σ-borane coordinated to nickel(0) and some related nickel(II) trihydride complexes

Article abstract of DOI:10.1021/ja056000m

The reactions of the complexes [(dcype)NiH]₂, 1, [(dippe)NiH]₂, 2, and [(dtbpe)NiH]₂, 3, with a mixture of BEt₃ and Super-Hydride (LiHBEt₃) afforded σ-borane nickel(0) compounds of the type [(dcype)Ni(σ-HBEt₂)], 4, [(dippe)Ni(σ-HBEt₂)], 5, [(dtbpe)Ni(σ-HBEt₂)], 6, respectively, with the concomitant formation in each case of [(dcype) ₂Ni₂(H)₃][BEt₄], 7, [(dippe) ₂Ni₂(H)₃][BEt₄], 8 and [(dtbpe) ₂Ni₂(H)₃][BEt₄], 9, respectively. X-ray crystal structures are reported for 4 and 8. The reaction of BEt ₃ and LiHBEt₃ was also reviewed in detail.

Full text of DOI:10.1021/ja056000m

Published on Web 12/06/2005
σ-Borane Coordinated to Nickel(0) and Some Related Nickel(II)
Trihydride Complexes
Marco G. Crestani,† Miguel Mun˜oz-Herna´ndez,‡ Alma Are´valo,†
Alberto Acosta-Ram´ırez,† and Juventino J. Garc´ıa*,†
Contribution from the Facultad de Qu´ımica, UniVersidad Nacional Auto´noma de Me´xico,
Me´xico, D. F. 04510, Me´xico, and Centro de InVestigaciones Qu´ımicas, UniVersidad Auto´noma
del Estado de Morelos, Morelos 62210, Me´xico
Received August 31, 2005; E-mail: juvent@servidor.unam.mx
Abstract: The reactions of the complexes [(dcype)NiH]2, 1, [(dippe)NiH]2, 2, and [(dtbpe)NiH]2, 3, with a
mixture of BEt3 and Super-Hydride (LiHBEt3) afforded σ-borane nickel(0) compounds of the type [(dcype)-
Ni(σ-HBEt2)], 4, [(dippe)Ni(σ-HBEt2)], 5, [(dtbpe)Ni(σ-HBEt2)], 6, respectively, with the concomitant formation
in each case of [(dcype)2Ni2(H)3][BEt4], 7, [(dippe)2Ni2(H)3][BEt4], 8 and [(dtbpe)2Ni2(H)3][BEt4], 9, respectively.
X-ray crystal structures are reported for 4 and 8.The reaction of BEt3 and LiHBEt3 was also reviewed in
detail.
Introduction
involving B-H activation and release. Some relevant examples
in that field have been published by Hartwig6 with the use of
The activation of unreactive bonds is currently a very active
area in organometallic chemistry, although a relatively limited
number of successful systems able to accomplish such cleavage
have been reported thus far.1 We have found the use of low-
valent late-transition metal complexes to be practical in the C-C
bond activation of aryl and hetero-aryl cyanides, that we have
recently extended to a variety of alkylnitriles using [(dippe)-
NiH]2. In all the cases, this leads to the formation of an η2-
nitrile complex of nickel (0) that in the case of aryl and hetero-
aryl cyanides undergoes oxidative addition, with mild warming,
to form the corresponding nickel(II) complexes. With the alkyl
nitriles, such oxidative addition is strongly dependent on the
chain length, and eventually it can be inhibited.2 Both types of
compounds were isolated and were fully characterized structur-
ally. As part of our ongoing studies in the field, we decided to
extend the chemistry of some of the nickel complexes to
investigate the reactivity of other interesting substrates such as
alkyl boranes and the closely related borohydrides, with the aim
of stabilizing boron-containing moieties, among them σ-boranes
coordinated to a low-valent late-transition metal such as nickel
(0).
early transition metals and by Sabo-Etienne7 with the use of
(3) (a) Braunschweig, H. Angew. Chem., Int. Ed. 1998, 37, 1786. (b)
Braunschweig, H.; Colling, M. Coord. Chem. ReV. 2001, 223, 1. (c) Irvine,
G. J.; Lesley, M. J. G.; Marder, T. B.; Norman, N. C.; Rice, C. R.; Robins,
E. G.; Roper, W. R.; Whittell, G. R.; Wright, L. J. Chem. ReV. 1998, 98,
2685. (d) Smith, M. R., III. Prog. Inorg. Chem. 1999, 48. 505. (e) Hartwig,
J. F.; Waltz, K. M.; Muhoro, C. N.; He, X.; Eisenstein, O.; Bosque, R.;
Maseras, F. In AdVances of Boron Chemistry; Siebert, W., Ed.; Spec. Publ.
No. 201; The Royal Society of Chemistry: Cambridge, 1997; p 373. (f)
Wadepohl, H. Angew. Chem., Int. Ed. Engl. 1997, 36, 2441.
(4) (a) Harwig, J. F.; De Gala, S. R. J. Am. Chem. Soc. 1994, 116, 3661. (b)
Lantero, D. R.; Motry, D. H.; Ward, D. L.; Smith, M. R., III. J. Am. Chem.
Soc. 1994, 116, 10811. (c) Lantero, D. R.; Ward, D. L.; Smith, M. R., III.
J. Am. Chem. Soc. 1997, 119, 9699. (d) Lantero, D. R.; Miller, S. L.; Cho,
J. Y.; Ward, D. L.; Smith, M. R., III. Organometallics 1999, 18, 235. (e)
Liu, D.; Lam, K.-C.; Lin, Z. J. Organomet. Chem. 2003, 680, 148. (f)
Pandey, K. K. Inorg. Chem. 2001, 40, 5092.
(5) (a) Baker, R. T.; Ovenall, D. W.; Calabrese, J. C.; Westcott, S. A.; Taylor,
N. J.; Williams, I. D.; Marder, T. B. J. Am. Chem. Soc. 1990, 112, 9399.
(b) Westcott, S. A.; Marder, T. B.; Baker, R. T.; Harlow, R. L.; Calabrese,
J. C.; Lam, K. C.; Lin, Z. Polyhedron 2004, 23, 2665. (c) Kono, H.; Ito,
K.; Nagai, Y. Chem. Lett. 1975, 1095. (d) Ma¨nning, D.; No¨th, H. Angew.
Chem, Int. Ed. Engl. 1985, 24, 878. (e) Westcott, S. A.; Taylor, N. J.;
Marder, T. B.; Baker, R. T.; Jones, N. J.; Calabrese, J. C. J. Chem. Soc.,
Chem. Commun. 1991, 304. (f) Knorr, J. R.; Merola, J. S. Organometallics
1990, 9, 3008. (g) Westcott, S. A.; Marder, T. B.; Baker, R. T.; Calabrese,
J. C. Can. J. Chem. 1993, 71, 930. (h) Kawamura, K.; Hartwig, J. F. J.
Am. Chem. Soc. 2001, 123, 8422. (i) Hartwig, J. F.; He, X. Organometallics
1996, 15, 5350. (j) Hartwig, J. F.; He, X. M. Angew. Chem., Int. Ed. Engl.
