Synthesis and reactivity of phosphametallacycles: Sterically induced epimerizations and retrocycloadditions

Article abstract of DOI:10.1021/om9607053

Elimination of methane from Cp₂Zr(PR*H)(Me) (R* = C₆H₂-2,4,6-t-Bu₃) (4) in the presence of diphenylacetylene or phenylpropyne afforded the [2 + 2] cycloaddition products Cp₂Zr-(P(R*)C(Ph)=CPh) (3) and Cp₂Zr(P(R*)C(Me)=CPh) (5), respectively. Alternatively, the [2 + 2] cycloaddition reaction between (Cp₂Zr=PR*)(PMe₃) (1) and phenylacetylene yielded Cp₂Zr(P(R*)C(H)=CPh) (6). Metallacycles 3 and 5 undergo facile [2 + 2] retrocycloaddition reactions; addition of 1 equiv of phenylpropyne to 3 resulted in an equilibrium mixture of 3 and 5. In contrast, addition of phenylacetylene to 3 yielded Cp₂Zr(C=CPh)(C(Ph)=C(Ph)-PHR*) (7), the product of C-H activation of the terminal alkyne. Attempts to synthesize a phosphametallacycle with less sterically hindered substituents on phosphorus by reaction of Cp₂ZrMeCl, diphenylacetylene, and LiHPMes (Mes = C₆H₂-2,4,6-Me₃) instead led to the formation of Cp₂Zr(P(Mes)P(Mes)C(Ph)=CPh) (8). Probing the mechanism of formation of 8 by reaction of (Cp₂ZrCl)₂(μ-PMes) with Li₂PMeS in the presence of diphenylacetylene afforded Cp₂Zr(P(Mes)C(Ph)=CPh) 9. However, reaction of 9 with H₂PMes instead resulted in the formation of the unstable compound Cp₂Zr(C(Ph)=C(Ph)PMesH)(PMesH) (10). Phosphametallacyclobutene 3 reacts with tert-butyl isocyanide, acetone, cyclohexanone, benzonitrile, benzaldehyde and styrene oxide to give the insertion products Cp₂Zr(C(=N-t-Bu)P(R*)C(Ph)=CPh) (12), Cp₂Zr(OCMe₂P(R*)C(Ph)=CPh) (13), Cp₂Zr(O(c-CC₅H₁₀)P(R*)C-(Ph)=CPh) (14), Cp₂Zr(N=C(Ph)P(R*)C(Ph)=CPh) (15), Cp₂Zr(OCHPhP(R*)C(Ph)=CPh) (16), and Cp₂Zr(OCH₂CHPhP(R*)C(Ph)=CPh) (17), respectively. Compounds 16 and 17 were also obtained by reaction of either benzaldehyde or styrene oxide with 13, 14, or 15, via [4 + 2] retrocycloadditions. Epimerization at phosphorus has been identified in complexes 3, 5, 6, 8, 9, and 12-15, and has been attributed to steric congestion in these species. Spectroscopic methods, X-ray crystallography, and molecular orbital calculations have been employed to address this issue.

Full text of DOI:10.1021/om9607053

Organometallics 1996, 15, 5729-5737
5729
Syn th esis a n d Rea ctivity of P h osp h a m eta lla cycles:
Ster ica lly In d u ced Ep im er iza tion s a n d
Retr ocycloa d d ition s
Tricia L. Breen† and Douglas W. Stephan*
Department of Chemistry and Biochemistry, University of Windsor,
Windsor, Ontario, Canada N9B 3P4
Received August 16, 1996X
Elimination of methane from Cp2Zr(PR*H)(Me) (R* ) C6H2-2,4,6-t-Bu3) (4) in the presence
of diphenylacetylene or phenylpropyne afforded the [2 + 2] cycloaddition products Cp2Zr-
(P(R*)C(Ph)dCPh) (3) and Cp2Zr(P(R*)C(Me)dCPh) (5), respectively. Alternatively, the [2
+ 2] cycloaddition reaction between (Cp2ZrdPR*)(PMe3) (1) and phenylacetylene yielded
Cp2Zr(P(R*)C(H)dCPh) (6). Metallacycles 3 and 5 undergo facile [2 + 2] retrocycloaddition
reactions; addition of 1 equiv of phenylpropyne to 3 resulted in an equilibrium mixture of 3
and 5. In contrast, addition of phenylacetylene to 3 yielded Cp2Zr(CtCPh)(C(Ph)dC(Ph)-
PHR*) (7), the product of CsH activation of the terminal alkyne. Attempts to synthesize a
phosphametallacycle with less sterically hindered substituents on phosphorus by reaction
of Cp2ZrMeCl, diphenylacetylene, and LiHPMes (Mes ) C6H2-2,4,6-Me3) instead led to the
formation of Cp2Zr(P(Mes)P(Mes)C(Ph)dCPh) (8). Probing the mechanism of formation of
8 by reaction of (Cp2ZrCl)2(µ-PMes) with Li2PMes in the presence of diphenylacetylene
afforded Cp2Zr(P(Mes)C(Ph)dCPh) 9. However, reaction of 9 with H2PMes instead resulted
in the formation of the unstable compound Cp2Zr(C(Ph)dC(Ph)PMesH)(PMesH) (10).
Phosphametallacyclobutene 3 reacts with tert-butyl isocyanide, acetone, cyclohexanone,
benzonitrile, benzaldehyde and styrene oxide to give the insertion products Cp2Zr(C(dN-t-
Bu)P(R*)C(Ph)dCPh) (12), Cp2Zr(OCMe2P(R*)C(Ph)dCPh) (13), Cp2Zr(O(c-CC5H10)P(R*)C-
(Ph)dCPh) (14), Cp2Zr(NdC(Ph)P(R*)C(Ph)dCPh) (15), Cp2Zr(OCHPhP(R*)C(Ph)dCPh)
(16), and Cp2Zr(OCH2CHPhP(R*)C(Ph)dCPh) (17), respectively. Compounds 16 and 17 were
also obtained by reaction of either benzaldehyde or styrene oxide with 13, 14, or 15, via [4
+ 2] retrocycloadditions. Epimerization at phosphorus has been identified in complexes 3,
5, 6, 8, 9, and 12-15, and has been attributed to steric congestion in these species.
Spectroscopic methods, X-ray crystallography, and molecular orbital calculations have been
employed to address this issue.
In tr od u ction
counterparts.5,6 Nonetheless, this reaction has been
applied to group 4 metal alkylidenes, imides, oxides, and
sulfides alike to yield metallacyclobutenes. Extensions
of this approach to phosphorus chemistry have drawn
less attention,7 although reports describing the prepara-
tion and structural studies of several terminal phos-
phinidenes (MdPR)8-10 and arsinidenes (M)AsR)11
have appeared in the literature. In a preliminary
communication12 we have reported the first examples
of phosphazirconacyclobutenes, obtained via [2 + 2]
cycloaddition reactions of alkynes with either the ter-
minal zirconium phosphinidene (Cp2ZrdPR*)(PMe3) (1;
R* ) 2,4,6-t-Bu3-C6H2) or the transient intermediate
The [2 + 2] cycloaddition reaction with alkynes is one
of the established reactivity patterns within the realm
of metal-ligand multiple bonds.1 This transformation
has frequently occurred with Fischer carbenes;1,2 how-
ever, relatively few examples are known for Schrock
alkylidenes1,3,4 and their multiply bonded heteroatomic
* To whom correspondence should be addressed. E-mail:
Stephan@UWindsor.ca.
† Current address: Department of Chemistry, Massachusetts In-
stitute of Technology, Cambridge, MA 02139.
X Abstract published in Advance ACS Abstracts, December 1, 1996.
(1) Nugent, W. A.; Mayer, J . M. Metal-Ligand Multiple Bonds;
Wiley: New York, 1988; and references cited therein.
(2) (a) Wulff, W. In Advances in Metal-Organic Chemistry; Liebe-
skind, L. S., Ed.; J AI: Greenwich, CT, 1989; Vol. 1. (b) Herndon, J .
W.; Tumer, S. U.; McMullen, L. A.; Matasi, J . J .; Schnatter, W. F. K.
In Advances in Metal-Organic Chemistry; Volume 3 Liebeskind, L. S.,
Ed.; J AI: Greenwich, CT, 1994; Vol 3.
(5) (a) Carney, M. J .; Walsh, P. J .; Hollander, F. J .; Bergman, R. G.
J . Am. Chem. Soc. 1989, 111, 8751. (b) Carney, M. J .; Walsh, P. J .;
Bergman, R. G. J . Am. Chem. Soc. 1990, 112, 6426. (c) Carney, M. J .;
Walsh, P. J .; Hollander, F. J .; Bergman, R. G. Organometallics 1992,
11, 761. (d) Polse, J . L.; Andersen, R. A.; Bergman, R. G. J . Am. Chem.
Soc. 1995, 117, 5393.
(3) (a) Tebbe, F. N.; Harlow, R. L. J . Am. Chem. Soc. 1980, 102,
6151. (b) McKinney, R. J .; Tulip, T. H.; Thorn, D. L.; Coolbaugh, T. S.;
Tebbe, F. N. J . Am. Chem. Soc. 1981, 103, 5584.
