Generation of oxazirconocene complexes from the reaction of Cp2(THF)Zr=N-t-Bu with organic and metal carbonyl functionalities: Apparently divergent behavior of transient [Cp2Zr=O]

Article abstract of DOI:10.1021/ja954050t

The reactivity of Cp₂(THF)Zr=N-t-Bu (1a) toward a series of organic and metal carbonyl complexes has been examined. The Zr=N linkage of 1a undergoes imido/oxo exchange reactions with the carbonyl compounds and generates three different types of oxozirconocene products: (Cp₂Zr=O)(n) (3), (Cp₂Zr)₂(μ-O)(μ-N-t-Bu) (9), and (Cp₂Zr)₂O₃CCPh₂ (12) were obtained from the reactions of 1a with RR'C=O (R = R' = Me (2b); R = Ph, R' = H (2c); R = i-Pr, R' = H (2d)), CpCo(CO)₂ (7), and Ph₂C=C=O (10), respectively. The coproducts in these reactions were imines RR'C=N-t-Bu (4b-d), isonitrile complexes CpCo(CO)(CN-t-Bu) (8a), and ketenimines Ph₂C=C=N-t-Bu (11a), respectively. With more highly hindered carbonyls containing α-hydrogen atoms, the reaction followed a different pathway leading to the formation of the enolate complexes Cp₂Zr(NH-t-Bu)(OCR₃CR₂R₁) (R₁ = H, R₂ and R₃ = (CH₂)₃CH(CCH₃)₃ (5e); R₁ = R₂ = H, R₃ = C(CH₃)₃ (5f); R₁ = R₂ = CH₃, R₃ = CH(CH₃)₂ (5g)). Possible mechanisms for these transformations, as well as the factors that might control the dependence of the fate of 'Cp₂Zr=O' on its method of generation, are discussed.

Full text of DOI:10.1021/ja954050t

6
396
J. Am. Chem. Soc. 1996, 118, 6396-6406
Generation of Oxozirconocene Complexes from the Reaction of
Cp (THF)ZrdN-t-Bu with Organic and Metal Carbonyl
2
Functionalities: Apparently Divergent Behavior of Transient
[
Cp ZrdO]
2
Sun Yeoul Lee and Robert G. Bergman*
Contribution from the Department of Chemistry, UniVersity of California,
Berkeley, Calfornia 94720
X
ReceiVed December 4, 1995
Abstract: The reactivity of Cp2(THF)ZrdN-t-Bu (1a) toward a series of organic and metal carbonyl complexes has
been examined. The ZrdN linkage of 1a undergoes imido/oxo exchange reactions with the carbonyl compounds
and generates three different types of oxozirconocene products: (Cp2ZrdO)n (3), (Cp2Zr)2(µ-O)(µ-N-t-Bu) (9), and
(
(
Cp2Zr)2O3CCPh2 (12) were obtained from the reactions of 1a with RR′CdO (R ) R′ ) Me (2b); R ) Ph, R′ ) H
2c); R ) i-Pr, R′ ) H (2d)), CpCo(CO)2 (7), and Ph2CdCdO (10), respectively. The coproducts in these reactions
were imines RR′CdN-t-Bu (4b-d), isonitrile complexes CpCo(CO)(CN-t-Bu) (8a), and ketenimines Ph2CdCdN-
t-Bu (11a), respectively. With more highly hindered carbonyls containing R-hydrogen atoms, the reaction followed
a different pathway leading to the formation of the enolate complexes Cp2Zr(NH-t-Bu)(OCR3CR2R1) (R1 ) H, R2
and R3 ) (CH2)3CH(CCH3)3 (5e); R1 ) R2 ) H, R3 ) C(CH3)3 (5f); R1 ) R2 ) CH3, R3 ) CH(CH3)2 (5g)).
Possible mechanisms for these transformations, as well as the factors that might control the dependence of the fate
of “Cp2ZrdO” on its method of generation, are discussed.
Introduction
oxometallocenes are notorious for their self-oligomerization and
have eluded successful trapping except for a few examples
The chemistry of complexes containing metal-nitrogen
multiply-bonded groups (MdNR2) has developed dramatically
in recent years.1 These compounds are useful for imido group
5
containing the sterically bulky (η -C5Me5) ligand (e.g.
12-16
[Cp*2MdO] (M ) Zr, V)).
In this paper we report
additional studies that indicate that the behavior of the transient
Cp2ZrdO” species generated during these reactions depends
transfer in catalytic processes2 as well as in organic synthesis.
-5
6-8
“
Furthermore, the exchange of multiply-bonded ligands between
metals offers a potentially useful synthetic approach to new
transition metal compounds.9
on the character of the oxygen source.
Results
An earlier publication from our group briefly reported that
the monomeric imido complex Cp2(THF)ZrdN-t-Bu (1a)
undergoes a spontaneous imido/oxo exchange reaction with
Ph2CdO (2a) and t-BuNdCdO to generate the oxozirconocene
oligomer (Cp2ZrdO)n (3) and the corresponding imine (4a) and
As shown in eq 1, it
was assumed that [Cp2ZrdO] is generated during the reaction
and rapidly oligomerizes to form 3. Monomeric group 4
Reactions with Organic Carbonyl Compounds. The car-
bonyl compounds (ketones and aldehydes) shown in Scheme 1
are divided into three groups (A, B, and C) based on their steric
encumbrance. Group A includes aldehydes and simple ketones
(2b-d). In group B are illustrated moderately sterically
hindered ketones containing either one bulky group (2e and 2f)
or two secondary alkyl groups (2g). Ketones in groups A and
B possess R-protons. The type C compound illustrated is a
sterically encumbered ketone without R-hydrogens (2h).
As with 2a, the reaction of the carbonyl compounds in group
A (2b-d) with 1a generates the corresponding imine products
carbodiimide products, respectively.1
0,11
(
4b-d) and 3 as shown eq 2. These reactions occur spontane-
ously at room temperature and quantitative amounts (>90% by
1
H NMR) of the corresponding imine products were cleanly
produced. However, the (Cp2ZrdO)n (3) produced is generated
as several different oligomers (based on several Cp resonances
around 6 ppm) that fall out of solution as a white precipitate.
Among those Cp resonances, the peak at 6.31 ppm in THF-d8
(or 6.27 ppm in C6D6) was always observed as a major
X
Abstract published in AdVance ACS Abstracts, June 1, 1996.
(1) For an excellent and comprehensive recent review, see: Wigley, D.
E. In Progress in Inorganic Chemistry; Karlin, K. D., Ed.; Wiley: New
York, 1994; Vol. 42.
(
(
(
(
2) Ivin, K. J. Olefin Metathesis; Academic Press: London, 1983.
3) Ge, Y.-W.; Sharp, P. R. Inorg. Chem. 1992, 31, 379.
4) Breslow, R.; Gellman, S. H. J. Am. Chem. Soc. 1983, 105, 6728.
5) Svatits, E. W.; Dawson, J. H.; Breslow, R.; Gellman, S. H. J. Am.
(10) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. Organometallics 1993,
12, 3705.
(11) Walsh, P. J. Thesis, University of California, Berkeley, 1990.
(12) Carney, M. J.; Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J.
Am. Chem. Soc. 1989, 111, 8751.
(13) Carney, M. J.; Walsh, P. J.; Hollander, F. J.; Bergman, R. G.
Organometallics 1992, 11, 761.
Chem. Soc. 1985, 107, 6427.
6) Evans, D. A.; Faul, M. M.; Bilodeau, M. T. J. Org. Chem. 1991, 56,
744.
(
6
(
(
7) Mcgrane, P. L.; Livinghouse, T. J. Org. Chem. 1992, 57, 1323.
8) Mcgrane, P. L.; Jensen, M.; Livinghouse, T. J. Am. Chem. Soc. 1992,
(14) Smith, M. R., III; Matsunaga, P. T.; Andersen, R. A. J. Am. Chem.
Soc. 1993, 115, 7049.
1
14, 5459.
(15) Howard, W. A.; Parkin, G. J. Am. Chem. Soc. 1994, 116, 606.
(16) Polse, J. L.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc.
1995, 117, 5393.
(9) Jolly, M.; Mitchell, J. P.; Gibson, V. C. J. Chem. Soc., Dalton Trans.
1
992, 1331.
S0002-7863(95)04050-9 CCC: $12.00 © 1996 American Chemical Society

Generation of Oxozirconocene Complexes
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6397
Scheme 1
ppm (10H) attributable to the cyclopentadienyl groups, a broad
singlet in the region 4-5 ppm (1H) due to the alkylamido
hydrogen, and a singlet near 1.2 ppm due to the tert-butylamido
group. In addition to these resonances, enolates 5e and 5f (when
R1 or R2 ) H) exhibit new vinyl protons at 4.52 ppm (for 5e)
and 3.78 and 3.47 ppm (for 5f; C6D6). The C{ H} NMR
spectra of 5e-g show a resonance near 160-180 ppm due to
the R-carbon and a resonance in the 80-110 ppm region
attributable to the â-vinyl carbon.
1
3
1
In contrast to the carbonyl compounds in groups A and B,
which react easily with imido complex 1a at the ambient
temperature, 2,2,4,4-tetramethyl-3-pentanone (2h) is inert to 1a
up to 75 °C for 1.5 days, presumably due to the steric
inaccessibility of the carbonyl moiety. Harsher conditions led
to decomposition of the starting material.
Crystal and Molecular Structure of 5e. Transition metal
1
enolates have been shown to bind to metal centers in an η -
component. This matches the chemical shift of the known
1
5,24-29
30
mode through the oxygen atom
or methylene group,
Typically, early transition
cyclotrimeric compound (Cp2ZrdO)3.1
7-20
No further attempt
3
31-33
or in an η -(oxo-π-allyl) mode.
metal enolates exist in the O-bound form while late metal
enolates are C-bound (a few cases of late transition metal
3
4-38
O-bound enolates are known).
To confirm the structure
of our enolate complexes, clear crystals of 5e were grown in
pentane at -35 °C and an X-ray crystallographic analysis was
performed. The data collection parameters are reported in Table
1
. Solution of the structure revealed complete disorder of the
i
enolate ligand about a pseudo-mirror plane containing the O-
and C16-atoms as shown in Figure 1. The disorder was best
modeled as having 82:18 occupancy of two conformations, the
major one containing C11-C20 and the minor one containing
C211-C220 (see the supporting information). The major
conformation also showed another type of disorder in the enolate
ring. This second disorder was fit to a 50:50 occupancy of C14
in two sites. The ORTEP diagram of one of the major
conformations of 5e is shown in Figure 2. Although bond
distances and angles shown Tables 2 and 3 are less reliable
than they might otherwise be due to the disorder, it is clear that
the enolate fragment is bound to zirconium through oxygen (Zr-
to characterize 3 was made, but the imine products were
identified by GCMS and by comparison with literature spectral
2
1,22
data.
The identity of one of the imine products (PhCHdN-
2
3
t-Bu (4c)) was also confirmed by independent preparation.
