Reactivity studies of the zirconium alkylidene complexes [η5-C5H3-1,3-(SiMe2CH 2PPri2)2]Zr=CHR(C1) (R = Ph, SiMe3)

Article abstract of DOI:10.1021/ja982695y

Reactivity studies of the zirconium alkylidene complexes [P₂Cp]Zr=CHR(Cl) (1a, R = Ph; 1b, R = SiMe₃; [P₂Cp] = η⁵-C₅H₃-1,3-(SiMe₂CH ₂PPrⁱ₂)₂) are described. The reaction of 1 with ethylene follows second-order kinetics to give the ethylene complex [P₂Cp]Zr(η²-C₂H₄)Cl (2), the structure of which was determined by X-ray crystallography. Addition of acetone to 1 generates the alkene RCH=CMe₂, although the anticipated Zr oxo species could not be isolated from this reaction. An insertion of CO into the Zr=C bond of 1 yields the ketene complex [P₂Cp]Zr(η²-C,O-OC=CHR)Cl (3), while the reaction with tert-butyl isocyanide gives the analogous ketenimine complex [P₂Cp]Zr(η²-C,N-Bu^tNC=CHR)Cl (4). The structure of ketene 3a (R = Ph), determined by X-ray diffraction, exhibits the E geometry, with the position of the ketene unit with respect to the ancillary [P₂Cp] ligand being opposite to that in the configuration of the precursor alkylidene 1a. The ketene complex 3 reacts with ethylene to give [P₂Cp]Zr(η²-C,O-CH₂CH ₂C(O)=CHR)Cl (5). The molecular structure of 5b (R = SiMe₃) was obtained by X-ray diffraction and reveals a five-membered zirconaoxacycle arising from the insertion of ethylene into the Zr-C bond of the ketene, which is subsequently coordinated to the metal as an enolate ligand. 5 undergoes a final insertion reaction with CO to give the asymmetric η²-acyl-ylide complex 6. For each reaction detailed above, dissociation of a labile pendant phosphine donor provides an open site for reactivity.

Full text of DOI:10.1021/ja982695y

J. Am. Chem. Soc. 1999, 121, 1707-1716
1707
Reactivity Studies of the Zirconium Alkylidene Complexes
[η5-C5H3-1,3-(SiMe2CH2PPri2)2]ZrdCHR(Cl) (R ) Ph, SiMe3)
Michael D. Fryzuk,*,† Paul B. Duval,† Shane S. S. H. Mao,† Steven J. Rettig,†,‡
Michael J. Zaworotko,§ and Leonard R. MacGillivray§
Contribution from the Departments of Chemistry, UniVersity of British Columbia, 2036 Main Mall,
VancouVer, BC, Canada V6T 1Z1, and St. Mary’s UniVersity, Halifax, NS, Canada B3H 3C3
ReceiVed July 29, 1998
Abstract: Reactivity studies of the zirconium alkylidene complexes [P2Cp]ZrdCHR(Cl) (1a, R ) Ph; 1b, R
) SiMe3; [P2Cp] ) η5-C5H3-1,3-(SiMe2CH2PPri2)2) are described. The reaction of 1 with ethylene follows
second-order kinetics to give the ethylene complex [P2Cp]Zr(η2-C2H4)Cl (2), the structure of which was
determined by X-ray crystallography. Addition of acetone to 1 generates the alkene RCHdCMe2, although
the anticipated Zr oxo species could not be isolated from this reaction. An insertion of CO into the ZrdC
bond of 1 yields the ketene complex [P2Cp]Zr(η2-C,O-OCdCHR)Cl (3), while the reaction with tert-butyl
isocyanide gives the analogous ketenimine complex [P2Cp]Zr(η2-C,N-ButNCdCHR)Cl (4). The structure of
ketene 3a (R ) Ph), determined by X-ray diffraction, exhibits the E geometry, with the position of the ketene
unit with respect to the ancillary [P2Cp] ligand being opposite to that in the configuration of the precursor
alkylidene 1a. The ketene complex 3 reacts with ethylene to give [P2Cp]Zr(η2-C,O-CH2CH2C(O)dCHR)Cl
(5). The molecular structure of 5b (R ) SiMe3) was obtained by X-ray diffraction and reveals a five-membered
zirconaoxacycle arising from the insertion of ethylene into the Zr-C bond of the ketene, which is subsequently
coordinated to the metal as an enolate ligand. 5 undergoes a final insertion reaction with CO to give the
asymmetric η2-acyl-ylide complex 6. For each reaction detailed above, dissociation of a labile pendant
phosphine donor provides an open site for reactivity.
Introduction
While alkylidene complexes are especially common for
metals from groups 5 and 6, those from group 4 have been
limited to a few thermally labile zirconium derivatives13,14 and
a handful of stable Ti examples,15-19 the majority of which have
been generated in situ.10 In the course of investigating the
reactivity of early-metal complexes stabilized by the hybrid
donor ancillary ligand η5-C5H3-1,3-(SiMe2CH2PPri2)2 ([P2Cp]),20
we reported the isolation of the first thermally stable zirconium
alkylidene complexes [P2Cp]ZrdCHR(Cl) (1a, R ) Ph; 1b, R
) SiMe3).21,22 These alkylidene derivatives have been structur-
Metal alkylidene complexes continue to attract considerable
attention by virtue of the diverse reactivity arising from the
metal-carbon multiple bond.1 These species have been utilized
as catalysts in a number of transformations involving alkenes2-5
and alkynes6 and in stoichiometric Wittig-like olefination
reactions with organic carbonyl functionalities.7-9 Probably the
most notable catalytic reaction is the olefin metathesis process10
for which the ring-opening version11 has had a huge impact in
polymer chemistry, while the ring-closing version12 is an
exciting new synthetic method in organic chemistry.
† University of British Columbus.
‡ Professional Officer, UBC X-ray Structural Laboratory.
§ St. Mary’s University.
(1) Wilkinson, G.; Stone, F. G. A.; Abel, E. W. ComprehensiVe
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10.1021/ja982695y CCC: $18.00 © 1999 American Chemical Society
Published on Web 02/13/1999

1708 J. Am. Chem. Soc., Vol. 121, No. 8, 1999
Fryzuk et al.
of significant features: An R-agostic C-H interaction orients
the alkylidene unit such that the substituent points toward the
cyclopentadienyl portion of the ancillary ligand, and the large
isopropyl substituents on the coordinated, chelating phosphine
donors sterically protect the alkylidene moiety and probably
contribute to high thermal stability of these species. Neverthe-
less, these complexes are reactive, and in this paper, we describe
cycloaddition reactions with alkenes, carbon monoxide, and
other unsaturated molecules. As these alkylidene complexes are
to our knowledge the only stable zirconium derivatives reported
to date, an investigation of the their reactivity patterns provides
a unique opportunity to examine the results in comparison to
the reactivity trends that have been noted for group 5 and 6
alkylidene complexes.
Figure 1. Molecular structure and numbering scheme for [P2Cp]Zr-
(η2-C2H4)Cl (2).
Results and Discussion
Reactivity of [P2Cp]ZrdCHR(Cl) with Alkenes. As shown
in eq 1, the alkylidene complexes [P2Cp]ZrdCHR(Cl) (1a, R
) Ph; 1b, R ) SiMe3) react with ethylene as evidenced by the
while the cis and trans isomers of the internal alkene PhCHd
CHCH3 are obtained in approximately equal quantities. Similar
results for 1b are observed.
In the 13C{1H} NMR spectrum of 2 (only peaks due to the
major isomer are observed), the ethylene carbon resonances are
located upfield at 35 ppm with a 1JCH value of 142 Hz, consistent
with hybridization intermediate between sp2 and sp3.23 The
ethylene protons give rise to a complex multiplet centered near
1.0 ppm in the 1H NMR spectrum, originating from an
3
AA′BB′XX′ spin system due to additional JPH coupling from
the sidearm phosphines. This coupling pattern remains un-
changed even at higher temperatures, indicating that the ethylene
unit is firmly bound with no evidence for rotation about the
metal-ethylene bond axis on the NMR time scale. These
spectroscopic data are similar to those of other early-metal
ethylene complexes24-28 and are consistent with a formulation
of 2 as a Zr(IV) zirconacyclopropane complex rather than as a
Zr(II) adduct. Attempts to determine the stereochemistry (syn
or anti) of the major isomer in solution by 1H NMR spectroscopy
by irradiating the Cp proton resonances in an attempt to observe
a possible nuclear Overhauser enhancement (nOe) on the protons
of the coordinated ethylene fragment were inconclusive.
Some insight into the Zr-ethylene bonding interaction was
furnished by a crystal structure determination of syn-2. The
molecular structure is shown in Figure 1, with the crystal-
lographic data given in Table 1 and relevant bond distances
and bond angles given in Table 2. The C(19)-C(20) bond
distance of 1.439(17) Å is lengthened relative to that of free
ethylene (1.337 Å)29 and is comparable (within 3σ) to that of
the only other monomeric Zr-ethylene complex that has been
structurally characterized, Cp2Zr(η2-C2H4)(PMe3),30 which has
a corresponding C-C bond length of 1.486(8) Å for the ethylene
unit. Such elongated C-C bond lengths are indicative of
slow color change from orange to dark red (12 h for 1a, 8 h for
1b) to generate two isomeric forms of the ethylene complex
[P2Cp]Zr(η2-C2H4)Cl (2) (9:1 ratio). Each isomer of 2 displays
a separate singlet in the 31P{1H} NMR spectrum and corre-
sponding resonances in the 1H NMR spectrum, consistent with
a structure in which the orientation of the ethylene unit is
directed either syn or anti with respect to the unique cyclopen-
tadienyl (Cp) carbon of the ancillary ligand.
