Reactions of zinc dialkyls with (perfluorophenyl)boron compounds: Alkylzinc cation formation vs C6F5 transfer

Article abstract of DOI:10.1021/om0103557

Reaction between ZnR₂ and [H(OEt₂)₂] [B(C₆F₅)₄] in ether leads to the salts [RZn(OEt₂)₃]-[B(C₆F₅)₄], while mixtures of ZnR₂ (R = Me, Et) and B(C₆F₅)₃ in toluene-d₈ undergo facile alkyl/C₆F₅ group exchange to give Zn(C₆F₅)₂·(toluene). Mixtures of ZnR₂ and B(C₆F₅)₃ in hydrocarbon/diethyl ether solvent mixtures react with alkyl transfer to afford the ion pairs [RZn(OEt₂)₃][RB(C₆ F₅)₃], whereas the reaction of ZnEt₂ with [Ph₃C][B(C₆F₅)₄] in toluene-d₈ proceeds with β-H abstraction to give ethene and Ph₃CH, with the subsequent rapid formation of Zn(C₆F₅)₂.

Full text of DOI:10.1021/om0103557

3772
Organometallics 2001, 20, 3772-3776
Rea ction s of Zin c Dia lk yls w ith (P er flu or op h en yl)bor on
Com p ou n d s: Alk ylzin c Ca tion F or m a tion vs C6F 5
Tr a n sfer
Dennis A. Walker,† Timothy J . Woodman,† David L. Hughes,‡ and
Manfred Bochmann*,†
Wolfson Materials and Catalysis Centre, School of Chemical Sciences, University of East
Anglia, Norwich NR4 7TJ , U.K., and Biological Chemistry Department, J ohn Innes Centre,
Norwich Research Park, Norwich NR4 7UH, U.K.
Received May 1, 2001
Reaction between ZnR2 and [H(OEt2)2][B(C6F5)4] in ether leads to the salts [RZn(OEt2)3]-
[B(C6F5)4], while mixtures of ZnR2 (R ) Me, Et) and B(C6F5)3 in toluene-d8 undergo facile
alkyl/C6F5 group exchange to give Zn(C6F5)2‚(toluene). Mixtures of ZnR2 and B(C6F5)3 in
hydrocarbon/diethyl ether solvent mixtures react with alkyl transfer to afford the ion pairs
[RZn(OEt2)3][RB(C6F5)3], whereas the reaction of ZnEt2 with [Ph3C][B(C6F5)4] in toluene-d8
proceeds with â-H abstraction to give ethene and Ph3CH, with the subsequent rapid formation
of Zn(C6F5)2.
In tr od u ction
(OEt2)2]+[RB(C6F5)3]-, which have been used as activa-
tors in high-temperature alkene polymerizations.6
As has recently been shown, aluminum trialkyls react
with B(C6F5)3 in hydrocarbon solvents under ligand
exchange; for example, the reaction of AlMe3 with
B(C6F5)3 provides a convenient route for the preparation
of Al(C6F5)3.1 Similar exchange reactions have been
observed between M(C6F5)3 (M ) Al, B) and MAO (or
MMAO)2 and in the reaction of AlR3 with [Ph3C]-
[B(C6F5)4].3 Some, such as AlEt3/B(C6F5)3 mixtures,
show modest ethene polymerization activity.4 This
propensity to ligand redistribution in main-group alkyls
is in contrast to the reactions of (perfluoroaryl)boron
compounds with early-transition-metal alkyls, notably
Cp2ZrMe2, which lead to alkyl abstraction and ionic or
zwitterionic products.5 On the other hand, in coordinat-
ing solvents the reaction between aluminum trialkyls
and B(C6F5)3 gives solvent-stabilized ion pairs, [R2Al-
The behavior of zinc alkyls under similar conditions
has not been studied so far. Some cationic zinc alkyl
complexes have been generated by adding nitrogen
macrocycles or crown ethers to zinc alkyls in the
presence of AlR3 or tetraphenylcyclopentadiene, to give
[RZn(crown)]+X- (X ) AlR4, C5HPh4).7 We were there-
fore interested in exploring the possibility of stabilizing
cationic zinc alkyls with weakly coordinating perfluo-
roarylborate anions.
Resu lts a n d Discu ssion
The reaction of ZnR2 with an equimolar amount of
“J utzi’s acid”,8 [H(OEt2)2]+[B(C6F5)4]-, in diethyl ether
proceeds quantitatively under alkane elimination to give
the salts [RZn(OEt2)3]+[B(C6F5)4]- (1, R ) Me; 2, R )
Et; 3, R ) But) (eq 1). These compounds are obtained
* To whom correspondence should be addressed. E-mail:
m.bochmann@uea.ac.uk.
[H(OEt2)2][B(C6F5)4] + ZnR2 Et O8
† University of East Anglia.
2
‡ Norwich Research Park.
(1) Biagini, P.; Lugli, G.; Abis, L.; Andeussi, P. U. S. Patent 5,602,-
269, 1997 (Enichem).
