Phosphorus-bridged ansa-metallocene complexes of titanium, zirconium, and hafnium: The syntheses and structures of [PhP(C5Me4)2]MX2 and [Ph(E)P(C5Me4)2]MX2 (E = O, S, Se) derivatives

Article abstract of DOI:10.1021/om9807396

A series of phosphorus-bridged ansa-metallocene complexes of titanium, zirconium, and hafnium, [PhP(C₅Me₄)₂]MX₂ and [Ph(E)P(C₅Me₄)₂]MX₂ (X = Cl, Me, CO, (Se₃)_0.5, (Te₃)_0.5; E = O, S, Se), has been synthesized. Structural characterization by X-ray diffraction indicates that, in comparison to their non-ansa counterparts (C₅Me₅)₂MX₂, the cyclopentadienyl groups in phosphorus-bridged complexes are displaced from symmetric η⁵-coordination toward η³-coordination. Such η³,η³-coordination creates more electrophilic metal centers than those in their permethylcyclopentadienyl counterparts, as judged by the v(CO) stretching frequencies of the zirconium dicarbonyl complexes Cp*₂Zr(CO)₂ (1946 and 1853 cm^-1) and [PhP(C₅Me₄)₂]Zr(CO)₂ (1959 and 1874 cm^-1).

Full text of DOI:10.1021/om9807396

6
Organometallics 1999, 18, 6-9
P h osp h or u s-Br id ged a n sa -Meta llocen e Com p lexes of
Tita n iu m , Zir con iu m , a n d Ha fn iu m : Th e Syn th eses a n d
Str u ctu r es of [P h P (C5Me4)2]MX2 a n d
[P h (E)P (C5Me4)2]MX2 (E ) O, S, Se) Der iva tives
J un Ho Shin, Tony Hascall, and Gerard Parkin*
Department of Chemistry, Columbia University, New York, New York 10027
Received September 1, 1998
Summary: A series of phosphorus-bridged ansa-metal-
locene complexes of titanium, zirconium, and hafnium,
[PhP(C5Me4)2]MX2 and [Ph(E)P(C5Me4)2]MX2 (X ) Cl,
Me, CO, (Se3)0.5, (Te3)0.5; E ) O, S, Se), has been
synthesized. Structural characterization by X-ray dif-
fraction indicates that, in comparison to their non-ansa
counterparts (C5Me5)2MX2, the cyclopentadienyl groups
in phosphorus-bridged complexes are displaced from
symmetric η5-coordination toward η3-coordination. Such
η3,η3-coordination creates more electrophilic metal cen-
ters than those in their permethylcyclopentadienyl coun-
terparts, as judged by the ν(CO) stretching frequencies
of the zirconium dicarbonyl complexes Cp*2Zr(CO)2
(1946 and 1853 cm-1) and [PhP(C5Me4)2]Zr(CO)2 (1959
and 1874 cm-1).
Our present approach to investigating the ansa-effect
is concerned specifically with heavily substituted, per-
methylated, ansa-metallocene derivatives of the type
[A(C5Me4)2]MXn. The principal reason for such a choice
is that permethylation typically stabilizes metal centers
with reactive functionalities, as judged by the isolation
of complexes that have no counterparts in the corre-
sponding unsubstituted cyclopentadienyl system.5
A
detailed comparison of closely related complexes
[A(C5Me4)2]MXn which differ in the nature of the ansa
bridge should, therefore, allow the features responsible
for the various ansa-effects to be ascertained. In this
regard, a variety of single-element bridges, including
B,6 Ge,7-10 Sn,9,11 P,12-15 As,14g,16 and S,17 have been
incorporated into ansa ligands, although they have
found much less application than their more ubiquitous
carbon and silicon analogues.2 Since phosphorus has a
ansa-Metallocenes [ACpR2]MXn,1 and in particular
zirconocene derivatives, have recently attracted consid-
erable attention. In large part, this interest derives from
the use of such complexes as catalyst precursors for ole-
fin polymerization.2 We are presently interested in
delineating the factors that are responsible for the ansa
bridge modifying the chemistry of a particular metal
center, i.e., the “ansa-effect”.3 For example, we have re-
cently reported that the [Me2Si] ansa bridge in [Me2Si-
(C5Me4)2]ZrX2 derivatives creates more electrophilic
metal centers than those in Cp*2ZrX2 counterparts.4 In
this paper, we report the syntheses and structural
characterization of related phosphorus-bridged metal-
locene complexes of titanium, zirconium, and hafnium.