The reactions of 1a with compounds 2e-g in the group B
1
also occur cleanly at 25 °C in >95% yield (by H NMR), but
do not generate the imine products or 3. Instead, the zir-
conocene enolate complexes 5e-g are formed by R-hydrogen
abstraction (eq 3). The enolate complexes were isolated in
1
5,24-26
1
O: 1.998(3) Å)
in an η -mode and the double bond is
localized between C11 and C12 (1.334(7) Å). The Zr-N-
C21 bond angle of 142.5(3)° in 5e is bent more strongly than
that in the analogous amido complexes, Cp2Zr(C6H3Cl2)(NH-
39
39,40
t-Bu) (147.6(2)°) and Cp2Zr(1-C9H7)(NH-t-Bu) (ca. 147.7°).
(
24) Veya, P.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Organometallics
991, 10, 2991.
25) Curtis, M. D.; Thanedar, S.; Butler, W. M. Organometallics 1984,
, 1855.
26) Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J.
Am. Soc. Chem. 1978, 100, 2716.
27) Sonnenberger, D. C.; Mintz, E. A.; Marks, T. J. J. Am. Chem. Soc.
1
(
3
(
(
analytically pure form by recrystallization from pentane (or
TMS2O) at -35 °C in 60-75% isolated yields. The H NMR
spectra of these enolates generally contain resonances near 6
1
984, 106, 3484.
1
(28) Stille, J. R.; Grubbs, R. H. J. Am. Chem. Soc. 1983, 105, 1664.
(29) de With, J.; Horton, A. D. Angew. Chem., Int. Ed. Engl. 1993, 32,
03.
9
(
17) Fachinetti, G.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. J. Am.
Chem. Soc. 1979, 101, 1767.
18) Kropp, K.; Skibbe, V.; Erker, G.; Kr u¨ ger, C. J. Am. Chem. Soc.
983, 105, 3353.
19) Erker, G.; Dorf, U.; Atwood, J. L.; Hunter, W. E. J. Am. Chem.
Soc. 1986, 108, 2251.
20) Boutonnet, F.; Zablocka, M.; Igau, A.; Jaud, J.; Majoral, J.-P.;
(30) Burkhardt, E. R.; Doney, J. J.; Bergman, R. G.; Heathcock, C. H.
J. Am. Chem. Soc. 1987, 109, 2022 and references therein.
(31) Ito, Y.; Aoyama, H.; Hirao, T.; Mochizuki, A.; Saegusa, T. J. Am.
Chem. Soc. 1979, 101, 494.
(32) Guggolz, E.; Ziegler, M. L. J. Organomet. Chem. 1980, 194, 317.
(33) Robertson, G. B.; Whimp, P. O. Inorg. Chem. 1973, 12, 1740.
(34) Slough, G. A.; Bergman, R. G.; Heathcock, C. H. J. Am. Chem.
Soc. 1989, 111, 938.
(
1
(
(
Schamberger, J.; Erker, G.; Werner, S.; Kr u¨ ger, C. J. Chem. Soc., Chem.
Commun. 1995, 823.
(
(35) Hartwig, J. F.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc.
1990, 112, 5670.
21) Klusener, P. A. A.; Tip, L.; Brandsma, L. Tetrahedron 1991, 47,
2
1
041.
(36) Hartwig, J. F.; Bergman, R. G.; Andersen, R. A. J. Am. Chem. Soc.
1990, 112, 3234.
(37) Dall’antonia, P.; Graziani, M. J. Organomet. Chem. 1980, 186, 131.
(38) Ito, Y.; Nakatsuka, M.; Kise, N.; Saegusa, T. Tetrahedron Lett. 1980,
21, 2873.
(39) Lee, S. Y.; Bergman, R. G. J. Am. Chem. Soc. 1995, 117, 5877.
(40) Lee, S. Y.; Bergman, R. G. Mauscript in preparation.
(22) Larsen, J.; Jorgensen, K. A. J. Chem. Soc., Perkin Trans. 2 1992,
213.
(23) A referee has pointed out the similarity of this transformation to
the aza-Wittig reaction. For a recent example of the aza-Wittig reaction
and leading references, see: Sakai, T.; Kodama, T.; Fujimoto, T.; Ohta,
K.; Yamamoto, I. J. Org. Chem. 1994, 59, 7144.

6
398 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
Lee and Bergman
Table 1. Crystal and Data Parameters for Complexes 5e and 12
compd nos.
5e
12
a
empirical formula
formula wt (amu)
C
24
H
36NOZr
72 68 7 4
C H O Zr
1410.2
445.77
crystal dimens (mm) 0.20 × 0.25 × 0.30 0.12 × 0.20 × 0.38
a (Å)
b (Å)
c (Å)
9.4933(2)
8.0068(2)
30.6878(9)
90
91.643(1)
90
16.621(4)
18.763(3)
19.417(5)
90
90
90
R (deg)
â (deg)
γ (deg)
3
V (Å )
2331.65(9)
6055.7(39)
space group
Z
diffractometer
detector
P2
4
1
/n
Pbca
4
CAD4
Siemens SMART
CCD area detector
crystal scintillation
counter, with PHA
-130
Figure 2. ORTEP view of one conformation of 5e. The ellipsoids are
scaled to represent the 50% probability surface.
temp (°C)
scan type
scan width (deg)
-130
ω
0.3
θ-2θ
0.90 + 0.35 tan θ
3-45
Table 2. Selected Bond Distances (Å) for 5e
2
θ range
3-46.5
Major Conformation
Minor Conformation
no. of unique reflcns 3600
2578
Zr1-O1
1.998(3)
2.060(3)
2.2534(4)
2.3562(4)
1.499(5)
1.321(5)
1.334(7)
1.524(6)
1.495(8)
1.48(1)
T
min/Tmax
0.931
270
0.041; 0.058
0.936
179
0.059; 0.069
0.092
2.24
Zr1-Nl
no. of variables
R; R
R
Zr1-Cp1
Zr1-Cp2
Nl-C21
w
all
R
2.46
int ) 0.034
goodness of fit
O1-C11
C11-C12
C11-C16
C12-C13
C13-C14
C14-C15
C15-C16
C16-C17
C17-C18
C17-C19
C17-C20
O1-C211
1.36(3)
1.30(4)
1.46(3)
1.73(4)
1.86(4)
1.27(4)
1.69(4)
1.63(3)
1.53(4)
1.68(5)
1.49(4)
a
C211-C212
C211-C16
C212-C213
C213-C214
C214-C215
C215-C16
C16-C217
C217-C218
C217-C219
C217-C220
Represents two dimers and one THF molecule of solvation.
1.48(2)
1.523(8)
1.542(7)
1.497(8)
1.500(9)
1.543(9)
C13-C141
C141-C15
1.46(2)
1.37(2)
Table 3. Selected Bond Angles (deg) for 5e
Major Conformation Minor Conformation
O1-Zr1-N1
99.9(1)
80.4(2)
O1-Zr1-C10
O1-Zr1-Cp1
O1-Zr1-Cp2
N1-Zr1-Cp1
N1-Zr1-Cp2
Cp1-Zr1-Cp2
Zr1-N1-C21
Zr1-O1-C11
O1-C11-C12
O1-C11-C16
C12-C11-C16
C11-C12-C13
C12-C13-C14
C13-C14-C15
C14-C15-C16
C11-C16-C17
C15-C16-C17
C16-C17-C19
C16-C17-C20
C18-C17-C19
C18-C17-C20
C19-C17-C20
Zr1-N1-H11
C21-N1-H11
107.56(8)
106.05(8)
102.73(10)
108.3(l)
128.76(2)
142.5(3)
148.0(3)
122.7(5)
114.7(4)
122.6(5)
124.2(5)
110.6(7)
110.2(9)
123.1(8)
115.0(4)
117.0(5)
113.0(5)
110.4(5)
106.1(6)
109.4(6)
107.1(5)
132.8
Zr1-O1-C211
150(1)
O1-C211-C212
O1-C211-C16
116(2)
116(2)
126(2)
123(2)
103(1)
101(2)
Figure 1. ORTEP view of the molecular structure of 5e showing one
of the major conformations in the disordered crystal. The ellipsoids
are scaled to represent the 50% probability surface.
C212-C211-C16
C211-C212-C213
C212-C213-C214
C213-C214-C215
Furthermore, the amido ligand is twisted significantly from the
O-Zr-N plane. This appears to be due to steric crowding by
the enolate ligand in 5e.
C211-C16-C217
C215-C16-C217
C16-C217-C219
C16-C217-C220
C218-C217-C219
C218-C217-C220
C219-C217-C220
112(1)
112(1)
108(2)
107(2)
98(2)
139(2)
84(2)
1
Low-Temperature H NMR Study of the Reaction of 1a
with 2b and 2d. The reaction of 1a with the carbonyl
compounds in group A occurs very rapidly even in THF-d8
where excess THF significantly inhibits the dissociation of THF
from the imido complex. However, the color of the reaction
mixture temporarily changes from yellow to red-orange upon
the addition of the ketone. The reaction was therefore monitored
84.5
C12-C13-C141
C13-C141-C15
114.5(8)
118(1)
1
at 220-263 K by H NMR spectrometry in THF-d8. This
revealed that an intermediate is first generated and then slowly
converted (above 243 K) to the corresponding imine 4b (or 4d)
and 3. From the reaction of 1a with 2b, the new intermediate
generated from the reaction of 2d shows resonances at δ 6.96
(d, J ) 9.28 Hz, 1H, CH), 6.30 (br s, 10H, C5H5; Cp’s
accidentally degenerate), 2.88 (m, 1H, CH(CH3)2), 1.22 (s, 9H,
C(CH3)3), and 0.96 (d, J ) 9.30 Hz, 6H, CH(CH3)2). From
(6b) gives rise to resonances at δ 6.28 (s, 10H, C5H5), 1.34 (s,
6
H, (CH3)2), and 1.22 (s, 9H, C(CH3)3). The intermediate (6d)

Generation of Oxozirconocene Complexes
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6399
these data, the intermediates are tentatively assigned as the
metallacycles formed by formal [2 + 2] cycloaddition of Cp2-
ZrdN-t-Bu with 2b (or 2d) as shown below. However, it was
unclear at this stage whether they exist in monomeric or dimeric
analogue of 1a, Cp2Zr(N-2,6-(CH3)2C6H3)(THF) (1b). The fact
that this arylimido complex does not react with benzene C-H
bonds allowed us to carry out the reaction of 1b with CpCo-
(CO)2 (7) in an aromatic rather than an oxygen-containing
solvent. The reaction of 1b with cobalt complex 7 at 75 °C in
C6H6 (as well as THF-d8) leads to the formation of CpCo(CO)-
4
3
(CN-2,6-(CH3)2C6H3) (8b) (46% isolated) and “Cp2ZrdO
oligomer” 3 (eq 5). Although 3 was observed instead of the
d
form (Vide infra). A second intermediate was also observed in
the reaction of 1a with 2d, but an assignment of its structure
was not possible due to the complex nature of the spectrum.