The organic byproducts that accompany the conversion of 1
to 2 were detected by 1H NMR spectroscopy and identified by
GC-MS. For example, from benzylidene 1a, the major product
(approximately 70%) is the terminal alkene PhCH2CHdCH2,
(23) Elschenbroich, C.; Salzer, A. Organometallics; 2nd ed.; Verlags-
gesellschaft: Weinham, Germany, 1992.
(24) McLain, S. J.; Wood, C. D.; Schrock, R. R. J. Am. Chem. Soc.
1979, 101, 4558.
(25) Takahashi, T.; Murakama, M.; Kunishige, M.; Saburi, M.; Uchida,
Y.; Kozawa, K.; Uchida, T.; Swanson, D. R.; Negishi, E. Chem. Lett. 1989,
761.
(26) Takahashi, T.; Suzuki, N.; Kageyama, M.; Nitto, Y.; Saburi, M.;
Negishi, E. Chem. Lett. 1991, 1579.
(19) Kahlert, S.; Go¨rls, H.; Scholz, J. Angew. Chem., Int. Ed. Engl. 1998,
37, 1857.
(20) Fryzuk, M. D.; Mao, S. S. H.; Duval, P. B.; Rettig, S. J. Polyhedron
1995, 14, 11.
(21) Fryzuk, M. D.; Mao, S. S. H.; Zaworotko, M. J.; MacGillivray, L.
R. J. Am. Chem. Soc. 1993, 115, 5336.
(27) Poole, A. D.; Gibson, V. C.; Clegg, W. J. Chem. Soc., Chem.
Commun. 1992, 237.
(28) Thorn, M. G.; Hill, J. E.; Waratuke, S. A.; Johnson, E. S.; Fanwick,
P. E.; Rothwell, I. P. J. Am. Chem. Soc. 1997, 119, 8630.
(29) Bartell, L. S.; Roth, E. A.; Hollowell, C. D.; Kuchitsu, K.; Young,
J. E. J. Chem. Phys. 1965, 42, 2683.
(22) Fryzuk, M. F.; Duval, P. B.; Mao, S. S. H.; Rettig, S. J.; Zaworotko,
M. J.; MacGillivray, L. R. Manuscript in preparation.
(30) Alt, H. G.; Denner, C. E.; Thewalt, U.; Raush, M. D. J. Organomet.
Chem. 1988, 356, C83.

Zirconium Alkylidene Complexes
J. Am. Chem. Soc., Vol. 121, No. 8, 1999 1709
Table 1. Crystallographic Data
syn-2a
Table 2. Selected Bond Lengths (Å) and Angles (deg) for syn-2
anti-3ab
5bc
Zr(1)-Cl(1)
Zr(1)-P(2)
Zr(1)-CP(2)
Zr(1)-CP(4)
Zr(1)-Cp(4)
Zr(1)-C(20)
P(1)-C(7)
2.500(4)
2.850(4)
Zr(1)-P(1)
2.872(4)
Zr(1)-CP(1)
Zr(1)-CP(3)
Zr(1)-CP(5)
Zr(1)-Cent(19)
P(1)-C(1)
2.564(11)
2.560(11)
2.47911)
2.2361(16)
1.824(12)
1.898(12)
1.886(14)
1.858(12)
1.869(12)
1.413(16)
1.413(16)
1.382(16)
formula
fw
C25H51ClP2Si2Zr C31H53ClOP2Si2Zr C30H61ClOP2Si3Zr
596.48
2.605(11)
2.477(11)
2.2361(1)
2.318(11)
1.865(13)
1.825(12)
1.911(13)
1.877(12)
1.900(13)
1.431(16)
1.412(16)
1.433(17)
686.55
710.69
crystal system
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
triclinic
P1h (No. 2)
15.432(3)
20.483(3)
20.995(7)
76.50(3)
83.12(7)
88.52(4)
6407(3)
8
monoclinic
P21/c (No. 14)
8.666(1)
24.244(1)
17.543(1)
90
100.936(8)
90
3618.9(6)
4
monoclinic
P21/c (No. 14)
12.6352(12)
16.520(2)
18.5436(4)
90
92.4321(4)
90
3867.1(4)
4
P(1)-C(10)
P(2)-C(13)
Si(1)-CP(1)
Si(2)-CP(3)
CP(1)-CP(2)
CP(2)-CP(3)
CP(4)-CP(5)
P(2)-C(6)
P(2)-C(16)
Si(1)-C(1)
Si(2)-C(6)
CP(1)-CP(5)
CP(3)-C(4)
C(19)-C(20)
Z
D
calc, g/cm3
1.24
1.260
1.221
F(000)
2528
6.0
1448
5.53
1512
5.49
Cl(1)-Zr(1)-P(1)
Cl(1)-Zr(1)-C(19)
P(1)-Zr(1)-P(2)
77.85(12) Cl(1)-Zr(1)-P(2)
98.8(3)
77.42(12)
Cl(1)-Zr(1)-C(20) 100.6(3)
µ, cm-1
crystal size,
mm
transm factors
scan type
scan range,
deg in ω
0.30 × 0.40
0.25 × 0.35
0.20 × 0.45
153.45(11) P(1)-Zr(1)-C(19)
78.1(3)
P(2)-Zr(1)-C(19) 115.2(3)
C(19)-Zr(1)-C(20) 35.9(4)
× 0.45
× 0.45
× 0.45
P(1)-Zr(1)-C(20) 113.6(3)
0.903-1.00
ω-2θ
0.96-1.00
ω-2θ
0.57-1.03d
ω
P(2)-Zr(1)-C(20)
Zr(1)-P(1)-C(1)
80.5(3)
111.7(4)
Zr(1)-P(2)-C(6)
111.7(4)
0.79 + 0.35 tan θ 0.5
CP1(1)-Si(1)-C(1) 102.0(6)
CP(3)-Si(2)-C(6) 102.4(5)
Si(1)-CP(1)-CP(2) 131.1(9)
Si(1)-CP(1)-CP(5) 123.5(9)
scan speed,
deg/min
16 (up to 9 scans)
P(1)-C(1)-Si(1)
111.6(6)
P(2)-C(6)-Si(2)
112.9(6)
data collected
(h,+k,(l
+h,+k,(l
460 frames,
50 s/f
2θmax, deg
crystal decay, %
40
60
2.0
60
no. of total reflns 11 928
11 425
10 783
36 109e
9656
no of. unique
11 917
reflns
Rmerge
0.023
0.036
5598
0.058
5373
no. of reflns with 7589
I g 3σ(I)
no. of variables
344
343
R(F) (I g 3σ(I)) 0.055
Rw(F) (I g 3σ(I)) 0.060
R(F2) (all data) 0.055
Rw(F2) (all data) 0.060
0.034
0.031
0.056
0.053
0.106
0.111
2.61
gof
3.71
1.49
max ∆/σ (final 0.000
cycle)
0.003
0.007
residual density, -0.550 to
-0.35 to
+0.31
-2.19 to +1.77
(near Zr)
e/Å3
+0.640
a Temperature 294 K; Nonius CAD-4 diffractometer; Mo KR
radiation (λ ) 0.709 30 Å); graphite monochromator; takeoff angle
6.0°; aperture 6.0 × 6.0 mm at a distance of 285 mm from the crystal;
stationary-background counts at each end of the scan (scan:background
time ratio 2:1); σ2(F2) ) [S2(C + 4B)]/(Lp)2 (S ) scan rate, C ) scan
count, B ) normalized background count); function minimized ∑w(|Fo|
Figure 2. Pseudo-first-order kinetic data for the reaction of [P2Cp]-
ZrdCHPh (1a) with ethylene.
2
2
- |Fc|)2 where w ) 4Fo /σ2(Fo ), R(F) ) ∑||Fo| - |Fc||/∑|Fo|, Rw(F)
2
) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2, and gof(F) ) [∑w(|Fo| - |Fc|)2/(m -
n)]1/2 b Temperature 294 K; Rigaku AFC6S diffractometer; Mo KR
.
distance of 2.68(2) Å in a cationic Zr(IV) olefin complex in
which d-π* back-bonding is necessarily absent.31
radiation (λ ) 0.710 69 Å); graphite monochromator; takeoff angle
6.0°; aperture 6.0 × 6.0 mm at a distance of 285 mm from the crystal;
stationary-background counts at each end of the scan (scan:background
time ratio 2:1); σ2(F2) ) [S2(C + 4B)]/(Lp)2 (S ) scan rate, C ) scan
count, B ) normalized background count); function minimized ∑w(|Fo|
Kinetic experiments were conducted to investigate the mech-
anism of the formation of the ethylene complex 2 from
alkylidene 1b. Figure 2 illustrates a plot of ln [1b] vs time for
reactions carried out to 2 half-lives for a number of different
ethylene concentrations. In all instances, the concentration of
ethylene remained essentially unchanged during the course of
the reaction, so that the results shown in Figure 2 follow pseudo-
first-order behavior consistent with overall second-order kinet-
ics: rate ) k[1a][C2H4].
