Borato-cyclopentadienyl half-sandwich complexes. Crystal structures of [NEt4][C5H5B(C6F5) 3]·CH2Cl2 and [NEt4]2[{C5H4B(C<su

Article abstract of DOI:10.1021/om980395j

Cation exchange of [Li(THF)₄]⁺[C₅H₅B(C ₆F₅)₃]^- with [NEt₄][BF₄] gives the stable, ether-free salt [NEt₄]-[C₅H₅B(

Full text of DOI:10.1021/om980395j

© Copyright 1998
Volume 17, Number 18, August 31, 1998
American Chemical Society
Communications
Bor a to-Cyclop en ta d ien yl Ha lf-Sa n d w ich Com p lexes.
Cr ysta l Str u ctu r es of [NEt4][C5H5B(C6F 5)3]‚CH2Cl2 a n d
[NEt4]2[{C5H4B(C6F 5)3}Zr (µ-Cl)Cl2]2
Simon J . Lancaster, Mark Thornton-Pett, David M. Dawson, and
Manfred Bochmann*
School of Chemistry, University of Leeds, Leeds LS2 9J T, U.K.
Received May 18, 1998
Summary: Cation exchange of [Li(THF)4]+[C5H5B(C6F5)3]-
Sch em e 1
with [NEt4][BF4] gives the stable, ether-free salt [NEt4]-
[C5H5B(C6F5)3], which reacts cleanly with Zr(NMe2)4 to
afford [NEt4][{C5H4B(C6F5)3}Zr(NMe2)3] in good yield.
The triamide is readily converted into the crystallo-
graphically characterized dimeric trichloride [NEt4]2-
[{C5H4B(C6F5)3}Zr(µ-Cl)Cl2]2.
Some time ago we described the synthesis of the
cyclopen t a dien yl-t r is(pen t a flu or oph en yl)bor a t e
[Li(THF)4]+[C5H5B(C6F5)3]- (1), its deprotonation by
butyllithium to the dianion [C5H4B(C6F5)3]2- (2), and
the synthesis of the anionic and zwitterionic metallocene
complexes 3 and 4 (Scheme 1).1 The zwitterions 4 are
attractive as alternatives to cationic metallocene-based
alkene polymerization catalysts.2,3 Very recently, Bon-
cella et al.4 published the synthesis of ether-free ana-
logues of 1, Li[C5H5B(C6F5)3] and Li[1,3-Me3SiC5H4B-
(C6F5)3], but found that attempts to generate zirconium
with Zr(NMe2)4 produced only complex mixtures, while
treatment with Cp*ZrMe3 led to elimination of B(C6F5)3
to give neutral metallocenes (eq 1). This report prompts
complexes by reacting these cyclopentadienylborates
(1) Bochmann, M.; Lancaster, S. J .; Robinson, O. B. J . Chem. Soc.,
Chem. Commun. 1995, 2081.
(2) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255. Kamin-
sky, W. J . Chem. Soc., Dalton Trans. 1998, 1413.
(3) Ruwwe, J .; Erker, G.; Fro¨hlich, R. Angew. Chem., Int. Ed. Engl.
1996, 35, 80. For related zwitterionic complexes see: Song, X.;
Bochmann, M. J . Organomet. Chem. 1997, 545-546, 597. Sun, Y.;
Spence, R. E. v. H.; Piers, W. E.; Parvez, M.; Yap, G. P. A. J . Am.
Chem. Soc. 1997, 119, 5132. Piers, W. E. Chem. Eur. J . 1998, 4, 13.
(4) Shafiq, F. A.; Abboud, K. A.; Richardson, D. E.; Boncella, J . M.
Organometallics 1998, 17, 982.
S0276-7333(98)00395-1 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 08/07/1998

3830 Organometallics, Vol. 17, No. 18, 1998
Communications
Sch em e 2
us to describe some of our results concerning the
synthesis of ether-free cyclopentadienyl-borates and
the syntheses of the zirconium borato-Cp half-sandwich
complexes [{C5H4B(C6F5)3}ZrX3]- (X ) NMe2, Cl, CH2-
Ph) in good yields.
The reaction of LiCp with B(C6F5)3 in THF gives [Li-
(THF)4][C5H5B(C6F5)3] (1), which on evaporation of the
solvent is isolated as a white solid. Exchange of the [Li-
(THF)4]+ cation is facile; treatment of 1 with [NEt4][BF4]
affords [NEt4][C5H5B(C6F5)3] (1a ), while the analogous
reaction with [PPh4]Cl gives [PPh4][C5H5B(C6F5)3] (1b).5
These ether-free compounds are soluble in polar solvents
and chlorocarbons but only sparingly soluble in toluene
and insoluble in hexane.
