMR (C6D6, 30 ЊC): δ 6.84–7.31 (aromatics); 6.63 [d,
3J(1H–1H) = 7.3 Hz, ortho-CH2Ph]; 5.25 (s, Cp); 1.58 (d), 1.10 [d,
2J(1H–1H) = 10.5 Hz, Zr–CH2]. 13C NMR (C6D6, 30 ЊC): δ 158.2
(Zr–O–C); 114.1 (Cp); 64.0 (Zr–CH2).
[CpZr(OC6HPh4-2,3,5,6)(ꢀ2-ButNCCH2Ph)2] (10). A sample
of 4 was placed in a NMR tube and dissolved in d6-benzene.
This solution was titrated with tert-butylisocyanide until the
bis(η2-iminoacyl) product was observed to have formed. Layer-
ing of the solution with hexane induced the formation of white
crystals of 10. Anal. calc. for C59H58N2OZr: C, 78.53; H, 6.48;
1
N, 3.10. Found: C, 76.44; H, 6.25; N, 2.79%. H NMR (C6D6,
[CpZr(OC6H2Ph-2-But-4,6)(CH2Ph)2] (5). A solvent sealed
flask was charged with [CpZr(CH2Ph)3] (750 mg, 1.75 mmol),
2-phenyl-4,6-di-tert-butylphenol (493 mg, 1.75 mmol) 2, and
benzene. The yellow mixture was stirred for three days and
evacuated to dryness to give a yellow glassy solid. Upon stand-
ing in minimal hexane yellow crystals (410 mg, 38%) of 5
formed. Anal. calc. for C39H44OZr: C, 75.55; H, 7.15. Found: C,
30 ЊC): δ 6.90–7.29 (aromatics); 5.07 (s, Cp); 4.09 (d), 3.75 [d,
1
2J(1H–1H) = 14.3 Hz, NCCH2Ph]; 1.20 (s, NCMe3). H NMR
(C7D8, Ϫ55 ЊC): δ 6.84–7.61 (aromatics); 4.98 (s, Cp); 4.15(d),
2
1
3.62 [d, J(1H–1H) = 13.0 Hz, NCCH2Ph]; 1.19 (s,NCMe3). H
NMR (C7D8, ϩ85 ЊC): δ 7.06–7.36 (aromatics); 5.24 (s, Cp);
4.14(d), 3.86 [d, 2J(1H–1H) = 14 Hz, NCCH2Ph]; 1.34 (s,
NCMe3). 13C NMR (C6D6, 30 ЊC): δ 233.2 (NCCH2Ph); 162.4
(Zr–O–C); 107.9 (Cp); 59.8 (NCMe3); 43.9 (NCCH2Ph); 30.8
(NCMe3).
1
73.88; H, 7.29%. H NMR (C6D6, 30 ЊC): δ 6.83–7.54 (aro-
2
matics); 5.49 (s, Cp); 2.23 [d, J(1H–1H) = 11.0 Hz, Zr–CH2];
2
1.55 (s), 1.26 (s, CMe3); 1.39 [d, J(1H–1H) = 11 Hz, Zr–CH2].
Selected 13C NMR (C6D6, 30 ЊC): δ 157.7 (Zr–O–C); 114.2 (Cp);
66.2 (Zr–CH2); 41.9, 35.4 (CMe3); 31.4, 30.5 (CMe3).
[CpZr(OC6H2Ph-2-But2-4,6)(ꢀ2-ButNCCH2Ph)2] (11).
sample of 8 (90 mg, 0.13 mmol) was dissolved in benzene. One
A
J. Chem. Soc., Dalton Trans., 2002, 3398–3405
3403

View Article Online
equivalent of tert-butylisocyanide (16 µL, 0.13 mmol) was
added and the mixture allowed to react for two days and then
evacuated to dryness affording a white solid. A minimal
amount of pentane was added and upon standing colorless
crystals formed (50 mg, 50%). Anal. calc. for C49H62N2OZr: C,
73.64; H, 8.33; N, 3.73. Found: C, 73.71; H, 8.12; N, 3.53%. 1H
NMR (C6D6, 30 ЊC): δ 7.01–7.56 (aromatics); 5.55 (br, Cp); 3.91
(br, NCCH2Ph); 1.53 (s), 1.30 (s, CMe3), 1.03 (br, NCMe3). 1H
NMR (C7D8, Ϫ45 ЊC): δ 6.73–7.62 (aromatics); 5.60 (s, Cp);
References
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2
4.19 (d), 3.99 (d), 3.72 (d), 3.63 [d, J(1H–1H) = 15, 17 Hz,
NCCH2Ph]; 1.59 (s), 1.37 (s, CMe3); 1.22 (s), 0.72 (s, NCMe3).