Although intermediates in the transformation of 1 to 2 were
not observed, the second-order kinetics, together with the organic
byproducts from reaction 1, are consistent with the reaction
mechanism depicted in Scheme 1. The initial coordination of
ethylene to 1 is likely assisted by dissociation of one of the
potentially labile sidearm phosphines. Subsequent cycloaddition
of the coordinated ethylene with the alkylidene moiety gives a
- |Fc|)2 where w ) 4Fo /σ2(Fo ), R(F) ) ∑||Fo| - |Fc||/∑|Fo|, Rw(F)
2
2
2
) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2, and gof(F) ) [∑w(|Fo| - |Fc|)2/(m -
n)]1/2 c Temperature 180 K; Rigaku/ADSC CCD diffractometer; Mo
.
KR radiation (λ ) 0.716 09 Å); graphite monochromator; takeoff angle
6.0°; aperture 94.0 × 94.0 mm at a distance of 39.124(8) mm from the
crystal; σ2(F2) ) (C + B)/(Lp)2 (C ) scan count, B ) background
count); function minimized ∑w(|Fo | - |Fc2|)2 where w ) 1/σ2(Fo ),
2
2
R(F2) ) ∑||Fo | - |Fc2||/∑|Fo |, Rw(F2) ) [∑w(|Fo | - |Fc2|)2/
2
2
2
2 2
2
∑w|Fo | ]1/2, and gof(F2) ) [∑w(|Fo | - |Fc2|)2/(m - n)]1/2. Data were
collected to 2θmax ) 63.7° (full sphere 4-40°, hemisphere 40-60°);
all data to 2θmax ) 60° were used in the refinement. d Includes crystal
decay, absorption, and scaling corrections. e Includes data to 2θmax
63.7°.
)
significant back-bonding from the zirconium and support the
metallacyclopropane bonding depiction for 2. Also consistent
with this formalism are the Zr-C bond lengths (average 2.319-
(11) Å) in syn-2, which are considerably shorter than the Zr-C
(31) Wu, Z.; Jordan, R. F.; Petersen, J. L. J. Am. Chem. Soc. 1995, 117,
5867.

1710 J. Am. Chem. Soc., Vol. 121, No. 8, 1999
Fryzuk et al.
Scheme 1
Cp] ligand restricts the size of molecules that can access the
metal center, even with sidearm phosphine dissociation. This
point is accentuated by the extremely slow reaction of 1 with
the relatively small cumulene allene, to give unidentified
products, and the total inability of these alkylidene derivatives
to undergo reaction with larger activated substrates such as
norbornene, 1,3-butadiene, and internal alkynes.
Reaction of [P2Cp]ZrdCHR(Cl) with Acetone. Another
reaction that is characteristic of early-metal alkylidene com-
plexes is a parallel of the Wittig reaction,8 and an example is
shown in the reaction of 1 with acetone (eq 2). The alkene
four-membered metallacycle (M), an intermediate that has been
trapped and isolated2,16,32 in analogous reactions between
alkylidene complexes and certain alkenes. â-Hydride elimination
of zirconacyclobutane M can occur via two pathways; in
Scheme 1, only the pathway that generates the terminal alkene
RCH2CHdCH2, the product of the more kinetically favored
route, is shown. In the presence of excess ethylene, the
zirconium center is trapped by a second equivalent of ethylene,
to generate the final product 2. It is noteworthy that products
resulting from alkene metathesis (RCHdCH2) were not detected,
an indication of the presumed rapid rate for the â-elimination
process. This particular mechanism has been generally observed
in the reaction of alkylidene complexes with ethylene,16,18,33
although further coupling from an additional equivalent of
ethylene to give a metallacyclopentane24,34,35 complex has also
been noted. However, it was observed that 2 does not react
further with additional ethylene. Formation of the anti isomer
of 2 could be rationalized by dissociation of the second
phosphine, followed by rotation of the cyclopentadienyl group,
at some point during the mechanism shown in Scheme 1.
In comparison with some group 5 alkylidene systems,34 the
slow formation of ethylene complex 2 indicates the steric and
electronic saturation at the Zr center in alkylidene 1. When the
slightly larger and more weakly binding olefin propene is
employed, the reaction is considerably slower, eventually
yielding unidentified paramagnetic products after more than 1
week. It is evident that steric crowding from the ancillary [P2-
RCHdC(CH3)2 was isolated and identified by GC-MS, but
unfortunately, a Zr-containing species could not be isolated from
this reaction. The 31P{1H} NMR spectrum of this reaction
mixture shows a variety of unidentified species, presumably due
to decomposition of the putative oxo species [P2Cp]ZrO(Cl).
Reaction of [P2Cp]ZrdCHR(Cl) with CX (X ) O, NBut).
In comparison to the extensive chemistry of alkylidene com-
plexes with alkenes and organic carbonyls, much less attention
has been directed toward their reactivity with carbon monoxide
and isonitriles. This is somewhat surprising, given that these
reactions have been noted to yield unusual ketene and keten-
imine complexes,16,36-38 species that have demonstrated their
synthetic utility in a variety of organic transformations.39-41 Of
the ketene complexes obtained by the insertion reaction of metal
alkylidenes and CO, structural analysis of the products detailing
the mode of insertion have not been reported.
A toluene solution of the alkylidene complex 1 reacts with
CO under ambient conditions over a period of 24 h to yield the
(36) Cramer, R. E.; Maynard, R. B.; Paw, J. C.; Gilje, J. W. Organo-
metallics 1982, 1, 869.
(37) Cramer, R. E.; Panchanatheswaran, K.; Gilje, J. W. J. Am. Chem.
Soc. 1984, 106, 1853.
(32) Wallace, K. C.; Dewan, J. C.; Schrock, R. R. Organometallics 1986,
5, 2162.
(38) Meinhart, J. D.; Anslyn, E. V.; Grubbs, R. H. Organometallics 1989,
8, 583.
(33) Fellman, J. D.; Schrock, R. R.; Rupprecht, G. A. J. Am. Chem. Soc.
1981, 103, 5752.
(39) Sierra, M. A.; Hegedus, L. S. J. Am. Chem. Soc. 1989, 111,
2335.
(34) McLain, S. J.; Wood, C. D.; Schrock, R. R. J. Am. Chem. Soc.
1977, 99, 3519.
(40) Anderson, B. A.; Wulff, W. D.; Rheingold, A. L. J. Am. Chem.
Soc. 1990, 112, 8615.
(35) McLain, S. J.; Sancho, J.; Schrock, R. R. J. Am. Chem. Soc. 1980,
102, 5610.
(41) Brandvold, T. A.; Wulff, W. D.; Rheingold, A. L. J. Am. Chem.
Soc. 1990, 112, 1645.

Zirconium Alkylidene Complexes
J. Am. Chem. Soc., Vol. 121, No. 8, 1999 1711
Table 3. Selected Bond Lengths (Å) and Angles (deg) for anti-3aa
Zr(1)-Cl(1)
Zr(1)-P(2)
Zr(1)-C(1)
Zr(1)-C(3)
Zr(1)-C(5)
Zr(1)-Cp
P(1)-C(12)
P(2)-C(7)
P(2)-C(15)
Si(1)-C(6)
Si(1)-C(9)
Si(2)-C(7)
Si(2)-C(11)
C(1)-C(2)
C(2)-C(3)
C(4)-C(5)
C(25)-C(26)
2.4976(8)
2.8517(8)
2.572(3)
2.562(3)
2.531(3)
2.25
1.851(3)
1.833(3)
1.850(3)
1.895(3)
1.863(4)
1.871(3)
1.854(3)
1.416(4)
1.423(4)
1.400(4)
1.465(4)
Zr(1)-P(1)
Zr(1)-O(1)
Zr(1)-C(2)
Zr(1)-C(4)
Zr(1)-C(24)
P(1)-C(6)
P(1)-C(13)
P(2)-C(14)
Si(1)-C(1)
Si(1)-C(8)
Si(2)-C(3)
Si(2)-C(10)
O(1)-C(24)
C(1)-C(5)
C(3)-C(4)
C(24)-C(25)
2.8261(8)
2.027(2)
2.582(3)
2.523(3)
2.172(3)
1.816(3)
1.853(3)
1.849(3)
1.866(3)
1.849(4)
1.856(3)
1.856(3)
1.374(3)
1.426(4)
1.427(4)
1.349(4)
Cl(1)-Zr(1)-P(1)
Cl(1)-Zr(1)-O(1)
Cl(1)-Zr(1)-Cp
P(1)-Zr(1)-O(1)
P(1)-Zr(1)-Cp
P(2)-Zr(1)-C(1)
P(2)-Zr(1)-C(3)
P(2)-Zr(1)-C(5)
P(2)-Zr(1)-Cp
87.66(3) Cl(1)-Zr(1)-P(2)
86.54(3)
141.42(6) Cl(1)-Zr(1)-C(24) 103.43(8)
107.1
85.17(5) P(1)-Zr(1)-C(24)
101.9
P(1)-Zr(1)-P(2)
156.25(2)
79.40(7)
85.10(5)
101.95(6)
83.77(7)
79.60(7)
116.11(8)
118.40(8)
87.44(8)
111.4
P(2)-Zr(1)-O(1)
129.25(6) P(2)-Zr(1)-C(2)
74.84(6) P(2)-Zr(1)-C(4)
115.64(7) P(2)-Zr(1)-C(24)
Figure 3. ORTEP view of 3a, showing 33% probability thermal
ellipsoids for the nonhydrogen atoms.
