Disproportionation of cationic zirconium complexes: A possible pathway to the deactivation of catalytic cationic systems

Article abstract of DOI:10.1021/om9701736

Protonolysis of the zirconium borohydride [(C₅H₄R)₂Zr(BH₄)₂] (R = H, Me, SiMe₃) with NHMe₂PhBPh₄ in THF leads to the corresponding cationic zirconium complex [(C₅H₄R)₂Zr-(BH₄)(THF)]BPh ₄, and the structure of [(C₅H₄Me)₂Zr(BH₄)(THF)]BPh ₄ was determined. In the presence of phosphine, PMe₂Ph, the formation of the cationic hydride [(C₅H₄R)₂ZrH-(PMe₂Ph) ₂]BPh₄ is observed by ¹H and ³¹P NMR followed by a disproportionation and a redox reaction with [BPh₄]^-, giving the neutral [(C₅H₄R)₂ZrH(μ-H)]₂ and the cationic Zr^III species [(C₅H₄R)₂Zr(PMe₂Ph) ₂]BPh₄ characterized by EPR spectroscopy and suggesting a probable pathway in the deactivation of cationic catalyst systems.

Full text of DOI:10.1021/om9701736

Organometallics 1997, 16, 5517-5521
5517
Disp r op or tion a tion of Ca tion ic Zir con iu m Com p lexes: A
P ossible P a th w a y to th e Dea ctiva tion of Ca ta lytic
Ca tion ic System s
Robert Choukroun,* Be´ne´dicte Douziech, and Bruno Donnadieu
Equipe Pre´curseurs Mole´culaires et Mate´riaux, Laboratoire de Chimie de Coordination du
CNRS, 205 route de Narbonne, 31077 Toulouse Cedex, France
Received March 3, 1997X
Protonolysis of the zirconium borohydride [(C5H4R)2Zr(BH4)2] (R ) H, Me, SiMe3) with
NHMe2PhBPh4 in THF leads to the corresponding cationic zirconium complex [(C5H4R)2Zr-
(BH4)(THF)]BPh4, and the structure of [(C5H4Me)2Zr(BH4)(THF)]BPh4 was determined. In
the presence of phosphine, PMe2Ph, the formation of the cationic hydride [(C5H4R)2ZrH-
(PMe2Ph)2]BPh4 is observed by 1H and 31P NMR followed by a disproportionation and a redox
reaction with [BPh4]-, giving the neutral [(C5H4R)2ZrH(µ-H)]2 and the cationic ZrIII species
[(C5H4R)2Zr(PMe2Ph)2]BPh4 characterized by EPR spectroscopy and suggesting a probable
pathway in the deactivation of cationic catalyst systems.
In tr od u ction
has been centered upon the synthesis of new substituted
cyclopentadienyl borohydrides of zirconium complexes.
The reaction in toluene of (C5H4R)2ZrCl2 (R ) H, Me,
SiMe3) and Cp2ZrClMe with LiBH4, a standard meth-
odology in the synthesis of the borohydride complexes,
enables us to easily obtain respectively the compounds
[(C5H4R)2Zr(BH4)2] (1, R ) H; 2, R ) Me; 3, R ) SiMe3)
and [Cp2Zr(CH3)(BH4)] (4).4b The 1H and 13C NMR
spectra of 1-4 show typical resonances for the C5H4R
ring (a typical AA′BB′ pattern is observed in the 1H
NMR spectra of 2 and 3, respectively). The BH4 ligands
are observed as a well-resolved 1:1:1:1 quadruplet in the
1H NMR spectra. The infrared pattern spectra of the
B-H-Zr bridge and the B-H terminal vibration are
characteristic of the Zr(µ-H)2BH2 interaction.4d
There is great current interest in the chemistry of
cationic d0 complexes [Cp2MR]+ (M ) Ti, Zr), due to
their implication as the active species in Ziegler-Natta
olefin polymerization. Several reports have dealt with
the bis(cyclopentadienyl)metal alkyl series [Cp2MR]+,
which are efficient systems for modeling polymerization
catalysis but show a rapid decay in activity for olefin
polymerization.1,2 As part of our contribution in this
area, we have investigated new types of cationic zirco-
nium borohydride complexes, [(C5H4R)2Zr(BH4)]+ (R )
H, Me, SiMe3), which should provide other insights into
the zirconium cationic chemistry, due to the presence
of a Zr-H-B bond. It is well-known that the zirconium
hydride complex [Cp2ZrH2]n can be prepared from the
corresponding borohydride complex [Cp2Zr(BH4)2] in the
presence of a base such as NEt3.3 We are able to take
advantage of this effective chemical method to produce
and generate hydride cationic species from [(C5H4R)2-
Zr(BH4)]+ (R ) H, Me, SiMe3).
