Synthesis, structural characterization, and catalytic properties of group 4 metal complexes incorporating a phosphorus-bridged indenyl-carboranyl constrained-geometry ligand

Article abstract of DOI:10.1021/om050079m

Interaction of ⁱPr₂NP(C₉H ₇)(C₂B₁₀H₁₁) with 1 equiv of M(NR₂)₄ in toluene gave constrained-geometry group 4 metal amides [η⁵:σ-ⁱPr₂NP(C ₉H₆)(C₂B₁₀H₁₀)]M(NMe ₂)₂ (R = Me, M = Ti (1), Zr (2), Hf (3); R = Et, M = Hf (4)) in good yields. Compound 2 reacted with 3 equiv of PhNCO to produce the tri-insertion product [η⁵:σ-ⁱPr ₂NP(C₉H₆)(C₂B₁₀H ₁₀)]Zr[η²-OC(NMe₂)NPh] [η ²-OC(NMe₂)N(Ph)C=(NPh)O] (5). No further insertion reaction occurred with another equivalent of PhNCO. Instead, the trimer (PhNCO)₃ was isolated. Compound 2 reacted with 2 equiv of n-BuLi in toluene to afford, after recrystallization from DME/toluene, the dilithium salt [Li(DME)₃] [η⁵:σ-ⁱPr ₂NP(C₉H₆)(C₂B₁₀H ₁₀)Li(DME)] (6). An equimolar reaction of 2 with acetylacetone resulted in the formation of Zr(acac)4. 2 exhibited an ethylene polymerization activity of 3.7 × 10³ g PE mol^-1 atm^-1 h^-1 upon activation with MMAO. Furthermore, 2 was also able to efficiently initiate the polymerization of ε-caprolactone to give polymers of high molecular weights (M_n > 40 000) and low polydispersities (M_wM_n < 1.4) through the action of the nucleophilic amido-nitrogen atom, which represents the first example of the polymerization of ε-caprolactone catalyzed by group 4 metal amides.

Full text of DOI:10.1021/om050079m

3118
Organometallics 2005, 24, 3118-3124
Synthesis, Structural Characterization, and Catalytic
Properties of Group 4 Metal Complexes Incorporating a
Phosphorus-Bridged Indenyl-Carboranyl
Constrained-Geometry Ligand
Hong Wang,† Hoi-Shan Chan,† Jun Okuda,‡ and Zuowei Xie*,†
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories,
Hong Kong, China, and Institute of Inorganic Chemistry, Aachen University of Technology
(RWTH), Prof.-Pirlet-Strasse 1, 52074 Aachen, Germany
Received February 4, 2005
Interaction of iPr2NP(C9H7)(C2B10H11) with 1 equiv of M(NR2)4 in toluene gave constrained-
geometry group 4 metal amides [η5:σ-iPr2NP(C9H6)(C2B10H10)]M(NMe2)2 (R ) Me, M ) Ti
(1), Zr (2), Hf (3); R ) Et, M ) Hf (4)) in good yields. Compound 2 reacted with 3 equiv of
PhNCO to produce the tri-insertion product [η5:σ-iPr2NP(C9H6)(C2B10H10)]Zr[η2-OC(NMe2)-
NPh][η2-OC(NMe2)N(Ph)Cd(NPh)O] (5). No further insertion reaction occurred with another
equivalent of PhNCO. Instead, the trimer (PhNCO)3 was isolated. Compound 2 reacted with
2 equiv of n-BuLi in toluene to afford, after recrystallization from DME/toluene, the dilithium
salt [Li(DME)3][η5:σ-iPr2NP(C9H6)(C2B10H10)Li(DME)] (6). An equimolar reaction of 2 with
acetylacetone resulted in the formation of Zr(acac)4. 2 exhibited an ethylene polymerization
activity of 3.7 × 103 g PE mol-1 atm-1 h-1 upon activation with MMAO. Furthermore, 2 was
also able to efficiently initiate the polymerization of ꢀ-caprolactone to give polymers of high
molecular weights (Mn > 40 000) and low polydispersities (Mw/Mn < 1.4) through the action
of the nucleophilic amido-nitrogen atom, which represents the first example of the
polymerization of ꢀ-caprolactone catalyzed by group 4 metal amides.
Introduction
ages where the trivalent phosphorus possesses a lone
pair of electrons.5
Ansa-bridged group 4 metallocenes have attracted
considerable attention because of their applications as
catalyst precursors for olefin polymerizations.1 It has
been well documented that the bridging atoms and the
molecular structures are among the important factors
that greatly impact the polymerization behavior of the
catalysts.1,2 Phosphorus-bridged systems have drawn
our attention since the phosphorus atom has a covalent
radius similar to that of silicon,3 and yet they have very
different electronic characteristics. In fact, phosphorus-
bridged ligands exhibit a wide range of structural
types: (1) metallocenes bridged by four-coordinate
phosphorus moieties where the formal pentavalent
phosphorus bears one positive charge,4 and (2) metal-
locenes bridged with three-coordinate phosphorus link-
The electronic effects of the RP linkages on the
catalytic activity of metallocene catalysts are an inter-
esting subject. As judged by both νco and the E° values,
the RP bridges behave as “electron-withdrawing” units,
leading to an electrophilic metal center.2,4g For example,
complex [PhP(η5-C5Me4)2]ZrCl2 showed an activity in
ethylene polymerization very similar to that of [Me2Si-
(η5-C5Me4)2]ZrCl2.4g On the other hand, complexes [PhP-
(η5-C13H8)2]ZrCl2 (2.54 × 106 g PE mol-1 atm-1 h-1 5d
)
and [η5: σ-tBuP(tBuC5H3)(NtBu)]TiCl2 (1.0 × 105 g PE
mol-1 atm-1 h-1 5b
were reported to be less active by
)
10-20 times in ethylene polymerization than [Me2Si-
(η5-C13H8)2]ZrCl2 (5.76 × 107 g PE mol-1 atm-1 h-1)6 and
(4) (a) Shin, J. H.; Bridgewater, B. M.; Parkin, G. Organometallics
2000, 19, 5155. (b) Brady, E. D.; Hanusa, T. P.; Pink, M.; Young, V.
G., Jr. Inorg. Chem. 2000, 39, 6028. (c) Leyser, N.; Schmidt, K.;
Brintzinger, H.-H. Organometallics 1998, 17, 2155. (d) Taillefer, M.;
Inguimbert, N.; Ja¨ger, L.; Merzweiler, K.; Cristau, H.-J. Chem.
Commun. 1999, 565. (e) Harder, S.; Lutz, M. Organometallics 1997,
16, 225. (f) Peckham, T. J.; Lough, A. J.; Manners, I. Organometallics
1999, 18, 1030. (g) Shin, J. H.; Hascall, T.; Parkin, G. Organometallics
1999, 18, 6. (h) Schaverien, C. J.; Ernst, R.; Terlouw, W.; Schut, P.;
Sudmerijer, O.; Budzelaar, P. H. M. J. Mol. Catal. A: Chem. 1998, 128,
245.