1996, 35, 315. (k) Burgess, K.; van der Donk, W. A.; Westcott, S. A.;
Marder, T. B.; Baker, R. T.; Calabrese, J. C. J. Am. Chem. Soc. 1992, 114,
9350. (l) Lam, W. H.; Shimada, S.; Batsanov, A. S.; Lin, Z.; Marder, T.
B.; Cowan, J. A.; Howard, J. A. K.; Mason, S. A.; McIntyre, G. J.
Organometallics, 2003, 22, 4557. (m) Nguyen, P.; Blom, H. P.; Westcott,
S. A.; Taylor, N. J.; Marder, T. B. J. Am. Chem. Soc. 1993, 115, 9329. (n)
Baker, R. T.; Calabrese, J. C.; Westcott, S. A.; Nguyen, P.; Marder, T. B.
J. Am. Chem. Soc. 1993, 115, 4367. (o) Callaghan, P. L.; Ferna´ndez-
Pacheco, R.; Jasim, N.; Lachaize, S.; Marder, T. B.; Perutz, R. N.; Rivalta,
E.; Sabo-Etienne, S. Chem. Commun. 2004, 242.
The area of borane and boryl reactivity has been actively
studied,3 particularly for transition metal complexes using a
variety of early-4 and late-transition metals,5 the isolation of
σ-borane complexes being of great interest due to their
participation in a number of catalytic systems with steps
† Facultad de Qu´ımica. Universidad Nacional Auto´noma de Me´xico.
‡ Centro de Investigaciones Qu´ımicas, Universidad Auto´noma del Estado
de Morelos.
(1) For a recent review of these topics, see: Topics in Organometallic
Chemistry. ActiVation of UnreactiVe Bonds and Organic Synthesis; Murai,
S., Ed.; Springer-Verlag: Berlin, 1999.
(6) (a) Hartwig, J. F.; Muhoro, C. N.; He, X.; Eisenstein, O.; Bosque, R.;
Maseras, F. J. Am. Chem. Soc. 1996, 118, 10936. (b) Muhoro, C. N.;
Hartwig, J. F. Angew. Chem., Int. Ed. Engl. 1997, 36, 1510. (c) Muhoro,
C. N.; He, X.; Hartwig, J. F. J. Am. Chem. Soc. 1999, 121, 5033. (d)
Schlecht, S.; Hartwig, J. F. J. Am. Chem. Soc. 2000, 122, 9435.
(2) (a) Garcia, J. J.; Jones, W. D. Organometallics 2000, 19, 5544. (b) Garcia,
J. J.; Brunkan, N. M.; Jones, W. D. J. Am. Chem. Soc. 2002, 124, 9547.
(c) Garcia, J. J.; Arevalo, A.; Brunkan, N. M.; Jones, W. D. Organometallics
2004, 23, 3997.
(7) (a) Montiel-Palma, V.; Lumbierres, M.; Donnadieu, B.; Sabo-Etienne, S.;
Chaudret, B. J. Am. Chem. Soc. 2002, 124, 5624. (b) Lachaize, S.; Essalah,
K.; Montiel-Palma, V.; Vendier, L.; Chaudret, B.; Barthelat, J.-C.; Sabo-
Etienne, S. Organometallics 2005, 24, 2935.
9
18066
J. AM. CHEM. SOC. 2005, 127, 18066-18073
10.1021/ja056000m CCC: $30.25 © 2005 American Chemical Society

σ
-Borane Coordinated to Nickel(0)
A R T I C L E S
polyhydride ruthenium (II) complexes. However, to the best of
our knowledge, there are no examples of the use of a late
transition metal with a d10 configuration to stabilize a coordi-
nated σ-borane.
We report here our findings on the reactivity of nickel (I)
hydride dimeric compounds to yield σ-borane nickel(0) com-
plexes of the type [(diphosphine)Ni(σ-HBEt2)], along with the
co-formation of [(diphosphine)2Ni2(H)3][BEt4].
rationalized in terms of the reaction that occurs, although an
exchange equilibrium between LiHBEt3 and BEt3 has also been
reported previously.10 The residual BEt3 could nevertheless be
exchanging with the (HBEt2)2 formed in the reaction, as the
chemical shifts of both species are seemingly displaced from
their ordinary values in THF (δ 78.3 for BEt3 and δ 27.8 for
(HBEt2)2) and appear at slightly closer proximity. In fact, this
situation has been reported to occur by Wrackmeyer when
(HBEt2)2 is independently prepared from BEt3 and BH3‚THF.11
Results and Discussion
As part of the present work, once the stoichiometric reaction
LiHBEt3 with BEt3 had been properly established, its role in
the integrity and performance of the commercial stocks of Super-
Hydride was investigated. At first glance, the reaction acts as a
disproportionation of the Super-Hydride solution into (HBEt2)2
and LiBEt4. Similarly, Brown has reported the disproportionation
of LiHB(OMe)3 into both LiBH2(OMe)2 and LiB(OMe)4 during
a series of studies performed during the 1950s.12 This result is
in agreement with Cole-Hamilton’s observation, using 11B NMR,
for the formation of a significant amount of [BH2Et2]- (δ
-16.54, t, 1J(11B,1H) ) 69 Hz) besides [BEt4]- (δ -16.02, s),
in a batch of Super-Hydride.8c The existence of the closely
related lithium dialkylboron-dihydrides, Li[BH2R2], of 9-bora-
bicyclo[3.3.1]nonane, 9-BBN, (δ -17.3), dicyclohexylborane
(δ -12.5), and disiamylborane (δ -14.9), has also been
confirmed by 11B NMR.13 The resonances of the latter were
reported to appear in the tetrahedral boron region of the 11B
NMR spectra, at slightly lower field than the corresponding
lithium tetraalkylborate analogues, which were concomitantly
formed when the precursor boranes were reacted with alkyl-
lithium sources such as n-BuLi. The lithium dialkylboron-
dihydride signals appeared as triplets with 1J(11B,1H) of 70 Hz
as expected for one boron bound to two hydrogen atoms,
whereas the tetraalkylborates appeared as singlets.