The reaction of [(C5H4R)2Zr(BH4)2] (1-3) or [Cp2Zr-
(BH4)Me] (4) with the ammonium salt NHMe2PhBPh4
proceeds rapidly when a THF solution of the reactants
is warmed from -78 °C to room temperature to yield
[(C5H4R)2Zr(BH4)(THF)]BPh4 (Scheme 1: 5, R ) H; 6,
R ) Me; 7, R ) SiMe3). Only 5 and 6 have been isolated
as white crystalline solids. We have been unable to
isolate 7, due to its higher solubility in the presence of
the trimethylsilyl group on the Cp ring, but 7 was
characterized in situ, via its reaction with phosphine
(see below). Complexes 5 and 6 have been characterized
by 1H and 13C NMR spectroscopy, infrared spectroscopy,
and elemental analysis. 1H NMR spectra were mea-
sured in THF-d8 and CD3CN, although their solubilities
are extremely low in these solvents (the presence of a
Me-substituted cyclopentadienyl ring does not increase
the solubility of 6). The products 5 and 6 decompose
rapidly in chlorinated solvents. Characteristic reso-
nances of the C5H4R ligand are observed (THF-d8: 5,
δ(Cp) 6.59 ppm; 6, δ(C5H4Me) 6.42, 6.25 ppm; 7, δ(C5H4-
SiMe3) 6.40, 6.21, 6.18, 5.74 ppm). The borohydride
peaks, which are well-resolved quadruplets in 1-3,
appear as broad unresolved quadruplet signals for 5-7
(5, 0.45 ppm, J BH ) 92 Hz; 6, 0.40 ppm, J BH ) 84 Hz; 7,
Resu lts a n d Discu ssion
Organometallic zirconium derivatives of tetrahy-
droborates have received much attention.4 Our research
X Abstract published in Advance ACS Abstracts, November 15, 1997.
(1) J ordan, R. F. In Chemistry of Cationic Dicyclopentadienyl Group
4 Metal-Alkyl Complexes; Advances in Organometallic Chemistry 32;
Academic Press: New York, 1991; p 325.
(2) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255.
(3) J ames, B. D.; Nanda, R. K.; Wallbridge, M. G. H. Chem.
Commun. 1966, 23, 849.
(4) (a) Fochi, G.; Guidi, G.; Floriani, C. J . Chem. Soc., Dalton Trans.
1984, 1253. (b) Nanda, R. K.; Wallbridge, M. G. H. Inorg. Chem. 1964,
3, 1798. (c) Marsella, J . A.; Caulton, K. G. J . Am. Chem. Soc. 1982,
104, 2361. (d) Marks, T. J .; Kolb, J . R. J . Am. Chem. Soc. 1975, 97,
3397. (e) Marks, T. J .; Kennelly, W. J .; Kolb, J . R.; Shimp, L. A. Inorg.
Chem. 1972, 11, 2540. (f) Luinstra, G. A.; Rief, U.; Prosenc, M. H.
Organometallics 1995, 14, 1551. (g) No¨th, H.; Schmidt, M. Organo-
metallics 1995, 14, 4601. (h) Gozum, J . E.; Girolami, G. S. J . Am. Chem.
Soc. 1991, 113, 3829. (i) J ames, B. D.; Nanda, R. K.; Wallbridge, M.
G. H. J . Chem. Soc. A 1966, 182. (j) Nanda, R. K.; Wallbridge, M. G.
H. Inorg. Chem. 1964, 3, 1798. (k) J ames, B. D.; Nanda, R. K.;
Wallbridge, M. G. H. Inorg. Chem. 1967, 6, 1979. (l) Wolczanski, P.
R.; Bercaw, J . E. Organometallics 1982, 1, 793. (m) J oseph, S. C. P.;
Cloke, F. G. N.; Cardin, C. J .; Hitchcock, P. B. Organometallics 1995,
14, 3566. (n) Hughes, A. K.; Meetsma, A.; Teuben, J . H. Organome-
tallics 1993, 12, 1936.
1
-0.16 ppm, J BH ) 90 Hz). When H NMR of 5 or 6 is
(5) Edelstein, N. Inorg. Chem. 1981, 20, 297.
(6) J ordan, R. F.; Bajgur, C. S.; Willet, R.; Scott, B. J . Am. Chem.
Soc. 1986, 108, 7410.
S0276-7333(97)00173-8 CCC: $14.00 © 1997 American Chemical Society

5518 Organometallics, Vol. 16, No. 25, 1997
Choukroun et al.
Ta ble 1. Bon d Len gth s (Å) a n d An gles (d eg)a
molecule 1
molecule 2
Zr(1)-O(1)
2.239(5)
2.54(1)
1.87(9)
1.93(9)
1.10(9)
1.30(9)
2.18
Zr(2)-O(2)
2.231(6)
2.55(1)
1.98(9)
1.92(8)
1.24(8)
1.27(9)
2.19
Zr(1)-B(1)
Zr(1)-H(1)
Zr(1)-H(2)
B(1)-H(1)
B(1)-H(2)
Cp-Zr (av)
Zr(2)-B(4)
Zr(2)-H(5)
Zr(2)-H(6)
B(4)-H(5)
B(4)-H(6)
Cp-Zr (av)
O(1)-Zr(1)-B(1)
99.6(3)
O(2)-Zr(2)-B(4)
103.5(3)
131.8(24)
74.6(26)
28.6(24)
28.8(26)
57.3(34)
O(1)-Zr(1)-H(1)
122.6(29) O(2)-Zr(2)-H(5)
O(1)-Zr(1)-H(2)
69.8(28)
23.1(29)
29.9(28)
O(2)-Zr(2)-H(6)
B(4)-Zr(2)-H(5)
B(4)-Zr(2)-H(6)
B(1)-Zr(1)-H(1)
B(1)-Zr(1)-H(2)
H(1)-Zr(1)-H(2)
52.9 (38) H(5)-Zr(2)-H(6)
C(11)-O(1)-C(14) 107.7(6)
C(29)-O(2)-C(32) 105.1(7)
H(5)-B(4)-H(6)
H(1)-B(1)-H(2)
Zr(1)-H(1)-B(1)
Zr(1)-H(2)-B(1)
89.5(61)
115.4(67) Zr(2)-H(5)-B(4)
102.2(54) Zr(2)-H(6)-B(4)
96.2(53)
101.7(51)
104.5(50)
Cp(1)-Zr(1)-Cp(2) 131.6
Cp(3)-Zr(2)-Cp(4) 132.3
F igu r e 1. View of the molecular structure of the [(C5H4-
a
Cp(1), Cp(2), Cp(3), and Cp(4) are the centroids of the C5H4
Me)2Zr(BH4)(THF)]+ cation. The BPh4- structure is normal.