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0009515 (Dow Chemical Co.). (b) Lee, C. H.; Lee, S. J .; Park, J . W.;
Kim, K. H.; Lee, B. Y.; Oh, J . S. J . Mol. Catal., A: Chem. 1988, 132,
231. (c) Carnahan, E. M.; Chen, E. Y.-W.; J acobsen, G. B.; Stevens, J .
C. PCT Int. Appl. WO 99/15534 (Dow Chemical Co.).
(3) Bochmann, M.; Sarsfield, M. J . Organometallics 1998, 17, 5908.
(4) Kim, J . S.; Wojcinski, L. M.; Liu, S.; Sworen, J . C.; Sen, A. J .
Am. Chem. Soc. 2000, 122, 5668. For ethene polymerizations with
cationic aluminum alkyls see also: Coles, M. P.; J ordan, R. F. J . Am.
Chem. Soc. 1997, 119, 8125. Ihara, E.; Young, V. G.; J ordan, R. F. J .
Am. Chem. Soc. 1998, 120, 8277. Radzewich, C. E.; Guzei, I. A.; J ordan,
R. F. J . Am. Chem. Soc. 1999, 121, 8673. Bruce, M.; Gibson, V. C.;
Redshaw, C.; Solan, G. A.; White, A. J . P.; Williams, D. J . Chem.
Commun. 1998, 2523. Qian, B.; Ward, D. L.; Smith, M. R. Organome-
tallics 1998, 17, 3070.
(5) Reviews: (a) Erker, G. Acc. Chem. Res. 2001, 34, 309. (b) Chen,
E. Y.-X.; Marks, T. J . Chem. Rev. 2000, 100, 1391. (c) J ordan, R. F.,
Ed. J . Mol. Catal. 1998, 128, 1. (d) McKnight, A. L.; Waymouth, R. M.
Chem. Rev. 1998, 98, 2587. (e) Bochmann, M. J . Chem. Soc., Dalton
Trans. 1996, 255. (f) Brintzinger, H. H.; Fischer, D.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
[RZn(OEt2)3]+[B(C6F5)4]- (1)
t
R ) Me (1), Et (2), Bu (3)
(6) (a) Klosin, J .; Roof, G. R.; Chen, E. Y.-X.; Abboud, K. A.
Organometallics 2000, 19, 4684. (b) Klosin, J .; Deline, D. N. WO 00/
11006, 1999 (Dow Chemical Co.). For related donor-stabilized cationic
aluminum alkyls see: Bott, S. G.; Alvanipour, A.; Morley, S. D.;
Atwood, D. A.; Means, C. M.; Coleman, A. W.; Atwood, J . L. Angew.
Chem., Int. Ed. Engl. 1987, 26, 485. Engelhardt, L. M.; Kynast, U.;
Raston, C. L.; White, A. H. Angew. Chem., Int. Ed. Engl. 1987, 26,
681. Self, M. F.; Penington, W. T.; Laska, J . A.; Robinson, G. H.
Organometallics 1991, 10, 36. Uhl, W.; Wagner, J .; Fenske, D.; Baum,
G. Z. Anorg. Allg. Chem. 1992, 612, 25. Atwood, D. A.; J egier, J . Chem.
Commun. 1996, 1507. Cosledan, F.; Hitchcock, P. B.; Lappert, M. F.
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(7) (a) Fabicon, R. M.; Pajerski, A. D.; Richey, H. G. J . Am. Chem.
Soc. 1991, 113, 6680. (b) Fabicon, R. M.; Parvez, M.; Richey, H. G.
Organometallics 1999, 18, 5163. (c) Tang, H.; Parvez, M.; Richey, H.
G. Organometallics 2000, 19, 4810.
10.1021/om0103557 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 07/20/2001

Reactions of Zinc Dialkyls with Boron Compounds
Organometallics, Vol. 20, No. 17, 2001 3773
the H NMR spectrum at δ 0.78 and a broad 11B NMR
peak at δ 89.5. In a similar fashion the reaction of ZnEt2
with B(C6F5)3 affords a mixture of Zn(C6F5)2, BEt3, BEt2-
(C6F5), and BEt(C6F5)2. In contrast to the analogous
reactions of aluminum trialkyls with B(C6F5)3, where
an equilibrium between various dimeric aluminum
species is established which is shifted toward the
formation of Al(C6F5)3 only upon removal of BMe3 in
vacuo,3 the conversion of ZnR2 to Zn(C6F5)2 is essentially
complete within ca. 3 min, which is the minimum
amount of time required to obtain the NMR spectra.
There was no evidence for ZnR(C6F5) intermediates. A
similar reaction of ZnMe2 with B(C6F5)3 in toluene-d8
containing 20 vol % 1,2-difluorobenzene as polar ion-
izing solvent proceeds in essentially the same fashion.
