Cleavage of carbon-carbon bonds in alkyl cyanides using nickel(0)

Article abstract of DOI:10.1021/om049700t

The reaction of the complex [(dippe)NiH]₂ (1) with a variety of alkyl cyanides afforded nickel(O) compounds of the type [(dippe) Ni(η²-RCN)], where R = Me, Et, Pr, ⁱPr, ^tBu, cyclopropyl, cyclobutyl, adamantyl (2-9, respectively). When compounds 2-9 were warmed to yield oxidative addition products, the thermal reaction proceeded only in the case of 2 to produce [(dippe)Ni(Me)(CN)] (10). Photochemical activation did produce oxidative addition products from compounds 2-8, which rapidly evolved to the β-elimination products of the organic moiety in most cases and to the formation of [(dippe)Ni(CN)₂] (11). Reaction of 1 with acetonitrile in the presence of BPh₃ gives [(dippe)Ni(η²-MeCNBPh₃)] (12), which does not undergo thermal C-CN cleavage upon heating. X-ray crystal structures are reported for 10-12.

Full text of DOI:10.1021/om049700t

Organometallics 2004, 23, 3997-4002
3997
Clea va ge of Ca r bon -Ca r bon Bon d s in Alk yl Cya n id es
Usin g Nick el(0)
J uventino J . Garc´ıa,*,† Alma Are´valo,† Nicole M. Brunkan,‡ and
William D. J ones‡
Facultad de Quı´mica, Universidad Nacional Auto´noma de Me´xico,
Me´xico City, Me´xico, D.F. 04510, and Department of Chemistry, University of Rochester,
Rochester, New York 14627
Received April 26, 2004
The reaction of the complex [(dippe)NiH]2 (1) with a variety of alkyl cyanides afforded
i
t
nickel(0) compounds of the type [(dippe)Ni(η2-RCN)], where R ) Me, Et, Pr, Pr, Bu,
cyclopropyl, cyclobutyl, adamantyl (2-9, respectively). When compounds 2-9 were warmed
to yield oxidative addition products, the thermal reaction proceeded only in the case of 2 to
produce [(dippe)Ni(Me)(CN)] (10). Photochemical activation did produce oxidative addition
products from compounds 2-8, which rapidly evolved to the â-elimination products of the
organic moiety in most cases and to the formation of [(dippe)Ni(CN)2] (11). Reaction of 1
with acetonitrile in the presence of BPh3 gives [(dippe)Ni(η2-MeCNBPh3)] (12), which does
not undergo thermal C-CN cleavage upon heating. X-ray crystal structures are reported
for 10-12.
In tr od u ction
photochemical activation of acetonitrile by Cp(CO)2Fe-
(SiMe3) has been recently reported.7
The activation of C-C bonds under mild conditions
is currently a very active area of research and remains
a challenge in organometallic chemistry. A limited
number of successful systems able to accomplish such
cleavage have been reported.1 While a variety of com-
pounds containing transition metals have been studied
in homogeneous reactions leading to C-C bond cleav-
age, the use of alkyl and aryl cyanides as substrates
has been scarcely studied. Relevant examples in that
field have been published by Parkin with the use of
ansa-molybdenocenes to activate acetonitrile under
photochemical conditions2 and by Brookhart and Berg-
man for the recently reported silicon-assisted activation
of alkyl and aryl cyanides.3 Very few others are known
for similar activations.4 The relevance of this activation
is connected to the fact that these intermediates are
involved in the selective functionalization of organic
nitriles in cross-coupling reactions,5 and also they are
involved in the cycloaddition of nitriles.6 A related
We have previously reported results concerning the
C-C bond activation of aryl and heteroaryl cyanides
using [(dippe)NiH]2, leading to the formation of an η2-
nitrile complex of nickel(0), which then undergoes
oxidative addition to form the corresponding nickel(II)
complex.8 Both types of compounds were isolated and
characterized by X-ray structural determinations. We
report here the extension to a variety of alkyl cyanides.
Our findings indicate that the initial η2 coordination of
the nitrile moiety is favored in all cases; however, the
C-CN bond cleavage can be accomplished thermally
only with acetonitrile, all other larger nitriles being
activated only with the use of photochemical conditions.
Resu lts a n d Discu ssion
Rea ction of [(d ip p e)NiH]2 (1) w ith Aceton itr ile.
The reaction at room temperature of [(dippe)NiH]2 with
CH3CN in THF yields quantitatively only one com-
pound, with the formulation of [(dippe)Ni(η2-CH3CN)]
(2) (Scheme 1). As observed in aromatic nitriles, the
* To whom correspondence should be addressed. E-mail: juvent@
servidor.unam.mx.
reaction afforded initially the η2-nitrile complex. The 31
P
† Universidad Nacional Auto´noma de Me´xico.
NMR spectrum was useful for characterization of the
Ni(0) compound, showing two slightly broadened asym-
metric doublets, characteristic of two types of phospho-
‡ University of Rochester.
(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.
(2) Churchill, D.; Shin, J . H.; Hascall, T.; Hahn, J . M.; Bridgewater,
B. M.; Parkin, G. Organometallics 1999, 18, 2403.
(3) (a) Taw, F. L.; White, P. S.; Bergman, R. G.; Brookhart, M. J .
Am. Chem. Soc. 2002, 124, 4192. (b) Taw, F. L.; Mueller, A. H.;
Bergman, R. G.; Brookhart, M. J . Am. Chem. Soc. 2003, 125, 9808.
(4) (a) Abba, M.; Yamamoto, T. J . Organomet. Chem. 1997, 532, 267.