rings C(1)-C(5), C(9)-C(13), C(17)-C(21), and C(22)-C(26).
registered in CD3CN, the presence of 1 equiv of free THF
is observed, suggesting that dissociation of THF occurs
and that 5 or 6 exists as the adduct [(C5H4R)2Zr-
(BH4)(CH3CN)n]+ (n ) 1, 2).7 The IR spectra show the
characteristic bands of µ2-bonded (via two hydrogen
bridges) BH4 to the metal atom in compounds 5 and 6.
(14) Å) which is oriented nearly perpendicular to the
plane defined by the methyl carbon, zirconium, and THF
oxygen atoms.6
Attempts to react 5 and 6 with triethylamine or
tetramethylethylenediamine (TMEDA) do not lead to
the zirconium hydride cationic species, and unchanged
1H NMR spectra of 5 and 6 are observed. Since the
cleavage of BH3 from tetrahydroborate complexes by
suitable σ donors is a common route to transition-metal
hydride species,4g 5 and 6 were treated in THF-d8 or
C6D6 with an excess of the phosphine PMe2Ph. The
formation of the cationic hydrides [(C5H4R)2ZrH(PMe2-
Ph)2]+ (8, R ) H; 9, R ) Me) is observed. The same
behavior was observed for the reaction of 7 with phos-
phine (prepared in situ from 3 and NHMePh2BPh4 in
THF-d8) to give 10 (R ) SiMe3). Their identification as
a cationic hydride diphosphine arose from 1H and 31P
NMR and from comparison with the data of the same
cationic hydride species obtained from hydrogenolysis
of [(C5H5)2ZrMe]+.7 The BH3-PMe2Ph adduct can be
recognized by 31P NMR (q, δ 9 ppm, J PB ) 56 Hz). No
reaction was observed with other bulky phosphines such
as PPh2Me, PPh3, and P(cyclohexyl)3.
Reduction occurs during the course of the reaction.
This slow process can be detected by the complete
disappearance of [(C5H4R)2ZrH(PMe2Ph)2]+ in 1-2 days.
At this stage, [(C5H4R)2ZrH(PMe2Ph)2]+ is entirely
consumed and the complex is not at this point detected
by 1H NMR, but the formation of the well-known
dihydride [(C5H4R)2ZrH(µ-H)]2 is observed8,9 (R ) Me,
SiMe3; for R ) H, the corresponding insoluble dihydride
is characterized by chemical derivatization with acetone
as Cp2Zr(O-i-Pr)2). The decay of 6 in the presence of 5
equiv of PMe2Ph and the formation of the dimeric
dihydride Zr complex were monitored by 1H NMR in
THF-d8 in a sealed tube. An approximate mole ratio of
4:1 is observed at the end of the reaction between the
starting complex 6 and [(C5H4Me)2ZrH(µ-H)]2. At the
same time, the reaction was monitored by EPR spec-
troscopy and a stable EPR 1:2:1 triplet signal was
observed with a characteristic coupling constant to two
Sch em e 1
[(C5H4R)2Zr(BH4)2] + [NHMe2Ph][BPh4] f
[(C5H4R)2Zr(BH4)(THF)][BPh4] +
1-3
1/2H2 + Me2PhN‚BH3
1, R ) H; 2, R ) CH3; 3, R ) SiMe3
[Cp2Zr(CH3)(BH4)] + [NHMe2Ph][BPh4] f
[Cp2Zr(BH4)(THF)][BPh4] + NMe2Ph + CH4
4
The solid-state structure of 6 was determined by
single-crystal X-ray diffraction and consists of discrete
-
(C5H4Me)2Zr(µ-H2BH2)(THF)+ and BPh4 ions. The
molecular structure of 6 shows two independent but
very similar molecules in the unit cell, and Figure 1 is
a perspective view of a single molecule. Selected bond
distances and bond angles are listed in Table 1. The
zirconium atom is at the center of a distorted tetrahe-
dron consisting of the centers of two cyclopentadienyl
rings, an oxygen atom, and the boron atom. An ad-
ditional structural feature is the Zr(1)B(1)H(1)H(2)
plane, which nearly includes the O(1) atom (distance of
O(1) to this plane 0.110 Å) and is almost perpendicular
to the Cp(1)-Zr-Cp(2) plane. The structure establishes
the presence of a µ2-bonded BH4 group,4g,h in agreement
with the Zr‚‚‚B distance,5 and confirms the analysis of
the IR data. The THF ligand is oriented almost in the
plane defined by boron, zirconium, and THF oxygen
atoms (dihedral angle C(11)-O(1)-C(14)/O(1)-Zr(1)-
B(1) ) 24°) with a Zr-O bond length longer than in the
THF ligand of [Cp2Zr(CH3)(THF)]+ (d(Zr-O) ) 2.122-
(8) J ones, S. B.; Petersen, J . L. Inorg. Chem. 1981, 20, 2889.