(5) For reviews of the application of heavily substituted cyclopen-
tadienyl ligands, see: (a) J aniak, C.; Schumann, H. Adv. Organomet.
Chem. 1991, 33, 291-393. (b) Okuda, J . Topics Curr. Chem. 1991, 160,
97-145.
(6) (a) Rufanov, K. A.; Kotov, V. V.; Kazennova, N. B.; Lemenovskii,
D. A.; Avtomonov, E. V.; Lorberth, J . J . Organomet. Chem. 1996, 525,
287-289. (b) Stelck, D. S.; Shapiro, P. J .; Basickes, N.; Rheingold, A.
L. Organometallics 1997, 16, 4546-4550. (c) Rufanov, K.; Avtomonov,
E.; Kazennova, N.; Kotov, V.; Khvorost, A.; Lemenovskii, D.; Lorbeth,
J . J . Organomet. Chem. 1997, 536-537, 361-373.
(7) Ko¨pf, H.; Klouras, N. Z. Naturforsch. 1983, 36B, 321-325.
(8) Chen, Y.-X.; Rausch, M. D.; Chien, J . C. W. Organometallics
1994, 13, 748-749.
(9) Schumann, H.; Esser, L.; Loebel, J .; Dietrich, A.; van der Helm,
D.; J i, X. Organometallics 1991, 10, 2585-2592.
(10) Ko¨pf, H.; Kahl, W. J . Organomet. Chem. 1974, 64, C37-C40.
(11) Herrmann, W. A.; Morawietz, M. J . A.; Herrmann, H.-F.; Ku¨ber,
F. J . Organomet. Chem. 1996, 509, 115-117.
(1) The term ansa (meaning bent handle, attached at both ends)
was first introduced with respect to metallocene chemistry by Brintz-
inger. See: Smith, J . A.; von Seyerl, J .; Huttner, G.; Brintzinger, H.
H. J . Organomet. Chem. 1979, 173, 175-185.
(12) For titanocene derivatives, see: Ko¨pf, H.; Klouras, N. Monatsh.
Chem. 1983, 114, 243-247.
(2) (a) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170.
(b) Grubbs, R. H.; Coates, G. W. Acc. Chem. Res. 1996, 29, 85-93. (c)
Mo¨hring, P. C.; Coville, N. J . J . Organomet. Chem. 1994, 479, 1-29.
(d) Kaminsky, W.; Arndt, M. Adv. Polym. Sci. 1997, 127, 143-187. (e)
Kaminsky, W. J . Chem. Soc., Dalton Trans. 1998, 1413-1418. (f)
Olabisi, O.; Atiqullah, M.; Kaminsky, W. J . M. S.-Rev. Macromol.
Chem. Phys. 1997, C37, 519-554. (g) Green, J . C. Chem. Soc. Rev.
1998, 27, 263-271. (h) Ivchenko P. V., Nifantev I. E. Z. Org. Khim.
1998, 34, 9-38.
(13) For zirconocene derivatives, see: (a) Anderson, G. K.; Lin, M.
Organometallics 1988, 7, 2285-2288. (b) Anderson, G. K.; Lin, M.
Inorg. Chim. Acta 1988, 142, 7-8. (c) Schaverien, C. J .; Ernst, R.;
Terlouw, W.; Schut, P.; Sudmeijer, O.; Budzelaar, P. H. M. J . Mol.
Catal. A-Chem. 1998, 128, 245-256. (d) Leyser, N.; Schmidt, K.;
Brintzinger, H.-H. Organometallics 1998, 17, 2155-2161.
(14) For studies on phosphorus-bridged ferrocene derivatives, see:
(a) Stoeckli-Evans, H.; Osborne, A. G.; Whiteley, R. H. J . Organomet.
Chem. 1980, 194, 91-101. (b) Honeyman, C. H.; Foucher, D. A.;
Dahmen, F. Y.; Rulkens, R.; Lough, A. J .; Manners, I. Organometallics
1995, 14, 5503-5512. (c) Butler, I. R.; Cullen, W. R.; Einstein, F. W.
B.; Rettig, S. J .; Willis, A. J . Organometallics 1983, 2, 128-135. (d)
Mizuta, T.; Yamasaki, T.; Nakazawa, H.; Miyoshi, K. Organometallics
1996, 15, 1093-1100. (e) Butler, I. R.; Cullen, W. R.; Rettig, S. J .