(b) Favero, G.; Movillo, A.; Turco, A. J . Organomet. Chem. 1983, 241,
251. (c) Morvillo, A.; Turco, A. J . Organomet. Chem. 1981, 208, 103.
(d) Parshall, G. W. J . Am. Chem. Soc. 1974, 96, 2360. (e) Gerlach, D.
H.; Kane, A. R.; Parshall, G. W.; J esson, J . P.; Muetterties, E. L. J .
Am. Chem. Soc. 1971, 93, 3543. (f) Burmeister, J . L.; Edwards, L. M.
J . Chem. Soc. A 1971, 1663.
rus environments with resonances at δ 63.4 (2J P-P
)
77 Hz) and δ 78.7 (2J P-P ) 77 Hz). Such J P-P coupling
constants are typical for similar low-valent nickel
(6) (a) Bruce, M. I.; Skelton, B. W.; White, A. H.; Zaitseva, N. N.
Dalton 2001, 3627. (b) Bruce, M. I.; Skelton, B. W.; White, A. H.;
Zaitseva, N. N. Inorg. Chem. Commun. 2001, 4, 617. (c) Bruce, M. I.;
Skelton, B. W.; White, A. H.; Zaitseva, N. N. J . Organomet. Chem.
2002, 650, 141.
(7) Nakazawa, H.; Kawasaki, T.; Miyoshi, K.; Suresh, C. H.; Koga,
N. Organometallics 2004, 23, 117.
(5) (a) Miller, J . A. Tetrahedron Lett. 2001, 42, 6991. (b) Miller, J .
A.; Dankwardt, J . W. Tetrahedron Lett. 2003, 44, 1907. (c) Miller, J .
A.; Dankwardt, J . W.; Penney, J . M. Synthesis 2003, 11, 1643.
(8) (a) Garcia, J . J .; J ones, W. D. Organometallics 2000, 19, 5544.
(b) Garcia, J . J .; Brunkan, N. M.; J ones, W. D. J . Am. Chem. Soc. 2002,
124, 9547.
10.1021/om049700t CCC: $27.50 © 2004 American Chemical Society
Publication on Web 07/09/2004

3998 Organometallics, Vol. 23, No. 16, 2004
Garc´ıa et al.
Sch em e 1
1
compounds.8 The H NMR spectrum shows two multi-
plets assigned to methyl resonances for the two types
of isopropyl groups along with two methylene multiplets
and one doublet at δ 2.42 (4J H-P ) 4.8 Hz) for the methyl
of the η2-coordinated acetonitrile. In the 13C NMR
spectrum, the acetonitrile CtN carbon is shifted down-
obtained if a slight excess of CH3CN is present. Evidence
for loss of CH3CN in 2 can be demonstrated by the
exchange of coordinated CH3CN with added CD3CN.
The highest yield of 10 was obtained after heating the
solution for 5 days at 80 °C. When a pure sample of 10
was redissolved in THF-d8, 2 was not seen to be
regenerated at room temperature or upon warming to
100 °C for 5 days, indicating that there is not an
equilibrium between 10 and 2. Photolyzing a THF
solution of 2 (λ > 300 nm) for 6 h led to the formation
of a mixture of 10 and of [(dippe)Ni(CN)2] (11). The
latter was characterized by a characteristic singlet in
the 31P NMR spectrum at δ 91.0 and confirmed by an
X-ray structure determination (vide infra).
X-r a y Str u ctu r e of [(d ip p e)Ni(CH3)(CN)] (10). The
complex derived from the oxidative addition of aceto-
nitrile to the dippe-nickel moiety is depicted in Figure
1; selected bond lengths and angles are given in Table
1. The molecule shows disorder between the methyl and
cyanide groups, which could be successfully modeled by
placing 50% of each group in each location. While this
disorder renders the distances obtained from the model
inaccurate, one can clearly see that the C-C bond has
been cleaved, giving the product [(dippe)Ni(CH3)(CN)].
The cyanide C1-N1 distance is 1.116(12) Å, and the
C1-Ni-C2 bond angle is 87.4(4)°.
2
field to δ 160.45 (dd, J C-P ) 20, 11 Hz), compared to δ
117.2 in the free nitrile. The signal assigned to the CH3
appears at δ 15.0 (3J C-P ) 18.5, 16.5 Hz), confirmed by
a HETCOR determination.
At room temperature in THF solution in the presence
of additional CH3CN, complex 2 slowly converts to the
new product [(dippe)Ni(Me)(CN)] (10), as the solution
changes from orange to yellow. Better yields are ob-
tained on warming the sample up to 80 °C (5 days, 90%
yield in solution by 31P NMR spectroscopy). The key
changes observed are as follows: the 31P NMR spectrum
displays a pattern of signals similar to those observed
for 2, with resonances at δ 80.65 (2J P-P ) 17.6 Hz) and
δ 81.75 (2J P-P ) 17.6 Hz). Such J P-P coupling constants
are typical for nickel(II). The 13C NMR spectrum shows
2
the CtN σ-coordinated to nickel at δ 128.4 (dd, J C-P
) 83, 30 Hz), and the signal assigned to the η1-CH3
appears at δ -6.4 (2J C-P ) 60.3, 26.1 Hz). The H NMR
1
spectrum is consistent with the oxidative addition of the
acetonitrile, where the signal assigned to the CH3 is at
3
δ 0.1 (dd, J H-P ) 9, 4 Hz). Complex 10 was also
Rea ction of [(d ip p e)NiH]2 (1) w ith La r ger Alk yl
Cya n id es. Similar to the reaction discussed above,
complex 1 reacted with a variety of alkyl cyanides other
than acetonitrile, in which the size and linearity
(branched or cyclic) was changed. In the case of CH3-
CH2CN in THF the reaction yielded only one product
with the formulation [(dippe)Ni(η2-CH3CH2CN)] (3)
characterized by an X-ray structure determination, the
latter confirming the proposal depicted in Scheme 1.