Stoichiometric Reaction of BEt3 with LiHBEt3: Concomi-
tant Formation of (HBEt2)2 and LiBEt4. The stoichiometric
reaction of BEt3 with Super-Hydride (LiHBEt3-THF), at room
temperature under argon, affords the concomitant formation of
(HBEt2)2 and LiBEt4; the reaction occurs immediately, after the
1
reactants have been mixed. The H NMR spectrum of this
mixture, shows two overlapping, broad resonance signals
centered at δ 0.86 and δ 0.84, that we have assigned as the
methylene and methyl protons of (HBEt2)2. The appearance of
the latter is consistent with the presence of a second pair of
multiplets centered at δ 0.6 (t of 1:1:1:1 q, 3J(1H,11B) ) 3 Hz)
and δ -0.2 (q of 1:1:1:1 q, 2J(1H,11B) ) 4.2 Hz) that correspond
to the methyl and methylene protons of [BEt4]-.8 A third small,
broad resonance that overlaps with the (HBEt2)2 proton signals
on the left-hand side (δ 1.02 to δ 0.95) was also observed in
1
the H NMR spectrum and was assigned to unreacted BEt3 by
direct comparison with an authentic sample of BEt3, also in
THF-d8.8a Unreacted LiHBEt3 was barely detectable, except for
a very small, broad signal centered at δ 0.002, presumably
associated to the [HBEt3]- hydride. The fact that the proton
resonances of both BEt3 and LiHBEt3 have practically disap-
peared, at least in the 1H NMR time scale, is consistent with a
thermodynamically favored reaction. Our interpretation of the
reaction that occurs is as follows:
Furthermore, in that work, the reaction of equimolar amounts
of the tetraalkylborate, lithium dialkyl-9-BBN, with 9-BBN was
examined. On standing, 9-BBN reacted slowly with the tet-
raalkylborate to form lithium dihydride-9-BBN and B-alkyl-9-
BBN. The process was thought to occur through the formation
of the corresponding lithium trialkylborohydride, as an inter-
mediate, which would rapidly lose the elements of lithium
hydride to the stronger Lewis acid, 9-BBN, forming the final
dialkylboron-dihydride and trialkylborane observed by 11B
NMR, as illustrated in Scheme 1. No traces of such intermediate
(lithium trialkylborohydride) could be obtained from the reaction
follow-up at the time.
2 BEt3 + 2 LiHBEt3 f (HBEt2)2 + 2 LiBEt4
(1)
The inspection of the 11B and the 11B{1H} NMR spectra of
the same reaction mixture, also shows that LiHBEt3 and BEt3
are consumed in a reaction where (HBEt2)2 and LiBEt4 are
formed. Both 11B and 11B{1H} NMR spectra feature the presence
of residual BEt3, δ 70.75 (br), besides of (HBEt2)2, δ 37.72
(br) and LiBEt4, δ -17.5, the latter appears as a narrow singlet
that sharpens further upon proton decoupling and thus evidences
the presence of a scalar coupling between the boron and the
hydrogen atoms. The resonance for LiBEt4 is also much sharper
in the 11B{1H} NMR spectrum than the corresponding BEt3
peak, indicating a lessening of quadrupolar interaction because
of tetrahedral symmetry.9 No remaining LiHBEt3 was observed
in either the 11B or the 11B{1H} NMR spectra. This can be
The reaction of 9-BBN with lithium dialkyl-9-BBN, as
pictured, is similar to the results reported by Cole-Hamilton with
Super-Hydride,8c as much as there is an excess of LiHBEt3 in
the bulk solution that is likely to react with the (HBEt2)2 formed
in situ to promote the equimolar formation of Li[BH2Et2] and
Li[BEt4]. Moreover, since the reaction between LiHBEt3 and
BEt3 as depicted in eq 1 is likely to be a simple reaction, the
presence of BEt3 in a batch of Super-Hydride should be enough
(8) For a description of the chemical shifts of the CH2 and CH3 protons in the
[BEt4]- anion, see: (a) Noth, H.; Vahrenkamp, H. J. Organomet. Chem.
1968, 12, 23. (b) Thaler, E.; Folting, K.; Huffman, J. C.; Caulton, K. G.
Inorg. Chem. 1987, 26, 374. For a complete description of the chemical
shift, multiplicity, and coupling constants for CH2 and CH3 to 11B in the
[BEt4]- anion in CD3NO2, see: (c) Smith, G.; Cole-Hamilton, D. J.;
Thornton-Pett, M.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1983,
2501.
(10) Brown, C. A. J. Organomet. Chem. 1978, 156, C17.
(11) Wrackmeyer, B. J. Organomet. Chem. 1976, 117, 313.
(12) (a) Brown, H. C.; Schlesinger, H. I.; Sheft, I.; Ritter, D. M. J. Am. Chem.
Soc. 1953, 75, 192. (b) Brown, H. C.; Mead, E. J.; Shoaf, C. J. J. Am.
Chem. Soc. 1956, 78, 3616.
(9) The 11B chemical shift of BEt3 is reported to be δ 86.6 while the chemical
shift of LiBEt4 is reported to be δ -17.48, relative to external BF3‚Et2O;
the chemical shift signs are updated according to present convention,
denoting the resonances downfield from this standard as positive: Thomp-
son, R. J.; Davis, J. C., Jr. Inorg. Chem. 1965, 4(10), 1464.
(13) Hubbard, J. L.; Kramer, G. W. J. Organomet. Chem. 1978, 156, 81.
9
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A R T I C L E S
Crestani et al.
Scheme 1. Reaction of 9-BBN with Lithium Dialkyl-9-BBN13
to engage in the disproportionation of the reagent. In our case,
a rationale for the fact that the we detect (HBEt2)2 instead of
the lithium dialkylborohydride, Li[BH2Et2], may be given in
terms of the spontaneity of the reaction and the stoichiometry
used for it, that prevents further reactivity between (HBEt2)2
and LiHBEt3, (HBEt2)2 being the stronger Lewis acid by analogy
to 9-BBN. In a Super-Hydride batch, however, there is always
an excess of LiHBEt3, with respect to the amount of (HBEt2)2
presumably formed from a former reaction with BEt3 as in eq
1, but (HBEt2)2 can react further with Super-Hydride to yield
Li[BH2Et2]. Consequently, the presence of Li[BH2Et2] and
lithium tetraalkylborate, may be expected, particularly in old
batches. An examination of the literature regarding examples
of in situ formation of LiBEt4 from Super-Hydride, in which
LiBEt4 happened to be reactive,8b,c,14 proved that although Super-
Hydride can be kept stable for quite long periods of time under
inert conditions (Brown, has reported a 1 year stability of
LiHBEt3 in THF solution under dry nitrogen15), decomposition
of the Super-Hydride solution into LiBEt4 does occur. The
degree of decomposition is very variable, ranging from a mere
impurity to a very large extent, such that the quantitative
formation of complexes with [BEt4]- in 30-80% yield have
been reported.8c,14
The reaction was interpreted as irreversible in the presence of
excess LiH as follows:15
THF, 25 °C
LiHBEt
(100%)
LiH + Et3B
8
(2)
3
24 h
It is unclear if the stability tests performed as part of that
publication were carried out using the same mixture employing
excess alkali metal hydride, but if that had been the case, it is
likely that the reversible formation of BEt3 from LiHBEt3 would
have been blocked. Commercial Super-Hydride solution, how-
ever, is not reported to be provided with excess LiH,16 which
in turn would explain the fact that LiHBEt3 can be decomposed
gradually into LiBEt4 and (HBEt2)2 or further, to Li[BH2Et2].8c
Reactions of the Nickel (I) Hydrides with the (HBEt2)2/
LiBEt4 Mixture: Concomitant Formation of the Ni(0)
σ-Alkylborane and Ni(II) Trihydride Complexes. Two equiva-
lents of the corresponding nickel (I) hydride 1, 2, or 3 were
added, at room temperature, to a mixture of Super-Hydride and
BEt3, and the concomitant formation of the Ni(0) σ-alkylboranes
4, 5, and 6 and the Ni(II) trihydride complexes 7, 8, and 9 was
verified spectroscopically in each case for every pair of
complexes: 4 and 7, 5 and 8, and 6 and 9. The stoichiometries
of the transformations that occur are depicted in Scheme 2.