Recrystallization of 1a from dichloromethane gives
colorless crystals of 1a ‚CH2Cl2 suitable for X-ray dif-
fraction. The structure of the anion in 1a is shown in
Figure 1.6 In agreement with the NMR data, the X-ray
results confirm that the 2-borato isomer is formed, in
contrast to the trimethylsilyl-Cp derivative reported by
Boncella et al.,3 where the B(C6F5)3 substituent is
attached at the 3-position.
F igu r e 1. Structure of the [C5H5B(C6F5)3]- anion in 1a .
Selected bond lengths (Å) and angles (deg): B-C(11),
1.660(3); B-C(21), 1.658(3); B-C(31), 1.660(3); B-C(41),
1.618(3); C(41)-C(42), 1.512(3); C(42)-C(43), 1.482(3);
C(43)-C(44), 1.340(4); C(44)-C(45), 1.468(3); C(45)-C(41),
1.349(3); C(11)-B-C(21), 103.1(2); C(11)-B-C(31), 111.9(2);
C(11)-B-C(41), 115.4(2); C(45)-C(41)-C(42), 106.5(2);
C(41)-C(42)-C(43), 105.2(2).
The deprotonation of cyclopentadienes with group 4
metal amides is a well-established method for the
synthesis of metallocene derivatives.7 Treatment of 1a
with 1 equiv of Zr(NMe2)4 in Et2O at room temperature
over a period of 6 h gives a clear dark yellow solution
from which, on standing, the tris(amido) complex [NEt4]-
[{C5H4B(C6F5)3}Zr(NMe2)3] (5) precipitates in 60% yield
(Scheme 2).8 The complex shows characteristic 1H NMR
signals at δ 6.01 and 6.08 (2 H each) for the C5H4 ring
and a singlet at δ 2.64 (18 H) for three NMe2 ligands.
Recrystallization from dichloromethane affords colorless
needle cushions, although X-ray-quality crystals could
not be obtained.
Compound 5 reacts smoothly with an excess of
Me3SiCl to give the trichloride (6) as colorless crystals.
The crystal structure9 shows the anion in 6 to be a
chloro-bridged dimer, [NEt4]2[{C5H4B(C6F5)3}Zr(µ-Cl)-
(8) 5: 6.09 g of 1a (8.61 mmol) and 2.54 g of Zr(NMe2)4 (9.49 mmol)
were combined in a flask, and 40 mL of diethyl ether was added at
room temperature. The reaction mixture was stirred for 6 h as the
solids gradually dissolved to give a yellow solution. The solution was
filtered to separate a small amount of insoluble material; crystallization
then began immediately. Cooling to 5 °C overnight gave off-white
needlelike cushions, yield 4.8 g (5.2 mmol, 60%). Anal. Calcd for C37H42
-
(5) 1a : a mixture of 43.26 g (50 mmol) of [Li(THF)4][C5H5B(C6F5)3]
and 10.9 g (50 mmol) of Et4NBF4 in 400 mL of CH2Cl2 was stirred for
3 h at room temperature. The solids were allowed to settle over 4 h
before separation by filtration. Concentration of the filtrate and cooling
to -20 °C overnight yielded 25.3 g of 1a ‚CH2Cl2 (64%). Anal. Calcd
for C52H27BCl2F15N: C, 48.5; H, 3.4; N, 1.8. Found: C, 49.1; H, 3.5; N,
1.5. For spectroscopic details and the synthesis of 1b see the Supporting
Information.
(6) Crystal data of 1a ‚CH2Cl2: C31H25BF15N‚CH2Cl2, fw 792.26,
monoclinic, space group P21/c, a ) 8.9303(7) Å, b ) 24.383(2) Å, c )
15.5493(13) Å, â ) 98.942(6)°, V ) 3344.7(5) Å3, Z ) 4, F(000) ) 1600,
5391 independent reflections, final R1 ) 0.0428, wR2 ) 0.1110 (I >
2σ(I)). The structure was solved by direct methods.
(7) Hughes, A. K.; Meetsma, A.; Teuben, J . H. Organometallics 1993,
12, 1936. Diamond, G. M.; Rodewald, S.; J ordan, R. F. Organometallics
1995, 14, 5. Diamond, G. M.; J ordan, R. F.; Petersen, J . L. Organo-
metallics 1996, 15, 4030. Diamond, G. M.; J ordan, R. F.; Petersen, J .
L. Organometallics 1996, 15, 4045. Christopher, J . N.; Diamond, G.
M.; J ordan, R. F.; Petersen, J . L. Organometallics 1996, 15, 4038.