Formation of 10 is competitive with loss of CH3CN and
decomposition of the [Ni(dippe)] fragment to a species
tentatively assigned as [Ni2(dippe)2] by analogy to Pd9
and Pt10 analogues, so that higher yields of 10 are
(9) Pan, Y.; Mague, J . T.; Fink, M. J . J . Am. Chem. Soc. 1993, 115,
3842.
(10) Simhai, N.; Iverson, C. N.; Edelbach, B. L.; J ones, W. D.
Organometallics 2001, 20, 2759.

Cleavage of C-C Bonds Using Nickel(0)
Organometallics, Vol. 23, No. 16, 2004 3999
F igu r e 1. Molecular structure of complex 10 with thermal
ellipsoids at the 30% probability level.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 10-12
atoms
10
11
12
F igu r e 2. Molecular structure of complex 11 with thermal
ellipsoids at the 30% probability level.
Distances
1.804(12)
2.1714(10)
1.116(12)
2.122(13)
Ni(1)-C(1)
Ni(1)-P(1)
C(1)-N(1)
Ni(1)-Xa
1.900(3)
2.1787(9)
1.109(3)
1.900(3)
1.837(3)
2.1403(8)
1.236(4)
1.904(2)
reaction mixture confirmed the presence of CH2dCH2
and H2 as singlets at δ 5.36 and 4.55, respectively.
As mentioned above, 11 can be formed thermally in
low yields for 2 but in higher yields in the independent
photolytic activation of 2 or 3 (also for 4-8, vide infra)
and can be envisaged as a disproportion product derived
from compounds of the type [(dippe)Ni(R)(CN)] and
[(dippe)Ni(H)(CN)]. However, the latter intermediate
seems to be unlikely, at least in the case of R ) Me,
due to the absence of â-hydrogens, but it nevertheless
is seen upon photolysis of 2. Compound 11 is depicted
in Figure 2; selected bond lengths and angles are given
in Table 1. The X-ray structure confirmed the compound
as containing two CN ligands: [(dippe)Ni(CN)2]. The
cyanide C1-N1 distance is 1.140(3) Å, and the C1-Ni-
C1A bond angle is 90.03(15)°.
Angles
88.40(5)
87.4(4)
101.0(3)
83.8(3)
P(1)-Ni(1)-P(1A)b
C(1)-Ni(1)-Xa
88.38(5)
90.46(15)
90.88(8)
90.88(8)
91.23(3)
38.53(11)
108.66(10)
121.27(7)
P(1)-Ni(1)-C(1)
P(1A)b-Ni(1)-Xa
a
b
For 10, X ) C(2); for 11, X ) C1(A); for 12, X ) N(1). P(2)
for 12.
(Scheme 1). The reaction afforded initially the η2-nitrile
complex. The 31P NMR spectrum was helpful to char-
acterize the corresponding Ni(0) compound, showing two
slightly broadened doublets, indicative of two types of
phosphorus environments with resonances at δ 64.5
(2J P-P ) 76 Hz) and δ 79.4 (2J P-P ) 76 Hz). No other
compound was detected by 31P NMR spectroscopy in the
crude reaction mixture. As with acetonitrile, the 1H
NMR spectrum shows four distinct methyl resonances
for the two types of isopropyl groups along with two
methylene multiplets. Two multiplets at δ 1.56 and 2.75
(4J H-P ) 4.0 Hz) are observed for the ethyl moiety of
the η2-coordinated propionitrile. In the 13C NMR spec-
trum, the acetonitrile CtN carbon is shifted downfield
By the very same procedure used for 3, complex 1
i
reacted with other RCN species, where R ) Pr, Pr,
tBu, cyclopropyl, cyclobutyl, adamantyl, in THF to yield
quantitatively only one product with the formulation
[(dippe)Ni(η2-RCN)] (4-9) (Scheme 1). Since the reac-
tion afforded the η2-nitrile complex initially, the 31P
NMR spectrum was the main diagnostic tool used to
identify the product as the corresponding Ni(0) com-
pound, showing two slightly broadened doublets, indica-
tive of two types of phosphorus environments with
resonances at δ ∼64 and ∼78. In all cases the values of
the J P-P coupling constants (73 Hz average) are in
agreement with the characteristic values found in
nickel(0) complexes, as quoted above for 2 and 3. No
other compound was detected by 31P NMR spectroscopy
in the crude reaction mixture. As for 2 and 3, further
warming of compounds 4-9 to 90 °C for 48 h did not
produce any other complex that could be detected by
NMR spectroscopy, only decomposition to [(dippe)2Ni],
metallic nickel, and the corresponding free nitrile.
Photolyzing THF solutions of 4-6 (λ > 300 nm) for
24 h to several days led to the slow precipitation of
[(dippe)Ni(CN)2] (11) as yellow crystals and to the
formation of the corresponding [(dippe)Ni(η2-C2H3R′)]
that remains in solution, along with small quantities
2
to δ 167.0 (dd, J C-P ) 30, 11 Hz), compared to δ 121.0
in the free nitrile. Further warming of the reaction
mixture up to 80 °C for 48 h did not produce any other
complex or isomeric form that could be detected by NMR
spectroscopy. Heating to higher temperatures led to
decomposition to [(dippe)2Ni],11 metallic nickel, and free
nitrile.