(5) (a) Malefetse, T. J.; Swiegers, G. F.; Coville, N. J.; Fernandes,
M. A. Organometallics 2002, 21, 2898. (b) Kotov, V. V.; Avtomonov, E.
V.; Sundermeyer, J.; Harms, K.; Lemenovskii, D. A. Eur. J. Inorg.
Chem. 2002, 678. (c) Ebels, J.; Pietschnig, R.; Kotila, S.; Dombrowski,
A.; Niecke, E.; Nieger, M.; Schiffner, H. M. Eur. J. Inorg. Chem. 1998,
331. (d) Alt, H. G.; Jung, M. J. Organomet. Chem. 1998, 568, 127. (e)
Butchard, J. R.; Curnow, O. J.; Smail, S. J. J. Organomet. Chem. 1997,
541, 407. (f) Curnow, O. J.; Huttner, G.; Smail, S. J.; Turnbull, M. M.
J. Organomet. Chem. 1996, 524, 267. (g) Fallis, K. A.; Anderson, G.
K.; Rath, N. P. Organometallics 1992, 11, 885. (h) Anderson, G. K.;
Lin, M. Organometallics 1988, 7, 2285. (i) Anderson, G. K.; Lin, M.
Inorg. Chim. Acta 1988, 142, 7.
† The Chinese University of Hong Kong.
‡ Aachen University of Technology.
(1) (a) Jordan, R. F. Adv. Organomet. Chem. 1991, 32, 325. (b)
Marks, T. J. Acc. Chem. Res. 1992, 25, 57. (c) Mo¨hring, R. C.; Coville,
N. J. J. Organomet. Chem. 1994, 479, 1. (d) Brintzinger, H.-H.; Fisher,
D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int.
Ed. Engl. 1995, 34, 1143. (e) Grubbs, R. H.; Coates, G. W. Acc. Chem.
Res. 1996, 29, 85. (f) Kaminsky, W. Macromol. Chem. Phys. 1996, 197,
3907. (g) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255. (h)
Kaminsky, W.; Arndt, M. Adv. Polym. Sci. 1997, 127, 144. (i) Britovsek,
G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38,
428. (j) Green, J. C. Chem. Soc. Rev. 1998, 27, 263. (k) Suzuki, N.;
Masubuchi, Y.; Yamaguchi, Y.; Kase, T.; Miyamoto, T. K.; Horiuchi,
A.; Mise, T. Macromolecules 2000, 33, 754.
(2) (a) Gladysz, J. A., Guest Editor, Issue 4, Special Issue for
Frontiers in Metal-Catalyzed Polymerization. Chem. Rev. 2000, 100,
1167. (b) Zachmanoglou, C. E.; Docrat, A.; Bridgewater, B. M.; Parkin,
G.; Brandow, C. G.; Bercaw, J. E.; Jardine, C. N.; Lyall. M.; Green, J.
C.; Keister, J. B. J. Am. Chem. Soc. 2002, 124, 9525.
(3) Pauling, L. The Nature of The Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; p 224.
10.1021/om050079m CCC: $30.25 © 2005 American Chemical Society
Publication on Web 05/18/2005

Phosphorus-Bridged Indenyl-Carboranyl Ligand
Organometallics, Vol. 24, No. 13, 2005 3119
[η5: σ-Me2Si(C5Me4)(NtBu)]TiCl2 (9.5 × 105 g PE mol-1
atm-1 h-1),7 respectively, suggesting that the RP moi-
eties function as “electron-donating” groups. It is also
noteworthy that [η5: σ-tBuP(tBuC5H3)(NtBu)]TiCl2 rep-
resents a rare example of a P-bridged constrained-
geometry catalyst.5b
Ti(NMe2)4 (225 mg, 1.0 mmol) at room temperature. The
reaction mixture was heated to 60 °C and stirred overnight.
The resulting dark red solution was filtered and concentrated
to about 5 mL. 1 was isolated as dark red crystals after this
solution stood at room temperature for 3 days (283 mg, 54%).
1H NMR (pyridine-d5): δ 8.23 (d, J ) 8.4 Hz, 1H, indenyl),
7.24 (t, J ) 7.2 Hz, 1H, indenyl), 7.15 (d, J ) 3.0 Hz, 1H,
indenyl), 6.92 (t, J ) 7.2 Hz, 1H, indenyl), 6.46 (d, J ) 3.0 Hz,
1H, indenyl), 6.14 (d, J ) 8.4 Hz, 1H, indenyl), 4.45 (m, 2H,
NCH(CH3)2), 3.02 (s, 6H, N(CH3)2), 2.54 (s, 6H, N(CH3)2), 1.39
(d, J ) 6.3 Hz, 6H, NCH(CH3)2), 1.09 (br, 3H, NCH(CH3)2),
0.76 (br, 3H, NCH(CH3)2). 13C NMR (pyridine-d5): δ 131.9 (d,
2JPC ) 43.0 Hz), 130.5 (d, 1JPC ) 55.0 Hz), 128.2, 127.6, 126.7,
125.5, 123.1, 122.7, 109.1 (C9H6), 99.8, 96.2 (d, 1JPC ) 64.0 Hz)
(cage C), 53.0 (br), 47.0 (br) (NCH(CH3)2), 54.0, 46.7 (N(CH3)2),
31.4, 27.2, 24.3, 23.9 (NCH(CH3)2). 11B NMR (pyridine-d5): δ
-1.1 (2B), -3.1 (1B), -4.8 (2B), -7.6 (2B), -9.7 (3B). 31P NMR
(pyridine-d5): δ 36.0. IR (KBr, cm-1): νBH 2562 (vs). Anal.
Calcd for C21H42B10N3PTi: C, 48.18; H, 8.09; N, 8.02. Found:
C, 48.49; H, 8.38; N, 7.79.
In view of the impact of the interesting electronic
effects of the RP linkages on the catalytic performance
of group 4 metal complexes and our earlier work on [η5:
σ-Me2A(C9H6)(C2B10H10)]M(NMe2)2 (M ) Ti, Zr, Hf;
A ) C, Si)8 and [η5: σ-iPr2NB(C9H6)(C2B10H10)]M-
(NMe2)2,9 we have extended our research on group
4 metal chemistry to include a newly developed iPr2NP-
bridged constrained-geometry carboranyl ligand sys-
tem,10 [iPr2NP(C9H6)(C2B10H10)]2-, in the hope that a
series of closely related complexes, [A(C9H6)(C2B10H10)]-
M(NMe2)2, which differ in the nature of the ansa
bridges, will allow the features responsible for the
various ansa effects (linkage effects) to be ascertained.
We report herein the synthesis and structural charac-
terization of group 4 metal complexes containing the
[iPr2NP(C9H6)(C2B10H10)]2- ligand as well as their cata-
lytic behavior in ethylene and ꢀ-caprolactone polymer-
izations.