(4) Wood, C. D.; McLain, S. J .; Schrock, R. R. J . Am. Chem. Soc.
1979, 101, 3210.
(6) (a) Walsh, P. J .; Hollander, F. J .; Bergman, R. G. J . Am. Chem.
Soc. 1988, 110, 8729. (b) Walsh, P. J .; Hollander, F. J .; Bergman, R.
G. Organometallics 1993, 12, 3705. (c) Walsh, P. J .; Baranger, A. M.;
Bergman, R. G. J . Am. Chem. Soc. 1992, 114, 1708. (d) Baranger, A.
M.; Walsh, P. J .; Bergman, R. G. J . Am. Chem. Soc. 1993, 115, 2753.
S0276-7333(96)00705-4 CCC: $12.00 © 1996 American Chemical Society

5730 Organometallics, Vol. 15, No. 26, 1996
Breen and Stephan
dark red-brown solution was filtered and the solvent removed
in vacuo. The oily residue was dissolved in diethyl ether, and
the solvent was again evaporated under reduced pressure to
[Cp2ZrdPR*] (2). These metallacyclic products insert
aldehyde, ketone, nitrile, epoxide, or isocyanate to afford
five-, six-, and seven-membered phosphametallacycles,
several of which undergo sterically induced [4 + 2]
retrocycloadditions. Epimerization at phosphorus and
the diastereoselectivity of the insertion reactions have
been examined by employing spectroscopic methods and
molecular orbital calculations. The ramifications of
these results are considered herein.
yield a flaky red-gold solid. 3: Yield: 588 mg (87%). 1H NMR
4
(25 °C, C6D6): δ 7.64 (d, |J | ) 7.2 Hz, 2H, Ph H), 7.51 (d, | J PH
|
) 2.3 Hz, 2H, Ar H), 7.08-6.57 (m, 8H, Ph H), 5.74 (s, 10H,
Cp), 1.54 (s, 18H, o-tBu), 1.40 (s, 9H, p-tBu). 13C{1H} NMR
(25 °C, C6D6): δ 210.6 (d, |J | ) 15.1 Hz, quat), 152.3 (s, quat),
151.4 (d, |J | ) 7.1 Hz, quat), 150.9 (s, quat), 149.2 (s, quat),
143.7 (s, quat), 141.1 (d, |J | ) 43.8 Hz, quat), 131.0 (s, arom
C-H), 128.1 (s, arom C-H), 127.4 (s, arom C-H), 125.6 (s,
arom C-H), 125.5 (s, arom C-H), 123.8 (s, arom C-H), 120.9
(s, arom C-H), 112.4 (s, Cp), 38.0 (s, o-C(CH3)3), 34.7 (s,
Exp er im en ta l Section
4
p-C(CH3)3), 33.4 (d, | J PC| ) 7.9 Hz, o-C(CH3)3), 31.3 (s,
Gen er a l Da ta . All preparations were performed under an
atmosphere of dry, O2-free N2 either by Schlenk line techniques
or with a Vacuum Atmospheres inert-atmosphere glovebox.
Solvents were reagent grade, distilled from the appropriate
drying agents under N2, and degassed by the freeze-thaw
method at least three times prior to use. All organic reagents
were purified by conventional methods. 1H and 13C{1H} NMR
spectra were recorded on a Bruker AC-300 operating at 300
and 75 MHz, respectively. 31P and 31P{1H} NMR spectra were
recorded on a Bruker AC-200 operating at 81 MHz. Trace
amounts of protonated solvents were used as references, and
chemical shifts are reported relative to SiMe4 and 85% H3-
PO4, respectively. Low- and high-resolution EI mass spectral
data were obtained employing a Kratos Profile mass spec-
trometer outfitted with a N2 glovebag enclosure for the inlet
port. Combustion analyses were performed by Galbraith
Laboratories, Inc., Knoxville, TN, or Schwarzkopf Laborato-
ries, Woodside, NY. H2PR* and H2PMes were purchased from
the Quantum Design Chemical Co. All other reagents were
purchased from the Aldrich Chemical Co. Cp2ZrMeCl,13 (Cp2-
ZrdPR*)(PMe3) (1),10c Cp2ZrMe(PHR*) (4),10c (Cp2ZrCl)2(µ-
PMes),14 LiPHR*‚3THF,15 LiPHMes‚2THF,16 and Li2PMes17
were prepared by literature methods.
p-C(CH3)3). 31P NMR (25 °C, C6D6): δ 55.3 (s). HRMS (EI):
m/ e calcd for C42H49PZr 674.2615, found 674.2605. 5: yield:
418 mg (68%). 1H NMR (25 °C, C6D6) δ 7.52 (s, 2H, Ar H),
3
7.28-6.94 (m, 5H, Ph H), 5.73 (s, 10H, Cp), 2.17 (d, | J PH| )
5.6 Hz, 3H, CH3), 1.67 (s, 18H, o-tBu), 1.36 (s, 9H, p-tBu). 13C-
{1H} NMR (25 °C, C6D6): δ 207.0 (d, |J | ) 14.5 Hz, quat), 152.5
(d, |J | ) 6.8 Hz, quat), 148.9 (s, quat), 148.0 (s, quat), 145.3
(s, quat), 128.3 (s, arom C-H), 125.3 (s, arom C-H), 124.1 (s,
arom C-H), 121.0 (s, arom C-H), 111.3 (s, Cp), 38.3 (s,
4
o-C(CH3)3), 34.4 (s, p-C(CH3)3), 33.2 (d, | J PC| ) 8.5 Hz,
2
o-C(CH3)3), 31.3 (s, p-C(CH3)3), 22.4 (d, | J PC| ) 16.9 Hz, CH3).
31P NMR (25 °C, C6D6): δ 70.1 (s). HRMS (EI): m/ e calcd for
C
37H47PZr 612.2458, found 612.2450.
Syn th esis of Cp 2Zr (P (R*)C(H)dCP h ) (6). To a benzene
solution of 1 (115 mg, 0.2 mmol) was added a benzene solution
of phenylacetylene (22.0 mL, 0.2 mmol). The reaction mixture
stood for 3 h, after which time the dark brown solution was
filtered and the solvent removed in vacuo. The oily residue
was dissolved in pentane, and the volume was reduced under
vacuum. Small red-brown crystals precipitated upon standing
overnight and were isolated by filtration. Yield: 107 mg (89%).
2
1H NMR (25 °C, C6D6): δ 7.61 (d, | J PH| ) 5.4 Hz, 1H, dCH),
4
7.39 (d, | J PH| ) 2.2 Hz, 2H, Ar H), 7.35-7.27 (m, 5H, Ph H),
Syn th esis of Cp 2Zr (P (R*)C(P h )dCP h ) (3) a n d Cp 2Zr -
5.60 (s, 10H, Cp), 1.71 (s, 18H, o-tBu), 1.31 (s, 9H, p-tBu). 13C-
{1H} NMR (25 °C, C6D6): δ 215.0 (d, |J | ) 11.6 Hz, quat), 150.9
(d, |J | ) 6.2 Hz, quat), 147.6 (s, quat), 146.5 (s, quat), 144.2
(d, |J | ) 20.0 Hz, quat), 128.6 (s, arom C-H), 127.9 (s, arom
C-H), 127.2 (s, arom C-H), 120.8 (s, arom C-H), 110.0 (s,
Cp), 104.5 (d, |J | ) 74.5 Hz, P-CH), 38.1 (s, o-C(CH3)3), 34.2
(P (R*)C(Me)dCP h ) (5). The preparations of 3 and 5 were
performed in a similar manner; thus, only one procedure is
described in detail. To a benzene solution of Cp2ZrMeCl (272
mg, 1.0 mmol) and diphenylacetylene (178 mg, 1.0 mmol) was
added a benzene solution of LiHPR*‚3THF (501 mg, 1.0 mmol).
The reaction mixture stood for 3 days, after which time the
4
(s, p-C(CH3)3), 33.1 (d, | J PC| ) 8.5 Hz, o-C(CH3)3), 31.2 (s,
p-C(CH3)3). 31P NMR (25 °C, C6D6): δ 85.0 (s).
Syn t h esis of Cp 2Zr (CtCP h )(C(P h )dC(P h )P H R *) (7).