The 11B NMR chemical shifts of 4, 5, and 6, 43.32 ppm for
4, 45.38 ppm for 5, and 48 ppm for 6, all appear downfield of
the free dialkylborane (HBEt2)2, indicative of the presence of
metal-boron bonding in these complexes,6d while the chemical
shifts of the [BEt4]- complexes 7, 8, and 9, all appear
respectively as high-field narrow singlets centered at δ -17.5,
that sharpen further upon 1H decoupling. The fact that complexes
7, 8, and 9, give rise to singlets in the 11B{1H} NMR spectrum
is consistent with uncoordinated boron atoms as is expected
for a tetraalkyl counterion such as [BEt4]-.
In light of such results, a rational explanation for the source
of BEt3 in the commercial Super-Hydride batches, leading to
the decomposition of Super-Hydride is also necessary. Assuming
that the Super-Hydride solution is provided without excess BEt3
and properly kept in absence of moisture and air and the
handling is done properly, it is likely that BEt3 can originate
from quenching of a small amount of LiHBEt3 by adventitious
water, giving free BEt3 and LiOH. Relevant to the discussion
at hand, Brown reported the preparation of LiHBEt3 from LiH
and BEt3, under ∼50% excess of the given metal hydride over
that required by the stoichiometry, so as to maintain the final
concentration of the reaction mixture at 1.0 M in trialkylborane.
The 1H NMR spectrum shows high field signals at -7, -6.96,
and -7.5 ppm, for 4, 5, and 6 respectively, implying direct
M-H bonding of the hydrogen atoms of the σ-coordinated
alkylboranes in these complexes.6d This set of signals can be
described as composed by featureless broad resonances; con-
sequently, the magnitude of the scalar coupling could not be
(14) (a) Smith, G.; Cole-Hamilton, D. J.; Thornton-Pett, M.; Hursthouse, M. B.
J. Chem. Soc., Dalton Trans. 1985, 387. (b) Carmichael, D.; Hitchcock, P.
B.; Nixon, J. F.; Pidcock, A. J. Chem. Soc., Chem. Commun. 1988, 1554.
(c) Fryzuk, M. D.; Lloyd, B. R.; Clentsmith, G. K. B.; Rettig, S. J. J. Am.
Chem. Soc. 1991, 113, 4332. (d) Fryzuk, M. D.; Lloyd, B. R.; Clentsmith,
G. K. B.; Rettig, S. J. J. Am. Chem. Soc. 1994, 116, 3804. (e) Cameron, T.
S.; Peach, M. E. J. Chem. Crystallogr. 1998, 28(12), 919.
(16) The presence of excess LiH, added to the commercial Super-Hydride
(Aldrich) is not indicated on the label of the bottle or in the MSDS available
for it.
(15) Brown, H. C.; Krishnamurty, S.; Hubbard, J. L. J. Am. Chem. Soc. 1978,
100(11), 3343.
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σ
-Borane Coordinated to Nickel(0)
A R T I C L E S
Scheme 2. Stoichiometries for the Concomitant Formation of the Ni(0) σ-Alkylborane Complexes and the Ni(II) Trihydride Complexes
Table 1. 31P{1H} NMR Chemical Shifts (ppm) of the Asymmetric
Doublets in Complexes 4, 5, and 6 and the JP-P Coupling
Constants (Hz)
The fact that the 31P NMR signals of 7, 8, and 9 appear as
quartets upon partial 1H coupling is consistent with the existence
of three equivalent hydrides in solution for all of these
complexes, as deduced also from the integration of the respective
2
complex
δ1
δ2
2JP
-P
4
5
6
72.16
77.52
95.90
58.27
66.43
84.12
77.8
67.8
63.9
1
high-field bridging hydride signals in the H NMR spectra.
Complexes 4 and 8 were also characterized by X-ray
crystallography (Figures 1 and 2, respectively). The acquisition
parameters for 4 and 8 are given in Table 2 and selected bond
distances and angles for each are given in Tables 3 and 4,
respectively.
Molecular Structure Analysis of Complex 4. The structure
of complex 4 was confirmed by single-crystal X-ray diffraction.
The Ni-B bond distance of 2.172(6) Å coincides with the
metal-boron bond distance in (MeCp)Mn(CO)2(η2-HBCy2)
(2.187(3) Å) which, to the best our knowledge, constitutes the
only example of a σ-alkylborane complex previously character-
ized by X-ray diffraction.6d The B-H (1.23(5) Å) and M-H
(1.47(5) Å) bond lengths of complex 4 are also comparable to
those of (MeCp)Mn(CO)2(η2-HBCy2) (1.24(2) Å and 1.49(2)
determined. The Ni(II) trihydride complexes 7, 8, and 9 all show
resonances at higher fields: -13.42 ppm for 7, -13.31 ppm
for 8 and, -15.5 ppm for 9. These sets of signals are well-
defined quintets with scalar coupling constants 2JH-P of 26 Hz
that integrate for three hydrides in every case; the multiplicity
exhibited by the three equivalent hydrides in 7, 8, and 9, is
indicative of the hydride coupling to the four equivalent
phosphorus atoms in the dimeric structures. A similar feature
is also present in the three starting hydrides 1, 2, and 3.17
Further characterization of the Ni(0) σ-alkylboranes 4, 5, and
6 and Ni(II) trihydride complexes 7, 8, and 9, was achieved
from the 31P{1H} NMR spectrum of the corresponding mixtures.
All the σ-alkylborane complexes exhibited two slightly broad-
ened asymmetric doublets, characteristic of two types of
phosphorus environments, with scalar coupling constants 2JP-P
typical of Ni(0) compounds (see Table 1).2 The fact that the
31P{1H} NMR resonances of compounds 4, 5, and 6 are
characteristic of a Ni(0) system is important as the three center
B-H-Ni connectivity is established for the σ-coordinated
HBEt2, allowing confirmation of the proposed structures,
discarding any oxidative addition.18
The Ni(II) trihydride complexes 7, 8, and 9, all exhibit a very
sharp singlet at low field in the 31P{1H} NMR spectrum: δ
88.5 for 7, δ 98.92 for 8, and δ 110.1 for 9. The latter resonances
1
are observed as quartets upon partial H coupling and become
1
broad and featureless when total coupling to H is permitted.
(17) (a) Vicic, D. A.; Jones, W. D. J. Am. Chem. Soc. 1997, 119, 10855. (b)
Vicic, D. A.; Jones, W. D. J. Am. Chem. Soc. 1999, 121, 7606.
(18) An oxidative addition to the B-H bond to produce a hydride-metal boryl
complex would likely result in a significant lowering of the 2JP-P coupling
constant value, expected to be on the order of 20 Hz for a Ni(II) system of
this type, on the basis of prior observations with [(dippe)Ni(R)(CN)] and
[(dippe)Ni(Ar)(CN)] complexes (see ref 2).
Figure 1. Molecular structure of complex 4 with thermal ellipsoids at the
50% probability level.
9
J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005 18069

A R T I C L E S
Crestani et al.