Preparation of [η5:σ-iPr2NP(C9H6)(C2B10H10)]Zr(NMe2)2
(2). A toluene (10 mL) solution of iPr2NP(C9H7)(C2B10H11) (389
mg, 1.0 mmol) was added to a toluene (10 mL) solution of Zr-
(NMe2)4 (267 mg, 1.0 mmol) with stirring at room temperature,
followed by the identical procedure reported for 1 to give 2 as
1
pale yellow crystals (385 mg, 68%). H NMR (pyridine-d5): δ
8.22 (d, J ) 8.4 Hz, 1H, indenyl), 7.25 (t, J ) 8.1 Hz, 2H,
indenyl), 7.18 (d, J ) 3.6 Hz, 1H, indenyl), 6.91 (t, J ) 8.1 Hz,
1H, indenyl), 6.46 (d, J ) 3.6 Hz, 1H, indenyl), 6.15 (d, J )
8.4 Hz, 1H, indenyl), 4.46 (m, 2H, NCH(CH3)2), 3.02 (s, 6H,
N(CH3)2), 2.53 (s, 6H, N(CH3)2), 1.39 (d, J ) 6.3 Hz, 6H, NCH-
(CH3)2), 1.09 (br, 3H, NCH(CH3)2), 0.68 (br, 3H, NCH(CH3)2).
Experimental Section
General Procedures. All experiments were performed
under an atmosphere of dry dinitrogen with the rigid exclusion
of air and moisture using standard Schlenk or cannula
techniques, or in a glovebox. All organic solvents were freshly
distilled from sodium benzophenone ketyl immediately prior
to use. M(NR2)411 (M ) Ti, Zr, Hf; R ) Me, Et) and iPr2(C9H7)-
(C2B10H11)10 were prepared according to literature methods.
All other chemicals were purchased from either Aldrich or
Acros Chemical Co. and used as received unless otherwise
noted. Infrared spectra were obtained from KBr pellets
prepared in the glovebox on a Perkin-Elmer 1600 Fourier
transform spectrometer. Molecular weights of polyesters were
estimated by gel permeation chromatography (GPC) using a
Waters 1515 instrument equipped with microstyragel columns
(HR1, HR2, HR3) and a RI detector at 30 °C. Polystyrene
standards purchased from American Polymer Standards were
used as a calibration standard, and THF was used as the
eluant at a flow rate of 1.0 mL/min. 1H and 13C NMR spectra
were recorded on a Bruker DPX 300 spectrometer at 300.13
and 75.47 MHz, respectively. 11B and 31P NMR spectra were
recorded on a Varian Inova 400 spectrometer at 128.32 and
161.91 MHz, respectively. All chemical shifts are reported in
δ units with reference to the residual protons of the deuterated
solvents for proton and carbon chemical shifts, to external BF3‚
OEt2 (0.00 ppm) for boron chemical shifts, and to external 85%
H3PO4 (0.00 ppm) for phosphorus chemical shifts. Elemental
analyses were performed by MEDAC Ltd., U.K.
2
13C NMR (pyridine-d5): δ 131.0 (d, JPC ) 31.4 Hz), 128.3 (d,
1JPC ) 56.0 Hz), 127.8, 125.1, 124.7, 123.9, 123.4, 111.8, 105.6
1
(C9H6), 98.4, 86.9 (d, JPC ) 41.0 Hz) (cage C), 56.2 (br), 50.6
(br) (NCH(CH3)2), 45.0, 44.7 (N(CH3)2), 31.0, 25.1, 22.1, 21.7
(NCH(CH3)2). 11B NMR (pyridine-d5): δ -1.8 (2B), -3.3 (1B),
-5.3 (2B), -8.1 (3B), -10.3 (2B). 31P NMR (pyridine-d5): δ
34.5. IR (KBr, cm-1): νBH 2571 (vs). Anal. Calcd for C21H42B10N3-
PZr: C, 44.49; H, 7.47; N, 7.41. Found: C, 44.56; H, 7.98; N,
7.01.
Preparation of [η5:σ-iPr2NP(C9H6)(C2B10H10)]Hf(NMe2)2
(3). This compound was prepared as pale yellow crystals from
the reaction of iPr2NP(C9H7)(C2B10H11) (389 mg, 1.0 mmol) with
Hf(NMe2)4 (354 mg, 1.0 mmol) in toluene (20 mL) using the
1
same procedure reported for 1: yield 392 mg (60%). H NMR
(pyridine-d5): δ 8.20 (d, J ) 8.1 Hz, 1H, indenyl), 7.54 (d, J )
3.0 Hz, 1H, indenyl), 7.30 (t, J ) 7.5 Hz, 1H, indenyl), 6.95 (t,
J ) 7.5 Hz, 1H, indenyl), 6.52 (d, J ) 3.0 Hz, 1H, indenyl),
6.29 (d, J ) 8.1 Hz, 1H, indenyl), 4.74 (m, 2H, NCH(CH3)2),
3.04 (s, 6H, N(CH3)2), 2.53 (s, 6H, N(CH3)2), 1.38 (d, J ) 6.3
Hz, 6H, NCH(CH3)2), 1.06 (br, 3H, NCH(CH3)2), 0.77 (br, 3H,
2
NCH(CH3)2). 13C NMR (pyridine-d5): δ 130.9 (d, JPC ) 41.9
Hz), 128.7 (d, 1JPC ) 55.9 Hz), 127.4, 125.1, 124.3, 123.4, 123.3,
1
110.8, 106.4 (C9H6), 104.7, 87.7 (d, JPC ) 56.4 Hz) (cage C),
56.3 (br), 50.7 (br) (NCH(CH3)2), 44.8, 44.3 (N(CH3)2), 31.0,
25.1, 22.1, 20.6 (NCH(CH3)2). 11B NMR (pyridine-d5): δ -1.8
(2B), -3.7 (1B), -5.5 (2B), -8.6 (3B), -12.8 (2B). 31P NMR
(pyridine-d5): δ 34.3. IR (KBr, cm-1): νBH 2566 (s). Anal. Calcd
for C21H42B10HfN3P: C, 38.56; H, 6.47; N, 6.42. Found: C,
38.93; H, 6.46; N, 6.36.
i
5
Preparation of [η :σ- Pr2NP(C9H6)(C2B10H10)]Ti(NMe2)2
(1). A toluene (10 mL) solution of iPr2NP(C9H7)(C2B10H11) (389
mg, 1.0 mmol) was added to a toluene (10 mL) solution of
(6) (a) Alt, H. G.; Ko¨ppl, A. Chem. Rev. 2000, 100, 1205. (b) Patsidis,
K.; Alt, H. G.; Palackal, S. J.; Hawley, G. R. Russ. Chem. Bull. 1996,
45, 2216.
(7) Schmidt, G. F.; Timmers, F. J.; Knight, G. W.; Lai, S.-Y.; Nickias,
P. N.; Rosen, R. K.; Stevens, J. C.; Wilson, D. R. (Dow Chemical
Company). Eur. Patent Appl. EP 0416815, March 13, 1991.
(8) Wang, H.; Wang, Y.; Li, H.-W.; Xie, Z. Organometallics 2001,
20, 5110.