To a benzene solution of 3 (135 mg, 0.2 mmol) was added
phenylacetylene (22.0 mL, 0.2 mmol). The reaction mixture
stood for 30 min, after which time the solvent was removed in
vacuo and the product dissolved in hexane. When the solution
stood for 12 h, a brown microcrystalline solid precipitated,
which was isolated by filtration. Yield: 134 mg (86%). 1H
NMR (25 °C, C6D6): δ 7.50-7.43 (m, 3H, Ph H), 7.10-6.48
(m, 14H, Ph H), 6.78 (d, |J PH| ) 301.6 Hz, 1H, PH), 6.22 (s,
5H, Cp), 5.90 (s, 5H, Cp), 1.68 (s, 9H, o-tBu), 1.62 (s, 9H, o-tBu),
1.19 (s, 9H, p-tBu). 13C{1H} NMR (25 °C, C6D6): δ 203.4 (s,
quat), 202.9 (s, quat), 157.9 (s, quat), 156.0 (d, |J | ) 9.4 Hz,
quat), 152.1 (s, quat), 151.5 (s, quat), 150.6 (s, quat), 149.8 (s,
quat), 149.5 (s, quat), 138.7 (s, quat), 134.1 (d, |J | ) 21.6 Hz,
quat), 130.8 (d, |J | ) 21.6 Hz, quat), 128.5 (s, arom C-H), 128.0
(s, arom C-H), 127.8 (s, arom C-H), 127.0 (s, arom C-H),
125.6 (s, arom C-H), 125.4 (s, arom C-H), 125.0 (s, arom
C-H), 123.9 (s, arom C-H), 122.4 (br s, arom C-H), 122.3
(br s, arom C-H), 108.6 (s, Cp), 108.5 (s, Cp), 38.2 (s,
o-C(CH3)3), 37.9 (s, o-C(CH3)3), 34.5 (s, p-C(CH3)3), 33.9 (s,
o-C(CH3)3), 33.1 (d, |J | ) 4.1 Hz, o-C(CH3)3), 31.2 (s, p-C(CH3)3).
31P NMR (25 °C, C6D6): δ -84.3 (d, |J PH| ) 300.9 Hz).
(7) For examples of late-metal-phosphametallocyclobutenes see: (a)
Al-J uaid, S. S.; Carmichael, D.; Hitchcock, P. B.; Lochschmidt, S.;
Marinetti, A.; Mathey, F.; Nixon, J . F. J . Chem. Soc., Chem. Commun.
1988, 1156. (b) Ajulu, F. A.; Carmichael, D.; Hitchcock, P. B.; Mathey,
F.; Medidine, M. F.; Nixon, J . F.; Ricard, L.; Riley, M. L. J . Chem.
Soc., Chem. Commun. 1992, 750. (c) Ajulu, F. A.; Hitchcock, P. B.;
Mathey, F.; Mechelin, R. A.; Nixon, J . F.; Pombeiro, A. J . L. J . Chem.
Soc., Chem. Commun. 1993, 142. (d) Al-J uaid, S. S.; Carmichael, D.;
Hitchcock, P. B.; Marinetti, A.; Mathey, F.; Nixon, J . F. J . Chem. Soc.,
Dalton Trans. 1991, 905. (e) Carmichael, D.; Hitchcock, P. B.; Nixon,
J . F.; Mathey, F.; Ricard, L. J . Chem. Soc., Dalton Trans. 1993, 1811.
(f) Carmichael, D.; Hitchcock, P. B.; Nixon, J . F.; Mathey, F.; Ricard,
L. J . Chem. Soc., Chem. Commun. 1989, 1389.
(8) (a) Hitchcock, P. B.; Lappert, M. F.; Leung, W. P. J . Chem. Soc.,
Chem. Commun. 1987, 1282. (b) Cowley, A. H.; Pellerin, B. J . Am.
Chem. Soc. 1990, 112, 6734.
(9) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 756.
(10) (a) Hou, Z.; Stephan, D. W. J . Am. Chem. Soc. 1992, 114, 10088.
(b) Hou, Z.; Breen, T. L.; Stephan, D. W. Organometallics 1993, 12,
3158. (c) Breen, T. L.; Stephan, D. W. J . Am. Chem. Soc. 1995, 117,
11914.
(11) Bonanno, J . B.; Wolczanski, P. T.; Lobkovsky, E. B. J . Am.
Chem. Soc. 1994, 116, 11159.
(12) Breen, T. L.; Stephan, D. W. J . Am. Chem. Soc. 1996, 118, 4204.
(13) J ordan, R. F. J . Organomet. Chem. 1985, 294, 321.
(14) Ho, J .; Stephan, D. W. Organometallics, 1991, 10, 3001.
(15) Cowley, A. H.; Kilduff, J . E.; Newman, T. H.; Pakulski, M. J .
Am. Chem. Soc. 1982, 104, 5820.
(16) Hey, E.; Weller, F. J . Chem. Soc., Chem. Commun. 1988, 782.
(17) (a) Hope, H.; Pestana, D. C.; Power, P. P. Angew. Chem., Int.
Ed. Engl. 1991, 30, 691. (b) Niediek, K.; Neumuller, B. Z. Anorg. Allg.
Chem. 1993, 619, 885.
Syn th esis of Cp 2Zr (P (Mes)P (Mes)C(P h )dCP h ) (8). To
a benzene solution of Cp2ZrMeCl (272 mg, 1.0 mmol) and
diphenylacetylene (178 mg, 1.0 mmol) was added a benzene
solution of LiHPMes‚2THF (302 mg, 1.0 mmol). The reaction

Phosphametallacycles
Organometallics, Vol. 15, No. 26, 1996 5731
mixture stood for 2 days, after which time the deep blue-green
solution was filtered and the volume of the solution was
reduced under vacuum. Hexamethyldisiloxane (ca. 6 mL) was
added, and the solution was allowed to stand for 1 week. Dark
wine red crystals were isolated by filtration and washed on
the frit with hexane. Yield: 133 mg (19%). 1H NMR (25 °C,
C6D6): δ 7.47 (br d, |J | ) 1.8 Hz, 2H, Ph H), 7.08-7.03 (m,
4H, Ph H), 6.92-6.86 (m, 3H, Ph H), 6.80-6.75 (m, 1H, Ph
H), 6.62-6.58 (m, 4H, Ph H), 5.75 (v br s, 10H, Cp), 2.73 (s,
6H, o-Me), 2.68 (br s, 6H, o-Me), 2.22 (s, 3H, p-Me), 1.91 (s,
3H, p-Me). 13C{1H} NMR (25 °C, C6D6): δ 199.3 (dd, |J | )
28.5 Hz, |J | ) 4.1 Hz, quat), 152.9 (d, |J | ) 7.3 Hz, quat), 149.5
(s, quat), 143.5 (s, quat), 143.0 (s, quat), 141.8 (dd, |J | ) 13.3
Hz, |J | ) 7.2 Hz, quat), 141.5 (dd, |J | ) 42.8 Hz, |J | ) 19.8
Hz, quat), 138.6 (s, quat), 135.6 (s, quat), 133.8 (dd, |J | ) 26.3
Hz, |J | ) 14.5 Hz, quat), 130.8 (d, |J | ) 12.8 Hz, arom C-H),
129.7 (br d, |J | ) 12.0 Hz, arom C-H), 128.1 (s, arom C-H),
127.7 (s, arom C-H), 127.4 (s, arom C-H), 126.9 (br s, arom
C-H), 126.2 (s, arom C-H), 123.2 (s, arom C-H), 110.5 (br s,
Cp), 24.4 (d, |J | ) 9.7 Hz, o-Me), 24.1 (d, |J | ) 9.5 Hz, o-Me),
20.8 (s, p-Me), 20.5 (s, p-Me). 31P NMR (25 °C, C6D6): δ 60.4
(d, |J PP| ) 349.8 Hz, Zr-P), -96.2 (d, |J PP| ) 349.8 Hz, P-P-C).
1H NMR (-80 °C, CD3C6D5): δ 7.20-6.49 (m, 14H, Mes H and
Ph H), 5.88 (s, 5H, Cp), 5.29 (s, 5H, Cp), 2.86 (s, 3H, Me), 2.80
(s, 3H, Me), 2.58 (s, 3H, Me), 2.23 (s, 3H, Me), 2.11 (s, 3H,
Me), 1.95 (s, 3H, Me). 31P NMR (-80 °C, CD3C6D5): δ 54.1
(d, |J PP| ) 348.9 Hz, Zr-P), -101.2 (d, |J PP| ) 348.9 Hz, P-P-
C). Anal. Calcd for C42H42P2Zr: C, 72.07; H, 6.05. Found:
C, 72.33; H, 5.82.