Photolyzing a THF solution of 3 (λ > 300 nm) for 23
h led to the formation of a yellow precipitate character-
ized as [(dippe)Ni(CN)2] (11), confirmed by an X-ray
structure determination (vide infra), and [(dippe)Ni(η2-
C2H4)] (62%) that remains in solution. The latter was
characterized as a singlet in the 31P NMR spectrum at
δ 72.76 and by comparison with an authentic sample.12
Also seen are singlets for [(dippe)2Ni2] (33%) and
[(dippe)2Ni] (5%) at δ 62.6 (s) and 53.99 (s), respec-
tively.13 The 1H NMR spectrum of the volatiles from the
(11) (a) Vicic, D. A.; J ones, W. D. J . Am. Chem. Soc. 1997, 119,
10855. (b) Vicic, D. A.; J ones, W. D. J . Am. Chem. Soc. 1999, 121, 7606.
(12) Po¨rschke, K. R. Angew. Chem., Int. Ed. Engl. 1987, 26, 12, 1288.
(13) The formation of both compounds was also observed on warming
the THF solutions of 1 for long periods of time, leading also to the
reductive elimination of H2.

4000 Organometallics, Vol. 23, No. 16, 2004
Garc´ıa et al.
to 1.236(4) Å in 12. The N-C-CH3 angle bends from
linear to 136.8(3)°. The Ni(1)-N(1) distance is almost
0.1 Å longer than the Ni(1)-C(1) distance, perhaps
reflecting the sterics associated with the bulky BPh3
group. The C(1)-C(2) distance of 1.501(4) Å is only
slightly longer than that in free acetonitrile (1.465 Å).16
Con clu sion s
We have shown that the complex [(dippe)NiH]2 is an
effective precursor of a Ni(0) species that can cleave
C-CN bonds of a variety of alkyl cyanides under
relatively simple and mild conditions. Such cleavage
was mediated by η2-coordinated nitriles and is irrevers-
ible. For the smaller substrate acetonitrile, such activa-
tion proceeds both thermally and photochemically; for
larger nitriles the process does not proceed thermally
but does occur under photochemical conditions. As the
size of the alkyl cyanide was increased, the C-CN
activation decreased dramatically, with the Ni(0) com-
plex derived from adamantyl cyanide being the most
stable. Lewis acid binding was actually found to inhibit
C-CN cleavage. Studies are currently underway to
extend the scope of this reaction.
F igu r e 3. Molecular structure of complex 12 with thermal
ellipsoids at the 30% probability level.
of free olefin, free nitrile, [(dippe)2Ni2], and traces of
1
[(dippe)2Ni]. The H NMR spectra of the volatiles from
each reaction mixture confirmed the presence of the
corresponding olefin, free nitrile, and H2. Note, however,
that irradiation of the cyclopropyl cyanide derivative 7
gave the cyclopropyl cyanide complex 7b, some 11, and
some of the Ni(0) decomposition product as well as free
nitrile, propene, and cyclopropane. Irradiation of the
cyclobutyl cyanide derivative 8 likewise gave the cy-
clobutyl cyanide complex 8b along with the cyclobutene
complex, free cyclobutene, 11, and cyclobutane. In sharp
contrast, the adamantyl complex 9 was both thermally
and photochemically stable under the reaction condi-
tions used. Small amounts of [(dippe)2Ni2] and [(dippe)2-
Ni] formed after 3 days of irradiation.
Rea ction w ith Aceton itr ile in th e P r esen ce of
BP h 3. It has been reported that Lewis acids such as
BPh3 accelerate and favor the cleavage of C-CN bonds
in allyl cyanides.14 Therefore, a solution of acetonitrile
and BPh3 in THF-d8 was added to a solution of 1. Over
the course of several minutes, the solution turned
yellow-brown, and a 31P NMR spectrum showed the
formation of a new complex with two doublets at δ 81.7
(2J P-P ) 43 Hz) and 61.7 (2J P-P ) 43 Hz) as the major
product (∼75%). The 1H NMR spectrum shows a doublet
at δ 1.95 for the methyl group of the nitrile. This product
is assigned as the BPh3 adduct [(dippe)Ni(η2-MeCN-
BPh3)] (12), in analogy to other similar adducts with
allyl cyanide.14 Heating this solution to 100 °C overnight
shows only the clean presence of 12, indicating that the
Lewis acid inhibits C-CN cleavage; such an inhibition
of oxidative addition, leading to the opposite effect (i.e.,
to the reductive elimination of RCN promoted by Lewis
acids), has been reported in related palladium com-
pounds.15 A single-crystal X-ray structure of 12 was
obtained (Figure 3), showing the η2 coordination as
proposed for 2 prior to binding of the Lewis acid. The
C-N bond is lengthened from 1.153 Å in acetonitrile16
Exp er im en ta l Section
All reactions were carried out using standard Schlenk and
glovebox techniques, under nitrogen. Solvents were dried and
distilled before use from sodium/benzophenone ketyl. Also,
deuterated solvents (Cambridge Isotope Laboratories) for NMR
experiments were distilled from sodium/benzophenone ketyl
and stored over 3 Å molecular sieves. All other chemicals, filter
aids, and chromatographic materials were reagent grade and
were used as received. 1H, 13C, and 31P NMR spectra were
determined on Bruker AMX400 and AVANCE400 spectrom-
eters in THF-d8 unless otherwise stated; chemical shifts (δ)
are relative to the deuterated solvent residual protons, and
31P NMR spectra are relative to external 85% H3PO4. Pho-
tolysis experiments were done using an Ace-Hanovia UV lamp,
Model 6515, or an Oriel 200 W Hg/Xe lamp. Desert Analytics
and USAI-UNAM carried out elemental analyses. The syn-
thesis of [(dippe)NiH]2 was carried out using the previously
reported procedure.11a All nitriles used were purchased from
Aldrich; liquid substrates were distilled and dried over mo-
lecular sieves, and solid substrates were dried under high
vacuum for 12 h. A Siemens SMART system with a CCD area
detector was used for X-ray structure determinations. All
complexes were purified by crystallization or column chroma-
tography.