101.9
O(1)-Zr(1)-C(1)
O(1)-Zr(1)-C(2)
O(1)-Zr(1)-C(4)
O(1)-Zr(1)-C(24)
C(24)-Zr(1)-Cp
Zr(1)-P(1)-C(12)
C(6)-P(1)-C(12)
138.49(8) O(1)-Zr(1)-C(3)
88.72(8) O(1)-Zr(1)-C(5)
37.99(8) O(1)-Zr(1)-Cp
thermally stable ketene complex [P2Cp]ZrC(O)dCHR(Cl) (3a,
R ) Ph; 3b, R ) SiMe3) in moderate yield (eq 3). Orange
149.4
Zr(1)-P(1)-C(6)
107.12(9)
111.42(10) Zr(1)-P(1)-C(13) 119.25(10)
105.6(1)
C(6)-P(1)-C(13)
Zr(1)-P(2)-C(7)
Zr(1)-P(2)-C(15) 115.04(10)
106.4(1)
111.01(10)
C(12)-P(1)-C(13) 106.2(1)
Zr(1)-P(2)-C(14)
C(7)-P(2)-C(14)
111.7(1)
106.5(1)
C(7)-P(2)-C(15)
C(1)-Si(1)-C(6)
C(1)-Si(1)-C(9)
C(6)-Si(1)-C(9)
C(3)-Si(2)-C(7)
104.4(1)
107.2(1)
108.9(2)
113.4(1)
104.4(1)
C(14)-P(2)-C(15) 107.6(2)
C(1)-Si(1)-C(8)
C(6)-Si(1)-C(8)
C(8)-Si(1)-C(9)
C(3)-Si(2)-C(10)
C(7)-Si(2)-C(10)
109.3(1)
107.9(2)
110.0(2)
109.2(1)
111.4(1)
C(3)-Si(2)-C(11) 110.6(1)
C(7)-Si(2)-C(11) 109.8(1)
C(10)-Si(2)-C(11) 111.2(2)
Zr(1)-O(1)-C(24)
Si(1)-C(1)-C(5)
C(1)-C(2)-C(3)
Si(2)-C(3)-C(4)
C(3)-C(4)-C(5)
P(1)-C(6)-Si(1)
Zr(1)-C(24)-O(1)
76.7(1)
130.0(2)
111.6(2)
128.8(2)
109.9(2)
112.4(1)
65.3(1)
Si(1)-C(1)-C(2)
C(2)-C(1)-C(5)
Si(2)-C(3)-C(2)
C(2)-C(3)-C(4)
C(1)-C(5)-C(4)
P(2)-C(7)-Si(2)
124.7(2)
105.2(2)
126.8(2)
104.4(2)
108.9(2)
111.2(1)
Zr(1)-C(24)-C(25) 169.5(2)
C(24)-C(25)-C(26) 129.7(3)
O(1)-C(24)-C(25) 125.2(3)
a Cp refers to the unweighted centroid of the C(1-5) ring.
reveals a smooth temperature dependence on the relative
concentrations, which correlates well to a van’t Hoff plot (ln K
versus 1/T). Unfortunately, assignment of the isomeric species
as either syn or anti was not possible because the spectroscopic
data are unable to distinguish between the two structures in
solution. There can be no nuclear Overhauser enhancement
(nOe) between the Cp ring protons and protons within the
ketene unit because these nuclei are too far apart. Our attempts
to introduce an NMR-active nucleus closer to the Cp ring
protons by substituting the chloride of 3 with either a fluoride
or an alkyl group were unsuccessful, and a heteronuclear nOe
experiment conducted on a sample of 3b containing a 13C-
labeled ketene carbon was also inconclusive. The interconver-
sion of the syn and anti isomers of 3 likely occurs via
dissociation of both phosphines followed by a 180° rotation of
the ancillary ligand around the Zr-Cp centroid axis.
crystals of 3a can be isolated from cold hexanes whereas 3b is
obtained as an orange oil which remains soluble in hydrocarbon
solvents.
Similar to the solution behavior noted previously for 2, both
3a and 3b exhibit two stereoisomers each, in either a 4:1 (3a)
or a 2:1 (3b) ratio. These species are identified by separate
singlets in the 31P{1H} NMR spectrum and by corresponding
1
resonances in the H NMR spectrum. Additionally, for each
isomer there is a triplet located downfield in the 13C{1H} NMR
spectrum for the ketene carbon, the observed splitting due to
2JPC coupling to two equivalent phosphines. For 3a, these
resonances are at 192 ppm (minor isomer) and 205 ppm (major
isomer), while 3b exhibits triplets at 203 ppm (major isomer)
and 216 ppm (minor isomer), respectively. Again, as with 2,
these stereoisomers are likely the structures syn-3 and anti-3,
which differ in the relative orientation of the ketene unit with
respect to the ancillary ligand. It is evident that both species
are in equilibrium, as variable-temperature NMR spectroscopy
Crystals suitable for X-ray analysis were obtained for ketene
3a, and the resulting molecular structure is shown in Figure 3.
The crystallographic data are shown in Table 1; relevant bond
distances and bond angles given in Table 3. The mononuclear

1712 J. Am. Chem. Soc., Vol. 121, No. 8, 1999
Fryzuk et al.
structure arises from the steric bulk of the ancillary ligand, a
feature in common with analogous early-metal ketene com-
plexes, where bulky substituents are required to prevent
dimerization.42-46 The η2-C,O coordination of the ketene
fragment is also a typical mode of binding to oxophilic
metals44,45,47,48 and is exhibited here by the short Zr-C(24) and
Zr-O distances of 2.172(3) and 2.027(2) Å, respectively, and
a correspondingly long C-O distance of 1.374(3) Å. These
parameters are similar to the analogous bond distances in another
monomeric Zr ketene complex, Cp*2Zr(py)(η2-C,O-OCd
CH2),44 which are 2.181(2), 2.126(1), and 1.338(2) Å, respec-
tively. The C(24)-C(25) distance of 1.349(4) Å is indicative
of a double bond, and the coplanarity of the ketene moiety is
illustrated by the dihedral angle of 1.9° involving O, C(24),
C(25), and C(26). Additionally, the phenyl ring is also nearly
coplanar with the ketene fragment with a tilt angle of 8°, an
alignment that presumably optimizes delocalization of electron
density over the organic fragment and reduces steric interactions
with the ancillary ligand.
Scheme 2
Two points can be made regarding the solid-state structure
of 3a in comparison to that of the precursor benzylidene 1a.21
First, in the solid state, the molecular structure of the ketene
complex corresponds to the anti stereoisomer of 3, a reversal
of the orientation noted for 1a both in solution and in the solid
state; presumably, anti-3 is the least soluble isomer of the two
ketene species in equilibrium in solution. The second point is
that the ketene carbon-carbon double bond has the E geom-
etry; in other words, migratory insertion of CO proceeds with
retention of stereochemistry about the zirconium-carbon double
bond. This geometry arises from the lack of rotation pre-
viously noted21 in the ZrdC bond of the precursor alkyli-
dene. Furthermore, no E/Z isomerization is observed for the
ketene complexes 3, and this contrasts with the behavior of
some other early-metal ketene complexes that have been
studied.47,48
The stoichiometry of this reaction is important because an
excess of the isonitrile reacts further with 4 to produce undefined
mixtures. Although the spectroscopic parameters for ketenimine
4 are similar to those of the analogous ketene complex, it is
interesting to note that, in contrast to the case of 3, only a single
isomer is observed for 4 in solution, presumably because the
isomerization process requires rotation of the Cp moiety and
this is impeded by the tert-butyl group attached to the nitrogen.
The steric effects of the large But group are also apparently
manifested in a pronounced broadening of all resonances in the
1H NMR spectrum of protons that are proximate to the tert-
butyl group of the isocyanide. For 4a, these include the ortho
protons on the phenyl ring and the complete portion of the
ancillary ligand that is syn to the ketenimine unit. Of note is
the absence of peak broadening for the vinyl proton as the trans
geometry situates this proton away from the influence of the
tert-butyl group, indicating that once again an E configuration
is adopted despite the apparent steric interaction between the
As an extension of the insertion reaction that produces 3, the
related reaction with isocyanides was investigated. The addition
of tert-butyl isocyanide to alkylidene 1a results in the formation
of the analogous ketenimine49-52 complex [P2Cp]Zr(η2-C,N-
ButNCdCHPh)Cl (4a; eq 4). To our knowledge this is the first
1
phenyl ring and the tert-butyl group. An H NOEDIFF NMR
experiment conducted on 4 established that the anti isomer is
(43) Bristow, G. S.; Hitchcock, P. B.; Lappert, M. F. J. Chem. Soc.,
Chem. Commun. 1982, 462.