The reaction of ZnMe2 with B(C6F5)3 in toluene on a
preparative scale proved to be a convenient route to Zn-
(C6F5)2‚(toluene) (4), which was isolated as a colorless,
hydrocarbon-soluble crystalline solid. All attempts to
remove the toluene by heating to 50 °C in vacuo failed,
and it is thought likely that the toluene is coordinated
to the electrophilic metal center in a manner similar to
that seen in Al(C6F5)3‚(toluene).11 Previously, Zn(C6F5)2
has been prepared from ZnCl2 and C6F5MgX,12 from
AgC6F5 and ZnI2,13 or by decarboxylation of Zn(O2-
CC6F5)2.14 Treatment of a light petroleum solution of 4
with hexamethylbenzene displaces the toluene in favor
of the more electron rich arene, to give microcrystalline
Zn(C6F5)2‚C6Me6 (5). In contrast, crystallization of Zn-
(C6F5)2 from benzene has been reported to give a
benzene-free product.15 Cooling samples of 5 to -80 °C
did lead to broadening of the methyl signal, but the slow
exchange limit could not be reached.
1
F igu r e 1. Structure of the [EtZn(OEt2)3]+ cation in 2,
showing the atomic numbering scheme. Hydrogen atoms
are omitted for clarity.
as colorless crystalline solids which show good solubility
in diethyl ether and dichloromethane but are sparingly
soluble in light petroleum. The borate anion shows a
sharp signal in the 11B NMR spectrum at around δ
-13.6, while the identity of the [MeZn(OEt2)3]+ cation
is confirmed by a singlet at δ -0.56 in the 1H NMR
spectrum. The 1H NMR spectra and elemental analyses
of all three compounds confirm the presence of three
coordinated ether molecules per zinc cation.
Crystals of 2 suitable for single-crystal X-ray diffrac-
tion were grown from diethyl ether solution at -20 °C.
The structure of the cation is shown in Figure 1. The
[EtZn(OEt2)3]+ cation displays a slightly distorted tet-
rahedral arrangement, with C-Zn-O angles ranging
from 115.37(10) to 123.60(9)°. The Zn-C bond length
of 1.964(3) Å is similar to that observed in the neutral
zinc complex [MeZnOBut]4 (1.955 Å),9 though slightly
shorter than the corresponding bond distance of 2.058-
When the reaction between ZnMe2 and B(C6F5)3 is
repeated in toluene-d8 in the presence of diethyl ether,
the ligand exchange chemistry described above is almost
totally suppressed. Instead, alkyl abstraction by B(C6F5)3
occurs, leading to the borate salt [MeZn(OEt2)3]+[MeB-
(C6F5)3]- (6) (eq 3). The degree of ion pairing of the
B(C6F5)3 + ZnR2 toluene-d /Et O8
8
2
(7) Å in the anionic complex [Et2Zn(µ-OBut)2ZnEt2]2- 10
.
In crystalline [ButZn(OEt2)3][B(C6F5)4] the Me3C-ZnO3
core adopts a staggered conformation; however, the
crystals deteriorated during data collection, and the
bonding parameters will not be discussed in detail.
The reactions of ZnR2 (for R ) Me, Et) with B(C6F5)3
were explored as in situ NMR experiments. Mixing
equimolar amounts of ZnMe2 with B(C6F5)3 in toluene-
d8 produces a mixture of species following rapid alkyl/
C6F5 exchange (eq 2). No ion pairs could be detected.
[RZn(OEt2)3]+[RB(C6F5)3]- (3)
R ) Me (6), Et (7)
1
[MeB(C6F5)3]- anion can be deduced from its H NMR
chemical shift; tight ion pairs with methyl bridges show
signals at ca. δ 0.1, as in Cp2ZrMe(µ-Me)B(C6F5)3,5b
whereas the free anion shows chemical shifts around δ
1.3. The value for 5 is δ 1.02. The noncoordinating
nature of the [MeB(C6F5)3]- anion is further confirmed
by the small chemical shift difference (∆δ 2.5 ppm)
between the m- and p-fluorine 19F NMR resonances.16
Diethyl ether solutions of ZnEt2 react similarly, to give
[EtZn(OEt2)3]+[EtB(C6F5)3]- (7).
toluene-d8
3B(C6F5)3 + 4ZnMe2
8
2BMe3 + BMe2(C6F5) + 4Zn(C6F5)2 (2)
Attempts to isolate 6 by solvent removal afforded a
colorless oil. Multinuclear NMR analysis showed that
The main products are BMe3 and Zn(C6F5)2 together
1
with a small amount of BMe2(C6F5), as shown by H,
19F, and 11B NMR spectroscopy. In particular, the
presence of BMe3 is very distinctive, with a singlet in
(11) Hair, G. S.; Cowley, A. H.; J ones, R. A.; McBurnett, B. G.; Voigt,
A. J . Am. Chem. Soc. 1999, 121, 4922.
(12) Noltes, J . G.; van den Hurk, J . W. G. J . Organomet. Chem. 1963,
64, 377.
(13) Miller, W. T.; Sun, K. K. J . Am. Chem. Soc. 1970, 92, 6985.
(14) Sartori, P.; Weidenbruch, M. Chem. Ber. 1967, 100, 3016.
(15) Sun, J .; Piers, W. E.; Parvez, M. Can. J . Chem. 1998, 76, 513.