yellow crystals formed over a 12 h period at room temperature
and were isolated by filtration. 12: yield 138 mg (91%). 1H
4
NMR (25 °C, C6D6): δ 7.52 (d, | J PH| ) 2.1 Hz, 2H, Ar H), 7.14-
6.68 (m, 10H, Ph H), 5.65 (s, 10H, Cp), 1.64 (s, 18H, o-tBu),
1.23 (s, 9H, p-tBu), 1.08 (s, 9H, p-tBu). 13C{1H} NMR (25 °C,
C6D6): δ 223.3 (d, |J | ) 43.6 Hz, quat), 198.5 (d, |J | ) 38.9
Hz, quat), 156.5 (s, quat), 156.3 (d, |J | ) 10.9 Hz, quat), 153.2
(d, |J | ) 50.5 Hz, quat), 151.2 (s, quat), 141.7 (d, |J | ) 32.0
Hz, quat), 132.2 (d, |J | ) 55.6 Hz, quat), 130.9 (s, arom C-H),
127.3 (s, arom C-H), 126.7 (s, arom C-H), 126.5 (s, arom
C-H), 124.9 (s, arom C-H), 123.9 (d, |J | ) 7.1 Hz, quat), 122.2
(s, arom C-H), 106.3 (s, Cp), 61.5 (s, N-C(CH3)3), 39.3 (s,
4
o-C(CH3)3), 34.7 (s, p-C(CH3)3), 34.4 (d, | J | ) 4.5 Hz, o-
C(CH3)3), 31.0 (s, C(CH3)3), 29.8 (s, C(CH3)3). 31P NMR (25
°C, C6D6): δ 17.8 (s). Anal. Calcd for C47H58NPZr: C, 74.36;
H, 7.70. Found: C, 74.78; H, 7.47. 13: yield 75 mg (51%). 1H
NMR (25 °C, C6D6): δ 7.38 (s, 2H, Ar H), 6.96-6.74 (m, 10H,
Ph H), 5.94 (br s, 10H, Cp), 1.72 (br s, 18H, o-tBu), 1.54 (br s,
3H, Me), 1.50 (br s, 3H, Me), 1.23 (s, 9H, p-tBu). 13C{1H} NMR
(25 °C, C6D6): δ 191.0 (d, |J | ) 31.5 Hz, quat), 154.4 (br s,
quat), 152.1 (d, |J | ) 7.0 Hz, quat), 150.4 (s, quat), 149.7 (s,
quat), 143.0 (d, |J | ) 19.8 Hz, quat), 132.9 (d, |J | ) 65.4 Hz,
quat), 131.7 (s, arom C-H), 127.1 (s, arom C-H), 126.0 (s,
arom C-H), 124.5 (s, arom C-H), 122.4 (br s, arom C-H),
121.4 (s, arom C-H), 110.8 (br s, Cp), 88.4 (d, |J | ) 36.0 Hz,
O-C), 39.8 (s, o-C(CH3)3), 39.7 (s, o-C(CH3)3), 35.2 (br s,
o-C(CH3)3), 34.4 (s, p-C(CH3)3), 33.9 (s, Me), 33.8 (s, Me), 31.1
(s, p-C(CH3)3). 31P NMR (25 °C, C6D6): δ 37.6 (s). 1H NMR
(-70 °C, CD3C6D5, 200 MHz): δ 7.44 (br s, 2H, Ar H), 7.20-
6.60 (m, 10H, Ph H), 6.10 (s, 5H, Cp), 5.79 (s, 5H, Cp), 1.86
(br s, 9H, o-tBu), 1.74-1.27 (br s, 24H, o-tBu, p-tBu, Me). 31P
Syn th esis of Cp 2Zr (P (Mes)C(P h )dCP h ) (9). To a ben-
zene suspension of (Cp2ZrCl)2(µ-PMes) (199 mg, 0.3 mmol) was
added a benzene solution of diphenylacetylene (107 mg, 0.6
mmol) and a benzene suspension of Li2PMes (54 mg, 0.33
mmol). The mixture was stirred vigorously for 2 days, after
which time it was filtered. The solvent was removed in vacuo
and the forest green product dissolved in diethyl ether.
Reduction of the volume resulted in the precipitation of a deep
green microcrystalline solid which was isolated by filtration.
Yield: 267 mg (81%). 1H NMR (25 °C, C6D6): δ 7.66 (d, |J | )
8.0 H, 2H, Ph H), 7.13-6.69 (m, 10H, Ph H), 5.83 (s, 10H,
Cp), 2.28 (s, 6H, o-Me), 2.19 (s, 3H, p-Me). 13C{1H} NMR (25
°C, C6D6): δ 206.2 (d, |J | ) 17.0 Hz, quat), 148.9 (d, |J | ) 4.9
Hz, quat), 140.4 (d, |J | ) 12.1 Hz, quat), 137.9 (d, |J | ) 12.2
Hz, quat), 135.5 (s, quat), 131.4 (d, |J | ) 50.9 Hz, quat), 131.3
(d, |J | ) 8.9 Hz, arom C-H), 129.4 (s, arom C-H), 128.1 (s,
arom C-H), 127.7 (s, arom C-H), 126.0 (s, arom C-H), 125.6
(s, arom C-H), 123.7 (s, arom C-H), 113.0 (s, Cp), 24.2 (s,
Me), 23.9 (s, Me), 20.5 (s, Me). 31P NMR (25 °C, C6D6): δ 31.4
(s).
NMR (-80 °C, CD3C6D5): δ 36.1 (s). Anal. Calcd for C45H55
-
OPZr: C, 73.62; H, 7.55. Found: C, 73.83; H, 7.68. 14: yield
90 mg (58%). 1H NMR (25 °C, C6D6): δ 7.52-6.70 (m, 12H,
Ar H and Ph H), 6.11 (br s, 5H, Cp), 5.86 (br s, 5H, Cp), 2.35-
1.20 (m, 10H, Cy H), 1.69 (br s, 18H, o-tBu), 1.23 (s, 9H, p-tBu).
13C{1H} NMR (25 °C, C6D6): δ 189.5 (d, |J | ) 29.0 Hz, quat),
152.3 (d, |J | ) 8.3 Hz, quat), 150.9 (s, quat), 150.3 (s, quat),
149.6 (s, quat), 143.5 (d, |J | ) 19.9 Hz, quat), 132.0 (d, |J | )
41.2 Hz, quat), 132.8 (s, arom C-H), 126.8 (s, arom C-H),
126.5 (s, arom C-H), 125.2 (s, arom C-H), 122.7 (s, arom
C-H), 111.4 (br s, Cp), 89.9 (d, |J | ) 31.2 Hz, O-C), 40.2 (s,
o-C(CH3)3), 35.5 (br s, o-C(CH3)3), 34.5 (s, p-C(CH3)3), 31.1 (s,
p-C(CH3)3), 25.6 (s, CH2), 22.7 (s, CH2), 22.5(d, |J | ) 8.4 Hz,
CH2). 31P NMR (25 °C, C6D6): δ 37.4 (s). 1H NMR (-80 °C,
CD3C6D5, 200 MHz): δ 7.79-6.65 (m, 12H, Ar H and Ph H),
6.17 (s, 5H, Cp), 5.67 (s, 5H, Cp), 2.4-1.2 (v br, 28H, o-tBu,
Cy H), 1.28 (s, 9H, p-tBu). 31P NMR (-80 °C, CD3C6D5): δ
31.6 (s). Anal. Calcd for C48H59OPZr: C, 74.47; H, 7.68.
Found: C, 74.88; H, 7.41. 15: yield 72 mg (46%). 1H NMR
Gen er a tion of Cp2Zr (P HMes)(C(P h )CP h P H(Mes)) (10).
To a benzene suspension of 9 (20 mg, 0.05 mmol) was added
a benzene solution of PH2Mes (7 mg, 0.05 mmol). The mixture
was stirred, and the reaction mixture was monitored by 31P
NMR spectrocopy. All attempts to isolate 10 were unsuccess-
4
(25 °C, C6D6): δ 7.60 (d, | J PH| ) 2.2 Hz, 2H, Ar H), 7.45-6.70
(m, 15H, Ph H), 5.89 (br s, 10H, Cp), 1.62 (br s, 18H, o-tBu),
1.24 (s, 9H, p-tBu). 13C{1H} NMR (25 °C, C6D6): δ 198.3 (d,
|J | ) 31.2 Hz, quat), 180.3 (d, |J | ) 36.4 Hz, quat), 153.6 (d,
|J | ) 13.3 Hz, quat), 151.7 (s, quat), 145.8 (d, |J | ) 6.5 Hz,
quat), 142.7 (d, |J | ) 22.3 Hz, quat), 138.0 (d, |J | ) 42.5 Hz,
quat), 131.7 (s, arom C-H), 129.4 (s, arom C-H), 128.6 (s,
arom C-H), 126.9 (s, arom C-H), 126.5 (s, arom C-H), 125.2
(s, arom C-H), 122.3 (s, arom C-H), 109.0 (br s, Cp), 40.4 (br
s, o-C(CH3)3), 34.8 (s, p-C(CH3)3), 34.4 (br s, o-C(CH3)3), 31.0
(s, p-C(CH3)3). 31P NMR (25 °C, C6D6): δ 21.3 (s). 1H NMR
(-60 °C, CD3C6D5, 200 MHz): δ 7.36-6.66 (m, 17H, Ar H and
Ph H), 6.05 (s, 5H, Cp), 5.60 (s, 5H, Cp), 1.64 (br s, 9H, o-tBu),
1.57 (br s, 9H, o-tBu), 1.29 (s, 9H, p-tBu). 31P NMR (-60 °C,
CD3C6D5): δ 21.5 (s). Anal. Calcd for C49H54NPZr: C, 75.53;
H, 6.99. Found: C, 75.19; H, 6.75. 16: yield 95 mg (61%). 1H
NMR (25 °C, C6D6): δ 7.81 (d, |J | ) 1.9 Hz, 1H, C-H), 7.40-
6.66 (m, 17H, Ph H and Ar H), 6.45 (s, 5H, Cp), 5.73 (s, 5H,
ful, as 10 proved to be unstable to air, moisture, and heat. 31
P
NMR (25 °C, C6D6): δ -91.5 (m, Zr-P, |J PP| ) 72 Hz, |J PH| )