(44) Moore, E. J.; Straus, D. A.; Armantrout, J.; Santarsiero, B. D.;
Grubbs, R. H.; Bercaw, J. E. J. Am. Chem. Soc. 1983, 105, 2068.
(45) Fachinetti, G.; Biran, C.; Floriani, C. J. Am. Chem. Soc. 1978, 100,
1921.
(46) Scott, M. J.; Lippard, S. J. J. Am. Chem. Soc. 1997, 119, 3411.
(47) Fermin, M. C.; Hneihen, A. S.; Maas, J. L.; Bruno, J. W.
Organometallics 1993, 12, 1845.
(48) Antin˜olo, A.; Otero, A.; Fajardo, M.; Lo´pez-Mardomingo, C.; Lucas,
D.; Mugnier, Y.; Lanfranchi, M.; Pellinghelli, M. J. Organomet. Chem.
1992, 435, 55.
(49) Antin˜olo, A.; Fajardo, M.; Lo´pez-Mardomingo, C.; Otero, A.;
Mourad, Y.; Mugnier, Y.; Aparicio, J.; Fonseca, I.; Florencio, F. Organo-
metallics 1990, 9, 2919.
(50) Antin˜olo, A.; Fajardo, M.; Gil-Sanz, R.; Lo´pez-Mardomingo, C.;
Mart´ın-Villa, P.; Otero, A.; Kubicki, M.; Mugnier, Y.; Krami, S.; Mourad,
Y. Organometallics 1993, 12, 381.
(51) Antin˜olo, A.; Fajardo, M.; Gil-Sanz, R.; Lo´pez-Mardomingo, C.;
Otero, A.; Atmani, A.; Kubicki, M.; Krami, S.; Mugnier, Y.; Mourad, Y.
Organometallics 1994, 13, 1200.
(52) Fandos, R.; Lanfranchi, M.; Otero, A.; Pellinghelli, M.; Ruiz, M.;
Teuben, J. Organometallics 1997, 16, 5283.
example of a ketenimine complex obtained from the insertion
of an isocyanide into an early-metal alkylidene complex.
(42) Meinhart, J. D.; Santarsiero, B. D.; Grubbs, R. H. J. Am. Chem.
Soc. 1986, 108, 3318.

Zirconium Alkylidene Complexes
J. Am. Chem. Soc., Vol. 121, No. 8, 1999 1713
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 5ba
Zr(1)-Cl(1)
Zr(1)-P(2)
Zr(1)-C(1)
Zr(1)-C(3)
Zr(1)-C(5)
Zr(1)-Cp
P(1)-C(12)
P(2)-C(7)
P(2)-C(21)
Si(1)-C(6)
Si(1)-C(9)
Si(2)-C(7)
Si(2)-C(11)
Si(3)-C(28)
Si(3)-C(30)
C(1)-C(2)
C(2)-C(3)
C(4)-C(5)
2.5234(10)
2.9007(11)
2.599(3)
2.635(3)
2.547(4)
2.30
1.846(4)
1.826(4)
1.857(4)
1.877(5)
1.836(6)
1.882(4)
1.845(4)
1.852(6)
1.856(5)
1.416(5)
1.426(5)
1.382(5)
Zr(1)-P(1)
Zr(1)-O(1)
Zr(1)-C(2)
Zr(1)-C(4)
Zr(1)-C(24)
P(1)-C(6)
P(1)-C(15)
P(2)-C(18)
Si(1)-C(1)
Si(1)-C(8)
Si(2)-C(3)
Si(2)-C(10)
Si(3)-C(27)
Si(3)-C(29)
O(1)-C(26)
C(1)-C(5)
C(3)-C(4)
C(24)-C(25)
2.9527(11)
2.036(2)
2.630(3)
2.569(3)
2.332(3)
1.829(5)
1.908(5)
1.864(4)
1.844(4)
1.828(6)
1.850(4)
1.850(4)
1.833(4)
1.833(5)
1.354(4)
1.430(5)
1.435(5)
1.519(5)
C(25)-C(26)
1.520(5) C(26)-C(27)
1.329(5)
86.31(3)
82.83(9)
159.21(3)
80.87(10)
93.50(7)
99.8
Cl(1)-Zr(1)-P(1)
Cl(1)-Zr(1)-O(1)
Cl(1)-Zr(1)-Cp
P(1)-Zr(1)-O(1)
P(1)-Zr(1)-Cp
81.39(3)
156.64(6)
103.0
91.28(7)
99.3
81.02(10) P(2)-Zr(1)-Cp
74.10(10) O(1)-Zr(1)-Cp
174.2
Cl(1)-Zr(1)-P(2)
Figure 4. ORTEP view 5b, showing 50% probability thermal ellipsoids
for the nonhydrogen atoms.
Cl(1)-Zr(1)-C(24)
P(1)-Zr(1)-P(2)
P(1)-Zr(1)-C(24)
P(2)-Zr(1)-O(1)
obtained, since irradiating the methyl resonance of the tert-butyl
group leads to an enhancement of the peak assigned to the two
equivalent Cp protons, while no effect is observed for the
corresponding resonance ascribed to the unique Cp proton.
However, if neither the precursor alkylidene 1a nor the product
ketenimine 4a undergoes syn/anti isomerization, then the
transformation from syn-1a to anti-4a must occur during the
migratory insertion of the isocyanide into the Zr-C alkylidene
bond (Scheme 2). In this instance, the bulky tert-butyl group is
directed away from the ancillary ligand until the final step
when the nitrogen atom binds to give the η2-C,N-coordinated
ketenimine complex. The same mechanism is likely operative
in the formation of ketene 3, although as mentioned previously,
this complex is capable of isomerizing after the product is
formed.
P(2)-Zr(1)-C(24)
O(1)-Zr(1)-C(24)
C(24)-Zr(1)-Cp
Zr(1)-P(1)-C(12)
C(6)-P(1)-C(12)
C(12)-P(1)-C(15)
Zr(1)-P(2)-C(18)
C(7)-P(2)-C(18)
C(18)-P(2)-C(21)
C(1)-Si(1)-C(8)
C(6)-Si(1)-C(8)
C(8)-Si(1)-C(9)
C(3)-Si(2)-C(10)
C(7)-Si(2)-C(10)
C(10)-Si(2)-C(11)
C(27)-Si(3)-C(29)
C(28)-Si(3)-C(29)
C(29)-Si(3)-C(30)
Si(1)-C(1)-C(2)
C(2)-C(1)-C(5)
Si(2)-C(3)-C(2)
C(2)-C(3)-C(4)
C(1)-C(5)-C(4)
P(2)-C(7)-Si(2)
100.1
Zr(1)-P(1)-C(6)
110.2(2)
117.5(2)
99.3(3)
114.19(15) Zr(1)-P(1)-C(15)
109.5(3)
105.0(2)
C(6)-P(1)-C(15)
Zr(1)-P(2)-C(7)
111.70(13)
117.49(13)
103.7(2)
104.2(2)
109.7(2)
104.1(3)
104.9(2)
109.9(2)
108.6(2)
111.2(2)
108.1(2)
108.5(3)
128.4(2)
127.4(3)
111.2(3)
126.7(3)
109.4(3)
114.1(3)
110.91(13) Zr(1)-P(2)-C(21)
105.5(2)
106.6(2)
111.1(2)
114.0(3)
113.1(4)
109.9(2)
113.9(2)
109.6(2)
114.2(2)
106.5(3)
108.2(3)
127.5(3)
104.9(3)
128.1(3)
104.6(3)
109.8(4)
111.7(2)
C(7)-P(2)-C(21)
C(1)-Si(1)-C(6)
C(1)-Si(1)-C(9)
C(6)-Si(1)-C(9)
C(3)-Si(2)-C(7)
C(3)-Si(2)-C(11)
C(7)-Si(2)-C(11)
C(27)-Si(3)-C(28)
C(27)-Si(3)-C(30)
C(28)-Si(3)-C(30)
Zr(1)-O(1)-C(26)
Si(1)-C(1)-C(5)
C(1)-C(2)-C(3)
Si(2)-C(3)-C(4)
C(3)-C(4)-C(5)
P(1)-C(6)-Si(1)
Further Insertion Reactivity of Ketenes [P2Cp]Zr(η2-C,O-
C(O)dCHR)Cl. Addition of ethylene to a toluene solution of
ketene 3 results in the slow formation of the insertion product
[P2Cp]Zr(η2-C,O-CH2CH2C(O)dCHR)Cl (5a, R ) Ph; 5b, R
) SiMe3; eq 5).
Zr(1)-C(24)-C(25) 110.4(2)
O(1)-C(26)-C(25) 112.1(3)
C(25)-C(26)-C(27) 126.0(3)
C(24)-C(25)-C(26) 112.9(3)
O(1)-C(26)-C(27)
Si(3)-C(27)-C(26)
121.9(3)
128.0(3)
a Cp refers to the unweighted centroid of the C(1-5) ring.
precursor 3 consists of an equilibrium mixture of two stereoi-
somers. This suggests either that one isomer of 3 is kinetically
more reactive or that both possible stereoisomers of 5 are
initially formed, followed by complete conversion of the less
stable isomer to the thermodynamically favored observed
product.