1H NMR (C7D8, ϩ85 ЊC): δ 6.9–7.6 (aromatics); 5.59 (s, Cp);
4.12 (d), 3.98 [d, 2J(1H–1H) = 16 Hz, NCCH2Ph]; 1.50 (s), 1.47
(s, CMe3); 1.08 (s, NCMe3). 13C NMR (C6D6, 30 ЊC): δ 231.2 (br,
NCCH2Ph); 166.7 (Zr–O–C); 108.9 (br, Cp); 58.8 (br, NCMe3);
42.5 (br, NCCH2Ph); 35.6, 33.9 (CMe3); 31.8, 30.1, 31.2 (CMe3)
and (NCMe3).
2 For the use of [(ArO)2TiCl2] reagents as Diels–Alder catalysts see
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3 A number of important organic transformations can be carried out
using titanium isopropoxide reagents, see (a) H. Urabi and F. Sato,
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6 P. T. Wolczanski, Polyhedron, 1995, 14, 3335.
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[(ArO)2Zr] units and an investigation of the coupling of imino-
acyl groups see J. H. Hardesty, T. A. Albright and S. Kahlal,
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Dalton Trans., 1977, 1946.
[CpZr(OC6H2Np-2-But2-4,6)(ꢀ2-ButNCCH2Ph)2] (12).
A
sample of 6 (300 mg, 0.45 mmol) was dissolved in benzene
and tert-butylisocyanide (0.10 mL, 0.90 mmol) added. The
mixture was stirred overnight and evacuated to dryness afford-
ing a yellow solid (370 mg, 67%). Recrystallization from
minimal pentane afforded X-ray quality crystals of 12. Anal.
calc. for C53H64N2OZr: C, 76.12; H, 7.72; N, 3.35. Found:
C, 76.32; H, 7.70; N, 3.42%. 1H NMR (C6D6, ϩ25 ЊC):
δ 7.00–8.32 (aromatics); 5.32 (br, Cp); 3.75 (br, NCCH2Ph);
1
1.59 (s), 1.27 (s, CMe3); 1.15 (s), 0.75 (s, NCMe3). H NMR
(C7D8, Ϫ45 ЊC): δ 6.97–8.49 (aromatics); 5.28 (s, Cp); 4.16
(d), 4.02 (d), 3.69 (d), 3.56 [d, 2J(1H–1H) = 15, 17 Hz,
NCCH2Ph]; 1.61(s), 1.31 (s, CMe3); 1.23 (s),0.72 (s, NCMe3).
1H NMR (C7D8, ϩ85 ЊC): δ 6.97–8.11 (aromatics); 5.25 (s, Cp);
2
4.07 (d), 3.89 (d), 3.89 (d), 3.83 [d, J(1H–1H) = 17, 17 Hz,
NCCH2Ph]; 1.54 (s), 1.29 (s, CMe3); 1.18 (s), 0.89 (s, NCMe3).
13C NMR (C6D6, 30 ЊC): δ 231.4, 228.9 (NCCH2Ph); 161.5
(Zr–O–C); 108.8 (Cp); 59.8, 57.9 (NCMe3); 43.0, 41.5 (NCCH2-
Ph); 35.7, 33.9 (CMe3); 31.7, 31.1, 30.2, 30.1 (CMe3) and
(NCMe3).
10 B. D. Steffey, N. Truong, D. E. Chebi, J. L. Kerschner, P. E. Fanwick
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X-Ray data collection and reduction
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Crystal data and data collection parameters are contained
in Table 5. A suitable crystal was mounted on a glass fiber
in a random orientation under a cold stream of dry nitrogen.
Preliminary examination and final data collection were per-
formed with Mo-Kα radiation (λ = 0.71073 Å) on a Nonius
KappaCCD. Lorentz and polarization corrections were
applied to the data.30 An empirical absorption correction using
SCALEPACK was applied.31 Intensities of equivalent reflec-
tions were averaged. The structure was solved using the struc-
ture solution program PATTY in DIRDIF92.32 The remaining
atoms were located in succeeding difference Fourier syntheses.
Hydrogen atoms were included in the refinement but restrained
to ride on the atom to which they are bonded. The structure was
refined in full-matrix least-squares where the function mini-
mized was Σw(|Fo|2 Ϫ |Fc|2)2 and the weight w is defined as w =
15 For
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2
2
1/[σ2(Fo ) + (0.0585P)2 + 1.4064P] where P = (Fo + 2Fc2)/3.
Scattering factors were taken from the International Tables for
Crystallography.33 Refinement was performed on a AlphaServer
2100 using SHELX-97.34 Crystallographic drawings were done
using ORTEP.35
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CCDC reference numbers 182088–182091.
See http://www.rsc.org/suppdata/dt/b2/b202244n/ for crystal-
lographic data in CIF or other electronic format.
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27 (a) G. R. Davis, J. A. Jarvis, B. T. Kilbourn and A. P. Piols,
Chem. Commun., 1971, 677; (b) U. Zucchini, U. Giannini and
Acknowledgements
We thank the National Science Foundation (Grant CHE-
0078405) for financial support of this research.
3404
J. Chem. Soc., Dalton Trans., 2002, 3398–3405

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