309.8 Hz), -130.7 (dd, C-P, |J PP| ) 72 Hz, |J PH| ) 205.4 Hz).
Syn th esis of Cp 2Zr (C(dN-t-Bu )P (R*)C(P h )dCP h ) (12),
Cp 2Zr (OCMe2P (R*)C(P h )dCP h ) (13), Cp 2Zr (O(c-C6H11)P -
(R*)C(P h )dCP h ) (14), Cp 2Zr (NdC(P h )P (R*)C(P h )dCP h )
(15), Cp 2Zr (OCHP h P (R*)C(P h )dCP h ) (16), a n d Cp 2Zr -
(OCH2CHP h P (R*)C(P h )dCP h ) (17). The reactions of 3
with tert-butyl isocyanide, acetone, cyclohexanone, benzoni-
trile, benzaldehyde, and styrene oxide were all performed in
a similar manner; thus, only one preparation is described in
detail. To a benzene solution of 3 (135 mg, 0.2 mmol) was
added tert-butyl isocyanide (22.6 mL, 0.2 mmol). The reaction
mixture stood for 30 min, after which time the solvent was
removed in vacuo and the product dissolved in pentane. Large
t
t
t
Cp), 2.06 (s, 9H, Bu), 1.28 (s, 9H, Bu), 1.10 (s, 9H, Bu). 13C-
{1H} NMR (25 °C, C6D6): δ 188.3 (d, |J | ) 33.9 Hz, quat), 160.3
(s, quat), 159.9 (s, quat), 155.6 (d, |J | ) 5.3 Hz, quat), 152.3
(d, |J | ) 9.6 Hz, quat), 150.5 (d, |J | ) 48.2 Hz, quat), 150.4 (s,

5732 Organometallics, Vol. 15, No. 26, 1996
Ta ble 1. Cr ysta llogr a p h ic Da ta
Breen and Stephan
8
12
13
14
16
17
formula
fw
C42H42P2Zr
699.96
C47H58NPZr
759.18
C45H55OPZr
734.12
C48H59OPZr
774.19
C49H55OPZr
782.17
C50H57OPZr
796.19
cryst size (mm) 0.35 × 0.27 × 0.33 0.23 × 0.25 × 0.26 0.44 × 0.22 × 0.30 0.22 × 0.21 × 0.45 0.31 × 0.20 × 0.23 0.32 × 0.37 × 0.30
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
16.61(1)
10.018(9)
21.215(5)
11.326(4)
21.129(6)
10.256(4)
90.08(3)
112.37(2)
93.70(3)
2263(1)
triclinic
P1h
13.26(1)
15.414(6)
11.085(8)
101.75(5)
112.10(5)
94.96(5)
2021(2)
triclinic
P1h
13.939(2)
15.083(2)
11.157(2)
102.15(2)
113.25(2)
94.43(1)
2073.0(9)
triclinic
P1h
31.385(6)
16.316(4)
16.685(4)
9.944(4)
41.12(2)
10.974(2)
93.60(4)
95.86(2)
106.37(3)
3522(3)
monoclinic
P21/n
4
4.31
8620(2)
monoclinic
4305(2)
monoclinic
P1h
4
3.27
1.23
8
cryst syst
space group
Z
Cc
8
3.26
1.21
8
4
2
2
µ, (cm-1
)
3.10
1.11
16
3.42
1.21
16
3.38
1.24
8
d(calcd), g/cm3 1.32
scan speed,
deg/min
8
index range
no. of data
collected
h,k,(l
h,(k,(l
(h,(k,l
h,(k,(l
(h,k,l
(h,k,l
6584
7977
7463.00
7299
4829
8171
2
no. of data Fo
1015
4051
2495
3268
1540
2707
2
> 3σ(F0
)
no. of variables 196
451
208
370
248
229
transmissn
factors
0.936-1.000
0.936-1.000
0.848-1.058
0.922-1.000
0.955-1.000
0.731-1.000
R, Rw, %a
6.45, 7.72
6.23, 6.32
1.87
8.0, 6.7
1.78
5.14, 6.35
1.46
7.8, 6.3
1.53
9.5, 7.6
2.34
goodness of fit 1.72
a
2
R ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) [∑(|Fo| - |Fc|)2|/∑|Fo| ]0.5
.
quat), 144.4 (d, |J | ) 24.3 Hz, quat), 143.5 (d, |J | ) 14.8 Hz,
quat), 132.9 (s, arom C-H), 131.4 (s, arom C-H), 126.3 (s,
arom C-H), 125.6 (s, arom C-H), 125.2 (s, arom C-H), 123.0
(s, arom C-H), 122.8 (s, arom C-H), 112.7 (s, Cp), 112.1 (s,
Cp), 89.0 (d, |J PC| ) 16.6 Hz, O-CH), 41.1 (s, o-C(CH3)3), 39.2
crystal system. Ultimately, 25 reflections (20° < 2θ < 25°)
were used to obtain the final lattice parameters and the
orientation matrices. Crystal data are summarized in Table
1. The observed extinctions were consistent with the space
groups. The data sets were collected in three shells (4.5° <
2θ < 50.0°), and 3 standard reflections were recorded every
197 reflections. Fixed scan rates were employed. Up to 4
repetitive scans of each reflection at the respective scan rates
were averaged to ensure meaningful statistics. In all cases
the background/scan time ratio was 0.5 and the scan range
was from 1.0° below KR1 to 1.0° above KR2. The number of
scans of each reflection was determined by the intensity. The
intensities of the standards showed no statistically significant
change over the duration of the data collections. The data
were processed using the TEXSAN crystal solution package
operating on a SGI Challenger mainframe with remote X-
3
(d, | J PC| ) 6.9 Hz, o-C(CH3)3), 36.5 (s, o-C(CH3)3), 34.6 (s,
4
p-C(CH3)3), 33.3 (d, | J PC| ) 18.1 Hz, o-C(CH3)3), 31.1 (s,
p-C(CH3)3). 31P NMR (25 °C, C6D6): δ 13.9 (s). Anal. Calcd
for C49H55OPZr: C, 75.24; H, 7.09. Found: C, 75.10; H, 7.14.
17: yield 108 mg (68%). 1H NMR (25 °C, C6D6): δ 7.56 (dd,
|J | ) 5.2 Hz, |J | ) 1.9 Hz, 2H, Ar H), 7.11-6.53 (m, 15H, Ph
H), 6.21 (s, 5H, Cp), 5.85 (s, 5H, Cp), 4.60 (m, 1H, C-H), 4.50
(m, 1H, C-H), 3.82 (m, 1H, C-H), 1.99 (s, 9H,o-tBu), 1.32 (s,
t
9H, o- Bu), 1.10 (s, 9H, p-tBu). 13C{1H} NMR (25 °C, C6D6):
δ 192.6 (d, |J | ) 53.3 Hz, quat), 157.4 (d, |J | ) 35.3 Hz, quat),
156.6 (s, quat), 156.0 (d, |J | ) 42.0 Hz, quat), 151.9 (d, |J | )
16.8 Hz, quat), 150.0 (s, quat), 144.5 (d, |J | ) 7.8 Hz, quat),
141.4 (s, quat), 131.7 (s, arom C-H), 130.5 (s, arom C-H),
129.9 (d, |J | ) 41.4 Hz, quat), 126.6 (s, arom C-H), 125.8 (s,
arom C-H), 125.7 (s, arom C-H), 124.2 (s, arom C-H), 122.7
(d, |J | ) 14.3 Hz, arom C-H), 122.4 (s, arom C-H), 112.1 (s,
2
2
terminals. The reflections with Fo > 3σFo were used in the
refinements.
Str u ctu r e Solu tion a n d Refin em en t. Non-hydrogen
atomic scattering factors were taken from the literature
tabulations.18,19 The zirconium atom positions were deter-
mined using direct methods by employing either the SHELX-
86 or direct-methods routines. The remaining non-hydrogen
atoms were located from successive difference Fourier map
calculations. The refinements were carried out by using full-
2
Cp), 112.0 (s, Cp), 80.9 (d, | J PC| ) 24.6 Hz, O-CH2), 59.6 (d,
3
|J PC| ) 41.1 Hz, CH), 40.4 (d, | J PC| ) 7.6 Hz, o-C(CH3)3), 40.0
4
(s, o-C(CH3)3), 34.8 (d, | J PC| ) 18.1 Hz, o-C(CH3)3), 34.6 (s,
p-C(CH3)3), 34.4 (s, o-C(CH3)3), 31.1 (s, p-C(CH3)3). 31P NMR
(25 °C, C6D6): δ -2.4 (d, |J | ) 13.9 Hz). Anal. Calcd for
matrix least-squares techniques on F, minimizing the function
2
C
50H57OPZr: C, 75.43; H, 7.22. Found: C, 75.86; H, 7.16.
w(|Fo| - |Fc|)2, where the weight w is defined as 4Fo2/2σ(Fo
)
Kin etic Stu d ies. NMR scale reactions were monitored as
and Fo and Fc are the observed and calculated structure factor
amplitudes. In the final cycles of each refinement, the number
of non-hydrogen atoms that were assigned anisotropic tem-
perature factors was limited so as to maintain a reasonable
data to variable ratio. Empirical absorption corrections were
applied to the data sets based on ψ-scan data. Hydrogen atom
positions were calculated and allowed to ride on the carbon to
which they are bonded, assuming a C-H bond length of 0.95
Å. Hydrogen atom temperature factors were fixed at 1.10
times the isotropic temperature factor of the carbon atom to
which they are bonded. The hydrogen atom contributions were
calculated but not refined. The final values of R, Rw, and the
a function of time by 31P NMR spectroscopy. Integrations of
the resonances were measured against an internal standard
of PPh3, which was shown separately to be inert.