There was no indication that either an enolate complex or the
dimer complex (Cp2Zr)2(µ-O)(µ-N-t-Bu) are generated during
either reaction. In contrast to the observation of metallacycle
intermediates (6b and 6d) in the reaction of 1a with 2b and 2d,
no intermediate was observed in the reaction of 1a with
benzophenone (2a) even at 238 K where the reaction proceeds
relatively slowly (t1/2 ) ca. 30 min).
analogue of dimer 9 in both solvents, the experiment in C H6
clearly demonstrates that THF is not required for the conversion
6
Reactions with Metal Complexes Containing CO Groups.
A study of the reactivity of 1a toward CO functionalities in
metal complexes was also carried out. We reported earlier that
treatment of 1a with CpMn(CO)3 or CpRe(CO)3 at 75 °C in
cyclohexane results in the selective activation of the cyclopen-
tadienyl C-H bonds of these molecules.39 However, when 1a
is treated with CpCo(CO)2 (7) in cyclohexane, the reaction
instantly gives a complex mixture of products and a precipitate
of the starting terminal imido complex into an oxozirconium
product. The imido complex 1a also reacts with 86% CO
13
1
3
labeled CpCo( CO) under the same conditions to give 9 and
2
1
3
13
13
CpCo( CO)( CN-t-Bu) (8a- C) with 84% incorporation of
label, as determined by integration of relative mass peaks from
EI mass spectroscopy.
1
Preliminary H NMR investigations suggest that the reaction
of 1a with CpV(CO) , CpFe(CH )(CO) , and (C H )Cr(CO)
3
4
3
2
6
6
1
falls out of solution. The H NMR spectrum of this precipitate
in C6D6 showed several Cp resonances indicating that the
material is a mixture.
8
in THF-d also yields 9 and the corresponding deoxygenated
4
4
3
metal carbonyl isocyanide complexes CpV(CO) (CN-t-Bu),
4
5
46
CpFe(CH )(CO)(CN-t-Bu), or (C H )Cr(CO) (CN-t-Bu),
3
6
6
2
When 1a is treated with excess (ca. 3 equiv) CpCo(CO)2
respectively. The rates of the reaction of 1a with CpV(CO)4
(7) in THF at 75 °C, the reaction mixture remains homogeneous.
and (C H )Cr(CO) are relatively fast, and the reactions occur
6
6
3
In this solvent the process appears to be considerably cleaner,
and CpCo(CO)(CN-t-Bu) (8a)4 and a new binuclear complex
identified as (Cp2Zr)2(µ-O)(µ-N-t-Bu) (9) are formed in 90%
even at 25 °C over several hours. The reaction of 1a with the
simple metal carbonyl complex Mo(CO) in THF-d at 25 °C
1,42
6
8
1
was also examined briefly by H NMR spectroscopy. In this
case, more than one tert-butyl resonance grows in during the
reaction, presumably due to the formation of a mixture of
isocyanide complexes Mo(CO)5-n(CN-t-Bu)n. Dimer 9 was also
formed cleanly as expected.
1
yield (by H NMR) (eq 4). Compounds 8a and 9 were separated
The observation of oxygen abstraction from metal complexes
containing carbonyl groups in THF induced us to re-examine
the reactions of CpM(CO)3 (M ) Mn, Re) with 1a in this solvent
rather than cyclohexane. The reaction of 1a with CpM(CO)3
(
M ) Mn, Re) in THF requires more vigorous reaction
conditions (105 °C, 4 days) than the same reaction in C6H12
75 °C, 1.5 days) since the coordinating ability of THF inhibits
(
based on their solubility in pentane. The pentane-soluble
the formation of free Cp2ZrdN-t-Bu, significantly decreasing
isonitrile compound 8a was isolated in 28% yield and identified
the reaction rate. The reaction in THF still generates the
4
1
39,40
by comparison of its spectra with data in the literature.
Pentane-insoluble 9 was crystallized from pentane/benzene in
cyclopentadienyl C-H activated products
as the major
species, but somewhat less than 30% of ligand exchange product
9 was also obtained (eq 6). New H NMR resonances for tert-
1
1
3
0% isolated yield. Dimer 9 shows a simple H NMR spectrum
(C6D6) with two singlets at 6.10 and 1.12 ppm attributable to
the cyclopentadienyl (20H) and tert-butyl (9H) protons, respec-
tively. To confirm the structure of 9, crystals for an X-ray study
were grown by slow evaporation of solvent from an ether
solution of the complex. Unfortunately, an X-ray crystal-
lographic analysis of 9 could not be fully refined due to disorder.
However, it allowed us to confirm the basic structure of the
metallacycle.
d
Attempts to confirm the source of the oxygen in 9 were also
made. To make sure that the oxygen did not come from the
reaction solvent THF, the reaction was carried out with an
(
(
41) Beaumont, I.; Wright, A. H. J. Organomet. Chem. 1992, 425, C11.
42) Doherty, J.; Fortune, J.; R., M. A.; Stephens, F. S. J. Chem. Soc.,
butyl groups were also observed near 1.15 ppm, presumably
due to the formation of the corresponding isonitrile complexes
Dalton Trans. 1984, 1111.

6
400 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
Lee and Bergman
CpM(CO)2(CN-t-Bu) (M ) Mn,47,48 Re ). However, they were
not clearly identified due to the complex nature of the spectra.
Reaction of 1a with Diphenylketene (10). The reactivity
of 1a toward a CdCdO functionality was also studied. When
the imido complex 1a is mixed with an excess of Ph2CdC)O
48
4
9
3
(
10) in benzene, it spontaneously reacts with /2 equiv of 10
1
to form Ph2CdCdN-t-Bu (11a) and /2 equiv of (Cp2Zr)2O3-
CCPh2 (12) (eq 7). In this case no [Cp2ZrdO]n (3) was
Figure 3. ORTEP view of the molecular structure of 12. The ellipsoids
observed. The ketenimine product 11a was isolated as a pale
yellow liquid in 70% yield. The existence of the CdCdN bond
in 11a is indicated by the NMR resonance of a quaternary
carbon at 182.7 ppm in the 13C{ H} NMR spectrum (C6D12)
and the CdN stretching at 2014 cm in the IR spectrum (THF).
Tris-oxo complex 12 was also isolated as the hemisolvate
are scaled to represent the 50% probability surface.
Table 4. Selected Intramolecular Distances (Å) and Angles (deg)
for Complex 12
1
-1
Bond Distances (Å)
Zr1-Zr2
Zr1-O3
Zr2-O3
Zr1-Cp2
Zr2-Cp4
C21-O2
C22-C23
3.536(2)
1.983(8)
1.958(7)
2.231
Zr1-O1
Zr2-O2
Zr1-Cpl
Zr2-Cp3
C21-O1
2.042(8)
2.037(9)
2.245
[
12‚0.5 THF] in analytically pure form by recrystallization from
1
13
THF/pentane at -35 °C in 65% isolated yield. Its H and C-
{
2.232
1
H}NMR spectra establish that 12 contains cyclopentadienyl
2.257
1.362(15)
1.365(17)
1.506(17)
1.358(14) C21-C22
and phenyl groups in a 2:1 ratio. The infrared spectrum of 12
-1
1.502(17) C22-C29
shows no ketene CdO stretch in the expected 2100 cm region.
Mass spectrometry (EI) shows an ion with m/e 665.7 which is
consistent with the formula shown in eq 7. The structure of 12
was confirmed by X-ray crystallography. The data collection
parameters are reported in Table 1. As shown in Figure 3, the
ORTEP diagram of [12‚0.5 THF] clearly demonstrates that the
compound contains a 6-membered ring composed of two
molecules of [Cp2ZrdO] and one molecule of Ph2CdCdO (10).
The C-O (ca. 1.36 Å) and Zr-O (ca. 2.00 Å) bond lengths
are consistent with single bonds, but C21dC22 (1.365(7) Å)
shows double bond character. The 6-membered ring is slightly
twisted with ca. 50° (O-Zr-O-C21) and ca. 15° (O-Zr-
O-Zr) torsion angles. Relevant bond lengths and bond angles
are listed in Table 4. Selected torsion angles are listed in Table
Bond Angles (deg)
Cpl-Zr1-O1
Cp1-Zr1-O3
Cp1-Zr1-Cp2
Cp3-Zr2-O2
Cp3-Zr2-O3
Cp3-Zr2-Cp4
Zr1-O3-Zr2
Zr2-O2-C21
O1-C21-C22
103.8
109.3
129.47
106.6
108.3
128.56
127.6(4)
133.8(9)
125.4(11)
Cp2-Zr1-O1
Cp2-Zr1-O3
O1-Zr1-O3
Cp4-Zr2-O2
Cp4-Zr2-O3
O2-Zr2-O3
Zr1-O1-C21
O1-C21-O2
O2-C21-C22
105.7
108.8
93.5(3)
104.9
108.9
94.0(3)
128.2(8)
114.5(12)
120.1(12)
C21-C22-C23 122.5(12)
C23-C22-C29 119.0(12)
C21-C22-C29 118.5(12)
Table 5. Selected Torsion Angles for Complex 12 in Degrees
atom 1
atom 2
atom 3
atom 4
angle
5
.
O3
O1
O3
O2
Zrl
Zrl
Zr2
Zr2
Zrl
Zrl
Zr2
Zr2
O1
O1
O2
O2
O1
O3
O2
O3
C21
Zr2
C21
Zrl
-55.84(1.07)
15.73(0.59)
-44.38(1.02)
13.96(0.57)
The formation of ketenimine 11a and the tris-oxo complex
1
1
2 was not affected by variation of the initial ratio of the ketene
0 to the imido complex 1a. Even in the reaction of 1a with
.5 equiv of 10, products 11a and 12 are still generated and ca.
0
C21
C21
C21
C21
O2
C22
O1
42.54(1.56)
2
/
3 of unreacted 1a remains after the completion of the reaction.
-136.69(1.13)
20.21(1.62)
Changing the solvent to THF retards the reaction (2 days at 25
C for completion), but the same products are generated without
C22
-160.52(0.95)
°
observation of any intermediate. The reaction of 1a with 10 in
toluene-d8 between -30 and -10 °C proceeds at a reasonable
rate (t1/2 ) ca. 30 min at -10 °C) allowing us to monitor the
1
reaction by H NMR spectroscopy. However, no intermediate
is observed at low temperature. Furthermore, product 12 is
thermally very stable. There is no evidence of further reaction,
and decomposition to generate [Cp2ZrdO]n (3) is not observed
until 12 has been held at 105 °C for 4 days.
(
43) Yamamoto, Y.; Mise, T.; Yamamzaki, H. Bull. Chem. Soc. Jpn.
1
978, 51, 2743.
(44) Coville, N. J.; Harris, G. W. J. Organomet. Chem. 1985, 293, 365.
(45) Yamamoto, Y.; Yamazaki, H. J. Organomet. Chem. 1975, 90, 329.
(46) Harris, G. W.; Albers, M. O.; Boeyens, J. C. A.; Coville, N. J.