(9) Zi, G.; Li, H.-W.; Xie, Z. Organometallics 2002, 21, 3850.
(10) Wang, H.; Wang, H. P.; Li, H.-W.; Xie, Z. Organometallics 2004,
23, 875.
(11) (a) Diamond, G. M.; Jordan, R. F.; Petersen, J. L. J. Am. Chem.
Soc. 1996, 118, 8024. (b) Diamond, G. M.; Jordan, R. F. Organome-
tallics 1996, 15, 4030.
Preparation of [η5:σ-iPr2NP(C9H6)(C2B10H10)]Hf(NEt2)2
(4). This compound was prepared as pale yellow crystals from
the reaction of iPr2NP(C9H7)(C2B10H11) (389 mg, 1.0 mmol) with
Hf(NEt2)4 (467 mg, 1.0 mmol) in toluene (20 mL) using the
identical procedure reported for 1: yield 340 mg (48%). 1H
NMR (pyridine-d5): δ 8.28 (d, J ) 7.8 Hz, 1H, indenyl), 7.52
(d, J ) 3.3 Hz, 1H, indenyl), 7.42 (m, 2H, indenyl), 7.24 (d, J
) 7.8 Hz, 1H, indenyl), 6.99 (d, J ) 3.3 Hz, 1H, indenyl), 4.74
(m, 1H, NCH(CH3)2), 3.28 (m, 1H, NCH(CH3)2), 3.59 (q, J )
6.9 Hz, 4H, N(CH2CH3)2), 2.80 (q, J ) 6.9 Hz, 4H, N(CH2-

3120 Organometallics, Vol. 24, No. 13, 2005
Table 1. Crystal Data and Summary of Data Collection and Refinement for 1-6
Wang et al.
1
2
3
4
5‚CH3CN
6
formula
C
21H42B10N3P-
C21H42B10N3P-
Zr
C21H42B10Hf N3P C25H50B10Hf-
N3P
C44H60B10N7O3-
PZr
C33H70B10Li2-
Ti
NO8P
cryst size (mm)
0.40 × 0.30 ×
0.30 × 0.20 ×
0.40 × 0.30 ×
0.80 × 0.60 ×
0.45 × 0.30 ×
0.80 × 0.50 ×
0.20
0.10
566.9
0.20
0.10
710.2
0.15
965.3
0.30
fw
523.6
654.1
761.9
cryst syst
space group
a, Å
triclinic
P(-1)
orthorhombic
P212121
9.088(2)
15.854(3)
20.741(4)
90
orthorhombic
P212121
9.083(3)
15.803(3)
20.704(4)
90
monclinic
P21/n
9.272(1)
17.799(1)
21.339(1)
90
101.15(1)
90
3455.1(3)
4
1.365
triclinic
P(-1)
triclinic
P(-1)
11.144(2)
15.657(3)
17.844(4)
106.77(3)
91.85(3)
98.91(3)
2935.3(10)
4
11.033(1)
12.101(1)
20.085(2)
102.19(1)
91.26(1)
102.50(1)
2552.7(3)
2
10.896(2)
14.752(2)
16.354(2)
77.52(1)
78.82(1)
69.93(1)
2390.2(4)
2
b, Å
c, Å
R, deg
â, deg
90
90
γ, deg
90
90
V, Å3
2988.4(10)
4
2971.8(10)
4
Z
Dcalcd, Mg/m3
radiation (λ), Å
2θ range, deg
µ, mm-1
F(000)
1.185
1.260
1.462
1.256
1.059
Mo KR (0.71073) Mo KR (0.71073) Mo KR (0.71073)
Mo KR (0.71073) Mo KR (0.71073) Mo KR (0.71073)
2.8 to 51.5
0.363
1104
5.0 to 50.1
0.438
1176
2919
325
4.0 to 50.0
3.581
1304
2965
325
3.0 to 56.0
3.086
1432
8304
361
2.1 to 50.0
0.292
1004
8961
595
3.0 to 56.1
0.099
820
11361
496
no. of obsd reflns 9060
no. of params
refnd
649
goodness of fit
R1
wR2
1.086
0.050
0.151
1.013
0.048
0.138
1.022
0.046
0.124
0.960
0.028
0.078
0.933
0.062
0.158
0.741
0.067
0.189
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1-4a
1b
2
3
4
(M)
(Ti)
(Zr)
(Hf)
(Hf)
av M-C(ring)
2.403(3) [2.411(3)]
2.208(3) [2.226(3)]
1.894(3) [1.889(3)]
97.3 (1) [97.7(1)]
103.9(2) [103.0(1)]
110.0 [109.9]
2.551(8)
2.354(8)
2.020(7)
98.7(3)
110.0(3)
106.6
2.515(15)
2.297(13)
2.004(12)
98.1(6)
2.531(3)
2.330(3)
2.012(3)
98.6(2)
107.5(2)
106.6
M-C(cage)
av M-N
C(ring)-P-C(cage)
N-M-N
107.2(6)
107.1
Cent-M-C(cage)
a Cent: the centroid of the five-membered ring of the indenyl group. b Distances and angles in brackets are those of a second molecule.
CH3)2), 1.39 (d, J ) 5.4 Hz, 6H, NCH(CH3)2), 1.07 (m, 9H),
0.83 (m, 9H) (NCH(CH3)2 + N(CH2CH3)2). 13C NMR (pyridine-
(NCH(CH3)2). 11B NMR (pyridine-d5): δ -2.6 (3B), -3.7 (2B),
-6.1 (2B), -8.3 (3B). 31P NMR (pyridine-d5): δ 37.3. IR (KBr,
cm-1): ν 3060 (w), 2964 (m), 2600 (m), 2562 (s), 1641(vs), 1577
(vs), 1490 (vs), 1443 (s), 1408 (s), 1262 (m), 1116(m), 1069 (m),
1019 (m), 798 (s), 747 (s). Anal. Calcd for C42H57B10N6O3PZr
(5): C, 54.58; H, 6.22; N, 9.09. Found: C, 54.61; H, 6.50; N,
8.81.
2
1
d5): δ 132.8 (d, JPC ) 31.3 Hz), 128.3 (d, JPC ) 55.9 Hz),
125.9 125.8, 125.7, 123.5 111.8, 111.0, 106.1 (C9H6), 103.2, 91.9
1
(d, JPC ) 49.2 Hz) (cage C), 50.9 (br), 44.9 (br) (NCH(CH3)2),
42.6, 39.9 (N(CH2CH3)2), 31.0, 25.1, 22.1, 21.5 (NCH(CH3)2),
13.6, 13.1 (N(CH2CH3)2). 11B NMR (pyridine-d5): δ -1.0 (2B),
-3.2 (1B), -4.7 (2B), -7.8 (2B), -10.1 (3B). 31P NMR (pyridine-
d5): δ 35.3. IR (KBr, cm-1): νBH 2576 (vs). Anal. Calcd for
C25H50B10HfN3P: C, 42.28; H, 7.10; N, 5.91. Found: C, 41.99;
H, 7.11; N, 5.58.