Table 4. Selected Bond Distances (Å) and Angles (deg) in
Complex 8
Bond Distances
Ni(1)-Ni(2)
2.33
Ni(1)-H(101)
Ni(1)-H(102)
Ni(2)-H(100)
Ni(2)-H(101)
Ni(2)-H(102)
1.37(3)
2.02(3)
1.73(3)
1.50(3)
1.40(3)
Ni(1)-P(1)
Ni(1)-P(2)
Ni(2)-P(3)
Ni(2)-P(4)
Ni(1)-H(100)
2.1421(10)
2.1384(10)
2.1536(10)
2.1281(10)
1.37(3)
Bond Angles
P(2)-Ni(1)-P(1)
P(4)-Ni(2)-P(3)
91.01(4) H(100)-Ni(2)-H(102)
69.4(16)
77.5(17)
101.4(11)
155.0(11)
89.75(4) H(101)-Ni(2)-H(102)
H(100)-Ni(1)-H(101) 81.3(17) P(3)-Ni(2)-H(101)
H(100)-Ni(2)-H(101) 66.6(15) P(4)-Ni(2)-H(101)
also very close to the Mn-B-H (41.1(9)°) angle in (MeCp)-
Mn(CO)2(η2-HBCy2).
Figure 2. Molecular structure of complex 8 with thermal ellipsoids at the
On comparing the M-B distance exhibited in 4 (2.172(6)
Å) with the M-H distance in the same compound (1.47(5) Å),
the difference between them may be explained by the presence
of σ-donor substituents on HBEt2 leading to a strong B-H bond,
that in fact exhibits the shortest bond length of the three center
core (1.23(5) Å).19 This is remarkable, considering the d10
configuration exhibited by the nickel center, which might well
have been expected to undergo oxidative addition of the B-H
bond.
30% probability level.
Table 2. Acquisition Parameters for 4 and 8
4
8
empirical formula
formula weight
crystal size/mm3
color of crystal, shape
temperature (K)
d(calcd)/Mg m-3
crystal system
space group
a/Å
C30H59BNiP2
551.23
C36H87BNi2P4
772.17
0.23 × 0.14 × 0.12 0.32 × 0.26 × 0.17
brown, rectangular
100
red, block
100
1.153
triclinic
Ph1
1.191
monoclinic
Cc
16.697(4)
11.156(2)
17.320(4)
90
107.592(4)
90
3075.0(11)
4
Molecular Structure Analysis of Complex 8. In the solid-
state structure of complex 8, two of the three hydrides are
bridging, while the third appears as a terminal hydride over one
of the two nickel atoms in the dimeric structure (Figure 2). The
9.704(2)
15.282(4)
15.492(4)
102.588(5)
96.823(5)
90.702(5)
2224.7(10)
2
b/Å
c/Å
R/deg
1
result contrasts with the H and 31P{1H} NMR spectra of this
â/deg
γ/deg
complex, suggesting either a triply bridged structure in solution
or rapid exchange of the hydrides in solution on the NMR time
scale. In fact, the fluxional behavior of the analogous complexes
[(dippe)2Ni2H3][BPh4],20 [(dcype)2Ni2H3][BPh4],20 [(dtbpe)2Pt2H3]-
[BPh4],21 [(dtbpp)2Pt2H3]X (X ) BPh4, OMe),21 [{Ph(t-Bu)-
(CH2)2PPh(t-Bu)}2Pt2H3]X (X ) BPh4, OMe),21 [(dppe)2Pt2H3]X
(X ) BF4, I, NO3, BPh4],22 [(dppp)2Pt2H3][BF4],22 [(dppb)2-
Pt2H3]X (X ) BF4, NO3),22 and [(cis-Ph2P(CH)2PPh2)Pt2H3]-
[BF4]22 in solution has been reported by several groups. From
these complexes, [(dippe)2Ni2H3][BPh4]20 is the one that has
V/Å3
Z value
µ/mm-1
0.752
1.012
θ range/deg
completeness to theta/%
no. of rflns collected
no. of indep rflns (Rint/%)
abs cor
2.23 to 25.04
95.9
1.36 to 28.32
89.9
5403
16089
3350 (3.33)
none
9949 (4.45)
none
full-matrix
refinement method
full-matrix
least-squares on F2 least-squares on F2
no. of data/restraints/parameters 3350/2/313
9949/0/420
0.895
goodness-of-fit on F2
1.054
final R indices (I > 2σ(I))/%
R ) 4.25, Rw ) 9.33 R ) 4.99, Rw ) 9.37
R ) 4.70, Rw ) 9.55 R ) 8.70, Rw ) 10.16
1
been found to be directly comparable to complex 8. The H
R indices (all data)/%
largest diff peak and hole/e Å-3 0.546 and -0.300
0.799 and -0.515
NMR spectrum of [(dippe)2Ni2(H)3][BPh4] exhibits only one
hydride signal at δ -13.357 with multiplicity of a quintet (2JH-P
of 26.6 Hz); the 31P{1H} NMR spectrum displays a sharp singlet
at δ 97.3. In the solid state, the dinuclear cations of both
complexes exhibit the same Ni-Ni separation of 2.3 Å. The
Ni2H3 core in complex 8 shows a marked asymmetry with the
following distances: Ni(2)-H(100) (1.73 Å), Ni(2)-H(101)
(1.50 Å), and Ni(2)-H(102) (1.40 Å), closely resembling the
case of [(dppe)2Pt2H3][BPh4].23
Table 3. Selected Bond Distances (Å) and Angles (deg) in
Complex 4
bond
Å
angle
deg
Ni(1)-B(1)
Ni(1)-H(31)
B(1)-H(31)
Ni(1)-P(1)
Ni(1)-P(2)
2.172(6)
1.47(5)
1.23(5)
2.2061(14)
2.2101(14)
H(31)-Ni(1)-B(1)
B(1)-H(31)-Ni(1)
Ni(1)-B(1)-H(31)
P(1)-Ni(1)-P(2)
B(1)-Ni(1)-P(1)
B(1)-Ni(1)-P(2)
C(27)-B(1)-C(29)
32.77
106.54
40.69
89.62(5)
131.12(18)
139.26(18)
114.8(4)
(19) A very similar effect has also been reported by Hartwig’s group, on
comparing the core geometries of a series of σ-coordinated HBcat, HBpin,
and HBCy2 complexes, in which the increase in hydridic character of the
B-H bond in the HBCy2 complex, due to an increased σ-donation from
the alkyl substituents, was also seen to shorten the M-H bond distance,
apparently resulting in a pivoting of the borane about the B-H bond (see
ref 6d).
Å, respectively), confirming the presence of diethylborane
σ-coordinated to the Ni(0) moiety [(dippe)Ni], consistent with
the spectroscopic data. The analysis of the angles in complex 4
shows further similarities with the σ-alkylborane complex
(MeCp)Mn(CO)2(η2-HBCy2); the angle described by the
H-Ni-B system in complex 4 is 32.7°, cf. H-Mn-B (33.2-
(7)°). The angle described by Ni(1)-B(1)-H(31) (40.69°) is
(20) Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. J. Chem. Soc., Dalton
Trans. 1996, 1305.