X-r a y Da ta Collection a n d Red u ction . X-ray-quality
crystals of 8, 12-14, 16, and 17 were obtained directly from
the preparation as described above. The crystals were ma-
nipulated and mounted in capillaries in a glovebox, thus
maintaining a dry, O2-free environment for each crystal.
Diffraction experiments were performed at 24 °C on a Rigaku
AFC5 diffractometer equipped with graphite-monochromatized
Mo KR (0.710 69 Å) radiation. The initial orientation matrix
was obtained from 20 machine-centered reflections selected
by an automated peak search routine. These data were used
to determine the crystal systems. Automated Laue system
check routines around each axis were consistent with the
(18) (a) Cromer, D. T.; Mann, J . B. Acta Crystallogr., Sect. A: Cryst.
Phys. Theor. Gen. Crystallogr. 1968, A24, 324. (b) Ibid. 1968, A24, 390.
(19) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, England, 1974.

Phosphametallacycles
Organometallics, Vol. 15, No. 26, 1996 5733
maximum ∆/σ on any of the parameters in the final cycles of
the refinements are given in Table 1. The locations of the
largest peaks in the final difference Fourier map calculation
as well as the magnitude of the residual electron densities in
each case were of no chemical significance. The phenyl rings
in 16 were refined with a constrained geometry in order to
maintain a statistically meaningful data to variable ratio, and
the correct enantiomorph was confirmed by inversion and
refinement of the model. Positional parameters, hydrogen
atom parameters, thermal parameters and bond distances and
angles have been deposited as Supporting Information.
EHMO Ca lcu la tion s. Extended Huckel molecular orbital
(EHMO) calculations were performed on a PowerMac 7100
workstation employing the CaChe software package.20 Models
were constructed on the basis of idealized geometries derived
from related crystallographic data.
The reversible formation of metallacycles 3 and 5 was
illustrated by the addition of trimethylphosphine to
either complex, which rapidly resulted in the quantita-
tive conversion to 1 along with the liberation of alkyne.
Similarly, addition of 1 equiv of 1-phenylpropyne to 3
resulted in alkyne exchange to give an equilibrium
mixture of 3 and 5 (Keq ) 1.1 at 25 °C) (eq 2).
R*
P
–PhC
PhC
CPh
CPh
PhC
CMe
CMe
[Cp2Zr
PR*]
Cp2Zr
Ph
–PhC
2
Ph
3
R*
P
(2)
Cp2Zr
Me
Resu lts a n d Discu ssion
Ph
5
Syn th esis of P h osp h a m eta lla cycles. The reaction
of terminal phosphinidene complex 1 with 1 equiv of
diphenylacetylene proceeded slowly only when the
released trimethylphosphine was successively removed
from solution under vacuum, resulting in the observa-
tion of a singlet at 55.3 ppm in the 31P NMR spectrum
of the reaction mixture. 1H and 13C{1H} NMR data
supported the assignment of this signal as phospha-
Comparable to related oxa-,5b-d thia-5b,c and azametal-
lacyclobutenes,6 these reactions are thought to occur
through [2 + 2] retrocycloadditions to generate the
transient intermediate [Cp2ZrdPR*] (2), which then
reacts with either PMe3 or alkyne.
In contrast to the above results, 3 did not undergo
exchange reactions with phenylacetylene; rather, C-H
activation across the Zr-P bond of 3 resulted in the
formation of the zirconocene alkynyl alkenyl complex
Cp2Zr(CtCPh)(CPhdC(Ph)PHR*) (7), which was iso-
lated in 86% yield (eq 3). The secondary phosphine
metallacyclobutene Cp2Zr(P(R*)C(Ph)dCPh) (3). A more
expeditious route to 3 paralleled our published route to
terminal phosphinidene 1.10c R-elimination of methane
from Cp2Zr(PR*H)Me (4) generated the transient ter-
minal phosphinidene intermediate [Cp2ZrdPR*] (2),
which underwent a [2 + 2] cycloaddition reaction with
diphenylacetylene to furnish 3 in 87% yield (eq 1). The
Ph
R*
H
P
PhC
CH
(3)
P
Cp2Zr
Ph
Cp2Zr
Ph
R*
R*
Ph
Ph
P
RC
CR′
–CH4
H
7
[Cp2Zr
Cp2Zr
PR*]
3
Me
2
moiety in 7 was indicated by the 31P NMR signal at
-84.9 ppm with a one-bond P-H coupling constant of
300.9 Hz. Furthermore, signals at 203.4 and 202.9 ppm
in the 13C{1H} NMR spectrum were indicative of two
quaternary carbons bound to zirconium. Compound 7
is similar to Cp2Zr(CtCPh)(C(Ph)dC(H)P(SiMe3)2), which
has recently been prepared by Hey-Hawkins et al. via
insertion of phenylacetylene into the Zr-P bond of Cp2-
Zr(P(SiMe3)2)(Cl), followed by reaction with lithium
phenylacetylide.21 It is interesting that the ZrdP
multiple bond of 1 tolerates the CsH group of the
terminal alkyne, while the ZrsP single bond of metal-
lacycle 3 does not. Presumably, the [2 + 2] retrocy-
cloaddition of 3 that generates intermediate 2 is far
slower than acidolysis of the ZrsP single bond of 3 by
the acetylenic C-H group.
4
R*
R*
P
P
HC
CPh
(1)
Cp2Zr
Cp2Zr
R′
PMe3
R
1
3: R, R′ = Ph
5: R = Ph, R′ = Me
6: R = Ph, R′ = H
use of 1-phenylpropyne as a trapping agent gave a 68%
yield of Cp2Zr(P(R*)C(Me)dCPh) (5); however, attempts
to use phenylacetylene only resulted in the formation
of product mixtures, presumably arising from C-H bond
metathesis pathways. Nonetheless, reaction of 1 with
phenylacetylene proceeded much more rapidly than
The analogue of 3 incorporating the less sterically
hindered mesityl substituent on phosphorus was an-
ticipated from the reaction of Cp2ZrMeCl and LiHPMes‚-
2THF (Mes ) C6H2-2,4,6-Me3) in the presence of diphe-
nylacetylene. However, fractional crystallization of the
resulting complex mixture of products instead gave 8
(eq 4), which exhibited signals in the 31P NMR spectrum
at 60.4 and -96.2 ppm with a P-P coupling constant
of 349.8 Hz. 1H and 13C{1H} NMR data were consistent
with other alkynes to cleanly provide Cp2Zr(P(R*)C-
(H)dCPh) (6) in 89% yield (eq 1). It is noteworthy that
reactions involving unsymmetrical alkynes are com-
pletely regioselective, exclusively producing complexes
in which the phenyl substituent is located R to the
metal. These observations are consistent with the trend
previously observed by Bergman et al. for zirconocene
oxo, sulfido,5b-d and imido complexes.6
(20) CaChe Worksystem Software is an integrated modeling, mo-
lecular mechanics, and molecular orbital computational software
package and is a product of CaChe Scientific Inc.
(21) (a) Hey-Hawkins, E.; Lindenberg, F. Chem. Ber. 1992, 125,
1815. (b) Lindenberg, F.; Hey-Hawkins, E. Z. Anorg. Allg. Chem. 1995,
621, 1531.

5734 Organometallics, Vol. 15, No. 26, 1996
Breen and Stephan
Me
CPh
+ LiHPMes•2THF + PhC
Mes
Cp2Zr
Cl
Mes
Ph
P
P
(4)
+ unidentified products
Cp2Zr
Ph
8 (minor product)
with the formulation of 8 as the diphosphametallacy-
clopentene Cp2Zr(P(Mes)P(Mes)C(Ph)dCPh), the struc-
ture of which was subsequently confirmed by an X-ray
crystallographic study (Figure 1). The geometry about
each phosphorus atom is pyramidal, and steric conges-
tion in the metallacycle is minimized by the transoid
disposition of the mesityl substituents. The Zr-P bond
length of 2.596(9) Å compares well with the shorter
Zr-P distance in the five-membered diphosphazircona-
cycle (η5-C5H3(SiMe3)2)2Zr(P(Ph)C6H4PPh-1,2) (2.560(4)
Å).22
F igu r e 1. ORTEP drawing of 8; 30% thermal ellipsoids
are shown. Selected bond distances (Å) and angles (deg)
are as follows: Zr(1)-P(1); 2.596(9); Zr(1)-C(36); 2.31(2);
P(1)-P(2), 2.19(1); P(2)-C(29): 1.81(3); P(1)-Zr(1)-C(36);
89.0(7); Zr(1)-P(1)-P(2); 94.2(4); P(1)-P(2)-C(29); 111.8-
(9).