(9) Larsonneur, A.-M.; Choukroun, R.; J aud, J . Organometallics
1993, 12, 3216.
(7) J ordan, R. F.; Bajgur, C. S.; Dasher, W. E.; Rheingold, A. L.
Organometallics 1987, 6, 1041.

Disproportionation of Cationic Zirconium Complexes
Organometallics, Vol. 16, No. 25, 1997 5519
equivalent phosphorus nuclei, suggesting the formation
of [(C5H4R)2Zr(PMe2Ph)2]+ (11) (g ) 1.986, a(31P) ) 32.4
G, a(91Zr) ) 23 G). The observation that the cationic
TiIII species [(C5H5)2Ti(THF)2]+ gives in the presence of
PMe3 a similar EPR 1:2:1 triplet signal with the same
hyperfine coupling constant to two equivalent phospho-
rus atoms (a(31P) ) 30.2 G) provides support for the
proposal of species 11.10 Further support for this
redistribution and redox reaction was independently
provided by reacting [Cp2ZrH(THF)]+ (synthesized by
hydrogenation of [Cp2Zr(CH3)(THF)]+ in THF7) for 1 day
with PMe2Ph. The product 11 can be easily identified
by EPR spectroscopy, whereas the presence of polymeric
[Cp2ZrH2]n was identified by chemical derivatization
in the presence of phosphine, cannot be stopped at its
early stage by adding ethylene to [(C5H4R)2ZrH(PMe2-
Ph)2]+. The expected ethyl complex [(C5H4R)2Zr(C2-
H5)(PMe2Ph)]+ is not observed by 1H NMR and 31P NMR
and the disproportionation/redox reaction still occurs,
although this reaction was already observed in the case
of [Cp2Zr(H)(PMe3)2][BPh4] with ethylene.7,14 The pres-
ence of the bulkier and less basic phosphine PMe2Ph,
instead of PMe3, seems responsible for the lack of
reactivity of ethylene observed in our case. We suggest
the formation of the monophosphine [(C5H4R)2Zr(H)-
(PMe2Ph)]+ as an intermediate to describe the formation
of both the hydride dimer complex [(C5H4R)2ZrH(µ-H)]2
via a four-center mechanism and the transient dica-
with acetone as Cp2Zr(O-i-Pr)2. The amount of ZrIII
,
tionic species [(C5H4R)2Zr(PMe2Ph)2]2+ 15
The presence
.
directly measured by comparison of EPR integration
with the area of a standard of TEMPO in THF, accounts
for about 40-45% yield from the starting complex 6, 7,
or [Cp2Zr(CH3)(THF)]+. The presence of the dihydride
species [(C5H4R)2ZrH(µ-H)]2 and the formation of a ZrIII
species is reminiscent of a disproportionation reaction
followed by a redox reaction with [BPh4]- recently
observed by us in the case of the cationic vanadium(IV)
[Cp2V(CH3)(CH3CN)][BPh4]11 (see Scheme 2). Effec-
of a dicationic zirconocene species was already suggested
by J ordan et al.1,16 along with the disproportionation
reaction observed with the cationic zirconium and
hafnium complexes [Cp2MCH3]+ in the presence of
NMe3 or CH3CN, respectively, and with [(C5Me5)Zr(CH2-
Ph)2]+. Also, the exchange reaction of ligands between
[Cp2Zr(CH3CN)3]2+ and PMe3 in CD3CN was identified
by NMR to be consistent with an equilibrium of
2+
[Cp2Zr(CH3CN)x(PMe3)3-x
]
species.15 Such an equi-
librium in our case with THF and PMe2Ph ligand
substitution could drive the dicationic species to undergo
a redox reaction with the [BPh4]- anion and lead to
paramagnetic 11. In order to clarify this point, the
dicationic species [Cp2Zr(CH3CN)3][BPh4]2 was moni-
tored by EPR spectroscopy in presence of 5 equiv of
PMe2Ph in THF-d8. Although the dicationic species is
insoluble in THF, after 5 days, [Cp2Zr(PMe2Ph)2][BPh4]
(11) is formed in low yield (3-5%, depending on the
experiments).17 This seems to demonstrate the puzzling
accessibility of the dicationic species [Cp2Zr(PMe2Ph)2]2+
(or [Cp2Zr(THF)(PMe2Ph)]2+). The contribution of the
σ-donor ability of THF and various phosphines, which
explains the different hydrogenation rates of cationic
[Cp2ZrCH3(THF)][BPh4] in the presence of phosphine,18
could be connected to the disproportionation redox
reaction of [Cp2ZrH(PMe2Ph)2][BPh4] in the presence of
THF and phosphine. On the other hand, the observa-
tion that [Cp2ZrH(PMe3)2]+ reacts with ethylene and not
[Cp2ZrH(PMe2Ph)2]+ seems to indicate that the contri-
bution of the steric effect of the phosphine ligand could
not be eliminated.
Sch em e 2
[(C5H4R)2Zr(BH4)(THF)][BPh4] + 3 PMe2Ph f
[(C5H4R)2ZrH(PMe2Ph)2][BPh4] + Me2PhP‚BH3
5-7
5, R ) H; 6, R ) CH3; 7, R ) SiMe3
[(C5H4R)2ZrH(PMe2Ph)2][BPh4] f
1/4[(C5H4R)2ZrH(µ-H)]2 +
1/2[(C5H4R)2Zr(PMe2Ph)2][BPh4]2
1/2[(C5H4R)2Zr(PMe2Ph)2][BPh4]2 f
1/2[(C5H4R)2Zr(PMe2Ph)2][BPh4] + 1/2BPh3 +
1/4PhPh
tively, we observed the formation of PhPh (identified
by GC/MS; the quantification of liberated PhPh was
impossible, attributable to the presence of other uni-
dentified boron species12,13 which leads us to underes-
timate PhPh) and BPh3 in the solution (identified by
11B NMR and by comparison with an authentic sample).