Reaction of 5 with Excess PhNCO. PhNCO (360 mg, 3.0
mmol) was added to a THF (20 mL) solution of 5‚CH3CN (97
mg, 0.1 mmol) at room temperature. The mixture was stirred
overnight. The resulting dark brown solution was concentrated
under vacuum to about 10 mL, to which was added 5 mL of
toluene. Colorless crystals (180 mg, 50%) were obtained after
this solution stood at -30 °C for 2 days. The product was
Preparation of [η5: σ-iPr2NP(C9H6)(C2B10H10)]Zr[η2-OC-
(NMe2)NPh][η2-OC(NMe2)N(Ph)Cd(NPh)O]‚CH3CN (5‚
CH3CN). A THF (10 mL) solution of PhNCO (357 mg, 3.0
mmol) was added dropwise to a THF (20 mL) solution of 2
(567 mg, 1.0 mmol) at room temperature with stirring, and
the mixture was then stirred for 2 days. Removal of the solvent
gave a pale yellow solid. Recrystallization from a mixed solvent
of THF/toluene/CH3CN (10 mL) at room temperature afforded
5‚CH3CN as pale yellow crystals (598 mg, 62%). 1H NMR
(pyridine-d5): δ 8.33 (d, J ) 7.8 Hz, 1H, indenyl), 7.87 (d, J )
7.8 Hz, 1H, C6H5), 6.98 (d, J ) 3.3 Hz, 1H, indenyl), 7.44-
7.15 (m, 16 H, indenyl+C6H5), 6.39 (d, J ) 3.3 Hz, 1H, indenyl),
6.02 (d, J ) 7.8 Hz, 1H, indenyl), 4.45 (m, 2H, NCH(CH3)2),
2.69 (s, 6H, N(CH3)2), 1.94 (s, 6H, N(CH3)2), 1.40 (d, J ) 6.3
Hz, 6H, NCH(CH3)2), 0.98 (d, J ) 6.3 Hz, 3H, NCH(CH3)2),
0.79 (d, J ) 6.3 Hz, 3H, NCH(CH3)2). 13C NMR (pyridine-d5):
1
identified as (PhNCO)3 by H and13C NMR.12
Reaction of 2 with n-BuLi. Isolation of [Li(DME)3][η5:
σ-iPr2NP(C9H6)(C2B10H10)Li(DME)] (6). A 1.6 M solution of
n-BuLi in hexane (1.3 mL, 2.0 mmol) was slowly added to a
toluene (20 mL) solution of 2 (594 mg, 1.0 mmol) with stirring
at -78 °C. The reaction mixture was warmed to room tem-
perature and stirred overnight. After removal of the solvent
under vacuum, the oily residue was extracted with a mixed
solvent of DME and toluene (3:1, 10 mL × 2). The solutions
were combined and concentrated to about 10 mL; 6 was
obtained as colorless crystals after this solution stood at room
temperature for 2 days (298 mg, 39%). 1H NMR (pyridine-d5):
δ 8.59 (d, J ) 7.8 Hz, 1H, indenyl), 7.94 (d, J ) 3.6 Hz, 1H,
indenyl), 7.87(d, J ) 7.8 Hz, 1H, indenyl), 7.11 (t, J ) 7.2 Hz,
1H, indenyl), 7.02 (t, J ) 7.2 Hz, 1H, indenyl), 6.83 (d, J ) 3.6
2
δ 164.9, 160.9, 152.3 (NCO), 132.9 (d, JPC ) 42.5 Hz), 128.9,
1
128.7, 128.5 (d, JPC ) 56.9 Hz), 127.9, 126.5, 125.5, 125.4,
125.1, 124.9, 124.7, 124.6, 121.9, 121.3, 118.9, 107.0 (C9H6 +
1
C6H5), 103.0, 91.6 (d, JPC ) 63.8 Hz) (cage C), 51.2 (br), 45.9
(12) Zhou, X.; Zhang, L.; Zhu, M.; Cai, R.; Weng, L.; Huang, Z.; Wu,
Q. Organometallics 2001, 20, 5700.
(br) (NCH(CH3)2), 38.3, 36.6 (N(CH3)2), 30.9, 25.1, 22.1, 20.6

Phosphorus-Bridged Indenyl-Carboranyl Ligand
Organometallics, Vol. 24, No. 13, 2005 3121
Hz, 1H, indenyl), 4.95 (m, 2H, NCH(CH3)2), 3.48 (s, 16H,
DME), 3.25 (s, 24H, DME), 1.60 (br, 6H, NCH(CH3)2), 1.38 (br,
3H, NCH(CH3)2), 0.77 (br, 3H, NCH(CH3)2). 13C NMR (pyri-
Scheme 1
2
1
dine-d5): δ 138.7 (d, JPC ) 39.8 Hz), 132.6, 127.9 (d, JPC
)
59.2 Hz), 121.8, 118.7, 117.4, 114.5, 113.5, 102.7 (C9H6), 90.5,
1
84.1 (d, JPC ) 74.9 Hz) (cage C), 71.4, 57.9 (DME), 51.6 (br),
44.2 (br) (NCH(CH3)2, 31.1, 25.4, 22.1, 21.8, (NCH(CH3)2). 11
B
NMR (pyridine-d5): δ -3.9 (4B), -6.9 (2B), -9.5 (4B). 31P NMR
(pyridine-d5): δ 40.3. IR (KBr, cm-1): νBH 2558 (vs). Anal.
Calcd for C25H50B10Li2NO4P (6 - 2DME): C, 51.63; H, 8.66;
N, 2.41. Found: C, 51.31; H, 9.09; N, 2.20.
Reaction of 2 with Acetylacetone. A toluene (10 mL)
solution of acetylacetone (Hacac) (50 mg, 0.5 mmol) was added
slowly to a toluene (10 mL) solution of 2 (297 mg, 0.5 mmol)
at -30 °C. The reaction mixture was then stirred at room
temperature for 4 h. After removal of toluene, the residue was
washed with hexane and extracted with a mixed solvent of
toluene and hexane (3:1; 15 mL). Slow evaporation gave
colorless crystals (83 mg, 34% based on Hacac), which were
identified as Zr(acac)4 by 1H and 13C NMR and unit cell
measurement.13
Ethylene Polymerization. This experiment was carried
out in a 150 mL glass reactor equipped with a magnetic stirrer
and gas inlets. The reactor was charged with the catalysts (3.0
µmol) together with MMAO (4.5 mmol) and toluene (50 mL).
The mixture was stirred at room temperature for 1 h. Ethylene
gas was then introduced to the reactor, and its pressure was
maintained continuously at 1 atm by means of bubbling. The
polymerization was terminated by addition of acidic ethanol
(100 mL). The white precipitate was filtered off and washed
with ethanol and acetone. The resulting powder was finally
dried in a vacuum oven at 80 °C overnight.