The mechanism of formation of 8 is not clear. One
possibility is that the highly reactive terminal phos-
phinidene intermediate [Cp2ZrdPMes] is generated and
trapped by cycloaddition with diphenylacetylene to give
the intermediate phosphametallacyclobutene Cp2Zr-
Sch em e 1
(P(Mes)C(Ph)dCPh) 9. Further reaction with 1 equiv
of primary phosphine H2PMes and elimination of hy-
drogen would then produce 8 (Scheme 1). In order to
probe the mechanism, an alternative synthetic route to
9 was devised. Reaction of (Cp2ZrCl)2(µ-PMes)14 with
Li2PMes in the presence of diphenylacetylene success-
fully yielded 9 in 81% yield. This species was analogous
in 1H and 13C{1H} NMR spectra to metallacycles 3, 5,
and 6. However, subsequent reaction of 9 with 1 equiv
of H2PMes yielded the zirconocene alkenyl phosphide
Cp2Zr(C(Ph)dC(Ph)PMesH)(PMesH) (10), which proved
to be very unstable and thus not isolable. The formation
of 8 was not detected in solutions of 9 or 10 upon aging
for several weeks or heating to 100 °C, thus dismissing
both species as intermediates en route to 8.
The most probable mechanism for the formation of 8
involves the generation of the unstable diphosphamet-
allacyclopropane Cp2Zr(P2Mes2) (11), which is trapped
through insertion of diphenylacetylene into a Zr-P bond
(eq 5). Sterically demanding cyclopentadienyl ligands
conocene complex Cp2Zr(N2Ph2)(THF) as described by
Bergman and co-workers.24
In ser tion Rea ction s of 3. The reaction of tert-butyl
isocyanide with 3 proceeded rapidly, giving a bright
yellow product which was formulated as Cp2Zr(C(dN-
Mes
t-Bu)P(R*)C(Ph)dCPh) (12) on the basis of spectroscopic
data (Scheme 2). Insertion into the ZrsP bond was
consistent with the two low-field resonances in the 13C-
{1H} NMR spectrum at 223.3 and 198.5 ppm. Prefer-
ential insertion into the ZrsP bond contrasts with
reactions of related aza-25 and oxametallacyclobutenes,26
in which insertions occur exclusively at the ZrsC bond,
but is compatible with the highly reactive nature of the
ZrsP bond. The hapticity of the imino fragment was
determined by an X-ray crystallographic study, which
clearly showed η2 coordination of the iminoacyl group
Mes
Ph
Mes
Mes
P
P
P
PhC
CPh
P
Cp2Zr
Cp2Zr
(5)
Ph
11
8
have been reported to stabilize diphosphametallacy-
clopropanes,10b,23 and insertion of alkyne into the Zr-P
bond of an acyclic phosphide has been previously
observed by Hey-Hawkins et al.21 The proposed mech-
anism is also comparable to the insertion of alkyne into
the Zr-N bond of the (η2-1,2-diphenylhydrazido)zir-
(24) Walsh, P. J .; Hollander, F. J .; Bergman, R. G. J . Organomet.
Chem. 1992, 428, 13.
(25) Hanna, T. A.; Baranger, A. M.; Walsh, P. J .; Bergman, R. G. J .
Am. Chem. Soc. 1995, 117, 3292.
(26) Vaughan, G. A.; Hillhouse, G. L.; Rheingold, A. L. J . Am. Chem.
Soc. 1990, 112, 7994.
(22) Bohra, R.; Hitchcock, P. B.; Lappert, M. F.; Leung, W.-P. J .
Chem. Soc., Chem. Commun. 1989, 728.
(23) Kurz, S.; Hey-Hawkins, E. J . Organomet. Chem. 1993, 462, 203.

Phosphametallacycles
Organometallics, Vol. 15, No. 26, 1996 5735
F igu r e 3. ORTEP drawing of 13; 30% thermal ellipsoids
are shown. Selected bond distances (Å) and angles (deg)
are as follows: Zr(1)-O(1), 1.934(9); Zr(1)-C(11), 2.30(1);
P(1)-C(18); 1.89(1); P(1)-C(25); 1.97(1); P(1)-C(28); 1.88-
(1); O(1)-Zr(1)-C(11); 87.1(5).
F igu r e 2. ORTEP drawing of 12; 30% thermal ellipsoids
are shown. Selected bond distances (Å) and angles (deg)
are as follows: Zr(1)-N(1); 2.221(6); Zr(1)-C(43); 2.217-
(7); Zr(1)-C(11); 2.389(8); P(1)-C(18); 1.856(8); P(1)-C(43);
1.707(8); N(1)-C(43); 1.274(9); C(11)-Zr(1)-C(43); 73.0-
(3); C(11)-Zr(1)-N(1); 106.0(2); N(1)-Zr(1)-C(43); 33.3-
(2); C(43)-P(1)-C(18); 98.3(4).
Sch em e 2
F igu r e 4. ORTEP drawing of 14; 30% thermal ellipsoids
are shown. Selected bond distances (Å) and angles (deg)
are as follows. Molecule a: Zr(1)-O(1); 1.919(5); Zr(1)-
C(11); 2.336(7); P(1)-C(18); 1.850(8); P(1)-C(25); 1.957-
(8); O(1)-Zr(1)-C(11); 85.8(2); Zr(1)-O(1)-C(25); 150.1(5).
afforded the similar six-membered metallacycles Cp2Zr-
(O(c-CC5H10)P(R*)C(Ph)dCPh) (14) and Cp2Zr(NdC-
to the zirconium center (Figure 2). The Zr(1)-C(43),
Zr(1)-N(1), and C(43)-N(1) bond distances are very
similar to those of the acyclic iminoacyl species Cp2Zr-
(η2-C(dNMe)CHPh2)(Me);27 however, the cyclic nature
of 12 enforces the “N-outside” coordination mode of the
imino group. This coordination mode is disfavored in
open-chain metallocene acyl and iminoacyl complexes28
but has been previously observed in cyclic titanocene
iminoacyls.29 The pyramidal geometry about phospho-
rus in 12 and the resulting inequivalence of the cyclo-
pentadienyl rings were not reflected in the temperature-
(Ph)P(R*)C(Ph)dCPh) (15) in 58% and 46% yield,
respectively (Scheme 2). X-ray crystallographic studies
of 13 and 14 confirmed the formulations of the phos-
phaoxametallacyclohexenes (Figures 3 and 4, respec-
tively). In each, the geometry at phosphorus is pyra-
midal and the C6H2-2,4,6-tert-Bu3 substituent adopts an
equatorial position relative to the ring. Unlike isocya-
nide insertion product 12, the inequivalence of the
cyclopentadienyl rings and methyl groups of 13 indi-
cated by the solid-state structure was consistent with
1
invariant H and 13C{1H} NMR spectra.
1
the H NMR spectrum at -80 °C. The fluxionality of
Ketone and nitrile insertions also occurred into the
ZrsP bond of 3. For example, insertion of acetone
rapidly produced the phosphaoxametallacyclohexene
13 was indicated by the single broad resonances ob-
1
served in the room-temperature H and 13C{1H} NMR
q
spectra (∆Gc ) 13.4 kcal/mol). Variable-temperature
NMR studies of 14 and 15 showed that they exhibited
similar dynamic behavior corresponding to ∆Gcq ) 14.1
and 13.0 kcal/mol, respectively. Related insertion of
isonitrile into Zr-P and Hf-As bonds has recently been
reported by Lindenberg et al.30
A process involving a [4 + 2] retrocycloaddition of
metallacycles 13-15 was indicated by reactivity studies.
Addition of 1 equiv of benzaldehyde to 13 resulted in
Cp2Zr(OCMe2P(R*)C(Ph)dCPh) (13) in 51% yield. Like-
wise, reactions of 3 with cyclohexanone and benzonitrile
(27) Cardin, D. J .; Lappert, M. F.; Raston, C. L. Chemistry of
Organo-Zirconium and -Hafnium Compounds; Wiley: New York, 1986;
pp 221-223.
(28) Tatsumi, K.; Nakamura, A.; Hofmann, P.; Stauffert, P.; Hoff-
mann, R. J . Am. Chem. Soc. 1985, 107, 4440.
(29) Ca´mpora, J .; Buchwald, S. L. Organometallics 1995, 14, 2039.

5736 Organometallics, Vol. 15, No. 26, 1996
Breen and Stephan
F igu r e 6. ORTEP drawing of 17; 30% thermal ellipsoids
are shown. Selected bond distances (Å) and angles (deg)
are as follows: Zr(1)-O(1); 1.92(1); Zr(1)-C(11); 2.36(1);
P(1)-C(18); 1.85(1); P(1)-C(25); 1.91(1); P(1)-C(33); 1.86-
(1); O(1)-Zr(1)-C(11); 96.2(4).
Sch em e 3
F igu r e 5. ORTEP drawing of the two molecules of 16 in
the asymmetric unit; 30% thermal ellipsoids are shown.
Selected bond distances (Å) and angles (deg) are as follows.