Organometallics 1987, 6, 872-880. (f) Houlton, A.; Roberts, R. M. G.;
Silver, J .; Drew, M. G. B. J . Chem. Soc., Dalton Trans. 1990, 1543-
1547. (g) Seyferth, D.; Withers, H. P., J r. Organometallics 1982, 1,
1275-1282
(3) Despite numerous studies on ansa-metallocene complexes, rela-
tively little attention has been given to delineating the ansa-effect in
well-defined systems. See for example: (a) Wochner, F.; Brintzinger,
H. H. J . Organomet. Chem. 1986, 309, 65-75. (b) Smith, J . A.;
Brintzinger, H. H. J . Organomet. Chem. 1981, 218, 159-167. (c) Dorer,
B.; Diebold, J .; Weyand, O.; Brintzinger, H. H. J . Organomet. Chem.
1992, 427, 245-255. (d) Chernega, A.; Cook, J .; Green, M. L. H.;
Labella, L.; Simpson, S. J .; Souter, J .; Stephens, A. H. H. J . Chem.
Soc., Dalton Trans. 1997, 3225-3243, and references therein. (e)
Fendrick, C. M.; Schertz, L. D.; Day, V. W.; Marks, T. J . Organome-
tallics 1988, 7, 1828-1838, and references therein.
(15) Wong, W.-K.; Chow, F. L.; Chen, H.; Au-Yeung, B. W.; Wang,
R.-J .; Mak, T. C. W. Polyhedron 1990, 9, 2901-2909.
(16) Klouras, N. Z. Naturforsch. 1991, 46B, 647-649.
(17) Rufanov, K. A.; Churakov, A. V.; Kazennova, N. B.; Lemen-
ovskii, D. A. J . Organomet. Chem. 1994, 481, C1-C3.
(4) Lee, H.; Desrosiers, P. J .; Guzei, I.; Rheingold, A. L.; Parkin, G.
J . Am. Chem. Soc. 1998, 120, 3255-3256.
10.1021/om9807396 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 12/12/1998

Communications
Organometallics, Vol. 18, No. 1, 1999
7
Sch em e 1
similar covalent radius to that of silicon (1.10 Å ver-
sus 1.17 Å),18 we are especially interested in developing
the chemistry of phosphorus-bridged analogues [RP-
(C5Me4)2]MX2 for comparison with the [Me2Si(C5Me4)2]-
ZrX2 system described above.
lurium does not functionalize the phosphorus atom but
reacts only at the Zr-C bond to give [PhP(C5Me4)2]Zr-
(η2-Te3) (Scheme 1).
The molecular structures of [PhP(C5Me4)2]MCl2 (M )
Ti, Zr, Hf), [MeP(C5Me4)2]ZrCl2, [PhP(C5Me4)2]MMe2 (M
) Ti, Hf), [PhP(C5Me4)2]Zr(CO)2, [Ph(E)P(C5Me4)2]ZrCl2
(E ) S, Se), [Ph(Se)P(C5Me4)2]Zr(η2-Se3), and [PhP-
(C5Me4)2]Zr(η2-Te3) have been determined by X-ray
diffraction,23 as illustrated for [PhP(C5Me4)2]ZrCl2 and
[Ph(S)P(C5Me4)2]ZrCl2 in Figures 1 and 2. Of most
interest are the geometric and electronic consequences
of incorporating different ansa bridges.24 In this regard,
the data listed in Table 1 demonstrate that the coordi-
nation of the cyclopentadienyl groups in [RP(C5Me4)2]-
MCl2 is similar to those in the corresponding [Me2Si-
In this regard, phosphorus-bridged ansa-metallocene
complexes of titanium, zirconium, and hafnium, [PhP-
(C5Me4)2]MCl2 (M ) Ti, Zr, Hf), are readily obtained via
15
treatment of [PhP(C5Me4)2]Li2 with the appropriate
metal chloride (Scheme 1).19,20 The dichloride complexes
[PhP(C5Me4)2]MCl2 are useful precursors to other met-
allocene derivatives, including the dimethyl [PhP-
(C5Me4)2]MMe2 (M ) Ti, Zr, Hf) and dicarbonyl [PhP-
(C5Me4)2]Zr(CO)2 complexes, as illustrated in Scheme
1. Most interestingly, the [PhP(C5Me4)2] ligand in [PhP-
(C5Me4)2]ZrCl2 may be readily elaborated into a new
series of ansa ligands bearing four-coordinate phospho-
rus, namely, [Ph(E)P(C5Me4)2]ZrCl2 (E ) O, S, Se), by
reaction with oxygen, sulfur, and selenium.21 Tellurium,
however, is unreactive toward [PhP(C5Me4)2]ZrCl2, pre-
sumably a reflection of the lower PdTe bond energy.22
Furthermore, whereas elemental selenium reacts with
[PhP(C5Me4)2]ZrMe2 to give [Ph(Se)P(C5Me4)2]Zr(η2-
Se3), the corresponding reaction with elemental tel-
(22) For example, the PdE bond energies in Bun3PE decrease rapidly
as the chalcogen becomes heavier: S, 96 kcal mol-1; Se, 75 kcal mol-1
;