P r ep a r a tion of [(d ip p e)Ni(η2-CH3CN)] (2) a n d [(d ip p e)-
Ni(Me)(CN)] (10). Complex 2 was prepared from [(dippe)-
NiH]2 (0.12 g, 0.18 mmol) and acetonitrile (19.5 µL, 0.37 mmol).
The reagents were mixed at room temperature, with the
acetonitrile being added to a THF solution (10 mL) of the nickel
dimer. After mixing, a strong effervescence was observed over
3 min and the solution was constantly stirred for 15 min, with
all of the released gas (H2) being vented to the drybox. The
solvent was then evaporated to dryness and the residue
recrystallized from hexanes and dried for 2 h under vacuum.
During the crystallization and drying process, the sample was
kept in a dry ice/acetone cold bath to prevent further reaction.
Compound 2 was obtained in 90% yield. If the reaction mixture
is left in solution at room temperature, complex 10 begins to
form after 2 h of reaction. After 72 h complex 10 is abundant,
but still a mixture of 2 and 10 is seen in solution. Both are
separated by chromatography on a neutral alumina column,
with hexanes as eluent; complex 2 eluted before 10. Yield: 68%
for 10. Anal. Calcd for 2, C16H35NNiP2: C, 53.07; H, 9.7; N,
(14) Brunkan, N. M.; Brestensky, D. M.; J ones, W. D. J . Am. Chem.
Soc. 2004, 126, 3627. Tolman, C. A.; Seidel, W. C.; Druliner, J . D.;
Domaille, P. J . Organometallics 1984, 3, 33.
(15) Huang, J .; Haar, C. M.; Nolan, S. P.; Marcone, J . E.; Moloy, K.
G. Organometallics 1999, 18, 297.
(16) Kratochwill, A.; Weidner, J . U.; Zimmermann, H. Ber. Dtsch.
Bunsen-Ges. 1973, 77, 408.

Cleavage of C-C Bonds Using Nickel(0)
Organometallics, Vol. 23, No. 16, 2004 4001
3.86. Found: C, 53.0; H, 9.7; N, 3.9. Anal. Calcd for 10, C16H35
-
spectrum shows both free tBuCN and isobutylene. 11 was
NNiP2: C, 53.07; H, 9.7; N, 3.86. Found: C, 52.9; H, 9.6; N,
3.83. NMR spectra for 2 (THF-d8): 1H, δ 1.0-1.12 (m, 12H,
CH3), 1.14-1.25 (m, 12 H, CH3), 1.5-1.65 (m, 4 H, CH2), 2.0-
observed as sparingly soluble crystals.
P r ep a r a tion of [(d ip p e)Ni(η2-(CH2)2CHCN)] (7). This
compound was prepared by a procedure similar to that
described above for 2, using 1 (0.10 g, 0.155 mmol) dissolved
in THF (10 mL) and adding cyclopropyl cyanide (23 µL, 0.31
mmol). Yield: 65%. Anal. Calcd for C18H37NNiP2: C, 55.7; H,
9.6; N, 3.6. Found: C, 55.6; H, 9.7; N, 3.55. NMR spectra for
7 in THF-d8: 1H, δ 0.81-0.88 (m, 4 H, CH2), 1.0-1.21 (m, 24
H, CH3), 1.55-1.63 (m, 4H, P(CH2)2P), 2.0-2.1 (m, 5 H, CH
and CHCN); 13C{1H}, δ 7.0 (s, CH2), 7.8 (m, CH), 19.5-20.5
(m, CH3), 21.4 (m, CH2), 23.3 (m, CH2), 25.5-26.2 (m, CH),
4
2.15 (m, 4 H, CH), 2.42 (d, J H-P ) 4.8 Hz, 3 H, CH3CN); 13C-
3
{1H}, δ 15.0 (dd, J C-P ) 18.5, 16.5 Hz, CH3), 19.5-20.5 (m,
CH3), 21.4 (m, CH2), 23.3 (m, CH2), 25.5-26.2 (m, CH), 160.45
2
(dd, J C-P ) 20, 11 Hz, CN); 31P{1H}, δ 63.4 (2J P-P ) 77 Hz),
78.7 (2J P-P ) 77 Hz). NMR spectra for 10 in THF-d8: 1H, δ
0.1 (dd, 3J H-P ) 9, 4 Hz, 3 H, CH3), 1.15-1.40 (m, 24 H, CH3),
1.61-1.87 (m, 4 H, CH2), 2.24-2.40 (m, 4 H, CH); 13C{1H}, δ
2
-6.4 (dd, J C-P ) 60.3, 26.1 Hz, CH3), 19.5-20.5 (m, CH3),
23.0-24.0 (m, CH2), 25.8-26.4 (m, CH), 128.4 (dd, 2J C-P ) 83,
2
170.3 (dd, J C-P ) 27, 9 Hz, CN); 31P{1H}, δ 64.4 (2J P-P ) 73
30 Hz, CN); 31P{1H}, δ 80.65 (2J P-P ) 17.6 Hz), 81.75 (2J P-P
)
Hz), 77.4 (2J P-P ) 73 Hz). Upon photolysis for 12 h, the 31P
17.6 Hz). Small quantities of a byproduct assigned as
[(dippe)2Ni2] (δ 62.6, s) can be seen in the 31P NMR spectrum
crude reaction mixture. Preparations employing an excess of
CH3CN contain less of this byproduct.