The mechanism of the reaction, namely a dispropor-
tionation and a redox reaction between ZrIV and [BPh4]-
The presence of paramagnetic species in cationic
polymerization was observed by others.19 Reductive
decomposition of the catalytic system (C5Me5)TiMe3/
B(C6F5)3 was recently studied by Grassi et al.,20 and an
(14) J ordan, R. F.; Bradley, P. K.; Baenziger, N. C.; LaPointe, R. E.
J . Am. Chem. Soc. 1990, 112, 1289.
(15) J ordan, R. F.; Echols, S. F. Inorg. Chem. 1987, 26, 383.
(16) (a) Crowther, D. J .; J ordan, R. F.; Baenziger, N. C.; Verma, A.
Organometallics 1990, 9, 2574. (b) Borkowski, S. L.; J ordan, R. F.;
Hinch, G. D. Organometallics 1991, 10, 1268.
(10) (a) The cationic species [Cp2Ti(THF)2][BPh4] was isolated and
fully characterized by an X-ray structure determination. Its EPR signal
in the presence of PMe3 gives the expected triplet for [Cp2Ti(PMe3)2]+
(g ) 1.989; a(31P) ) 30.2 G), whereas in the presence of PMe2Ph, an
EPR doublet is observed for the monophosphine adduct [Cp2Ti(PMe2-
Ph)]+ (g ) 1.986; a(31P) ) 26.7 G), probably due to the steric effect of
the phosphine and the size of the titanium radius. In both cases, a
large a(31P) is observed: Choukroun, R.; Douziech, B. Unpublished
results. For other a(31P) values: (b) Choukroun, R.; Gervais, D. J .
Chem. Soc., Chem. Commun. 1985, 224. (c) Williams, G. M.; Schwartz,
J . J . Am. Chem. Soc. 1982, 104, 1122. (d) Dioumaev, V. K.; Harrod, J .
F. Organometallics 1997, 16, 2798.
(17) The amount of ZrIII (three experiments) was directly measured
by comparison of EPR integration with the area of a standard amount
of TEMPO in THF. 1H NMR of a THF-d8 solution10 shows three Cp
resonances at 6.29 (broad s, 20%), 6.25 (d, J (31P-1H) ) 0.4 Hz, 30%),
and 6.16 ppm (d, J (31P-1H) ) 0.4 Hz, 50%), free CH3CN (1.97 ppm, 3
equiv), and PMe2Ph (broad s, 1.42 ppm). The unreacted dicationic
acetonitrile adduct is still present in the NMR tube.
(11) Choukroun, R.; Douziech, B.; Pan, C.; Dahan, F.; Cassoux, P.
Organometallics 1995, 14, 4471.
(12) Eisch, J . J .; Shah, J . H.; Boleslawski, M. P. J . Organomet. Chem.
1994, 464, 11.
(13) Aresta, M.; Quaranta, E. J . J . Organomet. Chem. 1995, 488,
211.
(18) J ordan, F. R.; Bajgur, C. S.; Dasher, W. E.; Rheingold, A. L.
Organometallics 1987, 6, 1041.
(19) (a) Bueschges, U.; Chien, J . C. W. J . Polym. Sci., Part A 1989,
27, 1525. (b) Chien, J . C. W.; Salajka, Z.; Dong, S. Macromolecules 1992,
29, 3199. (c) Dam, C.; Sartori, F.; Maldotti, A. Macromol. Chem. Phys.
1994, 195, 2818.

5520 Organometallics, Vol. 16, No. 25, 1997
Choukroun et al.
unreacted LiBH4 and LiCl and the filtrate evaporated to
dryness, giving a white powder (0.860 g; yield 95%). Anal.
Calcd for C16H34B2Si2Zr: C, 48.6; H, 8.6; Zr, 23.08. Found:
C, 48.63; H, 8.88; Zr, 23.05. 1H NMR (C6D6, 293 K, ppm): 6.24
(t, J CH ) 2,5 Hz, 4H, C5H4), 5.71 (t, J CH ) 2,5 Hz, 4H, C5H4),
0.27 (s, 18H, SiMe3), 0.75 (q, J BH ) 85 Hz, 8H, BH4). 13C NMR
ESR spectroscopy study suggests the formation of the
cationic TiIII complex [(C5Me5)TiMe]+. With the group
4 dicyclopentadienyl complex, the redistribution reac-
tion leads to a cationic ZrIII species in which there is no
metal-carbon bond left to produce the catalytic polym-
erization of olefins. Although this disproportionation
process is quite slow and requires donor ligands, a
pathway for the deactivation of cationic catalyst species
may be suggested to take into account our findings,
which can be mainly regarded as studies on the reactiv-
ity of cationic metallocenes (see Scheme 3). At present,
the mechanism of the disproportionation/redox reaction
observed in vanadium chemistry and in this work needs
further investigation with other cationic systems to
support a relationship with the deactivation of the
catalyst in the olefin polymerization.21
1
2
(C6D6, 293 K, ppm): 125.8 (dq, J CH ) 174 Hz, J CH ) 6.8 Hz,
1
2
C5H4), 120.5 (s, C5H4), 111.7 (dq, J CH ) 174 Hz, J CH ) 7.5
Hz, C5H4), 0.83 (q, J CH ) 122 Hz, SiMe3).