Polymerization of E-Caprolactone. A solution of 2 (20
mg, 3.6 × 10-3 mmol) in toluene, CH2Cl2, or THF (10 mL) was
maintained at the chosen temperature. Neat monomer was
then added using a syringe, with a monomer/2 molar ratio of
500:1 or 250:1. The yellow solution was stirred at different
temperatures for 2 h. The polymerizations were terminated
by methanol addition (10 mL). The resulting polymers were
precipitated from methanol (150 mL), filtered, and dried in a
vacuum. 1H NMR (CDCl3): δ 4.04 (t, J ) 6.6 Hz, 436H, OCH2),
2.99 (s, 3H, N(CH3)2), 2.93 (s, 3H, N(CH3)2), 2.29 (t, J ) 7.5
Hz, 436H, COCH2), 1.64 (m, 872H, CH2), 1.36 (m, 436H, CH2).
Results and Discussion
Amide Complexes. Our previous work showed that
interaction of group 4 metal dialkylamides M(NR2)4 (R
) Me, Et) with protic reagents Me2A(C9H7)(C2B10H11),
i
Me2A(C5H4)(C2B10H11) (A ) C, Si), and Pr2NB(C9H7)-
(C2B10H11) in toluene resulted in the clean formation of
the corresponding constrained-geometry group 4 metal
amides.8,9 The two acidic protons in iPr2NP(C9H7)-
(C2B10H11)10 would allow similar amine elimination
reactions to occur. Treatment of iPr2NP(C9H7)(C2B10H11)
with 1 equiv of M(NR2)4 (M ) Ti, Zr, R ) Me; M ) Hf,
R ) Me, Et) in toluene at 60 °C gave the desired
compounds [η5:σ-iPr2NP(C9H6)(C2B10H10)]M(NR2)2 (R )
Me, M ) Ti (1), Zr (2), Hf (3); R ) Et, M ) Hf (4)) in
48-68% yield (Scheme 1). Unlike the boron-bridged
i
ligand Pr2NB(C9H7)(C2B10H11), no deborated products
were detected.9 These reactions were closely followed
by 31P NMR, and the results indicated that such amine
elimination reactions did not proceed at all at room
temperature. Several new 31P NMR peaks appeared if
the reaction temperature was higher than 70 °C, sug-
gestive of the complexity of the reactions at higher
temperatures.
The 31P chemical shifts for 1-4 fell in the range 34.3-
36.0 ppm, which can be compared to the 40.1 and 74.1
ppm observed in the parent ligand iPr2NP(C9H7)-
1
(C2B10H11).10 Their H NMR spectra showed six mul-
X-ray Structure Determination. All single crystals were
immersed in Paraton-N oil and sealed under N2 in thin-walled
glass capillaries. Data were collected at 293 K on a Bruker
SMART 1000 CCD diffractometer using Mo KR radiation. An
empirical absorption correction was applied using the SADABS
program.14 All structures were solved by direct methods and
subsequent Fourier difference techniques and refined aniso-
tropically for all non-hydrogen atoms by full-matrix least-
squares calculations on F2 using the SHELXTL program
package.15a For noncentrosymmetric structures, the appropri-
ate enantiomorph was chosen by refining Flack’s parameter x
toward zero.15b There are two independent molecules in the
unit cell of 1. Most of the carborane hydrogen atoms were
located from difference Fourier syntheses. All other hydrogen
atoms were geometrically fixed using the riding model. Crystal
data and details of data collection and structure refinements
are given in Table 1. Selected bond distances and angles are
compiled in Table 2. Further details are included in the
Supporting Information.
tiplets in the aromatic region and the presence of
diastereotopic Pr2NP and NR2 groups, typically ob-
served in the constrained-geometry carboranyl group 4
metal amides.8,9 These results were consistent with the
13C NMR data. The 11B NMR spectra exhibited a 2:1:
2:2:3 splitting pattern for 1 and 4 and a 2:1:2:3:2
splitting pattern for 2 and 3, respectively.
The solid-state structures of 1-4 were all confirmed
by single-crystal X-ray analyses. Figures 1 and 2 show
the representative structures of compounds 2 and 4,
respectively. The central metal atom is η5-bound to the
five-membered ring of the indenyl group and σ-bound
to the cage carbon atom and two amido groups in a
distorted-tetrahedral geometry. The sum of the angles
around N and P atoms is ∼358° and 314°, respectively,
indicating that the P atom adopts a trigonal pyramidal
geometry. The planar geometry of the nitrogen atoms
suggests the presence of N(pπ)-M(dπ) or N(pπ)-P(dπ)
bonds.16,17 Table 2 lists the key structural data of
compounds 1-4. The Ti-C(ring), Ti-C(cage), and Ti-N
distances are obviously shorter than the corresponding
i
(13) Hoard, J. L.; Silverton, J. V. Inorg. Chem. 1963, 2, 235.
(14) Sheldrick, G. M. SADABS: Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen: Germany,
1996.
(15) (a) Sheldrick, G. M. SHELXTL 5.10 for windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray systems,
Inc.: Madison, WI, 1997. (b) Flack, H. D. Acta Crystallogr. 1983, A39,
876.
(16) Trinquier, G.; Ashby, M. T. Inorg. Chem. 1994, 33, 1306.
(17) Schick, G.; Loew, A.; Nieger, M.; Airola, K.; Niecke, E. Chem.
Ber. 1996, 129, 911.

3122 Organometallics, Vol. 24, No. 13, 2005
Wang et al.
Figure 3. Molecular structure of [η5:σ-iPr2NP(C9H6)-
(C2B10H10)]Zr[η2-OC(NMe2)NPh]-[η2-OC(NMe2)N-
(Ph)Cd(NPh)O] (5) (the solvated CH3CN molecule is not
shown). Selected bond distances (Å) and angles (deg): Zr1-
C1 ) 2.401(5), Zr1-C11 ) 2.666(5), Zr1-C12 ) 2.456(5),
Zr1-C13 ) 2.480(5), Zr1-C18 ) 2.675(5), Zr1-C19 )
2.653(5), av Zr1-C(ring) ) 2.586(5), Zr1-O1 ) 2.124(3),
Zr1-O2 ) 2.104(3), Zr1-O3 ) 2.161(3), Zr1-N6 ) 2.186(4),
Cent-Zr1-C1 ) 92.6, C2-P-C11 ) 98.2(2).
Figure 1. Molecular structure of [η5:σ-iPr2NP(C9H6)-
(C2B10H10)]Zr(NMe2)2 (2).
Å found in compound [PhP(η5-C5Me4)2]ZrCl2,4g while the
Cent-Zr-C(cage) angle of 106.6° in 2 is significantly
smaller than that of 125.9° in [PhP(η5-C5Me4)2]ZrCl2.