(21) Tulip, T. H.; Yamagata, T.; Yoshida, T.; Wilson, R. D.; Ibers, J. A.; Otsuka,
S. Inorg. Chem. 1979, 18(8), 2239.
(22) Knobler, C. B.; Kaesz, H. D.; Minghetti, G.; Bandini, A. L.; Bandittelli,
G.; Bonati, F. Inorg. Chem. 1983, 22, 2324.
(23) Chiang, M. Y.; Bau, R.; Minghetti, G.; Bandini, A. L.; Banditelli, G.;
Koetzle, T. F. Inorg. Chem. 1984, 23, 122.
9
18070 J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005

σ
-Borane Coordinated to Nickel(0)
A R T I C L E S
determinations. Elemental analyses for complexes 4-9 were carried
out by USAI-UNAM. Complexes 4-6 were found to give irreproduc-
ible results due to their extreme sensitivity.
Further examination of the marked asymmetry in the positions
of the hydrides in complex 8 was performed, since this
asymmetry reflects the greater steric constraint around Ni(2),
imposed by the terminal hydride. In this instance, the angles
H(100)-Ni(2)-H(102) (69.4°), H(101)-Ni(2)-H(102) (77.5°),
and P(3)-Ni(2)-P(4) (89.75°), all seem to prove this premise.
Reactions of the Nickel (I) Hydrides with (HBEt2)2: in
Situ Preparation of 4-6. Stoichiometric amounts of 1, 2, and
3 were added at ambient temperature to (HBEt2)2 solutions
independently prepared in THF, following Wrackmeyer’s
procedure.11 The reaction is spontaneous as verified by 1H, 31P,
and 11B NMR spectroscopies; the signals of the corresponding
σ-alkylborane complexes 4, 5, and 6 all appear at their respective
chemical shifts. None of the Ni(II) trihydride complexes 7, 8,
or 9 was formed in this preparation. Isolated yields of the
σ-alkylborane complexes, after workup, obtained by this route
(10-15%) are lower than the corresponding yields obtained for
these complexes, when the [BEt4]- trihydride complexes are
concomitantly formed. In turn, these results suggest that the
formation of the σ-alkylborane complexes is favored under the
latter route; the concomitant formation of 7, 8, and 9 is likely
to be the driving force for such reactions.
Reaction of BEt3 with LiHBEt3: Concomitant Formation of
(HBEt2)2 and LiBEt4. A stoichiometric amount of BEt3 (0.014 mL,
0.096 mmol) was added to a colorless solution of Super-Hydride (0.0115
mL, 0.096 mmol) in THF-d8. Reactants were mixed at ambient
temperature in an NMR tube, and the mixture was stirred for over a
1
minute. H NMR: δ 1.02-0.95 (br, BEt3), 0.95-0.78 (br, (HBEt2)2),
0.59 (t of 1:1:1:1 q, 12H, B-CH2-CH3, J(CH3B) ) 3 Hz), -0.195 (q of
1:1:1:1 q, 8H, B-CH2, , J(CH2B) ) 4.2 Hz). 11B{1H} NMR: δ 70.7
(br, BEt3), 37.72 (br, (HBEt2)2), -17.5 (s, LiBEt4).
Reaction of [(dcype)NiH]2 (1) with an LiHBEt3/BEt3 Mixture:
Concomitant Formation of [(dcype)Ni(σ-HBEt2)] (4) and [(dcype)2Ni2-
(H)3][BEt4] (7). In the glovebox, two equivalents of [(dcype)NiH]2 (1)
(92.6 mg, 0.096 mmol) was added at room temperature to a mixture
of BEt3 (0.014 mL, 0.096 mmol) and Super-Hydride (0.0115 mL, 0.096
mmol) in THF. The mixture changed from colorless to a deep-red
solution upon addition of the Ni(I) complex. The mixture was allowed
to react for 1 h, after which time it was evaporated to dryness on the
vacuum line, leaving a deep-red oily residue. The residue was dried
on the vacuum line for 4 h, after which time hexane was added to it.
The products were separated from the hexane solution via a short
alumina column (5 cm); 4 was recovered as a deep-red solution as the
first fraction, eluting with hexane, while 7 was recovered as the second
fraction as a brick-red solution, eluting only with THF. The solvent
was removed from both fractions on the vacuum line, and the residues
were vacuum-dried overnight (P < 10-4 mmHg). Yield of 4, after
workup: 30%. Yield of 7, after workup: 84%. Anal. Calcd for 7,
C60H119BNi2P4: C, 65.95; H, 10.97. Found: C, 65.75; H, 10.89. NMR
spectra for 4: 1H, δ -7.0 (br, σ-bonded B-H proton), 1.1-2.1 (m,
Conclusions
We have shown that complexes of the type [(diphosphine)-
NiH]2 are effective precursors to generate (diphosphine)Ni(0)
species able to coordinate a σ-borane, using of a blend of
boranes easily formed in situ, with the coformation of ionic
hydride dimers of Ni(II). Studies are currently underway to
extend the scope of this reaction to related systems.
2
48H, cyclohexyl); 31P{1H}, δ 72.16 (d, JP-P ) 77.8 Hz), 58.27 (d,
2JP-P ) 77.8 Hz); 11B, δ 43.32 (br). NMR spectra for 7: 1H, δ -13.42
2
(q, 3H, H-; JH-P ) 26.7 Hz), 1.2-2.1 (m, 96H, cyclohexyl); 31P-
Experimental Section
2
{1H}, δ 88.5 (s); 31P, δ 88.5 (q, JP-H ) 26.7 Hz);11B, δ -17.5 (s).
General Considerations. Unless otherwise noted, all manipulations
were carried out using standard Schlenk and glovebox techniques, under
argon. All the solvents used were dried and distilled from dark-purple
solutions of sodium/benzophenone ketyl. Deuterated solvents for NMR
experiments were purchased from Cambridge Isotope Laboratories and
stored over 3 Å molecular sieves in an MBraun glovebox (<1 ppm
H2O and O2). Super-Hydride (1.0 M LiHBEt3 in THF), BEt3, and BH3‚
THF were purchased from Aldrich and stored in the glovebox prior to
their use. (HBEt2)2 was prepared in situ following the literature
procedure.11 [(dippe)NiH]2 (2) was prepared from Super-Hydride and
[(dippe)NiCl2]24 suspended in hexane, similarly to the literature
procedure;17a [(dcype)NiH]2 (1) and [(dtbpe)NiH]2 (3) were prepared
analogously. The chelating bisphosphine ligands, dippe and dtbpe, were
synthesized25 from 1,2-bis(dichlorophosphino)ethane (Strem) and the
corresponding Grignard alkyls (Aldrich), and dcype was purchased from
Strem. Neutral alumina and silica were heated to 200 °C under vacuum
for 2 days and stored in the glovebox. All other chemicals and filter
aids were reagent grade and were used as received. Isolated complexes
Reaction of [(dippe)NiH]2 (2) with an LiHBEt3/BEt3 Mixture:
Concomitant Formation of [(dippe)Ni(σ-HBEt2)] (5) and [(dippe)2Ni2-
(H)3][BEt4] (8). The experiment was performed following the same
procedure described for 1, adding two equivalents of [(dippe)NiH]2
(2) (61.8 mg, 0.096 mmol) to a mixture of BEt3 (0.014 mL, 0.096 mmol)
and Super-Hydride (0.0115 mL, 0.096 mmol) in THF. After column
separation, 5 was recovered as a deep-red solution as the first fraction,
eluting with hexane, while 8 was recovered as the second fraction as
a brick-red solution, eluting only with THF. The solvent was removed
from both fractions on the vacuum line and the residues were vacuum-
dried overnight (P < 10-4 mmHg). Yield of 5, after workup: 26%.