Reaction of 1a with Ph2CdCdNTol (11b). To obtain
information on a transformation that might be analogous to the
reaction of 1a with diphenylketene (and also which might be
more amenable to mechanistic scrutiny) we decided to explore
the reactivity of 1a toward a ketenimine. Since Ph2CdCdN-
t-Bu (11a), generated as a byproduct during the reaction of 1a
with 10, is inert toward 1a at ambient temperature due to its
steric hindrance, the less hindered ketenimine Ph2CdCdNTol
Organometallics 1983, 2, 609.
47) Harris, G. W.; Boeyens, J. C. A.; Coville, N. J. J. Organomet. Chem.
983, 255, 87.
48) Terry, M. R.; Mercando, L. A.; Kelley, C.; Geoffroy, G. L.; Nombel,
(
1
(
P.; Lugan, N.; Mathieu, R.; Ostrander, R. L.; Owens-Waltermire, B. E.;
Rheingold, A. L. Organometallics 1994, 13, 843.
(
6.
49) Taylor, E. C.; Mckillop, A.; Hawks, G. H. Org. Synth. 1972, 52,
3

Generation of Oxozirconocene Complexes
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6401
Scheme 2
Scheme 3
n
Table 6. Products Formed on Reaction of 1 with Three Different
Classes of Carbonyl Compounds
oxygen containing
zirconocene products (A)
XCdO
XCdN-t-Bu (B)
(
1
11b) was prepared by literature methods.50,51 The reaction of
a with 2 equiv of 11b also spontaneously occurs at 25 °C to
generate azametallacyclobutane Cp2Zr(NTol)2CdCPh2 (13) and
1a (Scheme 2). The ketenimine adduct 13 is cleanly generated
RR′CdO (2b-d)
(Cp
2
2
ZrdO)
n
(3)
RR′CdN-t-Bu (4b-d)
CpCo(CO) (7) (Cp Zr) (µ-O)(µ-N-t-Bu) (9) CpCo(CO)(CdN-t-Bu) (8a)
2
2
Ph
2
CdCdO (10)
2
(Cp Zr)
2
O
3
CCPh
2
(12)
2
Ph CdCdN-tBu (11a)
1
at room temperature in toluene and can be isolated as black
block crystals in 65% yield by recrystallization from toluene/
pentane at -35 °C. Spectral data for 13 in C6D6 include new
resonances for the p-tolyl methyl group at 2.08 ppm (6H) in
Scheme 4
1
13
1
the H NMR and 20.9 ppm (CH3) in the C{ H} NMR.
1
Monitoring this reaction by H NMR spectrometry revealed
a stepwise process that is dependent upon the concentration of
1
1b. When a stoichiometric amount of 11b is carefully
introduced into a solution of 1a at room temperature, azamet-
allacyclobutane complex Cp2Zr(N-t-Bu)(NTol)CdCPh2 (14) is
1
generated spontaneously as a major product (ca. 80% by H
NMR; 67% isolated) although some 13 is also generated
(
1
Scheme 2). That 14 is a 1:1 adduct of [Cp2ZrdN-t-Bu] and
1b is demonstrated by its H NMR (C6D6) spectrum, which
1
shows resonances due to the tert-butyl group at 0.93 ppm (9H)
as well as a p-tolyl methyl resonance at 2.04 ppm (3H). When
a second equivalent of 11b is introduced, the product 14 instantly
reacts to produce 13 and 11a. In the absence of 11b, at ambient
temperature 14 is slowly converted to 0.5 equiv of the bridging
imido dimer (Cp2ZrNTol)2 (15) and 11a; 15 gradually precipi-
tates from the solution. The latter reaction was driven to
completion by heating to 45 °C and thin green needles of 15
were isolated in 42% isolated yield. An analogue of the bridging
dimer 15, (Cp2ZrNC6H4X)2 (X ) H or CMe3), has been
synthesized previously by 1,2-elimination of Cp2Zr(NHC6H4X)-
(
Me) at 85 °C.10,11 It was also observed earlier in a zirconium-
52,53
mediated imine metathesis reaction.
that undergo this reaction, and the products they lead to, are
summarized in Table 6.
At first, we assumed that the reaction of an oxametallacy-
Discussion
Mechanism of Imido/Oxo Exchange. The observations
reported here and in earlier papers1 suggest strongly that the
reaction between imido complex 1a and a wide range of
carbonyl functionalities involves initial dissociation of THF,
followed by overall [2 + 2] cycloaddition between the CO and
the ZrdN moiety of the coordinatively unsaturated intermediate
0,39
clobutane such as 6 would follow the known “Wittig-like” [2+2]
1,55-57
ligand exchange process,
in which cycloreversion of 6 in
the opposite sense would occur to provide the corresponding
CdN bonded products and the transient Cp2ZrdO (16) which
would rapidly oligomerize under the reaction conditions.
However, the reactions of 1a with various carbonyl sources
revealed an interesting result: the nature of the oxo-containing
zirconocene products (A, Table 6) depends upon the character
of the carbonyl reagents. This situation is summarized in
Scheme 4. For example, in contrast to the white precipitate of
oligomeric (Cp2ZrdO)n (3) that is produced when the imido
complex 1a is treated with organic carbonyls 2b-d, only (µ-
oxo)(µ-imido)dimer (9) is generated in the reaction of 1a with
metal carbonyls even under relatively vigorous reaction condi-
1
0,11
[Cp2ZrdN-t-Bu],
to give oxaazametallacyclobutanes 6.
Similar [2 + 2] cycloadditions were observed in the reactions
of 1a with alkenes, alkynes, and imines,
1
0
54
52,53
where four-
membered azametallacycles were isolated as products. In
contrast, metallaoxetanes 6 cannot be isolated, although two such
intermediates (6b and 6d) were detected by low-temperature
1
H NMR spectrometry. The three types of carbonyl compounds
(50) Stevens, C. L.; French, J. C. J. Am. Chem. Soc. 1953, 75, 657.
(51) Stevens, C. L.; Singhal, G. H. J. Org. Chem. 1964, 29, 34.
(52) Meyer, K. E.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc. 1994,
1
1
16, 2669.
(55) Cotton, F. A.; Hall, W. T. J. Am. Chem. Soc. 1979, 101, 5094.
(56) Rocklage, S. M.; Schrock, R. R. J. Am. Chem. Soc. 1980, 102, 7808.
(57) Nugent, W. A.; Harlow, R. L. J. Chem. Soc., Chem. Commun. 1978,
579.
(53) Meyer, K. E.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc. 1995,
17, 974.
(54) Lee, S. Y.; Bergman, R. G. Tetrahedron 1995, 51, 4255.

6
402 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
Lee and Bergman
tions (2-3 days at 75 °C in THF). On the other hand, the
reaction of 1a with diphenylketene 10 produces neither oxozir-
conocene oligomer 3 nor (µ-oxo)(µ-imido)dimer 9 even in the
presence of excess 1a. Instead, it generates the tris-oxo complex
Scheme 5
1
2 formed from two molecules of Cp2ZrdO (16) and one
molecule of 10. Furthermore, the formation of each product
3, 9, or 12) is not affected by modification of the reaction
(
conditions such as changing the solvent or the ratio of the two
starting materials. Finally, we58 found recently that thermolysis
of the 6-membered ring complex Cp2Zr-NArCMedCPhCHAr′O
at 75 °C extrudes an R,â-unsaturated imine and provides yet
another apparent source of Cp2ZrdO. In this case in the absence
of traps the oxo complex oligomerizes, as it does in the 1a +
2
b-d reaction. However, when the thermolysis is run in the
presence of Cp2ZrMe2, oligomerization is prevented and the
apparent oxozirconocene intermediate is trapped quantitatively
as the soluble µ-oxo complex (Cp2ZrMe)2O (Scheme 4).
Control experiments established that [Cp2·rdO]n (3) does not
react with Cp2ZrMe2, even at 75 °C.
The divergent behavior of the postulated “Cp2ZrdO” in these
different reactions leads to the inescapable conclusion that the
simple monomeric oxozirconocene complex cannot be the actual
product-forming intermediate in every case. One might assume,
for example, that transient 16 oligomerizes in the absence of
any compound capable of trapping it, but in the presence of
another molecule of [Cp2ZrdN-t-Bu] it affords (µ-oxo)(µ-
imido)dimer 9. One must then ask why in the diphenylketene
reaction no 9 is formed along with 12, which requires two Cp2-
ZrdO fragments to ultimately find each other. Even more
convincingly, addition of Cp2ZrMe2 to the reaction of 1a with
as shown in the Scheme to give 9 and the isonitrile product.
A third possible route to 9 that avoids free Cp ZrdO is shown
2
in path C of Scheme 5. Here intermediate 18 reacts directly
with the transient imido complex Cp2ZrdN-t-Bu to generate 9
in a concerted process. However, we do not see why such a
mechanism should occur with the intermediate formed from
metal carbonyl complexes but not with the analogous species
that are presumably formed from ketones and ketenes.
Most perplexing is the reaction with diphenylketene, where
two Cp2ZrdO fragments wind up in the final product, avoiding
oligomerization or trapping with 1a. Here we suggest that a
dimeric intermediate formed early in the reaction might be
2
1
b-d (or with 10) still gives oligomer 3 (or tris-oxo complex
5
9
2). No diversion of the intermediate to (Cp2ZrMe)2O is
observed, in striking contrast to the observation made in the
63-71
thermolysis of Cp2Zr-NArMedCPhCHAr′O described above.
To account for the behavior of 1a with metal carbonyls, where
involved.
An attractive possibility for this dimer is complex
20 in Scheme 6, since this only has to extrude 2 mol of the
observed ketenimine product Ph2CdCdN-t-Bu to generate the
subsequent bis-µ-oxo intermediate [Cp ZrO] . Insertion of the
(µ-oxo)(µ-imido) dimer 9 is formed, we suggest that stabilization
of the Cp2ZrdO fragment 16 by coordination to another metal
center may be occurring. Precedent for this can be found in
Proulx and Bergman’s report of the “Wittig type” metathesis
of CpTa(dCH2)(CH3) with PhRe(CO)5. Here an initial overall
2
2
CdO linkage of diphenylketene into a Zr-O bond in this
intermediate leads to the observed product. The type of double
coordination of oxygen to zirconium proposed for intermediate
[
2 + 2] addition, similar to the reaction between Cp2ZrdNR
2
0 is known, but it is influenced by the ring size of the
and CpCo(CO)2, occurs that leads to a product in which Cp2-
oxametallacycle formed. For instance, oxametallacycloheptene
complexes of zirconocene are mononuclear in solution and in
6
0
(CH3)TadO is weakly coordinated to a rhenium center. In
addition, a few other complexes in which a metal oxo moiety
72
64,71
63,70
the solid state whereas smaller ring sizes (3-,
5
4-,
and
is coordinated to another metal center have been docu-
65-69
-membered) of oxametallacycle derivatives are isolated
mented.6
1,62
The similarity of these reactions suggests the
as dimers. It therefore seems reasonable that the dimeric
structure illustrated in Scheme 6 might be accessible to the
possibility that the weak coordination of transient 16 to a metal
carbonyl fragment (for example, as in 17; Scheme 5) might
prevent the self-oligomerization of the highly reactive Cp2ZrdO
species, allowing it to react instead with [Cp2ZrdN-t-Bu] to
give (µ-oxo)(µ-imido)dimer 9 (path A in Scheme 5). Another
possible way that the Cp2ZrdO fragment can remain attached
to the cobalt carbonyl moiety is illustrated in path B in Scheme
(
63) Vaughan, G. A.; Hillhouse, G. L.; Lum, R. T.; Buchwald, S. L.;
Rheingold, A. L. J. Am. Chem. Soc. 1988, 110, 7215.