Molecule a: Zr(1)-O(1); 1.97(3); P(1)-C(18); 1.83(3); P(1)-
C(25); 1.94(4); P(1)-C(32); 1.94(2); O(1)-Zr(1)-C(11); 90-
(1). Molecule b: Zr(2)-O(2); 1.93(2); P(2)-C(67); 1.86(4);
P(2)-C(74); 1.87(4); P(2)-C(81); 1.95(2); O(2)-Zr(2)-C(60);
86(1).
loss of acetone from 13, as the rate of reaction was
independent of either benzaldehyde or styrene oxide
concentration. We have previously communicated12
that acetone is lost through a [4 + 2] retrocycloaddition,
which generates zirconocene alkylidene intermediate 18.
A subsequent irreversible [4 + 2] cycloaddition with
benzaldehyde yields 16, while the ring opening of
styrene oxide gives 17 (Scheme 3). Attempts to trap
the zirconocene alkylidene intermediate with excess
PMe3, pyridine, or 1-phenylpropyne were unsuccessful.
However, the vinylimido complexes of titanocene de-
scribed by Doxsee et al.31 and our report of the imido-
phosphaalkene complex (Cp2ZrdNC(Ph)dPMes*)-
(PMe3)10c are strong circumstantial evidence supporting
the viability of intermediate 18. In addition, similar [4
+ 2] retrocycloadditions have been reported for azaoxa-
metallacyclohexenes25 and oxatitanacyclohexenes.32 Since
ketone preferentially inserts into the metal-vinyl bond
in these complexes, the [4 + 2] retrocycloadditions
furnish (Cp2MdO)n along with either R,â-unsaturated
imines or conjugated dienes.
the liberation of free acetone and the formation of the
metallacycle Cp2Zr(OCHPhP(R*)C(Ph)dCPh) (16). Com-
plex 16 was also formed through corresponding reac-
tions with either 14 or 15; as an alternative, 16 could
be synthesized directly through the reaction of benzal-
dehyde with 3 to afford 16 in 61% yield (Scheme 2). The
single resonance in the 31P NMR spectrum of 16 attested
to the diastereoselectivity of the insertion reaction. A
subsequent X-ray crystallographic study revealed that
the supermesityl group on phosphorus and the ketonic
phenyl group both adopt equatorial positions and thus
are trans with respect to the metallacyclic ring (Figure
5). In a similar way, reactions of 3 or 13-15 with 1
equiv of styrene oxide resulted in the formation of
phosphaoxametallacycloheptene Cp2Zr(OCH2CHPhP-
(R*)C(Ph)dCPh) (17) in 68% yield (from 3) (Scheme 2).
X-ray crystallography was again employed to verify the
selective formation of the RR/SS enantiomeric pair
(Figure 6). In contrast to 13-15, neither 16 nor 17 is
a fluxional species; the solution 1H and 13C{1H} NMR
spectra are temperature invariant and correspond to the
solid-state structures.
A probable cause of the [4 + 2] retrocycloaddition in
13 is significant steric congestion in the six-membered
ring. The observation of close contacts between both
methyl groups and supermesityl tert-butyl fragments
Kinetic studies of the reactions of 13 with either
benzaldehyde or styrene oxide indicated a rate-limiting
(31) (a) Doxsee, K. M.; Farahi, J . B. J . Chem. Soc., Chem. Commun.
1990, 1452. (b) Doxsee, K. M.; Farahi, J . B.; Hope, H. J . Am. Chem.
Soc. 1991, 113, 8889.
(32) Doxsee, K. M.; Mouser, J . K. M. Tetrahedron Lett. 1991, 32,
1687.
(30) (a) Lindenberg, F.; Sieler, J .; Hey-Hawkins, E. Polyhedron 1996,
15, 459. (b) Lindenberg, F.; Muller, U.; Pilz, A.; Sieler, J .; Hey-Hawkins,
E. Z. Anorg. Allg. Chem. 1996, 622, 683.

Phosphametallacycles
Organometallics, Vol. 15, No. 26, 1996 5737
(five H‚‚‚H distances ranging from 2.098 to 2.234 Å) in
the solid-state structure support this premise. Substi-
tution of a methyl group with a hydrogen atom (e.g. in
16) results in a stable complex in which [4 + 2]
retrocycloadditions are not provoked.
Ster ica lly In d u ced Ep im er iza tion a t P h osp h o-
r u s. A feature common to metallacyclobutenes 3, 5, 6,
and 9, metallacyclopentenes 8 and 12, and metallacy-
clohexenes 13-15 is the discrepancy between the spec-
troscopic data and the expected pyramidal geometry at
phosphorus. This geometry imposes inequivalent en-
vironments on the two cyclopentadienyl rings; however,
each of these complexes exhibit only one resonance, or
two very broad resonances in the case of 14, attributable
1
to these ligands in the room-temperature H and 13C-
{1H} NMR spectra. This indicates either a planar
geometry or rapid inversion at phosphorus. These
alternatives could not be distinguished for 3 or 5, as
cooling to -80 °C merely resulted in the observation of
line broadening. In comparison, a pyramidal configu-
ration has been confirmed crystallographically for 8 and
12-14.
F igu r e 7. Plot of the EHMO total energy of the model
Cp2ZrPH(HCCH) as a function of the H-P-C-C torsion
angle.
phosphorus p orbital in which the phosphorus lone pair
resides. Regardless of the geometry at phosphorus, no
evidence was indicated either for an extended π-system
involving the lone pair on phosphorus and the alkenyl
π-bond or M-P multiple bonding.
From the kinetic and computational studies presented
in this paper, it is clear that steric effects in our family
of metallacycles are manifested in two ways: reduced
inversion barriers at phosphorus and the [4 + 2]
retrocycloadditions of 13-15. Interestingly, phospha-
oxametallacyclohexene 16 and phosphaoxametallacy-
cloheptene 17 are immune to both effects. This may be
attributed to reduced steric constraints due to the
presence of a hydrogen substituent on the metallacyclic
carbon atom R to phosphorus. Increased steric demands
(as in 13-15) result in the observed destabilization of
the metallacycle and dynamic behavior.
The kinetic studies described for 13 revealed a rate-
limiting loss of acetone, thus indicating the lack of a
rapid equilibrium between 13 and zirconocene alky-
lidene intermediate 18. Furthermore, variable-temper-
q
ature NMR studies of 13-15 yielded values of ∆Gc
consistent with a reduced barrier to inversion at phos-
phorus. In a similar way, preliminary kinetic investiga-
tions of the [2 + 2] retrocycloadditions exhibited by
phosphametallacyclobutenes 3 and 5 revealed a rate-
1
limiting loss of alkyne. These data, as well as H and
13C{1H} NMR data, indicate that the cause of the
fluxional process for these metallacycles is rapid inver-
sion at phosphorus rather than ring fragmentation.
Similar to the four- and six-membered metallacycles,
the NMR spectra of metallacyclopentenes 8 and 12 were
also inconsistent with metallacycle fragmentation. Fur-
thermore, neither complex underwent dissociative ex-
change with alkyne or PMe3. The NMR spectra of 12
were temperature-invariant; however, NMR spectra of
8 showed a marked temperature dependence. The
broad resonance due to the cyclopentadienyl rings split
and sharpened into two lines upon cooling to -80 °C
Su m m a r y
In summary, the first examples of phosphametalla-
cyclobutenes exhibit intriguing chemistry, such as [2 +
2] retrocycloadditions and insertions of unsaturated
polar organic molecules into the Zr-P bond. These and
related reactions have provided access to a family of
four-, five-, and six-membered phosphametallacycles.
Steric factors exert considerable influence over the
entire group of complexes and are manifested as reduced
inversion barriers at phosphorus and [4 + 2] retrocy-
cloadditions. In contrast, the phosphametallacyclohex-
ene derived from aldehyde insertion is not fluxional.
Furthermore, the insertion proceeds with a high degree
of P/C diastereoselectivity, a feature which augurs well
for future applications of these metallacycles in enan-
tioselective syntheses.
q
(∆Gc ) 13.8 kcal mol-1). The activation barrier is
within the range expected for metal-assisted inversion
at phosphorus, and the averaging of the cyclopentadi-
enyl resonances further implies that the process is
occurring at both phosphorus centers.
The feature common to the family of four-, five-, and
six-membered phosphametallacycles is considerable
steric congestion. We have previously suggested that
delocalization of the phosphorus lone pair into the p
orbital of the alkenyl moiety stabilizes a planar geom-
etry at phosphorus and consequently lowers the inver-
sion barrier.12 This view is incompatible with subse-
quent molecular orbital calculations, which indicate no
such extended π-interaction. The imposition of a planar
geometry at phosphorus also places the lone pair in an
orbital which is orthogonal to the vacant 1a1 orbital of
the zirconocene fragment. Furthermore, total energy
EHMO calculations for the model Cp2ZrPH(HCCH)
indicate that a pyramidal geometry at phosphorus is
about 60 kJ /mol more favorable than a planar config-
uration (Figure 7). The LUMO is the 1a1 orbital of the
Cp2M fragment,33 while the HOMO is largely the
Ack n ow led gm en t. Support from the NSERC of
Canada is acknowledged. T.L.B. is grateful for the
award of an NSERC postgraduate scholarship.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, thermal parameters, and bond distances and
angles for 8, 12-14, 16, and 17 (53 pages). Ordering informa-
tion is given on any current masthead page.
OM9607053
(33) Lauher, J .; Hoffmann, R. J . Am. Chem. Soc. 1976, 98, 1729.