Cp 2Zr (BH4)(Me) (4). A toluene solution of (C5H5)2Zr(CH3)-
Cl (1.06 g, 3.9 mmol) was stirred with LiBH4 (0.085 g, 3.9
mmol) for 72 h, at room temperature. The mixture was filtered
on Celite to remove the excess unreacted LiBH4 and LiCl, and
the filtrate was then concentrated to a small volume. A yellow
solid was observed during diffusion with hexane, which was
filtered and dried under vacuum, giving 0.47 g of product (yield
48%). Anal. Calcd for C11H17BZr: C, 52.58; H, 6.82. Found:
C, 53.0; H, 6.60. 1H NMR (toluene-d8, 293 K, ppm): 5.83 (s,
10H, C5H5), 0.36 (s, 3H, CH3), 0.32 (q, J BH ) 85 Hz, 4 H, BH4).
1H NMR (toluene-d8, 373 K, ppm): 5.89 (s, 10H, C5H5), 0.31
(s, 3H, CH3), 0.26 (q, J BH ) 86 Hz, 4 H, BH4). 13C{1H} NMR
(THF-d8, 293 K, ppm): 111.4 (d, J CH ) 180 Hz, C5H5), 21.6 (q,
J CH ) 120 Hz, CH3).
Sch em e 3
[Cp2MR]+ + excess L f
1/2Cp2MR2 + 1/2[Cp2M(L)n]2+
[(C5H5)2Zr (BH4)(THF )][BP h 4] (5). To a stirred THF solu-
tion of Cp2Zr(BH4)2 (0.4 g, 1.6 mmol) at -78 °C was slowly
added a THF solution of NHMe2PhBPh4 (0.685 g, 1.55 mmol)
cooled to -78 °C. After 5 min of stirring, a white crystalline
precipitate was obtained when the solution was slowly warmed
to room temperature. The solid was filtered, washed with cold
THF, and dried under vacuum, giving 0.5 g of product (yield
50%). Anal. Calcd for C38H42B2OZr: C, 72.73; H, 6.75; B, 3.45;
Zr, 14.53. Found: C, 72.19; H, 6.92; B, 3.40; Zr, 13.75. 1H NMR
(THF-d8, 326 K, ppm): 7.45 (br m, 8 H), 7.01 (t, J CH ) 7.3 Hz,
8 H), 6.86 (t, J CH ) 7.1 Hz, 4 H) (B(C6H5)4); 6.58 (s, 10 H, C5H5);
L ) donor ligands
Exp er im en ta l Section
Gen er a l P r oced u r e. All manipulations were performed
either on a high-vacuum line or in a glovebox under a purified
argon atmosphere. Solvents were distilled from Na/benzophe-
none for THF and Et2O and from Na/K alloy for pentane and
toluene. Cp2Zr(BH4)2,4a (C5H4Me)2ZrCl2,7 (C5H4SiMe3)2ZrCl2,22
23
and NHMe2PhBPh4 were synthesized by the literature
1
3.74, 1.90 (m, 8 H, THF); 0.45 (q, J BH ) 92 Hz, 4 H, BH4). H
methods. NMR spectra were recorded on Bruker WM 80, 200,
and 250 MHz instruments. EPR spectra were recorded on a
Bruker ER 200T spectrometer. Quantitative EPR measure-
ments were performed with an external standard of TEMPO
of known concentration, and the acquisition parameters were
kept constant for both the unknown and the standard sample
measurements. Chemical analyses were performed by either
the Service Central de Microanalyse du CNRS or by our
laboratory services.
NMR (CD3CN, 298 K, ppm): 7.28 (br m, 8 H), 7.00 (t, J CH
)
7.3 Hz, 8 H), 6.85 (t, J CH ) 7.2 Hz, 4 H) (B(C6H5)4); 6.25 (s, 10
H, C5H5); 3.65 (4H), 1.80 (4 H) (free THF); 1.53 (q, J BH ) 96
Hz, 4 H, BH4). 13C{1H} NMR (CD3CN, 293 K, ppm): 164.8,
136.8, 126.7, 122.8, (B(C6H5)4); 113.3 (C5H5); 68.3, 26.3 (free
THF). 11B{1H} NMR (C6D6/THF, 293 K, ppm): -6.2 (B(C6H5)4),
BH4 not observed. IR: 2467-2415 cm-1, B-Ht str; 2121 cm-1
B-Hb str.
,
[(C5H4Me)2Zr (BH4)(THF )][BP h 4] (6). To a stirred THF
solution of (C5H4Me)2Zr(BH4)2 (0.445 g, 1.6 mmol) at -78 °C
was slowly added a THF solution of NHPhMe2BPh4 (0.685 g,
1.55 mmol) cooled to -78 °C. After 5 min of stirring, a white
crystalline precipitate was observed when the solution was
warmed to room temperature. The solid was then filtered,
washed with cold THF, and dried under vacuum, giving 0.565
g of product (yield 54%). Anal. Calcd for C40H46B2OZr: C,
73.28; H, 7.07; Zr, 13.91. Found: C, 72.04; H, 7.09; Zr, 13.23.