64) Erker, G.; Hoffmann, U.; Zwettler, R.; Betz, P.; Kr u¨ ger, C. Angew.
Chem., Int. Ed. Engl. 1989, 28, 630.
65) Takaya, H.; Yamakawa, M.; Mashima, K. J. Chem. Soc., Chem.
Commun. 1983, 1283.
66) Erker, G.; Dehnicke, S.; Rump, M.; Kr u¨ ger, C.; Werner, S.; Nolte,
M. Angew. Chem., Int. Ed. Engl. 1991, 30, 1349.
67) Erker, G.; Mena, M.; Kr u¨ ger, C.; Noe, R. J. Organomet. Chem.
(
(
(
5
. Here only one Zr-N bond is initially cleaved in the first
intermediate 18, giving zwitterion 19, which could rearrange
(
1
991, 402, 67.
(
58) Hanna, T. A.; Baranger, A. M.; Walsh, P. J.; Bergman, R. G. J.
Am. Chem. Soc. 1995, 117, 3292.
59) Under the reaction conditions (75 °C), 1a reacts with Cp2ZrMe2 to
give a mixture of products.
(68) Erker, G.; Hoffmann, U.; Zwettler, R. J. Organomet. Chem. 1989,
367, C15.
(69) Mashima, K.; Yamakawa, M.; Takaya, H. J. Chem. Soc., Dalton
Trans. 1991, 2851.
(
(
(
60) Proulx, G.; Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 9802.
61) Housmekerides, C. E.; Ramage, D. L.; Kretz, C. M.; Shontz, J. T.;
(70) Erker, G.; Mena, M.; Kr u¨ ger, C.; Noe, R. Organometallics 1991,
10, 1201.
(71) Bristow, G. S.; Hitchcock, P. B.; Lappert, M. F. J. Chem. Soc.,
Chem. Commun. 1982, 462.
Pilato, R. S.; Geoffroy, G. L.; Rheingold, A. L.; Haggerty, B. S. Inorg.
Chem. 1992, 31, 4453.
(
62) Pilato, R. S.; Rubin, D.; Geoffroy, G. L.; Rheingold, A. L. Inorg.
(72) Erker, G.; Engel, K.; Atwood, J. L.; Hunter, W. E. Angew. Chem.,
Int. Ed. Engl. 1983, 22, 494.
Chem. 1990, 29, 1986.

Generation of Oxozirconocene Complexes
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6403
Scheme 6
Scheme 7
Scheme 8
4-membered oxametallacycle 6e. We considered the possibility
that (µ-oxo)(µ-imido)dimer 9 might form in the reaction of 1a
with diphenylketene, and could then undergo further reaction
with 10 to form the tris-oxo product 12. However, a control
experiment showed that 9 does not react with diphenylketene
under the 1a + diphenylketene reaction conditions.
observed to undergo overall [2 + 2] ring cleavage in the opposite
direction, generating the N-tert-butyl ketenimine 11a and dimer
15. The driving force for these reactions must be the release
of steric congestion caused by the presence of the N-tert-butyl
group in 14. Similar conversions were observed earlier in the
zirconium-mediated imine metathesis reactions studied by Meyer
Note Added in Proof. If dimer 20 and µ-oxo dimer
5
2,53
[
Cp2ZrdO]2 are the reactive intermediates in the ketene reaction,
and Bergman,
where azametallacyclobutane 19, in the
it occurred to us that a dimer analogous to 20 might also be
involved in the reaction of 1 with simple ketones. This could
be the true identity of the metastable species 6b (or 6d) detected
by NMR spectrometry when 1 is allowed to react with ketones
absence of excess imine, undergoes the elimination of imine to
give dimeric [Cp2Zr(NPh)]2 (Scheme 7). Extrapolation of
Meyer and Bergman’s kinetic results suggests that the reaction
of imido complex 1a with ketenimine 11b proceeds by a
dissociative mechanism involving formation of the transient
imido complex [Cp2ZrdNTol], which either dimerizes to give
15 or can be trapped by more N-phenyl ketenimine 11a to give
isolable adduct 13 as shown in Scheme 8.
2
b (or 2d) at low temperature (i.e., n ) 2 in the structure of 6b
and 6d shown earlier in this paper). As we have postulated
with 20, 6b and 6d (n ) 2) should also be capable of
decomposing to give [Cp2ZrdO]2 before [Cp2ZrdO]n is formed.
If this is the case, the µ-oxo dimer should be trappable by
diphenylketene in the acetone reaction. To test this idea, we
repeated the reaction of 1a with acetone at -35 °C and again
observed the formation of the intermediate 6b. Rather than
allowing this solution to warm and release imine 4b and
Summary
Imido/oxo exchange reactions between Cp2ZrdN-t-Bu (1a)
and various organic and organometallic carbonyl compounds
have been investigated. The reactivity of 1a toward organic
carbonyl compounds (aldehydes and ketones) depends strongly
on steric encumbrance and on the availability of R-hydrogens.
Reactions with moderately hindered organic carbonyls 2e-g
generate the enolate complexes 5e-g. In contrast, reactions
with less hindered ketones and aldehydes 2b-d undergo
[Cp2ZrdO]n, diphenylketene was added. Workup of the reac-
tion mixture gave imine but no [Cp2ZrdO]n; instead, as
predicted, a quantitative yield of 12 was formed.
In summary, it seems likely that none of the reactions reported
here extrude free Cp2ZrdO. We think the most likely source
“
Wittig-like” [2 + 2] cycloaddition/cycloreversion to form
of this intermediate is in the thermal fragmentation of Cp2Zr-
oxozirconocene oligomer 3 and imines 4b-d. The reactions
of 1a with CpCo(CO) (7) and Ph CdCdO (10) also undergo
NArCMedCPhCHAr′O, since this is the one reaction in which
we have been able to trap it with added Cp2ZrMe2, and the rate
of this process exhibits a zeroth-order dependence on the
concentration of the dimethylzirconium compound.
2
2
imido/oxo exchange but lead to the new types of oxozir-
conocene-containing products (µ-oxo)(µ-imido) dimer 9 and tris-
oxo complex 12, respectively, instead of 3. All these reactions
ultimately extrude the Cp2ZrdO fragment, but because this
moiety behaves differently in each reaction we do not believe
it is generated as the free monomeric species in each transfor-
mation. In the reaction with metal carbonyls the fragment
appears to be stabilized by coordination to the second “late”
transition metal center, and we propose that the reaction with
diphenylketene proceeds via a bis-µ-oxo zirconium dimer. It
seems likely that Cp2ZrdO is generated as a free intermediate
in the earlier-reported thermolytic fragmentation of Cp2Zr-
(NArCMeCPhCRCHO), since it can be trapped by an external
reagent in this reaction. Future work will be required to confirm
these hypotheses and find ways to reliably generate and explore
the chemistry of the elusive Cp2ZrdO.
Mechanism of the Ketenimine Reaction. To determine
whether the initial steps in the reaction of imido complex 1a
with diphenylketene seemed reasonable, we sought an analogous
reaction with ketenimines that might proceed somewhat less
rapidly and thereby allow us to detect reaction intermediates.
We knew from the reaction of 1a with diphenylketene that the
ketenimine product Ph2CdCdN-t-Bu (11a) is stable to further
reaction with 1a. We therefore investigated the reaction of 1a
with the less hindered ketenimine Ph2CdCdNTol (11b). As
summarized in Scheme 2, here it was possible to establish that
the reaction proceeded by initial overall [2 + 2] cycloaddition,
because the azametallacycle 14 could be detected and character-
ized by spectroscopic methods. The product 14 was also

6
404 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
Lee and Bergman
1
Experimental Section
tube was inserted into a pre-cooled probe set at -45 °C. The H NMR
spectrum of the reaction mixture showed an approximately 2:1:2:2 ratio
General. For a description of the instrumentation and general
procedures used, see earlier papers from this laboratory.
7
3
2 3 2 2
of 4d, 1a, intermediate [Cp ZrOCH(CH(CH ) )N-t-Bu] (6d), and
Unless otherwise specified, all reagents were purchased from
commercial suppliers and dried over activated molecular sieves (4 Å)
before use. Volatile compounds were flash distilled under reduced
pressure after drying (e.g. acetone (2b) and 2-methylpropanal (2d) were
dried over activated molecular sieves and flash-distilled at reduced
another unidentified intermediate (resonances at δ 6.28, 4.42 (d), 1.68
(m), and 0.89). Upon increasing the temperature of the probe,
resonances due to both intermediates decreased in intensity above -30
°C. The second intermediate disappeared faster than 6d and conversion
of 6d to 4d was only observed above 0 °C. 1H NMR (400 MHz, THF-
pressure). The metal carbonyl complexes (C
and CpRe(CO) were dissolved in benzene and dried over activated
molecular sieves; the benzene was removed under reduced pressure
after filtration. CpCo(CO) was passed through a small column of
activated alumina and distilled under reduced pressure. CpMn(CO)
6
H
6
)Cr(CO)
3
, CpV(CO)
4
,
d
8
, -10 °C) of 6d: 6.96 ppm (d, J ) 9.28 Hz, 1H, CH), 6.30 ppm (s,
10H, C ), 2.88 ppm (m, 1H, CH(CH ), 1.22 ppm (s, 9H, C(CH ),
and 0.96 ppm (d, J ) 9.30 Hz, 6H, CH(CH
H
5 5
)
3 2
3 3
)
3
3
)
2
).