NMR spectrum showed the presence of [(dippe)Ni(CN)(cyclo-
2
2
propyl] (δ 81.96, d, J P-P ) 22 Hz; δ 80.34, d, J P-P ) 22 Hz),
7b, [(dippe)Ni(η2-cyclopropene)] (δ 71.0, s), and [(dippe)2Ni2]
in a 10:1:3 ratio, along with a trace of [(dippe)2Ni] (∼1%). The
1H NMR spectrum shows free c-PrCN as well as some propene
and cyclopropane. 11 was observed as sparingly soluble
crystals.
P r ep a r a tion of [(d ip p e)Ni(η2-CH3CH2CN)] (3). This
compound was prepared by a procedure similar to that
described above, using 1 (0.212 g, 0.329 mmol) dissolved in
THF (10 mL) and adding propionitrile (47 µL, 0.660 mmol).
Yield: 75%. Anal. Calcd for C17H37NNiP2: C, 54.28; H, 9.9; N,
3.72. Found: C, 54.3; H, 9.8; N, 3.6. NMR spectra for 3 in THF-
d8: 1H, δ 1.0-1.25 (m, 27 H, CH3), 1.5-1.65 (m, 4 H, CH2),
2.0-2.1 (m, 4 H, CH), 2.75 (m, 2 H, CH2CN); 31P{1H}, δ 64.5
(2J P-P ) 76 Hz); 79.4 (2J P-P ) 76 Hz). Irradiation for 5 h gives
11 as sparingly soluble crystals and (dippe)Ni(C2H4) (δ 72.76,
s), along with [(dippe)2Ni2] (δ 62.6, s) and [(dippe)2Ni] (δ 53.99,
s) in a 12:6:1 ratio.
P r ep a r a tion of [(d ip p e)Ni(η2-CH3CH2CH2CN)] (4). This
compound was prepared by a procedure similar to that
described above for 2, using 1 (0.156 g, 0.242 mmol) dissolved
in THF (10 mL) and adding butyronitrile (42 µL, 0.484 mmol).
Yield: 77%. Anal. Calcd for C18H39NNiP2: C, 55.41; H, 10.1;
N, 3.59. Found: C, 55.35; H, 10.0; N, 3.56. NMR spectra for 4
in THF-d8: 1H, δ 1.0-1.30 (m, 27 H, CH3), 1.5-1.65 (m, 4 H,
P(CH2)2P), 1.70-1.8 (m, 2 H, CH2), 2.0-2.15 (m, 4 H, CH),
2.76 (m, 2 H, CH2CN); 31P{1H}, δ 64.3 (2J P-P ) 76 Hz), 78.8
(2J P-P ) 76 Hz). Upon photolysis for 12 h, the 31P NMR
spectrum shows the formation of [(dippe)Ni(η2-propene)] (δ
72.85, d, J ) 71 Hz; δ 67.38, d, J ) 71 Hz), [(dippe)2Ni2], and
[(dippe)2Ni] in a 6:5:0.1 ratio. The 1H NMR spectrum shows
both free propene and PrCN. H2 is seen at δ 4.54. 11 was
observed as sparingly soluble crystals.
P r ep a r a tion of [(d ip p e)Ni(η2-(CH2)3CHCN)] (8). This
compound was prepared by a procedure similar to that
described above for 2, using 1 (0.11 g, 0.170 mmol) dissolved
in THF (10 mL) and adding cyclobutyl cyanide (32 µL, 0.341
mmol). Yield: 76%. Anal. Calcd for C19H39NNiP2: C, 56.74;
H, 9.77; N, 3.48. Found: C, 56.6; H, 9.7; N, 3.5. NMR spectra
for 8 in THF-d8: 1H, δ 1.0-1.23 (m, 24 H, CH3), 1.56-1.62
(m, 4 H, P(CH2)2P), 2.0-2.1 (m, 4 H, CH), 2.27-2.33 (m, 6 H,
CH2), 3.5-3.57 (m, 1 H, CHCN); 31P{1H}, δ 64.4 (2J P-P ) 73
Hz), 77.4 (2J P-P ) 73 Hz). Upon photolysis for 12 h, the 31P
NMR spectrum showed the presence of [(dippe)Ni(CN)(cy-
2
2
clobutyl)] (δ 79.33, d, J P-P ) 12 Hz; δ 78.31, d, J P-P ) 12
Hz), 8b, [(dippe)Ni(η2-cyclobutene) (δ 71.21, s), and [(dippe)2Ni2]
in a 5:4:5 ratio, along with a trace of [(dippe)2Ni] (∼1%). The
1H NMR spectrum shows both cyclobutene (δ 5.97, s; δ 2.54,
s) and cyclobutane (δ 1.96, s) in a 1:3 ratio. 11 was observed
as sparingly soluble crystals.