We were able to isolate crystals of 5b suitable for an X-ray
structure determination; the molecular structure is shown in
Figure 4, with the X-ray data tabulated in Table 1 and the bond
distances and bond angles given in Table 4. From the molecular
structure, it can be seen that one ethylene molecule has inserted
into the Zr-C bond of the ketene unit, which is now bound to
Zr via the oxygen atom as an enolate fragment, to give a five-
membered metallacycle. The overall configuration of 5b is
retained from the precursor ketene complex where the chloride
is oriented syn to the unique cyclopentadienyl carbon, C(2).
One other structural point is the short C(26)-C(27) distance of
1.329(5) Å.
1
The H and 31P{1H} NMR spectra reveal that both 5a and
5b exist as a single species in solution, despite the fact that

1714 J. Am. Chem. Soc., Vol. 121, No. 8, 1999
Fryzuk et al.
The stereochemical preference for either the syn or the anti
orientation is a recurring theme for many of the complexes
involving the [P2Cp] ligand; for example, the alkylidene
complexes exist exclusively as the syn isomers whereas the
ketene insertion complex 5 is found as the anti stereoisomer.
Along the way, the ethylene complex 2 and the ketene
derivatives 3 are found as mixtures of stereoisomers. Examina-
tion of models based on solid-state structures does not provide
any hints as to the origins of these capricious preferences since
the apparent differences between the two sides of the [P2Cp]
ligand are unremarkable. If the steric differences are almost
negligible, then it seems likely that subtle electronic factors are
involved in favoring a particular configuration.
the ethylene portion of the metallacycle. For the two protons R
3
The reaction of the ketene complexes 3 with other small
molecules was examined; however, except for the reaction noted
above with ethylene, ketene 3 was found to be comparatively
inert, showing no reactivity with internal alkynes, butadiene,
alkylating reagents, or H2. Monomeric ketene complexes are
generally more reactive to substrates such as alkenes,23,43
alkynes,53 and H244 than are the corresponding dimeric deriva-
tives.53 It is presumed that the bulky nature of the ancillary
ligand may contribute to this lack of reactivity. In line with
this idea, the even more sterically encumbered ketenimine
complex 4 undergoes a considerably slower reaction with
ethylene (approximately 5 days), and a clean product could not
be isolated.
to the acyl carbon, this pattern is further complicated by JPH
coupling, which could be identified by decoupling the phos-
phorus resonance near 46 ppm. In the acyl-ylide complexes 6,
the newly inserted carbonyl carbon is a chiral center as is the
zirconium center. Nevertheless, for 6a, only one diastereomer
is observed, and for 6b, the observed 9:1 ratio of isomers is
likely due to the presence of syn and anti isomers. The low C1
symmetry of 6 is also evident in the cyclopentadienyl region
where three separate resonances are seen in the 1H NMR
spectrum. However, the remainder of the spectrum belies a more
symmetric environment, suggesting that the resonances associ-
ated with these groups are insensitive to the asymmetry of the
molecule.
The sequence of insertion reactions beginning with the
alkylidene 1 ceases with the acyl-ylide 6, which does not react
further with CO or with ethylene. The fact that one of the
phosphine arms is uncoordinated suggests that the coordination
environment around the zirconium center of 6 is effectively
saturated, thus preventing any further insertions.
Metallacycle 5 reacts with carbon monoxide to yield an η2-
acyl-ylide complex (6a, R ) Ph; 6b, R ) SiMe3) in which
the metallacycle has expanded to a six-membered ring to
accommodate the insertion of CO (eq 6); a single isomer is
Conclusions
The alkylidene complex 1 undergoes cycloaddition and
insertion reactions with a variety of unsaturated substrates. The
reactivity at the ZrdC bond is moderated by the sterically bulky
[P2Cp] ancillary ligand, which induces slow reaction rates and
imposes a limit on the size of substrates that can access the
metal. Although 1 is unreactive with larger olefins and in-
ternal alkynes, a reaction of 1 with ethylene follows second-
order kinetics to yield the ethylene complex 2 . The solid-
state structure of 2 features an elongated C-C bond length for
the coordinated ethylene molecule (compared to free ethylene)
in agreement with the presence of a zirconacyclopropane
unit.
(6)
Alkylidene 1 also undergoes migratory insertion reactions
with molecules such as CO and CNtBu to yield η2-coordinated
ketene and ketenimine complexes, 3 and 4, respectively. Ketene
3 in turn reacts with ethylene to give metallacycle 5, which
undergoes a final insertion of CO to give the η2-acyl-ylide
species 6 (Scheme 3). Such a four-carbon homologation of the
original benzylidene fragment is a variant on the alternating
copolymerization of CO and ethylene catalyzed by late metal
complexes such as those of Pd(II). However, as already noted,
for the Zr(IV) system described here, the alternating insertions
are stopped at the acyl-ylide stage because the metal center is
saturated.
observed in solution for 6a, while two species are evident in a
9:1 ratio for 6b. Particularly diagnostic of such a proposal is
the 31P{1H} NMR spectrum, in which one observes two singlets,
one located downfield near 46 ppm for the ylide phosphine and
an upfield peak near 7 ppm corresponding to a free phosphine;
the downfield resonance at 46 ppm is very similar to that found
for the ylide-formyl complex 7, for which a resonance at 39.7
ppm was found for the phosphine coordinated to the formyl
All of the reactions noted above involve an insertion into a
Zr-C bond, and a monomeric structure is observed due to the
large isopropyl substituents on the pendant phosphines of the
ancillary ligand. The potentially labile phosphines likely play
1
carbon.54 The H NMR spectrum of 6a reveals a complicated
second-order splitting pattern for the diastereotopic protons of
(54) Fryzuk, M. D.; Mylvaganum, M.; Zaworotko, M. J.; MacGillivray,
(53) Straus, D. A.; Grubbs, R. H. J. Am. Chem. Soc. 1982, 104, 5499.
L. R. Organometallics 1996, 15, 1134.

Zirconium Alkylidene Complexes
J. Am. Chem. Soc., Vol. 121, No. 8, 1999 1715
to dark red. The solvent was then removed in vacuo, the oily residue
was extracted with pentane, and the extract was filtered. Reducing the
solution to 7 mL and cooling to -40 °C produced dark red crystals.
Yield: 1.61 g (92%).
Scheme 3
Method 2. The procedure was identical to that for 1a above, reacting
1b with ethylene. A reaction conducted on the same scale as above
was complete within 8 h.
1H NMR (20 °C, C6D6): δ 0.22 and 0.23 (s, 6H, Si(CH3)2), 0.78
1
3
and 0.83 (d, 2H, 2JPH ) 5 Hz, SiCH2P), 0.99 and 1.04 (m, 2H, ZrCH2),
3
2
1.08, 1.17, 1.22, and 1.29 (dd, 6H, JPH ) 9 Hz, JHH ) 7 Hz, CH-
2
2
(CH3)2), 2.19 (m, 4H, JHH ) 7 Hz, JPH ) 7 Hz, CH(CH3)2), 4.32 (t,
4
4
1H, JHH ) 1 Hz, Cp H), 6.29 (d, 2H, JHH ) 1 Hz, Cp H). 31P{1H}
NMR (20 °C, C6D6): δ 19.5 (s). 13C{1H} NMR (20 °C, C6D6): δ -2.0
and 1.6 (Si(CH3)2), 9.3 (SiCH2P), 9.3, 13.5, 22.7, and 25.4 (CH(CH3)2),
31.4 (ZrCH2), 31.5 (CH(CH3)2), 106.8 (Cp CH), 125.9 (Cp CH). Anal.
Calcd for C25H51ClP2Si2Zr: C, 50.34; H, 8.62. Found: C, 50.35; H,
8.51.
5
6
Kinetic Studies of the Formation of 2. A stock solution was
prepared consisting of 1b (1.75 × 10-2 M) and internal ferrocene
standard (6.45 × 10-3 M). For a typical run, a 0.5 mL sample was
placed in a 5 mm NMR tube, the solution frozen and degassed, and a
partial pressure of ethylene introduced. The tube was then flame-sealed,
and 1H NMR spectra were recorded at approximately 40 min intervals
for a period of 2-3 half-lives. The concentrations of 5b and C2H4 for
each NMR spectrum were measured by peak integration relative to
the ferrocene standard; the ethylene concentration remained constant
during the reaction period. This procedure was repeated with different
ethylene concentrations, to give the plot shown in Figure 2. Similar
experiments were conducted at four different temperatures (20, 30, 40,
and 50 °C) for the same ethylene concentration to obtain separate
reaction rates, which were found to be consistent with second-order
kinetics.
an additional role in providing an open coordination site for
these insertion reactions to occur, which accounts for the absence
of further insertion chemistry with 6, where phosphine dis-
sociation to create a reactive site at the metal is not available.