Yield of 8, after workup: 83%. Anal. Calcd for 8, C36H87BNi2P4: C,
55.99; H, 11.35. Found: C, 55.8; H, 11.3. NMR spectra for 5: 1H, δ
-6.96 (br, σ-bonded B-H proton), 1.07-1.12 (m, 12H, CH3), 1.14-
1.24 (m, 12H, CH3), 1.54-1.58 (m, 4H, CH2), 2.10-2.15 (m, 4H, CH);
2
2
31P{1H}, δ 77.52 (d, JP-P ) 67.8 Hz), 66.43 (d, JP-P ) 67.8 Hz);
11B, δ 45.38 (br). NMR spectra for 8: 1H, δ -13.31 (q, 3H, H-; 2JH-P
) 26.7 Hz), 1.14-1.21 (m, 48H, CH3), 1.94-2.03 (m, 8H, CH2), 2.10-
2.18 (m, 8H, CH); 31P{1H}, δ 98.92 (s); 31P, δ 98.92 (q, 2JP-H ) 26.7
Hz);11B, δ -17.5 (s).
1
were purified by crystallization or column chromatography. H, 11B,
and 31P NMR spectra were recorded at ambient temperature on a 300
MHz Varian Unity spectrometer in THF-d8, unless otherwise stated,
and all 1H chemical shifts (δ, ppm) are reported relative to the residual
proton resonance in the deuterated solvent (δ 3.58, m, THF). 31P NMR
spectra were recorded relative to external 85% H3PO4. 11B NMR spectra
were recorded relative to external BF3‚Et2O in CDCl3. All NMR spectra
were obtained using thin wall (0.38 mm) WILMAD NMR tubes with
Youngs valves. A Bruker APEX CCD diffractometer with monochro-
matized Mo KR radiation (λ ) 0.71073Å) was used for X-ray structure
Reaction of [(dtbpe)NiH]2 (3) with an LiHBEt3/BEt3 Mixture:
Concomitant Formation of [(dtbpe)Ni(σ-HBEt2)] (6) and [(dtbpe)2Ni2-
(H)3][BEt4] (9). The experiment was performed following the same
procedure described for 1, adding two equivalents of [(dtbpe)NiH]2
(3) (72.6 mg, 0.096 mmol) to a mixture of BEt3 (0.014 mL, 0.096 mmol)
and Super-Hydride (0.0115 mL, 0.096 mmol) in THF. After column
separation, 6 was recovered as a deep-red solution, being the first
fraction, eluting with hexane, while 9 was recovered as a brick-red
solution, as the second fraction, eluting only with THF. The solvent
was removed from both fractions on the vacuum line, and the residues
were vacuum-dried overnight (P < 10-4 mmHg). Yield of 6, after
(24) Scott, F.; Kru¨ger, C.; Betz, P. J. Organomet. Chem. 1990, 387, 113.
(25) Cloke, F. G. N.; Gibson, V. C.; Green, M. L. H.; Mtetwa, V. S. B.; Prout,
K. J. Chem. Soc., Dalton Trans. 1988, 2227.
9
J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005 18071

A R T I C L E S
Crestani et al.
workup: 21%. Yield of 9, after workup: 83%. Anal. Calcd for 9,
C44H103BNi2P4: C, 59.75; H, 11.73. Found: C, 59.63; H, 11.71. NMR
spectra for 6: 1H, δ -7.5 (br, σ-bonded B-H proton), 1.3 (s, 36H,
preparation of 6 and 9 was also made analogously to the preparation
of 4 and 7, using a THF slurry of [(dtbpe)NiCl2] (1 g, 2.231 mmol)
and Super-Hydride (5.6 mL, 5.6 mmol). After the column separation,
6 was recovered as a deep-red solution as the first fraction, eluting
with hexane, and 9 was recovered as a brick-red solution as the second
fraction, eluting only with THF. The solvent was removed from both
fractions on the vacuum line, and the residues were vacuum-dried
overnight (P < 10-4 mmHg). Yield of 6, after workup: 6%. Yield of
9, after workup: 60%.
2
CH3), 1.5-1.6 (m, 4H, CH2); 31P{1H}, δ 95.90 (d, JP-P ) 63.9 Hz),
84.12 (d, 2JP-P ) 63.9 Hz); 11B, δ 48. NMR spectra for 9: 1H, δ -15.5
2
(q, 2H, H-; JH-P ) 26.5 Hz), 1.3 (s, 72H, CH3), 1.5-1.6 (m, 8H,
2
CH2); 31P{1H}, δ 110.1 (s); 31P, δ 110.1 (q, JH-P ) 26.5 Hz); 11B, δ
-17.5 (s).
Reaction of [(dcype)NiH]2 (1) with (HBEt2)2: Preparation of
[(dcype)Ni(σ-HBEt2)] (4). Three equivalents of [(dcype)NiH]2 (1)
(280.7 mg, 0.3 mmol) was added at room temperature to a mixture of
BEt3 (0.058 mL, 0.4 mmol) and BH3‚THF (0.019 mL, 0.2 mmol) in
THF. The mixture changed from colorless to a deep-red solution upon
addition of the Ni(I) complex. The mixture was allowed to react for 1
h, after which time it was filtered through a small alumina column (5
cm). Complex 4 was recovered as deep-red solution, which was
evaporated to dryness on the vacuum line; the residue was vacuum-
dried overnight (P < 10-4 mmHg). Yield of 4, after workup: 15%.
Reaction of [(dippe)NiH]2 (2) with (HBEt2)2: Preparation of
[(dippe)Ni(σ-HBEt2)] (5). The experiment was performed following
the same procedure described for 1, adding three equivalents of [(dippe)-
NiH]2 (2) (187.4 mg, 0.3 mmol) at room temperature to a mixture of
BEt3 (0.058 mL, 0.4 mmol) and BH3‚THF (0.019 mL, 0.2 mmol) in
THF. Yield of 5, after workup: 12%.