(16) Horton, A. D.; de With, J .; van der Linden, A. J .; van de Weg,
H. Organometallics 1996, 15, 2672.
(8) J utzi, P.; Mu¨ller, C.; Stammler, A.; Stammler, H. G. Organome-
tallics 2000, 19, 1442.
(9) Herrmann, W. A.; Bogdanovich, S.; Behm, J .; Denk, M. J .
Organomet. Chem. 1992, 430, C33.
(10) Fabicon, R. M.; Parvez, M.; Richey, H. G. J . Am. Chem. Soc.
1991, 113, 1412.

3774 Organometallics, Vol. 20, No. 17, 2001
Walker et al.
this oil contained large amounts of MeB(C6F5)2, Me2B-
(C6F5), and Zn(C6F5)2, as well as the expected product,
6. A repeat of the NMR experiment revealed the
presence of BMe3 alongside [MeZn(OEt2)3]+[MeB(C6F5)3]-,
in the ratio 1:15. Removing the solvents from this NMR
reaction in vacuo and redissolving the residue in CD2-
Cl2 showed the presence of BMe3, BMe2(C6F5), and 6 in
the ratio 4.3:1:7.8. Evidently BMe3, Zn(C6F5)2, and 6 are
in equilibrium in solution, and removal of BMe3 in vacuo
shifts the equilibrium toward the formation of Zn(C6F5)2,
thus preventing the isolation of pure 6. Compound 7
shows a very similar chemistry.
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
under nitrogen using standard Schlenk techniques. Solvents
were distilled under nitrogen from sodium (toluene), sodium
benzophenone (diethyl ether), sodium-potassium alloy (light
petroleum, bp 40-60 °C), and CaH2 (dichloromethane). Deu-
terated solvents were stored over 4 Å molecular sieves and
degassed by several freeze-thaw cycles. ZnMe2 (2.0 M solution
in toluene) and ZnEt2 (1.1 M solution in toluene) were used
as purchased. The compounds ZnBut ,19 [H(OEt2)2][B(C6F5)4],8
2
B(C6F5)3,20 and [Ph3C][B(C6F5)4]21 were prepared by literature
methods. NMR spectra were recorded on a Bruker DPX300
spectrometer. 1H and 13C NMR spectra are referenced to
residual solvent peaks relative to TMS, 19F NMR spectra (282.2
MHz) are relative to external CFCl3, and 11B NMR spectra
(96.2 MHz) are relative to BF3‚OEt2.
In contrast, the reaction of an excess of ZnEt2 with
[Ph3C][B(C6F5)4] in toluene-d8 takes a different course
and proceeds with â-H abstraction and ethene elimina-
tion (Scheme 1).17The reaction is swift, with the loss of
[MeZn (OEt2)3][B(C6F 5)4] (1). A solution of dimethylzinc
(0.13 mL, 2.0 M, 0.26 mmol) in toluene was added dropwise
to a suspension of [H(OEt2)2][B(C6F5)4] (0.24 g, 0.29 mmol) in
diethyl ether (20 mL) at room temperature. The mixture was
stirred for 1 h to allow the gas formation to subside. Removal
of volatiles in vacuo left a white powder which was recrystal-
lized from a diethyl ether/light petroleum mixture at -20 °C
to afford 1 as colorless crystals, yield 0.19 g (80.0%). Anal.
Calcd for C37H33BF20O3Zn: C, 45.26; H, 3.39. Found: C, 45.21;
+
the orange color of CPh3 within ca. 2 s. The NMR
spectra show the presence of Zn(C6F5)2 and BEt3.
Clearly 1 equiv of ZnEt2 requires only two aryl groups
to generate Zn(C6F5)2, and consequently further ex-
change between BEtx(C6F5)3-x for x ) 0-2 and ZnEt2,
as already described above, results in total [B(C6F5)4]-
consumption.
1
H, 3.34. H NMR (300 MHz, 27 °C, CD2Cl2): δ 3.80 (q, 12 H,
Sch em e 1
J HH ) 7.1 Hz, CH3CH2O), 1.25 (t, 18 H, J HH ) 7.1 Hz, CH3-
CH2O), -0.56 (s, 3 H, MeZn). 13C{1H} NMR (75.5 MHz, 27 °C,
[CPh3][B(C6H5)4] + ZnEt2 f
CD2Cl2): 68.0 (CH3CH2O), 14.5 (CH3CH2O), -14.4 (MeZn). 19
F
Ph3CH + “[ZnEt][B(C6F5)4]” + C2H4
NMR (282.4 MHz, 27 °C, CD2Cl2): δ -133.6 (br, 8 F, o-F),
-164.1 (t, 4 F, J FF ) 22.6 Hz, p-F), -168.0 (br, 8 F, m-F). 11B
NMR (96.3 MHz, 27 °C, CD2Cl2): δ -13.6.