Te, 52 kcal mol-1. See: Capps, K. B.; Wixmerten, B.; Bauer, A.; Hoff,
C. D. Inorg. Chem. 1998, 37, 2861-2864.
(23) [PhP(C5Me4)2]TiCl2 is orthorhombic, P212121 (No. 19), a
)
11.2280(5) Å, b ) 13.6608(6) Å, c ) 14.4726(7) Å, V ) 2219.9(2) Å3, Z
) 4. [PhP(C5Me4)2]ZrCl2 is orthorhombic, P212121 (No. 19), a ) 11.238-
(2) Å, b ) 13.833(2) Å, c ) 14.843(2) Å, V ) 2307.4(5) Å3, Z ) 4. [PhP-
(C5Me4)2]HfCl2 is orthorhombic, P212121 (No. 19), a ) 11.2717(5) Å, b
) 13.7817(6) Å, c ) 14.8385(6) Å, V ) 2305.1(2) Å3, Z ) 4. [MeP-
(C5Me4)2]ZrCl2 is monoclinic, C2/c (No. 15), a ) 15.3396(8) Å, b )
11.8005(6) Å, c ) 11.1134(6) Å, â ) 105.106(1)°, V ) 1942.2(2) Å3, Z )
4. [PhP(C5Me4)2]TiMe2 is monoclinic, P21/c (No. 14), a ) 8.6383(5) Å,
b ) 9.2278(5) Å, c ) 29.194(2) Å, â ) 93.588(1)°, V ) 2322.6(2) Å3, Z
) 4. [PhP(C5Me4)2]HfMe2 is monoclinic, P21/c (No. 14), a ) 8.6417(4)
Å, b ) 9.2480(5) Å, c ) 29.702(2) Å, â ) 93.781(1)°, V ) 2368.6(2) Å3,
Z ) 4. [PhP(C5Me4)2]Zr(CO)2 is monoclinic, P21/n (No. 14), a ) 14.0286-
(7) Å, b ) 10.6747(5) Å, c ) 16.3021(8) Å, â ) 110.625(1)°, V ) 2284.8-
(18) Pauling, L. The Nature of The Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; p 224.
(19) Likewise, the methyl-phosphine derivative [MeP(C5Me4)2]ZrCl2
may be prepared by an analogous procedure from [MeP(C5Me4)2]Li2.
(20) Representative examples of the syntheses follow. (a) [PhP-
(C5Me4)2]ZrCl2: benzene (200 mL) was added to a mixture of ZrCl4
(5.0 g, 21.5 mmol) and [PhP(C5Me4)2]Li2 (8.6 g, 23.7 mmol) at 0 °C,
after which the mixture was allowed to warm to room temperature
while stirring. The mixture was then heated at 80 °C for 3 days and
subsequently filtered. The residue was further extracted into benzene
(150 mL) and combined with the reaction filtrate. The volatile
components were removed in vacuo, and the residue obtained was
washed with pentane (2 × 20 mL) and dried in vacuo to give [PhP-
(C5Me4)2]ZrCl2 as a pale yellow solid (8.6 g, 79%). (b) [Ph(O)P(C5Me4)2]-
ZrCl2: a solution of [PhP(C5Me4)2]ZrCl2 (570 mg, 1.12 mmol) in toluene
(20 mL) was treated with oxygen at room temperature for 1 day. After
this period, the volatile components were removed in vacuo, and the
residue was washed with pentane and dried in vacuo to give [Ph(O)-
P(C5Me4)2]ZrCl2 as a white solid (520 mg, 88%).