The reactivity of the ethylene complex 2 contrasts with the
insertion chemistry presented here and, so, is reported separately
in another paper.55 Related work that is currently in progress is
involved with modifying the phosphine substituents from
isopropyl to methyl groups to examine the steric effects on the
reactivity of alkylidene and related complexes. Preliminary
results have indicated that reaction pathways may be altered
by this steric modification.
[P2Cp]ZrC(O)dCHPh(Cl) (3a). A solution of 1a (1.390 g, 2.11
mmol) in 60 mL of toluene was placed in a 200 mL bomb that was
affixed to a dual vacuum/nitrogen line. A small portion of solvent was
removed under vacuum, and an atmosphere of carbon monoxide was
introduced. The reaction mixture was left to stir at room temperature
for 48 h, during which the color of the solution gradually changed from
bright yellowish-orange to reddish-orange. The solution was then
filtered, and the filtrate was reduced to 3 mL and layered with hexanes.
Orange crystals were obtained from this solution at -40 °C. Yield:
Experimental Section
General Considerations. Unless otherwise stated, all manipulations
were performed under an atmosphere of prepurified nitrogen in a
Vacuum Atmospheres HE-553-2 glovebox equipped with an MO-40-
2H purification system or in standard Schlenk-type glassware on a dual
vacuum/nitrogen line. Reactions involving gaseous reagents were
conducted in Pyrex vessels (bombs) designed to withstand pressures
1
up to 10 atm. H NMR spectra (referenced to either C6D5H or C6D5-
1
1.26 g (87%). H NMR (20 °C, C6D6): δ 0.20 and 0.46 (s, 6H, Si-
CD2H for benzene or toluene, respectively) were performed on one of
the following instruments depending on the complexity of the particular
spectrum: Bruker WH-200, Varian XL-300, or Bruker AM-500. 13C
NMR spectra (referenced to solvent peaks) were run at 50.323 MHz
on the Bruker WH-200 or at 75.429 MHz on the XL-300 instrument,
and 31P NMR spectra (referenced to external P(OMe)3 at 141.0 ppm)
were run at 121.421 and 202.33 MHz on the XL-300 and Bruker AM-
500 instruments, respectively. All chemical shifts are reported in ppm
and all coupling constants are reported in Hz. Elemental analyses (Mr.
P. Borda) and GC-MS were performed within this department.
Reagents. Ethylene and carbon monoxide were obtained from
Matheson and dried over P2O5 before use. Labeled 13CO (Cambridge
Isotopes) was used as received. tert-Butyl isocyanide (Aldrich) was
prepared as a toluene solution (0.88 M). Hexanes, tetrahydrofuran
(THF), and toluene were predried over CaH2 followed by distillation
under argon from either sodium metal or sodium-benzophenone ketyl;
pentane was distilled from sodium-benzophenone ketyl. The deuterated
solvents C6D6 and C6D5CD3 were dried over sodium, vacuum-
transferred to a bomb, and degassed by freeze-pump-thaw techniques
before use. The procedures for the preparation of [P2Cp]ZrdCHR(Cl)
(1a, R ) Ph;21 5b, R ) SiMe322) have been described elsewhere.
[P2Cp]Zr(η2-CH2dCH2)Cl (2). Method 1. A solution of 1a (1.932
g, 2.93 mmol) in 60 mL of toluene was placed in a 200 mL reactor
equipped with a needle valve and affixed to a dual vacuum/nitrogen
line. A small portion of solvent was removed under vacuum, and an
atmosphere of ethylene was introduced at -78 °C. The reaction mixture
was warmed to room temperature and left to stir for 12 h, during which
the color of the solution gradually changed from bright yellowish-orange
(CH3)2), 0.70 (dd, 4H, 2JHH ) 6 Hz, 2JPH ) 7 Hz, SiCH2P), 0.67, 0.95,
3
2
1.20, and 1.36 (dd, 6H, JPH ) 9 Hz, JHH ) 7 Hz, CH(CH3)2), 2.10
(m, 4H, CH(CH3)2), 5.96 (s, 1H, CHPh), 6.60 (d, 2H, 4JHH ) 1 Hz, Cp
H), 7.09 (t, 1H, 3JHH ) 7 Hz, C6H5 para), 7.14 (t, 1H, 4JHH ) 1 Hz, Cp
3
3
H), 7.39 (t, 2H, JHH ) 7 Hz, C6H5 meta), 8.09 (d, 2H, JHH ) 7 Hz,
C6H5 ortho). 31P NMR (20 °C, C6D6): δ 9.5 (s). 13C NMR (20 °C,
C6D6): δ -1.4 and 0.7 (Si(CH3)2), 9.9 (SiCH2P), 17.5, 19.9, 26.2, and
30.9 (CH(CH3)2), 102.3 (CHPh), 117.1 (CpSi), 122.3 (Cp CH2), 125.1
(C6H5 para), 126.3 (Cp CH), 129.2 (C6H5 meta), 142.0 (C6H5 ortho),
205.1 (t, 2JCP ) 14 Hz, C(O)dC). Anal. Calcd for C31H53ClOP2Si2Zr:
C, 54.23; H, 7.78. Found: C, 54.35; H, 7.85.
[P2Cp]ZrC(O)dCHSiMe3(Cl) (3b). The procedure followed was
similar to that for 3a, reacting 1b (0.98 g, 1.50 mmol) in an atmosphere
of CO. The reaction mixture was left to stir at room temperature for
48 h, during which no color change in the solution was noted. The
solvent was then removed in vacuo, the oily residue extracted with
hexanes, and the extract filtered, yielding a hydrocarbon-soluble orange
oil from which crystals could not be obtained. Yield: 0.87 g (85%).
1
Spectroscopic data for the major isomer are as follows. H NMR (20
°C, C6D6): δ 0.18 and 0.41 (s, 6H, Si(CH3)2), 0.48 (s, 9H, CHSi(CH3)3),
0.82 (dd, 4H, 2JHH ) 5 Hz, 2JPH ) 7 Hz, SiCH2P), 1.12 (m, 24H, CH-
(CH3)2), 2.38 (m, 4H, CH(CH3)2), 4.39 (s, 1H, CHSi(CH3)3), 6.18 (t,
4
4
1H, JHH ) 1 Hz, Cp H), 6.43 (d, 2H, JHH ) 1 Hz, Cp H). 31P NMR
(20 °C, C6D6): δ 11.9 (s).
[P2Cp]ZrC(NtBu)dCHPh(Cl) (4a). A toluene solution of 0.088 M
tert-butyl isocyanide (6.4 mL, 0.56 mmol) was added dropwise with
stirring to a cooled (0 °C) solution of 1a (366 mg, 0.56 mmol) dissolved
in 60 mL of toluene. The reaction mixture was stirred at 0 °C for another
30 min and then slowly warmed to room temperature, during which
(55) Fryzuk, M. D.; Duval, P. B.; Rettig, S. J. Manuscript in preparation.

1716 J. Am. Chem. Soc., Vol. 121, No. 8, 1999
Fryzuk et al.
the color of the solution gradually changed from bright orange to dark
red. The solution was stirred at room temperature for another 12 h, the
solvent then removed in vacuo, the residue extracted with hexanes,
and the extract filtered. The solution was reduced to 5 mL, from which
dark red crystalline needles were obtained at -40 °C. Yield: 320 mg
°C, C6D6): δ 0.02, 0.19, 0.32, and 0.49 (s, 3H, Si(CH3)2), 0.48 (s, 9H,
CHSi(CH3)3), 0.60 (dd, 4H, 2JHH ) 7 Hz, 2JPH ) 7 Hz, SiCH2P), 0.85
and 1.09 (m, 12H, CH(CH3)2), 1.62 (m, 1H, CdCCH2), 1.67 (m, 4H,
CH(CH3)2), 2.04 (dd, 1H, CdCCH2), 2.21 (dd, 1H, ZrCCH2), 2.74 (dd,
1H, ZrCCH2), 4.04 (s, 1H, CHSi(CH3)3), 6.71 (dd, 1H, Cp H), 6.83
(dd, 1H, Cp H), 7.10 (dd, 1H, Cp H). 31P NMR (20 °C, C6D6): δ 46.2
(s), -5.9 (s). Anal. Calcd for C31H61ClO2P2Si3Zr: C, 50.40; H, 8.32.
Found: C, 50.42; H, 8.35.
X-ray Crystallographic Analysis of 2. Diffraction experiments were
performed at 23 °C on a Nonius CAD-4 diffractometer equipped with
graphite-monochromatized Mo KR (0.710 69 Å) radiation. The final
unit-cell parameters were obtained by least-squares procedures for 24
reflections with 2θ ) 30.00-43.00°. The data were processed and
corrected for Lorentz and polarization effects and for absorption. The
cell parameters were checked with CREDUC for cell reduction, and
checks for missing symmetry using MISSYM did not change the space
group selected.
The structure was solved by conventional heavy-atom methods, the
coordinates of the Zr, P, and Si atoms being determined from the
Patterson function and those of the remaining atoms from subsequent
difference Fourier syntheses. After anisotropic refinement of all non-
hydrogen atoms, methylene and ring sp2 hydrogen atoms were fixed
in calculated positions (dC-H ) 1.08 Å), with temperature factors based
upon the carbon to which they are bonded. Methyl hydrogen atoms
were located and fixed via inspection of a difference Fourier map, with
temperature factors based upon the carbon to which they are bonded.