“[ZnEt][B(C6F5)4]” f ZnEt(C6F5) + B(C6F5)3
ZnEt(C6F5) + B(C6F5)3 h Zn(C6F5)2 + BEt(C6F5)2
ZnEt2 + BEt(C6F5)2 h ZnEt(C6F5) + BEt2(C6F5)
ZnEt(C6F5) + BEt2(C6F5) h Zn(C6F5)2 + BEt3
[EtZn (OEt2)3][B(C6F 5)4] (2). [H(OEt2)2][B(C6F5)4] (0.92 g,
1.1 mmol) and diethylzinc (1.1 mL, 1.0 M, 1.1 mmol) in hexane
were reacted as described for 1. Recrystallization from a
diethyl ether/light petroleum mixture at -20 °C provided
colorless crystals, yield 0.83 g (79.1%). Anal. Calcd for C38H35
-
BF20O3Zn: C, 45.83; H, 3.54. Found: C, 45.64; H, 3.57. 1H
NMR (300 MHz, 25 °C, CD2Cl2): δ 3.91 (q, 12 H, J HH ) 7.2
Hz, CH3CH2O), 1.35 (t, 18 H, J HH ) 7.2 Hz, CH3CH2O), 1.21
(t, 3 H, J HH ) 8.1 Hz, CH3CH2Zn), 0.49 (q, 2 H, J HH ) 8.1 Hz,
CH3CH2Zn). 13C{1H} NMR (75.5 MHz, 27 °C, CD2Cl2): δ 67.0
(CH3CH2O), 14.5 (CH3CH2O), 11.5 (CH3CH2Zn), 0.8 (CH3CH2-
Zn). 19F NMR (282.4 MHz, 27 °C, CD2Cl2): δ -133.6 (br, 8 F,
Although the alkyl/C6F5 exchange observed in the
above reactions presumably involves alkyl-bridged in-
termediates RZn(µ-R)B(C6F5)3, no evidence for such
species was found. In an effort to further understand
the chemistry of these systems, reactions were under-
taken with the tetramethylethylenediamine adducts
ZnR2(TMEDA) (8, R ) Me; 9, R ) Et). Reactions of
equimolar amounts of either 8 or 9 with [Ph3C]-
[B(C6F5)4] or B(C6F5)3 in toluene-d8 provided complex
mixtures which were not analyzed further. However, the
reaction between ZnMe2(TMEDA) and B(C6F5)3 in a
1.5:1 molar ratio in dichloromethane-d2 at -70 °C
indicated the formation of the zwitterionic species
(TMEDA)ZnMe(µ-Me)B(C6F5)3, with sharp 1H NMR
signals at δ -0.41 and -0.83 assigned as the terminal
and bridging Zn-methyl groups, respectively. There are
also signals for the solvent-separated ions [MeB(C6F5)3]-
(δ 0.37) and a broad signal at δ -0.97 for a [ZnMe-
(TMEDA)]+ cation in rapid exchange with the excess
ZnMe2(TMEDA).18 When the system is warmed to room
temperature, the signals for (TMEDA)ZnMe(µ-Me)B-
(C6F5)3 broaden and merge with the signals for the
[MeB(C6F5)3]- anion and the [ZnMe(TMEDA)]+ cation
and excess ZnMe2(TMEDA).
o-F), -164.3 (t, 4 F, J FF ) 19.8 Hz, p-F), -168.1 (t, 8 F, J FF
)
19.8 Hz, m-F). 11B NMR (96.3 MHz, 27 °C, CD2Cl2) δ -13.6.
[Bu tZn (OEt2)3][B(C6F 5)4] (3). A suspension of [H(OEt2)2]-
[B(C6F5)4] (0.74 g, 0.95 mmol) in diethyl ether (10 mL) at 0 °C
was treated with a solution of di-tert-butylzinc (0.17 g, 0.95
mmol) in diethyl ether (10 mL). The reaction mixture was
stirred at 0 °C for 3 h. Removal of volatiles in vacuo left a
white powder, which was recrystallized from a diethyl ether/
light petroleum mixture at -20 °C to give colorless crystals of
3, yield 0.67 g (72.3%). Anal. Calcd for C40H39BF20O3Zn: C,
1
46.92; H, 3.84. Found: C, 46.83; H, 3.55. H NMR (300 MHz,
27 °C, CD2Cl2): δ 3.79 (q, 12 H, J HH ) 7.2 Hz, CH3CH2O), 1.31
(t, 18 H, J HH ) 7.2 Hz, CH3CH2O), 1.17 (s, 9 H, CMe3). 13C-
{1H} NMR (75.5 MHz, 25 °C, C6D6): δ 14.76 (CH3CH2O), 25.20
(CMe3), 32.27 (CMe3), 67.08 (CH3CH2O). 19F NMR (282.4 MHz,
27 °C, CD2Cl2): δ -133.6 (br, 8 F, o-F), -164.1 (t, 4 F, J FF
)
19.8 Hz, p-F), -168.0 (t, 8 F, J FF ) 19.8 Hz, m-F). 11B NMR
(96.3 MHz, 27 °C, CD2Cl2): δ -13.6.
(19) Lehmkuhl, O.; Olbrysch, O. Liebigs Ann. Chem. 1975, 1162.