P r ep a r a t ion of [(d ip p e)Ni(η2-(C10H15)CN)] (9). This
compound was prepared by a procedure similar to that
described above for 2, using 1 (0.136 g, 0.211 mmol) dissolved
in THF (10 mL) and adding adamantyl cyanide (0.0749 g, 0.464
mmol). Yield: 90%. Anal. Calcd for C25H47NNiP2: C, 62.26;
H, 9.82; N, 2.90. Found: C, 62.31; H, 9.9; N, 3.0. NMR spectra
for 9 in THF-d8: 1H, δ 1.0-1.21 (m, 24 H, CH3), 1.55-1.63
(m, 4 H, P(CH2)2P), 1.72-1.8 (m, 6 H), 1.96-2.15 (m, 13 H);
13C{1H}, δ 19.21 (s, CH3), 19.51 (s, CH3), 20.0-21.0 (m, CH2),
26.5-27.0 (m, CH), 30.0 (s, CH2), 35.6 (m, C), 37.9 (s, CH),
P r ep a r a tion of [(d ip p e)Ni(η2-(CH3)2CHCN)] (5). This
compound was prepared by a procedure similar to that
described above for 2, using 1 (0.191 g, 0.296 mmol) dissolved
in THF (10 mL) and adding isobutyronitrile (54 µL, 0.593
mmol). Yield: 79%. Anal. Calcd for C18H39NNiP2: C, 55.41;
H, 10.1; N, 3.59. Found: C, 55.43; H, 10.1; N, 3.65. NMR
spectra for 5 in THF-d8: 1H, δ 1.0-1.29 (m, 30 H, CH3), 1.54-
1.65 (m, 4 H, P(CH2)2P), 2.0-2.1 (m, 4 H, CH), 2.92 (m, 1 H,
CHCN); 31P{1H}, δ 64.4 (2J P-P ) 73 Hz), 78.6 (2J P-P ) 73 Hz).
Upon photolysis for 23 h, the 31P NMR spectrum showed the
presence of [(dippe)Ni(η2-propene)], [(dippe)2Ni2], and [(dippe)2-
2
43.8 (s, CH2), 175.1 (dd, J C-P ) 30, 10 Hz, CN); 31P{1H}, δ
64.4 (2J P-P ) 72 Hz), 77.7 (2J P-P ) 72 Hz). Upon photolysis
for 4 days, about half of the complex is gone and free RCN is
seen by 1H NMR spectroscopy. Both [Ni2(dippe)2] and [Ni-
(dippe)2] are seen by 31P NMR spectroscopy at δ 62.6 (s) and
53.99 (s), respectively, in a 6:1 ratio.
P r ep a r a tion of [(d ip p e)Ni(η2-CH3CN-BP h 3)] (12). A
solution of CH3CN (2.2 µL, 0.042 mmol) and BPh3 (8.9 mg,
0.037 mmol) in ∼0.5 mL of THF-d8 was added to a solution of
[(dippe)NiH]2 (11.9 mg, 0.019 mmol) in ∼0.5 mL of THF-d8.
After about 1 min, the solution became yellow-brown, as a gas
(H2) was evolved. A 31P NMR spectrum showed 12 as the major
product (∼75%). The solution was heated to 100 °C overnight.
The 31P NMR spectrum now showed 12 in ∼98% yield, giving
a 90% final isolated yield. Anal. Calcd for C34H50BNP2Ni: C,
67.59; H, 8.34; N, 2.32. Found: C, 67.43; H, 8.38; N, 2.61. NMR
spectra for 12 in THF-d8: 1H, δ 0.755 (dd, 3J H-P ) 15.8, 3J H-H
1
Ni] in a 1:1.5:0.1 ratio. The H NMR spectrum shows both free
iPrCN and traces of propene. 11 was observed as sparingly
soluble crystals.
P r ep a r a tion of [(d ip p e)Ni(η2-(CH 3)3CCN)] (6). This
compound was prepared by a procedure similar to that
described above for 2, using 1 (0.116 g, 0.180 mmol) dissolved
in THF (10 mL) and adding trimethylacetonitrile (40 µL, 0.36
mmol). Yield: 76%. Anal. Calcd for C19H41NNiP2: C, 56.46;
H, 10.2; N, 3.46. Found: C, 56.33; H, 10.1; N, 3.40. NMR
spectra for 6 in THF-d8: 1H, δ 1.0-1.25 (m, 33 H, CH3), 1.56-
1.64 (m, 4 H, CH2), 2.0-2.1 (m, 4 H, CH); 31P{1H}, δ 64.4 (2J P-P
) 71 Hz), 77.4 (2J P-P ) 71 Hz). Upon photolysis for 12 h, the
31P NMR spectrum showed the presence of unreacted [(dippe)-
Ni(η2-CNtBu)], [(dippe)2Ni2], [(dippe)Ni(η2-isobutylene)] (δ 72.0,
br, s), and [(dippe)2Ni] in a 1:3:0.1:0.1 ratio. The 1H NMR
3
3
) 7.0 Hz, 6 H, CH3), 0.907 (dd, J H-P ) 12.6, J H-H ) 7.0 Hz,
3
3
6 H, CH3), 1.156 (dd, J H-P ) 12.6, J H-H ) 7.1 Hz, 6 H, CH3),
3
3
1.199 (dd, J H-P ) 17.4, J H-H ) 7.1 Hz, 6 H, CH3), 1.70 (m, 4
H, P(CH2)2P), 1.943 (d, 4J H-P ) 5.1 Hz, 3 H, CH3CN), 2.15 (m,
3
3
4 H, CH), 6.922 (t, J H-H ) 6.8 Hz, 3 H, p-H), 7.010 (t, J H-H

4002 Organometallics, Vol. 23, No. 16, 2004
Garc´ıa et al.