2
Cp Zr(NH-t-Bu)(OCCH(CH CHC(CH
2
2
)
3
3 3
) ) (5e). To a solution
3
of 2-tert-butylhexan-1-one (2e) (102 mg, 0.66 mmol) in pentane was
slowly added 1a (220 mg, 0.60 mmol). The mixture was stirred for 1
h until the solution became homogeneous. Any pentane-insoluble
material was removed by filtration and then the solvent and excess 2e
were removed under vacuum. The residual white solid was recrystal-
7
4,75
was sublimed before use (40 °C, 100 mtorr). CpFe(CH
Ph CdCdO (10), and Ph CdCdNTol (11b)
2 2
3
)(CO)
were prepared by
the literature methods. Synthesis of compounds Cp Zr(dNR)(THF)
R ) C(CH (1a), 2,6-(CH
(1b)) are reported elsewhere.1
CH CdN-t-Bu (4b). To 1a (69.7 mg, 0.19 mmol) in THF (1
mL) was added acetone (2b) (14 µL, 0.19 mmol). Upon addition of
b, the color of the solution temporarily changed from yellow to red-
2
,
4
9
50,51
2
0,11
(
3
)
3
3 2 6 4
) C H
(
3 2
)
lized from pentane at -35 °C to afford colorless crystals of 5e (210
1
mg, 0.47 mmol, 78%). H NMR (400 MHz, C
6
D
6
): δ 6.01 (s, 5H,
2
C
1
2
5
H
5
), 5.95 (s, 5H, C
H, CH(CH ), 2.23 (m, 2H, CH
H, CH ), 1.50 (m, 2H, CH ), 1.23 (s, 9H, C(CH
). C{ H} NMR (400 MHz, C ): δ(C) 163.8, 56.6, 34.0;
δ(CH) 110.8, 110.6, 101.7, 48.9; δ(CH ) 27.6, 25.4, 23.1; δ(CH ) 34.6,
0.1. IR (C ): 3340 (w), 2943 (s), 1633, 1475, 1374, 1273, 1217
s), 1033, 977, 783, 691 cm . Anal. Calcd for C24
5
H
5
), 4.65 (br, 1H, NH), 4.52 (t, J ) 4.08 Hz,
), 1.91 (m, 1H, CH(CH ), 1.74 (m,
), 1.13 (s, 9H,
orange and a white solid precipitated from solution. The volatile
materials (including THF) were collected by flash-distillation under
reduced pressure and identified by GCMS and IR spectroscopy. The
2
)
3
2
3 3
)
2
2
3 3
)
1
3
1
C(CH
3
)
3
6 6
D
1
13
sample of 4b for the H and C NMR data was separately prepared in
2
3
1
8 8
THF-d by the same procedure. H NMR (400 MHz, THF-d ): δ 1.88
3
(
6 6
D
1
3
1
(
(
(
s, 3H, CH
400 MHz, THF-d
THF): 1669 (s), 1457 (w), 1393 (w), 1356 (w) cm
Reactions of 1a with Organic Carbonyls 2c-d. An NMR tube
3
), 1.84 (s, 3H, CH
3
), 1.20 (s, 9H, C(CH
3 3
) ). C{ H} NMR
-1
H37NOZr: C, 64.52;
8
): δ(C) 162.4, 54.9; δ(CH
3
) 31.3, 30.8, 21.5. IR
H, 8.35; N, 3.14. Found: C, 64.22; H, 8.33; N, 2.90.
Crystal Structure Determination of 5e. Colorless crystals of 5e
were obtained by two recrystallizations from pentane solution at -35
-
1
.
-
2
was charged with 1a (5 mg, 1.4 × 10 mmol) and excess 2c-d (2-3
°
0
C. A fragment having approximate dimensions of 0.20 × 0.25 ×
equiv) in THF-d (0.4 mL). A white precipitate was produced upon
8
.30 mm was mounted on a glass fiber using Paratone N-hydrocarbon
1
mixing the reagents. A H NMR spectrum of the reaction mixture
showed resonances due to a new imine and several peaks around 6
oil. All measurements were made on a Siemens SMART diffractometer
with graphite monochromated Mo KR radiation. Cell constants and
an orientation matrix obtained from a least-squares refinement using
the measured positions of 6597 reflections with I > 3σ in the range
ppm due to generation of (Cp
d were identified by comparison of their spectra with literature spectral
data. Compound 4c was also confirmed by independent preparation.
2 n
ZrdO) (3). The imine products 4c and
4
3
.00 < 2θ < 45.00° corresponded to a primitive monoclinic cell with
1
H NMR (400 MHz, THF-d
8
) of PhCHdN-t-Bu (4c): δ 8.27 (s, 1H,
the following dimensions: a ) 9.4933(2) Å, b ) 8.0068(2) Å, c )
NH), 7.75 (d, J ) 3.56 Hz, 2H, phenyl), 7.35 (m, 3H, phenyl), 1.26 (s,
3
3
0.6878(9) Å, â ) 91.643(1)°, V ) 2331.65(9) Å . For Z ) 4 and fw
3
2
1 1
9
H, C(CH
)
3 3
) (lit. H NMR (CDCl
3
): δ 8.32 (s, 1H, CH), 7.78-7.84
)).
CHCHdN-t-Bu (4d): δ 7.52
d, J ) 4.17 Hz, 1H, CH), 2.30 (m, 1H, CH(CH ), 1.10 (s, 9H,
), 1.01 (d, J ) 6.88 Hz, 6H, CH(CH ) (lit.
): δ 7.41 (d, J ) 6.8 Hz, 1H, CH), 2.41 (m, 1H, CH(CH
.16 (s, 9H, C(CH ), 1.05 (d, J ) 5.9 Hz, 6H, CH(CH )).
)
445.77, the calculated density is 1.27 g/cm . The systematic absences
of h01: h + l * 2n and 0k0: k * 2n uniquely determine the space
group to be P2 /n. The data were collected at a temperature of -103
1 °C. Frame data were collected using ω scans of 0.3° and a total
(
m, 2H, phenyl), 7.40-7.45 (m, 3H, phenyl), 1.36 (s, 9H, C(CH )
3 3
1
8 3 2
H NMR (300 MHz, THF-d ) of (CH )
1
(
3 2
)
(
2
1,22 1
C(CH
)
3 3
)
3 2
H NMR
),
counting time of 10 s per frame.
(CDCl
3
3 2
)
Data were integrated using the program SAINT and box parameters
of 1.6 × 1.6 x 0.6° out to a maximum 2θ value of 46.5°. The data
were corrected for Lorentz and polarization effects. No decay correction
was applied. The linear absorption coefficient µ for Mo KR radiation
1
)
3 3
3 2
)
Spectroscopic Observation of [Cp ZrOC(CH N-t-Bu] (6b). In
2
3
)
2
2
-
2
the dry box, an NMR tube was charged with 1a (26.4 mg, 7.2 × 10
mmol) in THF-d (0.4 mL) and sealed with a rubber septum. The tube
was removed from the drybox and cooled to -78 °C, then acetone
-1
8
is 4.8 cm . The data were corrected for absorption using an empirical
correction based on multiple measurements of equivalent reflections
as calculated using the program XPREP (v. 5.03; part of the SHELXTL
crystal structure determination program, Siemens Industrial Automation,
Inc., Madison, WI (1995)) (µR ) 0.06, Tmax ) 0.87, Tmin ) 0.81). The
9504 integrated and corrected reflections were averaged to yield 3600
unique reflections (Rint ) 0.034).
-
2
(
2b) (5.5 µL, 7.5 × 10 mmol) was injected by syringe. The tube
was then shaken and inserted into a pre-cooled NMR probe (-50 °C):
1
at this point H NMR analysis showed an approximately 2:1 ratio of
6
b and 4b. Conversion of the remaining 6b to 4b was monitored at
10 °C. At this temperature, resonances for products 4b and 3
-
continued to grow as resonances for intermediate 6b decreased in
The structure was solved by direct methods and expanded using
Fourier techniques. Inspection of the model following refinement of
most of the atoms with anisotropic thermal parameters showed a pattern
of difference Fourier peaks consistent with a total disorder of the enolate
ligand around a pseudo-mirror plane containing the O and C16 as shown
in Figure 1. A major conformation contains C11-C20 and a minor
one (see the supporting information) contains C211-C220. Peaks
corresponding to all atoms of the disorder were located and refined
with Biso fixed to the average of the Biso of the majority component.
Adjustment of the disorder ratio revealed a shallow minimum in the
residuals near an 18:82 ratio of two conformations. Hydrogen atoms
were included in calculated positions for the majority component but
not refined. The final cycle of full-matrix least-squares refinement was
based on 2828 observed reflections (I > 3.00σ(I)) and 270 variable
parameters and converged (largest parameter shift was 0.04 times its
esd). The standard deviation of an observation of unit weight ((∑ω-
intensity. Upon warming to room temperature, the only major
1
resonances observed were attributable to products 4b and 3. H NMR
(
6
400 MHz, THF-d
H, (CH ), 1.22 (s, 9H, C(CH
Low-Temperature NMR Study of the Reaction of 1a with
CH CHCHO (2d). In the drybox, an NMR tube was charged with
8
, -10 °C) of 6b: δ 6.28 (s, 10H, C
5 5
H ), 1.34 (s,
)
3 2
3 3
)
).
(
Cp
3 2
)
-
2
2
Zr(dN-t-Bu)(THF) (1a) (20.1 mg, 5.5 × 10 mmol) in THF-d
8
(0.4 mL) and sealed with a rubber septum. The tube was removed
-
2
from the box and cooled to -78 °C, then 2d (4 mg, 5.6 × 10 mmol)
was injected by syringe. At this point the tube was treated similarly
to the reaction described above that was performed to observe 6b. The
(
73) Baranger, A. M.; Bergman, R. G. J. Am. Chem. Soc. 1994, 116,
3
1
822.
(74) Piper, T. S.; Wilkinson, G. J. Inorg. Nucl. Chem. 1956, 3, 104.
75) Clifford, A. F.; Mukherjee, A. K. J. Inorg. Nucl. Chem. 1963, 25,
(
2
1/2
065.
(|F
o
| - |F
c
|) /(N
o
- N
v
)) : N
o
) number of observations, N ) number
v

Generation of Oxozirconocene Complexes
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6405
of variables) was 2.46. The weighting scheme was based on counting
statistics and included a factor (p ) 0.031) to downweight the intense
reflections. The maximum and minimum peaks on the final difference
Fourier map corresponded to 0.41 and -0.49 e /Å , respectively. The
structure consists of separated molecules of the compound packed in
the unit cell and there are no abnormally short intermolecular contacts.
δ(C) 62.9; δ(CH) 112.1; δ(CH
1027, 791, 631 (s) cm . MS (EI): m/e 529.9 (M ). Anal. Calcd for
3
) 37.3. IR (C
6
D
6
): 2959, 2356, 1168,
-
1
+
C
24
H
29NOZr
N, 2.52.