(2) Å3, Z ) 4. [Ph(S)P(C5Me4)2]ZrCl2 is triclinic, P1h (No. 2), a
)
10.1388(5) Å, b ) 11.1709(5) Å, c 22.326(1) Å, R ) 76.203(1)°, â )
81.759(1)°, γ ) 89.880(1)°, V ) 2429.0(2) Å3, Z ) 4. [Ph(Se)P(C5Me4)2]-
ZrCl2 is triclinic, P1h (No. 2), a ) 10.0792(5) Å, b ) 11.3485(6) Å, c )
22.345(1) Å, R ) 103.990(1)°, â ) 98.018(1)°, γ ) 90.026(1)°, V )
2454.3(2) Å3, Z ) 4. [Ph(Se)P(C5Me4)2]Zr(η2-Se3) is triclinic, P1h (No.
2), a ) 9.4988(5) Å, b ) 10.0998(5) Å, c ) 13.8780(7) Å, R ) 84.413-
(1)°, â ) 83.125(1)°, γ ) 73.096(1)°, V ) 1262.0(1) Å3, Z ) 2. [PhP-
(C5Me4)2]Zr(η2-Te3) is monoclinic, P21/c (No. 14), a ) 10.8377(6) Å, b
) 14.6807(8) Å, c ) 16.6853(9) Å, â ) 104.009(1)°, V ) 2575.8(2) Å3, Z
) 4.
(24) For other discussions concerned with ansa-metallocene geom-
etries, see: (a) Hortmann, K.; Brintzinger, H.-H. New. J . Chem. 1992,
16, 51-55. (b) Shaltout, R. M.; Corey, J . Y.; Rath, N. P. J . Organomet.
Chem. 1995, 503, 205-212. (c) Bajgur, C. S.; Tikkanen, W. R.; Petersen,
J . L. Inorg. Chem. 1985, 24, 2539-2546.
(21) For similar functionalization of phosphorus-bridged ferrocene
derivatives, see ref 14g.

8
Organometallics, Vol. 18, No. 1, 1999
Communications
Ta ble 1. Geom etr ica l Da ta for Cp *2MX2, [Me2Si(C5Me4)2]MX2, a n d [RP (C5Me4)2]MX2 Der iva tives
d(M-Cpcent)/Å
d(M-C)/Å
d(M-C) range/Å
R/deg
â/deg
γ/deg
a
Cp*2TiCl2
2.128
2.136
2.117
2.250
2.243
2.226
2.225
2.234
2.302
2.230
2.222
2.212
2.404-2.484
2.365-2.552
2.341-2.528
2.525-2.540
2.476-2.627
2.448-2.606
2.435-2.608
2.449-2.634
2.452-2.637
2.498-2.580
2.461-2.604
2.439-2.598
0.080
0.187
0.187
0.015
0.151
0.158
0.173
0.185
0.185
0.082
0.143
0.159
137.4
132.2
129.4
130.5
128.5
125.8
125.9
126.3
126.3
137.5
128.9
126.3
135.4
120.6
118.4
134.9
119.0
116.0
116.5
116.0
115.5
134.2
119.5
117.0
1.0
5.8
5.5
-2.2
4.8
4.9
4.7
5.2
5.4
1.7
4.7
4.7
b
c
[Me2Si(C5Me4)2]TiCl2
[PhP(C5Me4)2]TiCl2
c
Cp*2ZrCl2
[Me2Si(C5Me4)2]ZrCl2
[MeP(C5Me4)2]ZrCl2
[PhP(C5Me4)2]ZrCl2
[Ph(S)P(C5Me4)2]ZrCl2
[Ph(Se)P(C5Me4)2]ZrCl2
c
Cp*2HfCl2
c
[Me2Si(C5Me4)2]HfCl2
[PhP(C5Me4)2]HfCl2
a
b
McKenzie, T. C.; Sanner, R. D.; Bercaw, J . E. J . Organomet. Chem. 1975, 102, 457-466. Varga, V.; Hiller, J .; Gyepes, R.; Polasek,
M.; Sedmera, Thewalt, U.; Mach, K. J . Organomet. Chem. 1997, 538, 63-74. c Lee, H.; Bonnano, J .; Shin, J . H.; Hascall, T.; Parkin, G.
Unpublished results.