(20) Massey, A. G.; Park, A. J .; Stone, F. G. A. Proc. Chem. Soc.
(London) 1963, 212. Pohlmann, J . L.; Brinkmann, F. E. Z. Naturforsch.,
B 1965, 20B, 5.
(21) Chien, J . C. W.; Tsai, W.-M.; Rausch, M. D. J . Am. Chem. Soc.
1991, 113, 8570. Ewen, J . A.; Elder, M. J . Eur. Patent Appl. EP 0,-
426,637, 1991. Bochmann, M.; Lancaster, S. J . J . Organomet. Chem.
1992, 434, C1.
+
(17) For examples of â-H abstraction by CPh3 from main-group
alkyls see: J erkunica, J . M.; Taylor, T. G. J . Am. Chem. Soc. 1971,
93, 6278. Hannon, J . S.; Taylor, T. G. J . Org. Chem. 1981, 46, 3645.
(18) Further cooling did not lead to a resolution of this signal. The
formation of highly fluxional [Zn2Me3(TMEDA)2]+ is possible but could
not be proven.

Reactions of Zinc Dialkyls with Boron Compounds
Organometallics, Vol. 20, No. 17, 2001 3775
Rea ction of Zn Me2 w ith B(C6F 5)3 in Tolu en e-d 8. A
solution of B(C6F5)3 (30 mg, 59 µmol) in toluene-d8 (4 mL) was
treated with a solution of ZnMe2 (0.04 mL, 80 µmol, 2 M) in
toluene. The reaction was complete in the time taken to place
the sample in the NMR spectrometer (ca. 3 min). The solution
contained BMe3, BMe2(C6F5), and Zn(C6F5)2. BMe3: 1H NMR
(300 MHz, 25 °C, toluene-d8) δ 0.78 (s); 11B NMR (96.3 MHz,
25 °C, toluene-d8) δ 89.5. BMe2(C6F5): 1H NMR (toluene-d8) δ
25 °C, C7D8, ether): δ 67.62 (OCH2CH3), 14.42 (OCH2CH3),
11.15 (br, BMe), -14.93 (ZnMe). 19F NMR (282.4 MHz, 25 °C,
C7D8/ether): δ -132.7 (d, 6 F, J FF ) 19.8 Hz, o-F), -165.6 (t,
3 F, J FF ) 19.8 Hz, p-F), -168.1 (m, 6 F, m-F). 11B NMR (96.3
MHz, 27 °C, C7D8/ether): δ -11.4.
Gen er a tion of [EtZn (OEt 2)3][EtB(C6F 5)3] (7). A solution
of B(C6F5)3 (30 mg, 59 µmol) in toluene-d8 (4 mL) and ether
(0.5 mL) was treated with a solution of ZnEt2 (0.05 mL, 55
µmol, 1.1 M) in toluene. 1H NMR (300 MHz, 25 °C, C7D8/
ether): δ 3.38 (q, 12 H, J ) 7.1 Hz, OCH2CH3), 1.63 (br q, 2
H, J ) 7.1 Hz, BCH2CH3), 1.06 (t, 3 H, J ) 8.1 Hz, ZnCH2CH3),
1.03 (br t, 3 H, J ) 7.0 Hz, BCH2CH3), 0.91 (q, 18 H, J ) 7.1
Hz, OCH2CH3), 0.13 (q, 2 H, J ) 8.1 Hz, ZnCH2CH3). 13C{1H}
NMR (75.5 MHz, 25 °C, C7D8/ether): δ 67.49 (OCH2CH3), 15.18
(vbr, BCH2CH3), 13.50 (OCH2CH3), 12.51 (BCH2CH3), 11.40
(ZnCH2CH3), -0.47 (ZnCH2CH3). 19F NMR (282.4 MHz, 25 °C,
C7D8/ether): δ -132.2 (d, 6 F, J FF ) 22.6 Hz, o-F), -165.5 (t,
3 F, J FF ) 19.8 Hz, p-F), -168.1 (m, 6 F, m-F). 11B NMR (96.3
MHz, 27 °C, C7D8/ether): δ -9.1.
Rea ction of Zn Et2 w ith [P h 3C][B(C6F 5)4] in Tolu en e-
d 8. A solution of [Ph3C][B(C6F5)4] (0.020 g, 21 µmol) in toluene-
d8 (0.4 mL) was treated with a solution of ZnEt2 (0.09 mL, 1.1
M, 99 µmol) in toluene. The orange color faded to colorless
immediately. The products of the reaction were characterized
by NMR. Apart from the reaction products ethene and triph-
enylmethane, and some excess ZnEt2, there were also signals
for BEt3 and [B(C6F5)4]-.
1.07 (t, 6 H, J ) 1.9 Hz, Me); 11B NMR (toluene-d8) δ 83.8; 19
F
NMR (282.4 MHz, 25 °C, toluene-d8) δ -131.23 (m, 2 F),
-151.83 (m, 1 F), -163.15 (m, 2 F). Zn(C6F5)2: 19F NMR (282.4
MHz, 25 °C, toluene-d8) δ -118.46 (m, 2 F), -153.74 (t, 1 F,
J FF ) 19.8 Hz), -161.33 (m, 2 F).