CpCo(CO)(2,6-(CH ) C H NC) (8b). A glass bomb was charged
2
: C, 54.40; H, 5.52; N, 2.64. Found: C, 54.65; H, 5.82;
-
3
3
2
6
3
with 1b (208 mg, 0.57 mmol) and 7 (321 mg, 1.78 mmol) in C H (10
6
6
Cp
-butanone (2f) (52 mg, 0.52 mmol) in pentane was slowly added 1a
150 mg, 0.41 mmol). The mixture was stirred for 1 h until the solution
2
Zr(NH-t-Bu)OC(CH
2
)-t-Bu (5f). To a solution of 3,3-dimethyl-
mL). The bomb was degassed with 1 freeze-pump-thaw cycle, heated
1
2
(
to 75 °C for 1 day, and then analyzed by H NMR spectrometry. No
major resonances near 6 ppm were observed, but resonances attributable
became homogeneous. Any pentane-insoluble material was removed
3 2 6 3
to CpCo(CO)(2,6-(CH ) C H NC) (8b) were generated during the
by filtration and then the solvent and excess 2f were removed under
reaction. After the zirconium-containing products were removed from
the reaction mixure by filtration through florisil (×2), the red solution
was chromatographed on silica gel (using a 1:1 ratio of hexane and
vacuum. The residual solid was recrystallized from pentane at -35
1
°
C to provide colorless crystals of 5f (134 mg, 0.34 mmol, 83%). H
43
NMR (400 MHz, C
6
D
12): δ 6.09 (s, 10H, C
5
H
5
), 4.64 (br, 1H, NH),
), 1.02
12): δ(C) 176.6, 56.8,
): 3128,
971 (s), 2907, 2879, 1595, 1365, 1300 (s), 1208 (s), 1189 (s), 1041,
benzene) to separate 8b from CpCo(2,6-(CH
3
)
2
C
6
H
3
NC)
2
(12% by
1
3
3 3
.78 (s, 1H, OCHH), 3.47 (s, 1H, OCHH), 1.18 (s, 9H, C(CH )
H NMR) and to afford 8b as a red-brown solid (72.6 mg, 0.26 mmol,
13
1
1
(s, 9H, C(CH
3 3
) ). C{ H} NMR (400 MHz, C
6
D
46%). H NMR (400 MHz, C
6 6 2 3 2 6 3
D ) of CpCo(CO) (2,6-(CH ) C H -
3
2
9
7.6; δ(CH) 111.3; δ(CH ) 82.3; δ(CH
2
3
) 34.9, 28.8. IR (C
D
6 6
NC): δ 6.72 (t, J ) 7.48 Hz, 1H, aryl), 6.63 (d, J ) 7.41 Hz, 2H,
13
1
aryl), 4.79 (s, 5H, C
5 5 3
H ), 2.08 (s, 6H, CH ). C{ H} NMR (400 MHz,
-
1
86,792, 580 cm . Anal. Calcd for C20
H31NOZr: C, 61.17; H, 7.96;
C
6
D
6
): δ(C) 133.8, 130.2, 128.5; δ(CH) 127.8, 126.4, 83.3; δ(CH )
3
-
1
N, 3.57. Found: C, 61.10; H, 8.10; N, 3.33.
6 6
18.6 (one quaternary C was not located). IR (C D ): 2071, 1955 cm
(lit.43 IR (C
D ): 2075, 1956 cm ).
-1
Cp Zr(NH-t-Bu)(OC(C(CH )CH(CH ) (5g). A glass bomb (20
2
)
3 2
)
3 2
6 6
mL) was loaded with 1a (119 mg, 0.33 mmol) and 2,4-dimethyl-3-
pentanone (2g) (49 mg, 0.43 mmol) in THF (7 mL). The bomb was
degassed with 1 freeze-pump-thaw cycle and heated to 45 °C for 5
h. After removal of solvent and excess ketone under reduced pressure,
the residual white solid was recrystallized from pentane at -35 °C to
Reactions of 1a with Various Metal Carbonyls (CpV(CO) , CpFe-
4
(CH )(CO) , (C H )Cr(CO) , or Mo(CO) ). An NMR tube was
3
2
6
6
3
6
-
2
charged with 1a (14 mg, 3.8 × 10 mmol) and a metal carbonyl
complex (3 equiv) in THF-d (0.5 mL). The tube was degassed with
8
1 freeze-pump-thaw cycle and sealed on a vacuum line. The reaction
1
1
provide white crystals of 5g (102 mg, 0.25 mmol, 76%). H NMR
was then monitored using H NMR until no starting imido complex 1a
(
(
400 MHz, C
septet, J ) 6.85 Hz, 1H, (CH
), 1.24 (s, 9H, C(CH ), 1.11 (d, J ) 6.85 Hz, 6H, (CH
): δ(C) 159.8, 98.6, 56.5; δ(CH) 111.5,
) 34.6, 20.6, 19.1, 18.8. IR (C ): 3350 (w), 3103 (w),
961 (s), 2731 (w), 1660, 1475, 1387, 1360, 1271 (s), 1210 (s), 1077
6
D
6
): δ 5.96 (s, 10H, C
5
H
5
), 4.21 (br, 1H, NH), 2.88
), 1.76 (s, 3H,
CH).
was observed (2.5 days at 25 °C for CpV(CO) , 1 day at 75 °C for
4
3
)
2
CH), 1.77 (s, 3H, CH
3
CpFe(CH )(CO) , 6 h at 25 °C for (C H )Cr(CO) , and 15 h at 25 °C
3
2
6
6
3
1
CH
3
3
)
3
3
)
2
for Mo(CO) ). The reactions proceeded cleanly by H NMR and always
6
13
1
C{ H} NMR (400 MHz, C
0.4; δ(CH
D
6 6
generated new resonances at 6.25 (20H) and 1.31 (9H) ppm due to
formation of 9. The corresponding isocyanide complex (CpV(CO)3-
(CN-t-Bu), CpFe(CH )(CO)(CN-t-Bu), or C H Cr(CO) (CN-t-Bu), re-
3
2
(
3
6 6
D
3
6
6
2
-
1
s), 1033, 989, 775 cm . Anal. Calcd for C21
H
33NOZr: C, 62.02; H,
.18; N, 3.44. Found: C, 61.90; H, 8.25; N, 3.31.
CpCo(CO)(CN-t-Bu) (8a). A glass bomb (50 mL) was loaded with
a (361 mg, 0.99 mmol) and CpCo(CO) (7) (546 mg, 3.03 mmol) in
spectively) was also generated except for the reaction of Mo(CO) in
6
8
which several tert-butyl resonances near 1.5 ppm were observed
(presumably due to formation of a mixture of Mo(CO)6-n(CN-t-Bu) ).
n
1
2
Zirconium-containing 9 was removed by passing the solution through
a small column of activated alumina. Evaporation of the solvent from
the filtrate afforded the isocyanide product and excess metal carbonyl
THF (ca. 20 mL). The bomb was degassed with 1 freeze-pump-
thaw cycle and heated to 75 °C for 1.5 days. After the solvent and
excess 7 were removed under reduced pressure, the residual solid was
extracted with pentane. The pentane solution was passed through a
small column (0.25 in. by 2 in.) of activated alumina to remove residual
complex. The 1H NMR spectra of the isocyanide products were
1
compared to literature spectral data. H NMR (300 MHz, C
6
D
6
) of
4
CpV(CO)
3
(CN-t-Bu): δ 4.57 (s, 5H, C
H NMR (C ): δ 4.58 (s, 5H, C
NMR (300 MHz, CDCl ) of CpFe(CH
), 1.38 (s, 9H, C(CH ), -0.07 (s, 3H, CH
(CDCl ): δ 4.62 (s, 5H, C ), 1.44 (s, 9H, C(CH
)). H NMR (400 MHz, CDCl ) of (C )Cr(CO)
4.93 (s, 6H, C ), 1.37 (s, 9H, C(CH ) (lit. H NMR (CDCl
5.43 (s, 6H, C ), 1.38 (s, 9H, C(CH )).
Reactions of 1a with CpM(CO) (M ) Mn, Re) in THF-d
NMR tube was charged with 1a (12 mg, ca. 33 µmol) and CpM(CO)
(M ) Mn, Re) (3 equiv) in THF-d (0.4 mL). The tube was degassed
5
H
5
), 0.89 (s, 9H, C(CH
), 0.90 (s, 9H, C(CH
)(CO)(CN-t-Bu): δ 4.48 (s, 5H,
3 3
)
3 3
)
) (lit.4
1
)). 1H
(Cp
2
Zr)
2
(µ-O)(µ-N-t-Bu) (9). Evaporation of pentane from the filtrate
6
D
6
5
H
5
1
afforded red solid 8a (62 mg, 0.26 mmol, 53%). H NMR (400 MHz,
3
3
1
3
1
45 1
C
(
D
6 6
): δ 4.76 (s, 5H, C
400 MHz, C ): δ(C) 208.4, 161.6, 57.0; δ(CH) 82.7; δ(CH
IR (Nujol): 2990, 2117, 2072, 2028, 1948, 1375, 1217 cm . (lit.
5
5
H ), 0.90 (s, 9H, C(CH
3
)
3
). C{ H} NMR
C
5
H
5
3
)
H
3
3
) (lit. H NMR
), -0.06 (s, 3H,
(CN-t-Bu): δ
): δ
D
6 6
3
) 30.5.
3
5
5
3 3
)
-1
41
1
CH
3
3
6
H
6
47 1
2
1
H NMR (C
6 6
D
): δ 4.75 (s, 5H, C
5
H
5
), 0.91 (s, 9H, C(CH
3
)
3
)).
H
6 6
3
)
3
3
1
3
13
CpCo( CO)
CpCo(CO)
2
(7- C). A glass bomb (10 mL) was loaded with
6
H
6
3 3
)
2
(7) (170 mg, 0.47 mmol). After the bomb was degassed
3
8
. An
1
3
with 2 freeze-pump-thaw cycles, it was filled with CO to 1.5 atm
and shaken for 1 day. This process was repeated one more time. Two
3
8
1
3
13
cycles of CO exchange provided 86 ( 4% CO labeled CpCo-
with 1 freeze-pump-thaw cycle and sealed on a vacuum line. The
reaction mixture was heated to 110 (M ) Re) or 135 °C (M ) Mn)
1
3
13
13
13
(
CO)
2
(7- C). C incorporation of 7- C was determined by EI mass
1
spectroscopy (determined by integration of relative mass peaks) as well
as C NMR spectra and IR spectra.
for 3.5 days and monitored by H NMR spectrometry. The ratio of
13
1
products was measured by one-pulse integration of the H NMR spectra.
1
3
13
13
13
13
1
5
CpCo( CO)( CN-t-Bu) (8a- C). CpCo( CO)( CN-t-Bu) was
prepared in a fashion analogous to the synthesis of 8a except that 86%
In the reaction of CpMn(CO)
)Mn(CO) was generated and ca. 30% of 9 observed. In the
reaction of CpRe(CO)
and (Cp Zr) (NH-t-Bu)
3 2
, ca. 60% of Cp Zr(NH-t-Bu)(η :η -
C
5
H
4
3
13
13
13
1
5
CO labeled CpCo( CO)
2
(7- C) was used in place of unlabeled 7.
3
, ca. 85% of Cp
2
Zr(NH-t-Bu)(η :η -C
5 4 3
H )Re(CO)
1
3
1
1
5
EI mass spectroscopy as well as spectral data ( C NMR spectra and
IR) showed that CpCo( CO)( CN-t-Bu) was generated with 84 ( 4%
2
2
2
(η :η :η -C
5
H
3
)Re(CO) were observed and only
3
13
13
15% of 9 was generated. During both reactions, tert-butyl resonances
at 1.15 ppm were generated (presumably due to formation of CpM-
1
3
incorporation of C label.
Cp Zr) (µ-O)(µ-N-t-Bu) (9). A glass bomb (50 mL) was loaded
with 1a (361 mg, 0.99 mmol) and CpCo(CO) (7) (546 mg, 3.03 mmol)
in THF (ca. 20 mL). The reaction mixture was degassed with 1
freeze-pump-thaw cycle and heated to 75 °C for 1.5 days. After
removal of solvent and excess 7 under reduced pressure, the residual
solid was washed with pentane. The pentane-insoluble material was
then collected and dissolved in warm Et
from the solution at room temperature afforded block red crystals of 9
(
2
(
2
2
(CO)
2
(CN-t-Bu) (M ) Mn, Re)), but not clearly indentified due to the
Zr(NH-t-Bu)-
)Re(CO) , and (Cp
are reported elsewhere.