Ta ble 2. Su m m a r y of Cr ysta llogr a p h ic Resu lts for 10-12
10 11
16H35NNiP2 16H32N2NiP2
12
C34.5H50BN2P2Ni
formula
C
C
fw
359.08 373.09
624.22
cryst size/mm
0.10 × 0.16 × 0.25
0.2 × 0.2 × 0.05
0.20 × 0.28 × 0.32
color, shape
yellow, irreg block
yellow, prism
colorless
d(calcd)/Mg m-3
1.204
1.251
1.140
cryst syst
space group
a/ Å
tetragonal
I4hc2
14.6416(5)
tetragonal
I4hc2
14.3969(5)
monoclinic
P21/c
8.9614(6)
b/ Å
c/ Å
14.6416(5)
18.4819(9)
90
90
14.3969(5)
19.0492(9)
90
90
21.0752(13)
19.6719(12)
90
101.8490(10)
90
R/deg
â/deg
γ/deg
90
90
V/ Å3
3962.1(3)
3948.3(3)
3636.1(4)
Z
8
8
4
µ/mm-1
1.133
1.97-23.26
8716
1433 (3.2)
SADABS
1.141
2.00-23.23
8670
1430 (3.5)
SADABS
0.645
1.93-28.27
23720
8749 (3.7)
SADABS
θ range/deg
no. of rflns collected
no. of indep rflns (Rint/%)
abs cor
range of trans factors
refinement method
no. of data/restraints/params
GOF on F2
0.749-0.928
FLSQ on F2
1433/0/111
1.018
0.801-0.928
FLSQ on F2
1430/0/96
0.767-0.928
FLSQ on F2
8749/0/367
1.035
1.025
R indices (I > 2σ(I))/%
R indices (all data)/%
largest diff peak and hole/e Å-3
R1 ) 0.0325, wR2 ) 0.0858
R1 ) 0.0356, wR2 ) 0.0878
0.216 and -0.171
R1 ) 0.0276, wR2 ) 0.0562
R1 ) 0.0339, wR2 ) 0.0579
0.208 and -0.198
R1 ) 0.0544, wR2 ) 0.1499
R1 ) 0.0857, wR2 ) 0.1620
0.846 and -0.399
3
) 7.2 Hz, 6 H, m-H), 7.315 (d, J H-H ) 8.3 Hz, 6 H, o-H); 31P-
absences and intensity statistics by using the XPREP program
(Siemens, SHELXTL 5.04). The structures were solved by
using direct methods and refined by full-matrix least squares
on F2.19 For both of the structures, the non-hydrogen atoms
were refined with anisotropic thermal parameters and hydro-
gens were included in idealized positions, giving data to
parameter ratios of greater than 10:1. Compound 10 showed
a disorder between the methyl and cyanide groups, which could
be successfully modeled by placing 50% of each group in each
location. The crystal of compound 12 also contained a disor-
dered CH3CN molecule situated on a center of symmetry that
was modeled approximately as an “N-C-N” moiety. Further
experimental details of the X-ray diffraction studies 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 all of the structures.
{1H}, δ 81.7 (2J P-P ) 43 Hz), 61.7 (2J P-P ) 43 Hz).
P h otolysis exp er im en ts. A typical experiment was per-
formed using THF solutions of 100 mg of each complex in 5
1
mm sealed NMR tubes, and the reaction was followed by H
and 31P NMR. These experiments were carried out on com-
pounds 2-9 under nitrogen, at room temperature (λ > 300
nm), with results as described in the text.
Cr ysta llogr a p h ic Stu d ies. Single crystals suitable for
X-ray studies were obtained for compounds 10-12 by cooling
concentrated solutions of each compound at -30 °C in a
drybox. The crystals were mounted under Paratone 8277 on
glass fibers and immediately placed under a cold nitrogen
stream at -80 °C on the X-ray diffractometer. The X-ray
intensity data were collected on a standard Siemens SMART
CCD area detector system equipped with a normal-focus
molybdenum-target X-ray tube operated at 2.0 kW (50 kV, 40
mA). A total of 1321 frames of data (1.3 hemispheres) were
collected using a narrow frame method with scan widths of
0.3° in ω and exposure times of 30 s/frame using a detector-
to-crystal distance of 5.09 cm (maximum 2θ angle of 56.54°)
for all of the crystals. The total data collection time was
approximately 12 h for 30 s/frame exposures. Frames were
integrated with the Siemens SAINT program to 0.75 Å for all
of the data sets. The unit cell parameters for all of the crystals
were based upon the least-squares refinement of three-
dimensional centroids of >5000 reflections.17 Data were cor-
rected for absorption using the program SADABS.18 Space
group assignments were made on the basis of systematic
Ack n ow led gm en t. We thank the DGAPA-UNAM
and CONACYT-NSF for travel support (NSF Grant No.
INT0102217), and the U.S. Department of Energy
(Grant No. FG02-86ER13569) for their support of this
work.
Su p p or tin g In for m a tion Ava ila ble: Tables giving com-
plete crystallographic data for 10-12; these data are also
available as CIF files. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM049700T
(18) The SADABS program is based on the method of Blessing;
(17) It has been noted that the integration program SAINT produces
cell constant errors that are unreasonably small, since systematic error
is not included. More reasonable errors might be estimated at 10×
the listed value.
see: Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33-38.
(19) Using the SHELX95 package, R1 ) (∑||Fo| - |Fc||)/∑|Fo| and
wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2, where w ) 1/[σ2(Fo2) + (aP)2
bP] and P ) [f 0(Maximum of 0 or Fo2) + (1 - f)Fc2].
+
2