BF15N4Zr: C, 47.8; H, 4.6; N, 6.0. Found: C, 47.4; H, 4.6; N, 5.8. For
spectroscopic data see the Supporting Information. 6: To a solution of
6.81 g of 5 (7.32 mmol) in 30 mL of CH2Cl2 was added via syringe at
-78 °C 5.69 mL (44.8 mmol) of SiClMe3. The reaction mixture was
warmed slowly to room temperature and stirred for 6 h. A small
amount of precipitate was separated by filtration before concentrating
the solution to 20 mL and cooling to -20 °C to give colorless cubic
crystals. Further concentration and cooling gave a second crop of
crystals, combined yield 4.5 g (2.28 mmol, 62%). Anal. Calcd for
C
62H48B2Cl6F30N2Zr2‚2CH2Cl2: C, 38.9; H, 2.7; N, 1.4. Found: C, 39.3;
H, 2.7; N, 1.6. 1H NMR (300 MHz, CD2Cl2, 20 °C): δ 6.77 (br, 2H,
2,5-CpB), 6.67 (br, 2H, 3,4-CpB), 3.26 (q, 8H, J HH′ ) 7.3, NCH2CH3),
1.30 (t, 12H, J HH ) 7.3, NCH2CH3). 13C{1H} NMR (75.47 MHz, CD2-
Cl2, 20 °C): δ 148.75 (d, J CF ) 238.8 Hz, o-C of C6F5), 138.78 (d, J CF )
246.5 Hz, p-C of C6F5), 137.13 (d, J CF ) 250.1 Hz, m-C of C6F5), 125.06
(2,5-CpB), 122.23 (3,4-CpB), 52.87 (NCH2CH3), 7.49 (NCH2CH3). 11B
NMR (96.24 MHz, CD2Cl2, 20 °C): δ -15.21. 19F NMR (282.39 MHz,
CD2Cl2, 20 °C): δ -132.07 (d, J FF ) 21.2 Hz, o-F), -161.93 (t, J FF
20.2 Hz, p-F), -165.40 (t, J FF ) 20.3 Hz, m-F).
)

Communications
Organometallics, Vol. 17, No. 18, 1998 3831
sponding aluminate anion [C5H5Al(C6F5)3]- is even more
labile, and its formation is already reversed by the
addition of THF to diethyl ether solutions (eq 3). The
displacement of Cp- from the Cp-borate is of course no
longer possible once 1 has been deprotonated to the
dianion 2 or the Cp ring is coordinated to the metal.
Complex 7 is obtained in much higher yield (55%) by
alkylating 6 with PhCH2MgCl and is isolated as an
amorphous, spectroscopically pure orange-yellow pow-
der.12
In our earlier communication1 we reported the forma-
tion of a zirconium tribenzyl species which, on the basis
of spectroscopic data, was formulated as [Li(THF)4]+-
[(C6F5)2B(C5H4)2{Zr(CH2Ph)3}2]-. Following our recent
synthesis of the cyclopentadienyl-boranes (C6F5)2B-
(C5H5) and (C6F5)2B(C5H4SiMe3),13 we attempted to
reproduce the synthesis of [(C6F5)2B(C5H5)2]- and
[(C6F5)2B(C5H4SiMe3)2]- as precursors to such bi-nuclear
complexes. However, all attempts to isolate bis(cyclo-
pentadienyl)-borate anions by reacting (C6F5)2B(C5H4R)
(R ) H or SiMe3) with cyclopentadienyl anions under a
variety of conditions invariably led to intractable oils
and decomposition products. A reexamination of the
earlier data, therefore, leads us to conclude that the
compound originally described as a borato-bridged di-
nuclear species was in fact mononuclear [Li(THF)4]-
[(C6F5)3B(C5H4)Zr(CH2Ph)3], which has NMR param-
eters very close to those of 7, with small chemical shift
differences being most likely due to the presence of the
different cations.
F igu r e 2. Structure of the anion in 6‚2CH2Cl2. Selected
bond lengths (Å) and angles (deg): Zr(1)-Cl(1), 2.6035(7);
Zr(1)-Cl(2), 2.503(3); Zr(1)-Cl(3), 2.503(3); Zr(1)-Cl(3),
2.4200(8); Zr(1)-F(112), 2.441(2); Zr(2)-F(212), 2.420(2);
Cl(1)-Zr(1)-Cl(2), 72.80(2); Cl(2)-Zr(1)-Cl(3), 79.81(3);
Cl(2)-Zr(1)-Cl(4), 83.73(3); Cl(4)-Zr(1)-F(112), 157.20-
(4); Zr(1)-Cl(1)-Zr(2), 108.00(3).