Rea ction of Zn Me2 w ith B(C6F 5)3 in Tolu en e-d 8/1,2-
Diflu or oben zen e. A solution of B(C6F5)3 (30 mg, 59 µmol) in
a mixture of toluene-d8 (4 mL) and 1,2-difluorobenzene (1 mL)
was treated with a solution of ZnMe2 (0.04 mL, 80 µmol, 2 M)
in toluene-d8. The reaction was completed in the time taken
to place the sample in the NMR spectrometer (ca. 3 min). The
solution contained BMe3, BMe2(C6F5), BMe(C6F5)2, and Zn-
(C6F5)2. BMe(C6F5)2: 1H NMR (300 MHz, 25 °C, toluene-d8/
1,2-difluorobenzene) δ 1.48 (q, 3 H, J ) 1.78 Hz, Me); 11B NMR
(96.3 MHz, 25 °C, toluene-d8/1,2-difluorobenzene) δ 75.2; 19F
NMR (282.4 MHz, 25 °C, toluene-d8) δ -130.55 (m, 2 F),
-147.92 (m, 1 F), -162.17 (m, 2 F).
Rea ction of Zn Et2 w ith B(C6F 5)3 in Tolu en e-d 8. A
solution of B(C6F5)3 (30 mg, 59 µmol) in toluene-d8 (4 mL) was
treated with a solution of ZnEt2 (0.07 mL, 77 µmol, 1.1 M) in
toluene. The reaction was complete in the time taken to place
the sample in the NMR spectrometer. The solution contained
BEt3, BEt2(C6F5), BEt(C6F5)2, and Zn(C6F5)2. BEt3: 1H NMR
(300 MHz, 25 °C, toluene-d8) δ 1.16 (q, 6 H, J ) 7.7 Hz,
CH3CH2-B), 1.01 (t, 9 H, J ) 7.7 Hz, CH3CH2-B); 11B NMR
(96.3 MHz, 25 °C, toluene-d8) δ 89.7. BEt2(C6F5): 1H NMR (300
MHz, 25 °C, toluene-d8) δ 1.42 (q, 4 H, J ) 7.6 Hz, CH3CH2-
B), 0.92 (t, 6 H, J ) 7.6 Hz, CH3CH2-B); 11B NMR (96.3 MHz,
25 °C, toluene-d8) δ 87.8; 19F NMR (282.4 MHz, 25 °C, toluene-
d8) δ -131.08 (m, 2 F), -154.24 (m, 1 F), -161.70 (m, 2 F).
BEt(C6F5)2: 1H NMR (toluene-d8) δ 1.87 (q, 2 H, J ) 7.6 Hz,
CH3CH2-B), 0.98 (t, 3 H, J ) 7.6 Hz, CH3CH2-B); 11B NMR
(toluene-d8) δ 77.3; 19F NMR (toluene-d8) δ -134.85 (m, 2 F),
-148.14 (m, 1 F), -162.51 (m, 2 F).
Rea ction of Zn Me2(TMEDA) w ith B(C6F 5)3 in Dich lo-
r om eth a n e-d 2. A solution of ZnMe2(TMEDA) (TMEDA ) 1,2-
C2H4(NMe2)2; 7 mg, 33 µmol) in dichloromethane-d2 (3 mL)
was treated with a solution of B(C6F5)3 (10 mg, 20 µmol) also
in dichloromethane-d2 (3 mL) at -70 °C. The products were
characterized by NMR. Besides signals for [MeB(C6F5)3]- and
the resonances of coordinated TMEDA, the solution contained
signals for (TMEDA)ZnMe(µ-Me)B(C6F5)3 and a broad peak for
the Me signals of rapidly interchanging [ZnMe(TMEDA)]+/
ZnMe2(TMEDA), which could not be resolved on cooling to -80
°C. (TMEDA)ZnMe(µ-Me)B(C6F5)3: 1H NMR (300 MHz, -70
°C, CCl2D2): δ -0.41 (s, 3 H, µ-Me), -0.83 (s, 3 H, ZnMe). 11B
NMR (96.3 MHz, -70 °C, CCl2D2): δ -12.0 (br). When the
system was warmed to room temperature, the signals for
(TMEDA)ZnMe(µ-Me)B(C6F5)3 broadened and merged with
the signals for [MeB(C6F5)3]- and [ZnMe(TMEDA)]+/ZnMe2-
(TMEDA).
Zn (C6F 5)2‚(tolu en e) (4). A solution of B(C6F5)3 (3.01 g, 5.88
mmol) in toluene (50 mL) was treated with a solution of ZnMe2
in toluene (4.41 mL, 8.82 mmol, 2 M) at room temperature.
The mixture was stirred for 30 min. Removal of volatiles left
a white solid, which was recrystallized from light petroleum
(60 mL) at -20 °C overnight to give Zn(C6F5)2‚(toluene) as
X-r a y Cr ysta llogr a p h y. Crystals are clear, colorless plates.