H(19) was located via difference Fourier map inspection and refined.
All crystallographic calculations were conducted with the PC version
of the NRCVAX program package locally implemented on an IBM-
compatible 80486 computer.
X-ray Crystallographic Analyses of 3a and 5b. Crystallographic
data appear in Table 1. The final unit-cell parameters were obtained
by least-squares procedures based on 25 reflections with 2θ ) 23.4-
32.0° for 3a and on 27 256 reflections with 2θ ) 4.0-63.7° for 5b.
The intensities of three standard reflections, measured every 200
reflections throughout the data collection, decayed linearly by 2.0%
for 3a. The data were processed and corrected for Lorentz and
polarization effects, decay (for 3a), and absorption (empirical, based
on azimuthal scans for 3a and symmetry analysis of redundant data
for 5b).56,57
1
(77%). H NMR (20 °C, C6D6): δ 0.20 (br s, 6H, Si(CH3)2), 0.40 (s,
6H, Si(CH3)2), 0.69 (m, 4H, SiCH2P), 1.03 (m, 24H, CH(CH3)2), 1.57
(s, 9H, N(CH3)3), 1.82 (m, 2H, CH(CH3)2), 2.49 (br m, 2H, CH(CH3)2),
6.55 (s, 1H, CHPh), 6.80 (d, 2H, 4JHH ) 1 Hz, Cp H), 6.89 (t, 1H, 4JHH
) 1 Hz, Cp H), 7.02 (t, 1H, 3JHH ) 7 Hz, C6H5 para), 7.37 (t, 2H, 3JHH
) 7 Hz, C6H5 meta), 8.20 (br m, 2H, C6H5 ortho). 31P NMR (20 °C,
C6D6): δ 11.8 (s). IR (C6D6): νCN 1504 cm-1. Anal. Calcd for C35H62-
ClNP2Si2Zr: C, 56.68; H, 8.43; N, 1.89. Found: C, 56.85; H, 8.49; N
1.91.
[P2Cp]ZrCH2CH2C(O)dCHPh(Cl) (5a). A solution of 3a (1.09
g, 1.59 mmol) in 60 mL of toluene was placed in a bomb that was
affixed to a dual vacuum line. The headspace was partially evacuated,
and an atmosphere of ethylene was introduced. The solution was left
to stir at room temperature for 48 h, during which the orange color of
the solution slowly turned red. The solvent was then removed in vacuo,
the oily residue extracted with hexanes, and the extract filtered. The
solution was reduced to 5 mL, from which orange crystals were obtained
at -40 °C. Yield: 0.87 g (77%). 1H NMR (20 °C, C6D6): δ 0.24 and
2
2
0.49 (s, 6H, Si(CH3)2), 0.72 (dd, 4H, JHH ) 6 Hz, JPH ) 7 Hz,
SiCH2P), 0.97 and 1.17 (m, 12H, CH(CH3)2), 1.50 (m, 2H, ZrCH2-
3
CH2), 2.09 and 2.21 (m, 2H, CH(CH3)2), 3.41 (t, 2H, JHH ) 7 Hz,
4
ZrCH2CH2), 5.43 (s, 1H, CHPh), 6.79 (d, 2H, JHH ) 2 Hz, Cp H),
7.01 (t, 1H, 4JHH ) 1 Hz, Cp H), 7.06 (t, 1H, 3JHH ) 7 Hz, C6H5 para),
7.42 (t, 2H, 3JHH ) 7 Hz, C6H5 meta), 8.05 (d, 2H, 3JHH ) 7 Hz, C6H5
ortho). 31P NMR (20 °C, C6D6): δ 7.8 (s). Anal. Calcd for C33H57-
ClOP2Si2Zr: C, 55.47; H, 8.04. Found: C, 55.67; H, 8.19.
[P2Cp]ZrCH2CH2C(O)dCHSiMe3(Cl) (5b). The procedure fol-
lowed was analogous to that for 5a above, reacting 3b (0.80 g, 1.17
mmol) with an atmosphere of ethylene. The reaction mixture was left
to stir at room temperature for 36 h, during which there was no change
to the orange color of the solution. The solution was concentrated to 2
mL and layered with hexanes, from which orange crystals were obtained
at -40 °C from a solution consisting of toluene/hexanes in a 1:1
1
mixture. Yield: 0.66 g (79%). H NMR (20 °C, C6D6): δ 0.28 and
2
0.48 (s, 6H, Si(CH3)2), 0.47 (s, 18H, CHSi(CH3)3), 0.91 (d, 4H, JHH
) 6 Hz, SiCH2P), 1.11 (m, 24H, CH(CH3)2), 1.39 (m, 2H, ZrCH2-
The structures were solved by conventional heavy-atom methods,
the coordinates of the heavy atoms being determined from the Patterson
functions and those of the remaining atoms from subsequent difference
Fourier syntheses. All non-hydrogen atoms were refined with aniso-
tropic thermal parameters. Hydrogen atoms were fixed in idealized
positions (C-H ) 0.98 Å, BH ) 1.2Bbonded atom). A secondary extinction
correction was applied for 3a (Zachariasen type 2 isotropic), the final
value of the extinction coefficient being 2.03(4) × 10-7. No correction
for secondary extinction was necessary for 5b. Neutral-atom scattering
factors and anomalous dispersion corrections were taken from refs 58
and 59.
CH2), 2.21 (m, 4H, CH(CH3)2), 3.34 (t, 2H, 3JHH ) 7 Hz, ZrCH2CH2),
4
4.22 (s, 1H, CHSi(CH3)3), 6.59 (d, 2H, JHH ) 1 Hz, Cp H), 6.90 (t,
4
1H, JHH ) 1 Hz, Cp H). 31P NMR (20 °C, C6D6): δ 8.2 (s). Anal.
Calcd for C30H61ClOP2Si3Zr: C, 50.70; H, 8.65. Found: C, 50.60; H,
8.57.
[P2Cp]ZrC(O)CH2CH2C(O)dCHPh(Cl) (6a). A solution of 5a
(0.64 g, 0.90 mmol) in 30 mL of toluene was placed in a bomb that
was affixed to a dual vacuum line. An atmosphere of carbon monoxide
was introduced at -78 °C, and the reaction mixture was warmed to
room temperature and stirred for 24 h, during which the reddish solution
gradually faded to an orange-yellow color. The solvent was then reduced
to 5 mL and layered with hexanes, from which yellow crystals were
obtained at -40 °C. Yield: 0.54 g (80%). 1H NMR (20 °C, C6D6): δ
Acknowledgment. Financial support for this research was
provided by the NSERC of Canada in the form of a Research
Grant to M.D.F. and a postgraduate scholarship to P.B.D.
2
2
0.01 and 0.28 (s, 6H, Si(CH3)2), 0.61 (dd, 2H, JHH ) 6 Hz, JPH ) 6
2
2
Hz, SiCH2P), 0.71 (dd, 2H, JHH ) 6 Hz, JPH ) 6 Hz, SiCH2P), 0.91
(m, 24H, CH(CH3)2), 1.62 (m, 4H, CH(CH3)2), 2.19 (m, 2H, CdCCH2),
2.75 (m, 2H, ZrCCH2), 5.06 (s, 1H, CHPh), 6.72 (dd, 1H, Cp H), 6.83
Supporting Information Available: Listings of atomic
positional and thermal parameters for 2, 3a, and 5b. This
material is available free of charge on the Internet at
http://pubs.acs.org.
3
(dd, 1H, Cp H), 7.02 (t, 1H, JHH ) 7 Hz, C6H5 para), 7.23 (dd, 1H,
3
3
Cp H), 7.30 (t, 2H, JHH ) 7 Hz, C6H5 meta), 7.94 (d, 2H, JHH ) 7
Hz, C6H5 ortho),. 31P NMR (20 °C, C6D6): δ 46.8 (s), -5.1 (s). Anal.
Calcd for C34H57ClO2P2Si3Zr(C7H8)0.5: C, 57.11; H, 7.80. Found: C,
57.30; H, 7.80.
JA982695Y
(56) teXsan: Crystal Structure Analysis Package; Molecular Structure
Corp.: The Woodlands, TX, 1985 and 1992.
(57) d*TREK: Area Detector Software; Molecular Structure Corp.: The
Woodlands, TX, 1997.
(58) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K. (present distributor Kluwer Academic Publishers:
Boston, MA), 1974; Vol. IV.
(59) International Tables for Crystallography; Kluwer Academic Pub-
lishers: Boston, MA, 1992; Vol. C.
[P2Cp]ZrC(O)CH2CH2C(O)dCHSiMe3(Cl) (6b). The procedure
followed was similar to that for 6a, reacting 5b (0.50 g, 0.70 mmol)
with an atmosphere of CO. There was no obvious color change to the
orange solution after stirring at room temperature for 48 h. The solvent
was then removed, the residue extracted with hexanes, and the extract
filtered. A yellow-orange crystalline solid was isolated from a cold,
1
concentrated hexanes solution. Yield: 0.39 mg (76%). H NMR (20