Reactivity. Our earlier work showed that unsatur-
ated molecules can insert into the Zr-N bonds of [η5:
σ-Me2A(C9H6)(C2B10H10)]Zr(NMe2)2 (A ) C, Si) to give
multi-insertion products.18 Compound 2 reacted with
PhNCO to afford the tri-insertion product [η5:σ-iPr2NP-
(C9H6)(C2B10H10)]Zr[η2-OC(NMe2)NPh][η2-OC(NMe2)N-
(Ph)Cd(NPh)O] (5). In the presence of excess PhNCO,
no further insertion product was isolated; rather, tri-
merization of PhNCO proceeded to give (PhNCO)3. In
other words, 2 can catalyze the trimerization of PhNCO,
a property that is similar to that of [η5:σ-Me2Si(C9H6)-
(C2B10H10)]Zr(NMe2)2.18 Figure 3 shows the molecular
structure of 5, indicating that the central Zr atom is
fully protected by the surrounding ligands and no
coordination sites are available for further insertion.
The fourth equivalent of PhNCO can react only with
the coordinated ligand, leading to the formation of
trimer.
Figure 2. Molecular structure of [η5:σ-iPr2NP(C9H6)-
(C2B10H10)]Hf(NEt2)2 (4).
values observed in the zirconium and hafnium ana-
logues because of the size effects. The effects of the
linkages on the rigidity and structural parameters of
[η5:σ-A(C9H6)(C2B10H10)]Zr(NMe2)2 type compounds are
observed as shown in Table 3: (1) both the Zr-C(cage)
and Zr-C(ring) distances decrease in the order iPr2NP
i
> Me2Si > Pr2NB > Me2C, (2) the Cent-Zr-C(cage)
i
i
angles increase in the order Me2C < Pr2NB < Pr2NP
< Me2Si, and (3) the C(ring)-A-C(cage) angles follow
Compound 2 reacted with 2 equiv of n-BuLi in toluene
to give, after recrystallization from DME/toluene, the
dilithium salt of [Li(DME)3][η5: σ-iPr2NP(C9H6)(C2B10H10)-
Li(DME)] (6) in 39% isolated yield. This is not very
unusual in view of the formation of CpZr(nBu)3 and CpLi
from the reaction of Cp2ZrCl2 with 3.3 equiv of n-BuLi
in benzene.19 This result suggests that the alkyllithium
i
i
the order Pr2NB > Me2C > Me2Si > Pr2NP. Thus, 2
can be viewed as a more rigid compound than the Si-
linked analogue, as suggested by the Cent-Zr-C(cage)
angles. The Zr-C(ring) distance of 2.551(8) Å in 2 is
comparable to the corresponding value of 2.527(3)
Table 3. Key Structural Data for [η5: σ-A(C9H6)(C2B10H10)]Zr(NMe2)2
A
av Zr-C(ring)
Zr-C(cage)
2.345(2)
2.326(7)
2.348(5)
2.354(8)
av Zr-N
2.026(2)
2.016(8)
2.019(4)
2.020(7)
C(ring)-A-C(cage)
114.0(2)
Cent-Zr-C(cage)
103.0
ref
iPr2NB
Me2C
2.522(2)
2.521(8)
2.541(5)
2.551(8)
9
8
8
109.4(6)
104.8(2)
98.7(3)
101.6
109.9
106.6
Me2Si
iPr2NP
this work

Phosphorus-Bridged Indenyl-Carboranyl Ligand
Organometallics, Vol. 24, No. 13, 2005 3123
Scheme 2
Figure 4. Molecular structure of the anion [η5:σ-iPr2NP-
(C9H6)(C2B10H10)Li(DME)]- in 6. Selected bond distances
(Å) and angles (deg): Li1-C2 ) 2.116(8), Li1-C11 )
2.456(7), Li1-C12 ) 2.309(7), Li1-C13 ) 2.590(8), Li1-
C18 ) 2.736(8), Li1-C19 ) 2.816(8), av Li1-C(ring) )
2.581(8), Li1-O1 ) 2.002 (8), Li1-O2 ) 2.055 (8), O1-
Li1-O2 ) 80.1(3), Cent-Li-C2 ) 116.6.
might not be a good alkylating reagent for the syntheses
of group 4 metal alkyl compounds incorporating con-
strained-geometry carboranyl ligands. The molecular
structure of 6 was confirmed by a single-crystal X-ray
analysis. It consists of well-separated, alternating lay-
ers of discrete tetrahedral anions [η5:σ-iPr2NP(C9H6)-
(C2B10H10)Li(DME)]- and octahedral cations [Li(DME)3]+.
In the anion, the Li+ ion is η5-bound to the indenyl group
and σ-bound to the cage carbon atom and coordinated
to two oxygen atoms from one DME molecule in a
distorted-tetrahedral geometry as shown in Figure 4.
The average Li-C(ring) distance of 2.581(8) Å and the
Li-C(cage) distance of 2.116(8) Å compare to the
corresponding values of 2.332(8) and 2.149(7) Å observed
resultant metal compounds. In contrast, the electron-
rich phosphorus atom could decrease the Lewis acidity
of the central metal atom, leading to the lower catalytic
activity. Our work supports the argument that the RP
moiety serves as an “electron-donating” group in met-
allocene catalysts.
Polymerization of E-Caprolactone. Polylactones
are an important class of biodegradable polymers. Rare
earth metal complexes were found to efficiently catalyze
the polymerization of lactones because of the highly
electropositive nature of the lanthanides.22 Both lan-
thanide-amide complexes22d-g and organozirconium cat-
ions23 can initiate the ring-opening polymerization of
ꢀ-caprolactone. Up to now, group 4 metal amides have
not been reported to initiate the polymerization of
lactones. In view of the role of the carboranyl moiety in
MMA polymerization,24 we wondered if group 4 metal
amides containing constrained-geometry carboranyl
ligands could initiate the polymerization of lactones. To
our surprise, 2 was able to initiate the polymerization
of ꢀ-caprolactone, and the results are summarized in
Table 4. Solvent, reaction temperature, and monomer-
to-catalyst ratio all affected the polymerization results.
THF was found to be the best solvent. As the reaction
in
[Li(THF)4][{[(µ-η5):σ-Me2Si(C5Me4)(C2B10H10)]Li-
(THF)}2Li].20
An equimolar reaction of 2 with acetylacetone re-
sulted in the isolation of the known compound Zr(acac)4
in 34% yield. The 31P NMR was used to monitor this
reaction and showed that even at -30 °C two new peaks
at about 74.0 and 41.0 ppm attributable to the neutral
i
ligand Pr2NP(C9H7)(C2B10H11)10 were observed. The
high acidity of acetylacetone may lead to the low
selectivity of the equimolar reaction, resulting in the
completed protonation of 2.21 The above reactions are
outlined in Scheme 2.