A crystal of dimensions ca. 0.4 × 0.3 × 0.1 mm coated with
dry Nujol was mounted on a glass fiber under a cold nitrogen
stream. Data were collected at 140 K on a Rigaku R-Axis IIc
image plate diffractometer equipped with a rotating-anode
X-ray source (Mo KR radiation, λ ) 0.710 69 Å) and graphite
monochromator. Using 4° oscillations, 46 exposures of 15 min
were made. Data were processed using the DENZO/SCALE-
PACK22 programs. The structure was determined by the
automated Patterson routines in the SHELXS program23 and
refined by full-matrix least-squares methods, on F2 values, in
SHELXL.24 The non-hydrogen atoms were refined with aniso-
tropic thermal parameters. Hydrogen atoms in the cation were
included in idealized positions, and their Uiso values were set
to ride on the Ueq values of the parent carbon atoms. At the
conclusion of the refinement, wR2 ) 0.095 and R1 ) 0.04726
for all 7018 reflections weighted w ) [σ2(Fo2) + (0.0416P)2 +
needlelike crystals, yield 3.33 g (76.6%). Anal. Calcd for C12F10
-
Zn‚C7H8: C, 46.42; H, 1.64. Found: C, 45.93; H, 1.46. 1H NMR
(300 MHz, 25 °C, C6D6): δ 6.98-7.13 (m, 5 H, Ph), 2.10 (s, 3
H, Me). 19F NMR (C6D6): δ -118.3 (m, 4 F, o-F), -152.9 (t, 2
F, J FF ) 19.8 Hz, p-F), -160.9 (m, 4 F, m-F).
Zn (C6F 5)2‚C6Me6 (5). A solution of Zn(C6F5)2‚(toluene) (1.02
g, 2.07 mmol) in toluene (20 mL) was treated with hexameth-
ylbenzene (0.334 g, 2.06 mmol). After the mixture was stirred
for 1 h, the solvent was removed and the colorless residue
recystallized from light petroleum at -20 °C to give 5 as a
white microcrystalline solid, yield 0.96 g (82.3%). Anal. Calcd
for C12F10Zn‚C12H18: C, 51.31; H, 3.23. Found: C, 51.95; H,
1
3.49. H NMR (300 MHz, 25 °C, C6D6): δ 2.03 (s, 18 H, Me).
13C NMR (75.5 MHz, 25 °C, C6D6): δ 16.79 (Me), 132.48 (C6).
19F NMR (282.4 MHz, 25 °C, C6D6): δ -118.1 (m, 4 F, o-F),
-153.2 (t, 2 F, J FF ) 19.8 Hz, p-F), -160.9 (m, 4 F, m-F).
Gen er a tion of [MeZn (OEt2)3][MeB(C6F 5)3] (6). A solution
of B(C6F5)3 (40 mg, 79 µmol) in toluene-d8 (4 mL) and ether
(0.5 mL) was treated with a solution of ZnMe2 (0.04 mL, 80
µmol, 2 M) in toluene. The reaction was instantaneous. 1H
NMR (300 MHz, 25 °C, C7D8/ether): δ 3.34 (q, 12 H, J ) 7.2
Hz, OCH2CH3), 1.02 (br s, 3 H, BMe), 0.88 (t, 18 H, J ) 7.2
Hz, OCH2CH3), -0.73 (s, 3 H, ZnMe). 13C{1H} NMR (75.5 MHz,
2
1.53P]-1 with P ) (Fo + 2Fc2)/3; for the “observed” data only,
(22) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(23) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(24) Sheldrick, G. M.; SHELXL-Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1993.
(25) International Tables for X-ray Crystallography; Kluwer Aca-
demic Publishers: Dordrecht, The Netherlands, 1992; Vol. C, pp 500,
219, 193.
(26) Anderson, S. N.; Richards, R. L.; Hughes, D. L. J . Chem. Soc.,
Dalton Trans. 1986, 245.

3776 Organometallics, Vol. 20, No. 17, 2001
Walker et al.
R1 ) 0.036. In the final difference map, the highest peaks (to
ca. 0.34 e Å-3) were in the ether ligands. Scattering factors
for neutral atoms were taken from ref 25. Computer programs
used were as noted above or in Table 4 of ref 26.
Crystal Data for 2: C14H35O3Zn‚C24BF20, fw 995.8; mono-
clinic; P21/c, a ) 14.824(1) Å, b ) 15.947(1) Å, c ) 18.037(1)
Å; â ) 108.25(1)°; V ) 4049.4(4) Å3; Z ) 4; Dcalcd ) 1.633 g/cm3;
µ ) 0.736 mm-1; F(000) ) 2008; 1.7 e θ e 25.4°; -17 e h e
17, -19 e k e 19, -21 e l e 21; 22 855 reflections collected,
of which 7018 were independent (Rint ) 0.079) and 5735
observed (I > 2σ(I)); no. of data/restraints/parameters 7018/
0/568; goodness of fit, S ) 1.031.
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: Full listings of
crystallographic details. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM0103557