F igu r e 3. Definition of R, â, and γ for ansa-metallocene
geometries.
are also accompanied by a small tilting (γ) of the
cyclopentadienyl groups from the M-Cpcent vector to-
ward the ansa bridge; that is, the Cpcent-M-Cpcent angle
(R) is greater than the angle between the Cp ring
normals (â).26 This modified η3,η3-coordination geometry
F igu r e 1. Molecular structure of [PhP(C5Me4)2]ZrCl2.
creates a more electrophilic metal center, as judged by
the ν(CO) stretching frequencies of the dicarbonyl
complexes in pentane, Cp*2Zr(CO)2 (1946 and 1853
cm-1),27 [Me2Si(C5Me4)2]Zr(CO)2 (1956 and 1869 cm-1),28
and [PhP(C5Me4)2]Zr(CO)2 (1959 and 1874 cm-1). On
this basis, the phosphorus-bridged ansa ligand [PhP-
(C5Me4)2] may be regarded as engendering a more
electrophilic metal center than does the [Me2Si(C5Me4)2]
ligand.29
In the presence of methylalumoxane, [PhP(C5Me4)2]-
ZrCl2 is an active catalyst for ethylene polymerization,
with an activity that is comparable to that for [Me2Si-
(C5Me4)2]ZrCl2, but less than that for Cp*2ZrCl2.30,31
To summarize, a series of phosphorus-bridged ansa-
metallocene complexes of titanium, zirconium, and haf-
(25) It should be noted, however, that a greater disparity in bond
angle (ca. 7°) has been predicted for a related system. See ref 13c.
(26) For further comparison, the corresponding values for [Me2C-
(C5H4)2ZrCl2 are: R (116.6°), â (108.6°), and γ (4.0°). See ref 24b.
F igu r e 2. Molecular structure of [Ph(S)P(C5Me4)2]ZrCl2.
(27) Literature values in Nujol are 1942 and 1850 cm-1. See:
Manriquez, J . M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J . E. J .
Am. Chem. Soc. 1976, 98, 6733-6735.
(C5Me4)2]MCl2 derivatives. Indeed, the C-P-C bond
angles are only slightly smaller (ca. 2°) than the
(28) Values in KBr discs are 1947 and 1861 cm-1. See ref 4.
(29) For further discussion of this notion with respect to [Me2Si-
corresponding C-Si-C angles in [Me2Si(C5Me4)2]MCl2
(C5Me4)2] ligands see ref 4 and references therein.
(30) For example, the room-temperature activities (g mmol-1 atm-1
derivatives.25 By comparison to the non-ansa complexes,
min-1) for C2H4 polymerization at 1 atm carried out with ca. 0.015
however, the cyclopentadienyl groups of the [Me2Si] and
[RP] ansa-bridged complexes are displaced from sym-
metric η5-coordination toward η3-coordination. For ex-
ample, whereas the M-C bond lengths for each
Cp*2MCl2 derivative are equal to within 0.08 Å, the
corresponding M-C bond lengths vary by 0.14-0.19 Å
for each of the ansa complexes (Table 1). Such changes
mmol catalyst and 6.9 mmol methylalumoxane in toluene (30 mL)
are: Cp*2ZrCl2 [5.3(4)], [Me2Si(C5Me4)2]ZrCl2 [1.9(1)], and [PhP-
(C5Me4)2]ZrCl2 [1.7(1)]. The chalcogenido derivatives exhibit similar
activities: [Ph(O)P(C5Me4)2]ZrCl2 [1.8(1)], [Ph(S)P(C5Me4)2]ZrCl2 [1.7(3)],
[Ph(Se)P(C5Me4)2]ZrCl2 [1.9(2)].
(31) It should be noted that Schaverien has also reported that the
phosphorus-bridged [PhP(C5H4)(fluorenyl)]ZrCl2 and [PhP(indenyl)2]-
ZrCl2 derivatives are active catalysts for propylene polymerization. See
ref 13c.

Communications
Organometallics, Vol. 18, No. 1, 1999
9
nium, namely, [PhP(C5Me4)2]MX2 (R ) Me, Ph) and
[Ph(E)P(C5Me4)2]MX2 (E ) O, S, Se), have been syn-
thesized. By comparison with Cp*2Zr(CO)2, the phos-
phorus-bridged ansa-metallocene derivative [PhP-
(C5Me4)2]Zr(CO)2 possesses a more electrophilic zirco-
nium center.
Schaverien for a preprint of ref 13c, and David Churchill
for valuable technical assistance. G.P. is the recipient
of a Presidential Faculty Fellowship Award (1992-
1997).
Su p p or tin g In for m a tion Ava ila ble: Experimental and
crystallographic information (107 pages). Ordering information
is given on any current masthead page.
Ack n ow led gm en t. We thank the U.S. Department
of Energy, Office of Basic Energy Sciences (DE-FG02-
93ER14339), for support of this research, Dr. Colin
OM9807396