1H NMR (THF-d8, 293 K, ppm): 7.40 (br m, 8 H), 6.99 (t, J CH
) 7.2 Hz, 8 H), 6.84 (t, J CH ) 7.1 Hz, 4 H) (B(C6H5)4); 6.42 (4
H), 6.25 (4 H) (C5H4Me); 3.74, 1.89 (m, 8 H, THF); 2.34 (s, 6H,
Me); 0.40 (q, J BH ) 84 Hz, 4 H, BH4). 13C{1H} NMR (THF-d8,
293 K, ppm): 137.7, 126.3, 122.4 (B(C6H5)4); 138.4, 130.8, 128.5
(C5H4Me); 16.2 (CH3). 11B{1H} NMR (C6D6/THF, 293 K,
ppm): -6.4 (B(C6H5)4); BH4 not observed. IR: 2472-2429
cm-1, B-Ht str; 2119 cm-1, B-Hb str.
[(C5H4SiMe3)2Zr (BH4)(THF )][BP h 4] (7). An NMR sample
was prepared as follows: NHMe2PhBPh4 (0.156 g, 0.35 mmol)
was added to a THF-d8 solution of 3 (0.140 g,; 0.35 mmol).
Evolution of B2H6 occurred, which was characterized by MS.
1H NMR (THF-d8, 293 K, ppm): 7.8-6.5 (m, B(C6H5)4, NMe2-
Ph); 6.40, 6.21, 6.08, 5.74 (pseudo q, 8 H, J CH ) 3 Hz, C5H4);
0.38 (s, 18 H, SiMe3); -0.16 (br q, J BH ) 90 Hz, 4 H, BH4).
11B{1H} NMR (C6D6/THF, 293 K, ppm): -6.2 (B(C6H5)4); BH4
not observed.
(C5H4Me)2Zr (BH4)2 (2). A toluene solution of (C5H4-
Me)2ZrCl2 (2.0 g, 6.2 mmol) was stirred with an excess of LiBH4
(0.68 g, 31.2 mmol) for 48 h, at room temperature. The
mixture was filtered on Celite to remove the excess unreacted
LiBH4 and LiCl and the filtrate concentrated to a small volume
and left overnight at -30 °C. A white solid product was
collected by filtration, washed with pentane, and dried under
vacuum, giving 1.3 g of product (yield 75%). Anal. Calcd for
C
12H22B2Zr: C, 51.63; H, 7.94. Found: C, 51.46; H, 7.91. 1H
NMR (C6D6, 293 K, ppm): 5.60 (t, J CH ) 2,7 Hz, 4 H, C5H4),
5.44 (t, J CH ) 2,6 Hz, 4 H, C5H4), 1.92 (s, 6 H, Me), 0.80 (q,
J BH ) 85 Hz, H, BH4).
(C5H4SiMe3)2Zr (BH4)2 (3). An Et2O solution of (C5H4-
SiMe3)2ZrCl2 (1 g, 2.3 mmol) was stirred with an excess of
LiBH4 (0.4 g, 18 mmol) for 48 h, at room temperature. The
mixture was evaporated to dryness; then toluene was added.
The mixture was filtered on Celite to remove the excess
(20) Grassi, A.; Zambelli, A.; Laschi, F. Organometallics 1996, 15,
480. We reason that a [CpMR2]+ complex provides access to a [CpMR]+
species (and other unidentified complexes) via a redistribution reaction
(the presence of a metal-carbon bond in the coordination sphere of
the cationic [CpMR]+ reflects the possibility of having access to a new
catalytic cationic system).
(21) Other proposed deactivation pathways are (i) the formation of
dinuclear species by R- or â-CH activation and (ii) aryl or fluoride
transfer from the counteranion to the cationic complex.
(22) Lappert, M. F.; Pickett, C. J .; Riley, P. I.; Yarrow, P. I. W. J .
Chem. Soc., Dalton Trans. 1981, 805.
P r ep a r a tion in Situ of 8 a n d 9. : In an NMR tube, excess
PMe2Ph (at least 5 equiv) is added to a THF-d8 suspension of
5 (0.120 g, 0.19 mmol) or 6 (0.10 g, 0.15 mmol). Immediate
(23) (a) Bochmann, M.; Wilson, L. J . Chem. Soc., Chem. Commun.
1986, 1610. (b) Crane, F. E., J r. Anal. Chem. 1956, 28, 1794.

Disproportionation of Cationic Zirconium Complexes
Organometallics, Vol. 16, No. 25, 1997 5521
Ta ble 2. Cr ysta l Da ta a n d Da ta Collection a n d
Refin em en t Deta ils for Com p ou n d 6
solubilization occurs, giving the cationic hydride complex
[(C5H4R)2ZrH(PMe2Ph)2]BPh4 (R ) H (8), Me (9)). 8: 1H NMR
(THF-d8, 293 K, ppm) 8-6.9 (m, B(C6H5)4, Ph), 5.68 (t, J HP
)
Crystal Data and Data Collection
3 Hz, 10 H, (C5H5), 2.17 (t, J HP ) 103 Hz, 1 H, Zr-H), 1.7
(pseudo t, J HP ) 3.5 Hz, 12 H, Zr(PMe2Ph)2), 1.6 (d, J HP ) 10.4
Hz, 6 H, PMe2Ph‚BH3), 1.4 (free PMe2Ph); 31P{1H} NMR (THF-
d8, ppm) 21.0 (ZrH(PMe2Ph)2), 9.4 (q, J BP ) 56 Hz, PMe2-
Ph‚BH3), -40 (free PMe2Ph). 9: 1H NMR (THF-d8, 293 K,
ppm) 7.9-6.8 (m, B(C6H5)4, Ph), 5.6-5.2 (quint, J HP ) 2,6 Hz,
8H, C5H4), 2.24 (s, 6H, CH3), 2.23 (t, J HP ) 104 Hz, 1H, ZrH),
1.97 (pseudo t, J HP )3, 6 Hz, 12H, Zr(PMe2Ph)2), 1.71 (d, J HP
) 10,4 Hz, 6 H, PMe2Ph‚BH3), 1.5 (free PMe2Ph); 31P (THF-
d8, ppm) 22.6 (d, J HP ) 102 Hz, ZrH(PMe2Ph)2), 9 (m, PMe2-
Ph‚BH3), -40 (free PMe2Ph); 11B (THF-d8, ppm) -6.4 (s,
B(C6H5)4), -38 (d, J BP ) 56 Hz, PMe2Ph-BH3).