CdCdN-t-Bu (11a). There are three ways to obtain ketenimine
complex nature of the spectra. The spectral data for Cp
2
2
1
5
1
5
(η :η -C
Zr) (NH-t-Bu)
Ph
5 4
H
)Mn(CO)
3
1
, Cp
2
Zr(NH-t-Bu)(η :η -C
H
5 4
3
2
-
1
5
39,40
2
2
(η :η :η -C )Re(CO)
5
H
3
3
2
generated as a by-product during the synthesis of 12, 13, and 15.
Isolation of 11a from those reactions is described below. (A) The
procedure was the same as that used in the synthesis of 12. After
crystallization of 12, the mother liquor was passed through dried florisil
(5 × 0.8 cm) two times to destroy any residual zirconium-containing
2 2
O. Slow evaporation of Et O
1
79 mg, 0.15 mmol, 30%). H NMR (400 MHz, C
6
D
6
): δ 6.10 (S,
1
3
1
0H, C H
5 5
), 1.12 (s, 9H, C(CH
3
)
3
). C{ H} NMR (400 MHz, C ):
6 6
D

6
406 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
Lee and Bergman
compounds. Evaporation of the filtrate under reduced pressure afforded
to dark brown. The solution was stirred for 1 h and the solvent was
removed under reduced pressure. The residue was washed with pentane
and recrystallized from toluene layered with pentane at -35 °C to afford
dark brown block crystals of 13 (169 mg, 0.28 mmol, 65%). The
1
1a as a yellow oil (43 mg, 0.17 mmol, 71%). (B) The procedure was
the same as that used in the synthesis of 13. After 13 was crystallized
from the pentane solution, the mother liquor was passed through florisil
(
5 × 0.8 cm) two times to destroy any residual zirconium-containing
2
pentane extract mostly consisted of Ph CdCdN-t-Bu (11a), but some
compounds. Evaporation of the filtrate under reduced pressure also
afforded 11a as a yellow oil (62 mg, 0.25 mmol, 58%). (C) The
reaction procedure was the same as that used in the synthesis of 15.
After isolation of insoluble 15, the mother liquor was passed through
florisil to destroy any residual zirconium-containing compounds.
Removal of the solvent from the filtrate under reduced pressure also
afforded 11a (25 mg, 0.10 mmol, 73%). Several attempts failed to
give material suitable for elemental analysis and so the ketenimine was
characterized spectroscopically. H NMR (400 MHz, C
(
13 was also dissolved in the solution. Dark brown crystals of 13 would
1
also be grown from the pentane solution at -35 °C. H NMR (400
6 6
MHz, C D ): δ 7.46 (dd, J ) 7.2 Hz, J ) 1.1 Hz, 4H, Ph-H), 7.09
(dd, J ) 7.4 Hz, J ) 8.0 Hz, 4H, Ph-H), 6.83 (d, J ) 8.1 Hz, 4H,
Tol-H), 6.80 (tt, J ) 7.4 Hz, J ) 1.1 Hz, 2H, Ph-H), 6.62 (d, J ) 8.1
13
1
Hz, 4H, Tol-H), 5.88 (s, 10H, C
(400 MHz, C ): δ(C) 149.2, 144.8, 142.5, 129.3, 92.1; δ(CH) 130.8,
6 6
128.8, 127.7, 123.3, 120.1, 115.9; δ(CH ) 20.9. IR (C D ): 3075, 3039,
5 5 3
H ), 2.08 (s, 6H, CH ). C{ H} NMR
6 6
D
3
1
-1
6
6
D ): δ 7.41
2958, 2913, 1965, 1505 (s), 1316, 810, 689 cm . MS (EI): m/e 609.8
+
d, J ) 8.4 Hz, 4H, Ar-H), 7.15 (dd, J ) 7.93 Hz, J ) 7.6 Hz, 4H,
(M ). Anal. Calcd for C38
H N
34 2
Zr: C, 74.83; H, 5.62; N, 4.59.
13
Ar-H), 7.15 (t, J ) 7.39 Hz, 2H, Ar-H), 1.16 (s, C(CH
{
1
3
)
3
, 9H). C-
12): δ(C) 183.1, 136.4, 60.3; δ(CH) 129.0,
) 30.8 (one quaternary C was not located). IR
Found: C, 74.64; H, 5.74; N, 4.46.
Cp Zr(N-t-Bu)(NTol)CCPh (14). To 1a (156 mg, 0.43 mmol) in
toluene (6 mL) was added Ph CdCdNTol (11b) (122 mg, 0.43 mmol).
1
H} NMR (400 MHz, C
6
D
2
2
27.9, 126.0; δ(CH
3
2
-
1
(
THF): 2015 (s), 1601, 1742, 1496, 757, 695 cm
Cp Zr) CCPh (12). To a solution of 1a (89 mg, 0.24 mmol)
in 10 mL of C was added Ph CdCdO (10) (111 mg, 0.57 mmol).
.
Upon addition of 11b, the color of the solution changed from yellow
to dark brown. The solvent was immediately removed under reduced
pressure. The residue was washed with pentane to remove Ph CdCdN-
2
(
2
2
O
3
2
6
H
6
2
Upon the addition of 10, the color of the solution changed from yellow
to orange. The solution was then stirred for 10 min. Slow vapor
diffusion of pentane into the solution followed by slow cooling to -35
t-Bu (11a) and then recrystallized from toluene layered with pentane
at -35 °C to afford 14 as a red-brown precipitate (165 mg, 0.29 mmol,
67%). Because 14 decomposes to 15 and 11a at the ambient
-
2
1
1
1
°
C afforded orange crystals of 12 (53 mg, 7.9 × 10 mmol, 65%). H
NMR (400 MHz, THF-d ): δ 7.34 (dd, J ) 8.2 Hz, J ) 1.1 Hz, 4H,
Ph-H), 7.15 (dd, J ) 8.1 Hz, J ) 7.5 Hz, 4H, Ph-H), 6.91 (dd, J ) 7.3
temperature, spectral data other than H NMR were not obtained.
NMR (400 MHz, C ): δ 7.38 (d, J ) 7.3 Hz, 4H, Ph-H), 7.15 (t, J
) 7.6 Hz, 4H, Ph-H), 6.89 (t, J ) 7.0 Hz, 2H, Ph-H), 6.83 (d, J ) 8.2
Hz, 2H, Tol-H), 6.76 (d, J ) 7.7 Hz, 2H, Tol-H), 6.01 (s, 10H, C ),
2.04 (s, 3H, CH ), 0.92 (s, 9H, C(CH ).
[Cp Zr(NTol)] (15). A glass vessel with a vacuum stopcock (15
mL) was charged with 14 (79 mg, 0.14 mmol) in C (4 mL). The
H
8
6 6
D
1
3
1
Hz, J ) 1.2 Hz, 2H, Ph-H), 6.35 (s, 20H, C
MHz, THF-d ): δ(C) 166.8, 144.7, 90.5; δ(CH) 130.8, 127.7, 123.0,
14.0. IR (THF): 3110 (w), 1536 (s), 1329 (w), 1319 (w), 1018 (w),
5
H
5
). C{ H} NMR (400
5 5
H
8
3
3 3
)
1
2
2
-
1
9
89 (w), 772, 697, 612, 556, 480 cm . HRMS (EI) m/e calcd for
6 6
H
+
+
C H
34 30
O
3
Zr
2
668.0308 (M ); found 668.0305 (M ).
bomb was degassed with 1 freeze-pump-thaw cycle and heated to
45 °C for 1.5 days. A green solid precipitated from the solution; it
was collected, rinsed 2 times with pentane, and recrystallized from THF
layered with pentane at -35 °C to afford thin green needles of 15 (19
Crystal Structure Determination of [12‚0.5THF]. A yellow
crystal of 12 (which turned out to be the cyclic organometallic complex
crystallized with 0.5 molecules of THF) was obtained by slow vapor
diffusion of pentane into a THF solution followed by cooling to -35
-
2
1
mg, 2.9 × 10 mmol, 42%). H NMR (300 MHz, C
J ) 7.9 Hz, 4H, Tol-H), 6.25 (s, 20H, C ), 5.75 (d, J ) 8.3 Hz, 4H,
). C{ H} NMR (400 MHz, THF-d ): δ(C)
156.1,126.1; δ(CH) 128.8, 121.0, 113.3; δ(CH ) 20.6. IR (Nujol):
3076, 2510, 2368 (w), 2342 (w), 1705 (w), 1607, 1563, 1492 (s), 1245
6 6
D ): δ 7.00 (d,
°
C. A fragment cleaved from this crystal was mounted as described
5 5
H
13
1
for 5e. X-ray data were collected as for 5e except that an Enraf-Nonius
CAD-4 diffractometer was used. The final cell parameters and specific
data collection parameters for this data set are given in Table 1.
The 3022 raw intensity data were converted to structure factor
amplitudes and their esd’s by correction for scan speed, background,
and Lorentz and polarization effects. No correction for crystal
decomposition was necessary. An empirical absorption correction based
Tol-H), 2.35 (s, 6H, CH
3
8
3
-
1
(s), 1201, 1113, 1024, 891, 794 (s), 661, 573 cm . MS (EI): m/e
650 (M ). Anal. Calcd for C34
+
H
34
N
2
Zr
2
: C, 62.53; H, 5.25; N, 4.29.
Found: C, 62.48; H, 5.23; N, 4.44.
Acknowledgment. We acknowledge the National Institutes
of Health (Grant No. R37-GM25459) for generous financial
support of this work. We are grateful to Dr. F. J. Hollander,
staff crystallographer of the U.C. Berkeley X-ray diffraction
facility (CHEXRAY), for determination of the X-ray structures.
on azimuthal scan data was applied to the data (Tmax ) 0.998, Tmin
)
0
.934, used by the program DIFABS in MOLEN). The structure was
solved by Patterson methods and refined Via standard least-squares and
Fourier techniques (hydrogen atoms ignored). The final residuals for
2
2
1
79 variables refined against the 1753 data set for which F > 3σ(F )
are given in Table 1. The largest peak in the final difference Fourier
map had an electron density of 0.66 e /A , and the lowest excursion
was -0.27 e /A . The p-factor, used to reduce the weight of intense
reflections, was set to 0.03 in the last cycles of refinement. Only the
zirconium atom was refined with anisotropic thermal parameters.
-
3
Supporting Information Available: Tables of X-ray dif-
fraction data (positional and anisotropic thermal parameters and
full intramolecular distances and angles) for 5e and 12 (23
pages). Ordering information is given on any current masthead
page.
-
3
Cp
mL of toluene was added Ph
Upon addition of 11b, the color of the solution changed from yellow
2
Zr(NTol)
2
CdCPh
2
(13). To 1a (156 mg, 0.43 mmol) in 20
2
CdCdNTol (11b) (244 mg, 0.86 mmol).
JA954050T