Ethylene Polymerization. Compounds 1-4 under-
went preliminary testing for catalytic activity in ethyl-
ene polymerization using modified methylalumoxane
(MMAO) as cocatalyst (Al/M ) 1500) in toluene at 25
°C (1 atm of ethylene). Among them, 1, 3, and 4 showed
very low catalytic activity, whereas 2 exhibited an
activity of 3.7 × 103 g PE mol-1 atm-1 h-1. The molar
mass and the polydispersity of the resulting polyethyl-
ene were 2.16 × 105 g/mol and 1.87, respectively. Thus,
2 was proved to be much less active than its Me2C-,
Me2Si-, and iPr2NB-bridged analogues.8,9 In view of their
structural parameters (Table 3), we may conclude that
the electronic properties of the bridging atoms lead to
the significant differences in catalytic activities in
ethylene polymerization. The electron-deficient boron
atom may increase the Lewis acidity of the central metal
atom, resulting in the higher catalytic activity of the
(18) Wang, H.; Li, H.-W.; Xie, Z. Organometallics 2003, 22, 4522.
(19) Kondakov, D.; Negishi, E.-i. Chem. Commun. 1996, 963.
(20) Zi, G.; Yang, Q.; Mak, T. C. W.; Xie, Z. Organometallics 2001,
20, 2359.
(21) Collier, M. R.; Lappert, M. F.; Pearce, R. J. Chem. Soc., Dalton
Trans. 1973, 445.
(22) (a) Palard, I.; Soum, A.; Guillaume, S. M. Chem. Eur. J. 2004,
10, 4054, and references therein. (b) Woodman, T. J.; Schormann, M.;
Hughes, D. L.; Bochmann, M. Organometallics 2004, 23, 2972. (c)
Satoh, Y.; Ikitake, N.; Nakayama, Y.; Okuno, S.; Yasuda, H. J.
Organomet. Chem. 2003, 667, 42. (d) Roesky, P. W.; Gamer, M. T.;
Puchner, M.; Greiner, A. Chem. Eur. J. 2002, 8, 22. (e) Qian, C.; Nie,
W.; Chen, Y.; Sun, J. J. Organomet. Chem. 2002, 645, 82. (f) Matsuo,
Y.; Mashima, K.; Tani, K. Organometallics 2001, 20, 3510. (g) Hultzsch,
K. C.; Spaniol, T. P.; Okuda, J. Organometallics 1997, 16, 4845. (h)
Yamashita, M.; Takemoto, Y.; Ihara, E.; Yasuda, H. Macromolecules
1996, 29, 1798.
(23) (a) Thomas, D.; Arndt, P.; Peulecke, N.; Spannenberg, A.;
Kempe, R.; Rosenthal, U. Eur. J. Inorg. Chem. 1998, 1351. (b) Arndt,
P.; Thomas, D.; Rosenthal, U. Tetrahedron Lett. 1997, 38, 5467. (c)
Mukaiyama, T.; Hayakawa, M.; Oouchi, K.; Mitani, M.; Yamada, T.
Chem. Lett. 1995, 737.
(24) Hong, E.; Kim, Y.; Do, Y. Organometallics 1998, 17, 2933.

3124 Organometallics, Vol. 24, No. 13, 2005
Table 4. Polymerization of E-Caprolactone by 2a
Wang et al.
entry
solvent
[monomer]/2
temp (°C)
conversion (%)
Mn (×10-4)bg/mol
Mw (×10-4)bg/mol
Mw/Mn
1
2
3
4
5
6
THF
THF
250
500
500
500
500
500
25
25
25
25
45
60
58
55
4.7
33
92
95
2.34
4.23
10.52
3.27
5.32
5.67
3.00
5.34
14.17
4.56
6.88
7.54
1.29
1.26
1.35
1.39
1.29
1.33
CH2Cl2
toluene
THF
THF
a Conditions: 2: 20 mg, 3.6 × 10-3 mmol, 2 h. b Determined by GPC relative to polystyrene standards.
Scheme 3
showed that (1) the zirconium amide was able to
catalyze the trimerization of PhNCO, and PhNCO
inserted exclusively into the Zr-N bonds, and (2) both
the Zr-C(cage) σ-bond and Zr-indenyl π-bond were
broken in the reactions of 2 with n-BuLi or Hacac to
generate [Li(DME)3][η5:σ-iPr2NP(C9H6)(C2B10H10)Li-
(DME)] and Zr(acac)4, respectively.
The zirconium amide 2 catalyzed ethylene polymer-
ization with an activity of 3.7 × 103 g PE mol-1 atm-1
h-1 in the presence of MMAO, which is the lowest one
among its carbon-, silcon-, and boron-linked analogues,
although their geometries are similar. The results
suggest that the electronic properties of the bridging
atoms have great effects on the catalytic performance
of the group 4 metal compounds. The electron-rich
phosphorus can decrease the electron-deficiency of the
metal center, leading to a lower catalytic activity in
ethylene polymerization. This work supports the argu-
ment that the RP moiety acts as an “electron-donating”
group in metallocenes.5b,d
The zirconium amide 2 was able to initiate the ring-
opening polymerization of ꢀ-caprolactone to give poly-
esters with high molecular weights and low polydisper-
sities. This represents the first example of the polymer-
ization of lactones catalyzed by group 4 metal amides.
This result also shows that carboranyl ligands can
enhance the electrophilicity of the group 4 metal center.
It is another example to illustrate the role of carborane
in catalysis.
temperature increased, polymerization became very
rapid with 95% conversion; the molar masses and
polydisperisities of the polymers were slightly increased.
The resulting polyesters were generally of high molar
masses (Mn > 40 000) and showed narrow polydisper-
sities (Mw/Mn < 1.4). The 1H NMR experiments showed
that the two NMe2 peaks at 3.02 and 2.53 ppm in 2
disappeared immediately upon addition of 2 equiv of
ꢀ-caprolactone, and the new resonances at 2.93 and 2.99
ppm attributable to the -CONMe2 group were gener-
ated. These two peaks were also observed in the 1H
NMR spectra of the resulting polyesters. These observa-
tions are consistent with the reported polymerization
of ꢀ-caprolactone using Y{N(SiMe3)2}3 as catalyst.22g On
the basis of these facts, it is most likely that the attack
by one of the nucleophilic amido-nitrogen atoms at the
lactone carbonyl-carbon atoms is the initial step of the
polymerization followed by acyl bond cleavage as shown
in Scheme 3. Evidently the increase in the electron-
donating ability of the RP-bridged ligand resulted in a
more nucleophilic amido group.
Acknowledgment. This work was supported by
grants from the Research Grants Council of The Hong
Kong Special Administration Region (Project No. 403103),
and the German Academic Exchange Service (DAAD),
Deutsche Forschungsgemeinschaft (DFG), and the Re-
search Grants Council of the Hong Kong Joint Research
Scheme (Reference No. G_HK011/02). We thank Ms.
Mingli Gao for carrying out ethylene polymerization
experiments. Z.X. acknowledges the Croucher Founda-
tion for a Senior Research Fellowship Award.
Supporting Information Available: Crystallographic
data and data collection details, atomic coordinates, bond
distances and angles, anisotropic thermal parameters, and
hydrogen atom coordinates for 1-6 as CIF files. This material
is available free of charge via the Internet at http://pubs.acs.org.
Conclusion
i
Several new group 4 metal amides with a Pr2NP-
bridged constrained-geometry carboranyl ligand were
synthesized and fully characterized. Reactivity studies
OM050079M