P r ep a r a tion in Situ of 10. In an NMR tube, NHMe2-
PhBPh4 (44 mg, 0.15 mmol) was added to a THF-d8 solution
of 3 (60 mg, 0.15 mmol); then 5 equiv of PMe2Ph was added,
which gave [(C5H4SiMe3)2ZrH(PMe2Ph)2]BPh4 (10). 1H NMR
(THF-d8, 293 K, ppm): 7.82-6.82 (m, B(C6H5)4, Ph), 6.10 (s,
4H, C5H4), 5.49 (s, 4H, C5H4), 1.9 (t, J HP ) 3.2 Hz, 12H,
Zr(PMe2Ph)2), 1.6 (d, J HP ) 10.4 Hz, 6 H, PMe2Ph‚BH3), 1.4
(free PMe2Ph), 0.32 (s, 18 H, SiMe3). 31P NMR (THF-d8,
ppm): 19.9 (d, J HP ) 113 Hz, ZrH(PMe2Ph)2), 9 (q, J BP ) 56
Hz, PMe2Ph‚BH3), -40 (free PMe2Ph).
Cr ysta llogr a p h y Stu d y for th e Com p ou n d [(C5H4Me)-
Zr (BH4)(THF )]BP h 4 (6). Data collection was performed at
low temperature (T ) 180 K) on a IPDS STOE diffractometer
using graphite-monochromatized Mo KR radiation equipped
with Oxford Cryostream cooling device. Details on data
collection, crystal parameters, and refinements are sum-
marized in Table 2. Corrections were made for Lorentz and
polarization effects on the data. Computations were performed
by using the CRYSTALS package24 adapted for a PC. The
atomic scattering factors for all atoms were taken from the
literature.25 The structure was solved by direct methods using
SIR9226 and subsequent difference Fourier maps. All hydro-
gen atoms were located by difference Fourier maps, but their
coordinates were introduced in processes of refinement as fixed
contributors in calculated positions (C-H ) 0.96 Å) and
recalculated after each cycle of refinement. Their U(iso) values
were fixed 20% higher than those of the carbon atoms to which
they were attached, except for the hydrogen atoms of BH4,
chem formula
fw
cryst syst
space group
a (Å)
[(C5H4Me)Zr(BH4)(THF)]BPh4
655.65
monoclinic
P21/n
26.405(2)
9.5866(8)
28.473(2)
110.275(6)
6761
8; 3.48
1.29
colorless
0.50 × 0.30 × 0.10
block
Mo KR
180
43329
9305
b (Å)
c (Å)
â (deg)
cell vol (Å3)
Z; D (g cm-3
)
µ (cm-1
cryst color
)
cryst size (mm)
cryst form
radiation type
temp (K)
no. of reflns collected
no. of reflns merged
Rav
0.052
24.2
θmax (deg)
Refinement
refinement on
F
Ra
Rw
0.056
0.068
none
1
1.07
6261
I > σ(I)
826
b
abs cor
weighting scheme
goodness of fitc
no. of rflns used
observn criterion
no. of params refined
a
b
R ) ∑(||Fo| - |Fc||)/∑|Fo|. Rw ) [∑w(||Fo| - |Fc||)2/∑w(|Fo|)2]1/2
.
c Goodness of fit ) [∑(|Fo - Fc|)2/(Nobservns - Nparams)]1/2
.
which were refined isotropically. All non-hydrogen atoms were
anisotropically refined; full-matrix least-squares refinements
were carried out by minimizing the function ∑w(||Fo| - |Fc||)2,
where Fo and Fc are the observed and calculated structure
factors. Models reached convergence with the formulas R )
∑(||Fo| - |Fc||)/∑|Fo| and Rw ) [∑w(||Fo| - |Fc||)2/∑w(|Fo|)2]1/2
.
A diagram was produced by using the program CAMERON.27
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tal data and data collection and structure refinement details,
bond distances and angles, and positional and thermal pa-
rameters for 6 (14 pages). Ordering information is given on
any current masthead page.
(24) Watkin, D. J .; Prout, C. K.; Carruthers, R. J .; Betteridge, P.
CRYSTALS, Issue 10; Chemical Crystallography Laboratory, Oxford,
U.K., 1996.
(25) International Tables for X-Ray Crystallography; Kynoch
Press: Birmingham, U.K., 1974; Vol. IV.
(26) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guargiardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. SIR92, a Program for Automatic
Solution of Crystal Structures by Direct Methods. J . Appl. Crystallogr.
1994, 27, 435.
OM9701736
(27) Watkin, D. J .; Prout, C. K.; Pearce, L. J . CAMERON; Chemical
Crystallography Laboratory, University of Oxford, Oxford, U.K., 1996.