Cl2]2 (Figure 2), despite the very significant bulk of the
-B(C6F5)3 substituents. If one assumes one coordina-
tion site to be occupied by the Cp ligand, Cp and the
four Cl ligands around zirconium occupy five positions
of a distorted octahedron, which is completed by a close
contact between zirconium and one of the ortho-F atoms
of the C6F5 groups. The average Zr‚‚‚F distance of
2.430(2) Å is comparable to similar Zr‚‚‚F interactions
in (C5Me5)Zr(C6F5){η4-C4H5B(C6F5)2} (2.4292(15) Å)10
and Cp2Zr{η3-C4H6B(C6F5)3} (2.423(3) Å).11
The reaction of 1a with Zr(CH2Ph)4 in diethyl ether
gives CpZr(CH2Ph)3 and [NEt4][PhCH2B(C6F5)3], while
the same reaction in toluene leads to a mixture of
CpZr(CH2Ph)3 with minor quantities of NEt4[{C5H4B-
(C6F5)3}Zr(CH2Ph)3] (7). This behavior is readily un-
derstood by considering the formation of [C5H5B(C6F5)3]-
from Cp- and B(C6F5)3 as an equilibrium reaction which
may be reversed under certain conditions. For example,
while in THF the formation of [C5H5B(C6F5)3]- from Cp-
and B(C6F5)3 is essentially quantitative, the addition of
pyridine gives Cp- and py‚B(C6F5)3 (eq 2). The corre-
Ack n ow led gm en t. This work was supported by the
Engineering and Physical Sciences Research Council.
Su p p or tin g In for m a tion Ava ila ble: Text giving pre-
parative and spectroscopic details for 1a , 1b, 5, and the
formation of [C5H5Al(C6F5)3]- and tables giving crystal data
and structure refinement details, atomic coordinates, displace-
ment parameters, and bond lengths and angles for 6 (25
pages). Ordering information is given on any current mast-
head page.
OM980395J
(9) Crystal data of 6: C62H48B2Cl6F30N2Zr2‚2CH2Cl2, fw 1977.64,
triclinic, space group P1h, a ) 11.345 30(10) Å, b ) 18.8050(2) Å, c )
18.8553(2) Å, R ) 90.809(7)°, â ) 106.220(5)°, γ ) 103.812(7)°, V )
3736.82(7) Å3, Z ) 2, F(000) ) 1960, 12 925 independent reflections,
final R1 ) 0.0374, wR2 ) 0.0986 (I > 2σ(I)). The structure was solved
by Patterson methods.
(10) (a) J ime´nez Pindado, G.; Thornton-Pett, M.; Bowkamp, M.,
Meetsma, A.; Hessen, B.; Bochmann, M. Angew. Chem. 1997, 109,
2457; Angew. Chem., Int. Ed. Engl. 1997, 36, 2358. (b) J ime´nez
Pindado, G.; Thornton-Pett, M.; Bochmann, M. J . Chem. Soc., Dalton
Trans. 1997, 3115.
(12) 7: from 1.66 g of 5 (1.7 mmol) and PhCH2MgCl (1.0 M, 10 mL)
in Et2O (30 mL, 0 °C). Extraction with CH2Cl2 and evaporation of the
solvent gave 7 as a golden foam (1.0 g, 0.93 mmol, 55%). 1H NMR (300
MHz, CD2Cl2, 20 °C): δ 7.10 (t, 6H, J HH ) 6.2 Hz, m-H, Ph), 6.87 (t,
3H, J HH ) 7.3 Hz, p-H, Ph), 6.58 (d, 6H, J HH ) 7.1 Hz, o-H, Ph), 6.10
(br, 2H, 2,5-CpB), 5.53 (t, 2H, J HH ) 3.0 Hz, 3,4-CpB), 2.89 (q, 8H,
J HH ) 7.3 Hz, NCH2CH3), 1.43 (s, 6H, CH2Ph), 1.14 (tr, 12 H, J HH )
7.3 Hz, NCH2CH3). 13C{1H} NMR (75.47 MHz, CD2Cl2, 20 °C): δ 148.1
(d, J CF ) 232.7 Hz, o-C of C6F5), 146.55 (ipso-C of Ph), 137.74 (d, J CF
) 231.4 Hz, p-C of C6F5), 136.35 (d, J CF ) 234.2 Hz, m-C of C6F5),
128.43 (m-C of Ph), 126.84 (o-C of Ph), 121.19 (p-C, Ph), 117.06 (2,5-
CpB), 115.13 (3,4-CpB), 66.72 (CH2Ph), 52.10 (NCH2CH3), 6.78
(NCH2CH3). 11B NMR (96.29 MHz, CD2Cl2, 20 °C): δ -14.07.
(13) Duchateau, R.; Lancaster, S. J .; Thornton-Pett, M.; Bochmann,
M. Organometallics 1997, 16, 4995.
(11) (a) Temme, B.; Erker, G.; Karl, J .; Luftmann, R.; Fro¨hlich, R.;
Kotila, S. Angew. Chem. 1995, 107, 1867; Angew. Chem., Int. Ed. Engl.
1995, 34, 1755. (b) Karl, J .; Erker, G.; Fro¨hlich, R. J . Am. Chem. Soc.
1997, 119, 11165.