Crystallographic Studies The X-ray diffraction data for both 4 and
8 were collected with the use of the program SMART26 on a Bruker
APEX CCD diffractometer with monochromatized Mo KR radiation
(λ ) 0.71073). Space group assignments were made on the basis of
systematic absences and intensity statistics by using the XPREP
program. Cell refinement and data reduction were carried out with the
use of the program SAINT; the program SADABS was employed to
make incident beam, decay, and absorption corrections in the SAINT-
Plus v. 6.0 suite.27 Then the structures of 4 and 8 were solved by direct
methods with the program SHELXS and refined by full-matrix least-
squares techniques with SHELXL in the SHELXTL v. 6.1 suite.28
Crystallographic Analysis of 4. Brown single crystals of 4, suitable
for X-ray diffraction studies, were obtained by cooling a concentrated
solution of 4 in hexane at -30 °C for 5 d in the glovebox. The crystals
of 4 were mounted under Paratone 8277 on glass fibers and immediately
placed under a cold nitrogen stream at 100 K on the X-ray diffracto-
meter. Crystal data for 4 are provided in Table 2. A total of 5403
reflections were collected, 3350 of which were unique (Rint ) 3.33%).
The space group was determined to be Cc. For Z ) 4 and a formula
weight of 551.23, the calculated density was 1.191 Mg/m3. No
absorption correction was applied. The structure was solved by direct
methods and was expanded using Fourier techniques. H31 was located
on the difference Fourier map. Remaining hydrogen atoms were
generated in calculated positions and constrained with the use of a riding
model. The final model involved anisotropic displacement parameters
for all non-hydrogen atoms. The final cycle of full-matrix least-squares
refinement on F2 was based on 3350 observed reflections (I > 2σ(I))
and 313 variable parameters and converged with unweighted and
weighted agreement factors of R ) 4.25% and Rw ) 9.33%. The
goodness-of-fit on F2 after refinement was found to be 1.054. The
complete crystal data for 4, as the rest of the experimental details of
the X-ray diffraction studies for it, are provided in Table 2. Positional
parameters for all atoms, anisotropic thermal parameters, and all bond
lengths and angles, as well as fixed hydrogen positional parameters,
are given in the Supporting Information for 4.
Reaction of [(dtbpe)NiH]2 (3) with (HBEt2)2: Preparation of
[(dtbpe)Ni(σ-HBEt2)] (6). The experiment was performed following
the same procedure described for 1, adding three equivalents of [(dtbpe)-
NiH]2 (3) (220.1 mg, 0.3 mmol) at room temperature to a mixture of
BEt3 (0.058 mL, 0.4 mmol) and BH3‚THF (0.019 mL, 0.2 mmol) in
THF. Yield of 6, after workup: 10%.
Reaction of [(dcype)NiCl2] with Super-Hydride: Concomitant
Preparation of [(dcype)Ni(σ-HBEt2)] (4) and [(dcype)2Ni2(H)3][BEt4]
(7). In addition to the concomitant preparation of 4 and 7 described
above that started from complex 1, the concomitant preparation of 4
and 7 starting from the precursor complex [(dcype)NiCl2] and Super-
Hydride in a one-pot reaction was also performed. A stirred slurry of
4 equiv of [(dcype)NiCl2] (1 g, 1.81 mmol) in THF was prepared in
the glovebox, and to this was added dropwise at room temperature 10
equiv of Super-Hydride (4.5 mL, 4.5 mmol). The slurry gradually
changed from an orange to a dark-red solution, with constant evolution
of hydrogen gas all of which was vented to the glovebox. The mixture
was allowed to react for 1 h, after which time the solution was filtered
through a frit packed with a small amount (2 cm) of neutral alumina
already eluted with THF. The solvent was then removed from the filtrate
on the vacuum line, leaving a deep-red oily residue. The residue was
dried on the vacuum line for 4 h, after which time hexane was added
to it. The products were separated from the hexane solution via a small
alumina column (5 cm); 4 was recovered as a deep-red solution as the
first fraction, eluted with the hexane, and 7 was recovered as a brick-
red solution as the second fraction, eluting only with THF. The solvent
was removed from both fractions on the vacuum line, and the residues
were vacuum-dried overnight (P < 10-4 mmHg). Yield of 4, after
workup: 10%. Yield of 7, after workup: 65%.
Crystallographic Analysis of 8. Red single crystals of 8, suitable
for X-ray diffraction studies, were obtained by cooling a concentrated
solution of 8 in THF at -30 °C for 5 d in the glovebox. The crystals
of 8 were mounted under LVAC FOMBLIN Y on glass fibers and
immediately placed under the cold nitrogen stream at 100 K on the
X-ray diffractometer. A total of 16089 reflections were collected, 9949
of which were unique (Rint ) 4.45%). The space group was determined
to be Ph1. For Z ) 2 and a formula weight of 772.17, the calculated
density was 1.153 Mg/m3. No absorption correction was applied. The
structure was solved by direct methods and was expanded using Fourier
techniques. H100, H101, and H102 were located on the difference
Fourier map. Remaining hydrogen atoms were generated in calculated
positions and constrained with the use of a riding model. The final
model involved anisotropic displacement parameters for all non-
hydrogen atoms. The final cycle of full-matrix least-squares refinement
on F2 was based on 9949 observed reflections (I > 2σ(I)) and 420
variable parameters and converged with unweighted and weighted
agreement factors of R ) 4.99% and Rw ) 9.37%. The goodness-of-
Reaction of [(dippe)NiCl2] (2) with Super-Hydride: Preparation
of [(dippe)Ni(σ-HBEt2)] (5) and [(dippe)2Ni2(H)3][BEt4] (8). The
preparations of 5 and 8 were analogous to those of 4 and 7, using a
THF slurry of [(dippe)NiCl2] (1 g, 2.551 mmol) and Super-Hydride
(6.4 mL, 6.4 mmol). After the column separation, 5 was recovered as
a deep-red solution as the first fraction, eluting with hexane, and 8
was recovered as a brick-red solution as the second fraction, eluting
only with THF. The solvent was removed from both fractions on the
vacuum line, and the residues were vacuum-dried overnight (P < 10-4
mmHg). Yield of 5, after workup: 7%. Yield of 8, after workup: 58%.
(26) Sheldrick, G. M. SMART; Bruker AXS, Inc.: Madison, WI, 2000.
(27) Sheldrick, G. M. SAINT-Plus 6.0; Bruker AXS, Inc.: Madison, WI, 2000.
(28) Sheldrick, G. M. SHELXTL 6.10; Bruker AXS, Inc.: Madison, WI, 2000.
Reaction of [(dtbpe)NiCl2] (3) with Super-Hydride: Preparation
of [(dtbpe)Ni(σ-HBEt2)] (6) and [(dtbpe)2Ni2(H)3][BEt4] (9). The
9
18072 J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005

σ-Borane Coordinated to Nickel(0)
A R T I C L E S
fit on F2 after refinement was found to be 0.895. The complete crystal
data for 8, as the rest of the experimental details of the X-ray diffraction
studies for it, are provided in Table 2. Positional parameters for all
atoms, anisotropic thermal parameters, and all bond lengths and angles,
as well as fixed hydrogen positional parameters, are given in the
Supporting Information for 8.
We are grateful to Todd B. Marder for his insightful analysis
on several aspects of this work.
Supporting Information Available: Tables of complete
crystallographic data for 4 and 8. X-ray crystallographic data
in CIF format. This material is available free of charge via
Internet at http://pubs.acs.org.
Acknowledgment. We thank DGAPA-UNAM (IN-205603)
and CONACYT (C02-42467) for their support of this work.
JA056000M
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