Nickel complexes involved in the isomerization of 2-methyl-3-butenenitrile

Article abstract of DOI:10.1021/om061037g

The nickel(0) fragment [(P-P)Ni], where (P-P) = dcype (1,2- bis(dicyclohexylphosphino)ethane) or dtbpe (1,2-bis(di-tert-butylphosphino) ethane), reacts with the cyano-olefins involved in the isomerization process of 2-methyl-3-butenenitrile (2M3BN), produ

Full text of DOI:10.1021/om061037g

1712
Organometallics 2007, 26, 1712-1720
Nickel Complexes Involved in the Isomerization of
2-Methyl-3-butenenitrile
Alberto Acosta-Ram´ırez,† Areli Flores-Gaspar,† Miguel Mun˜oz-Herna´ndez,§ Alma Are´valo,†
William D. Jones,‡ and Juventino J. Garc´ıa*,†
Facultad de Qu´ımica, UniVersidad Nacional Auto´noma de Me´xico, Me´xico City, Me´xico D. F. 04510,
Me´xico, Centro de InVestigaciones Qu´ımicas, UniVersidad Auto´noma del Estado de Morelos, CuernaVaca,
Morelos, 62210, Me´xico, and Department of Chemistry, UniVersity of Rochester, Rochester, New York
14627
ReceiVed NoVember 10, 2006
The nickel(0) fragment [(P-P)Ni], where (P-P) ) dcype (1,2-bis(dicyclohexylphosphino)ethane) or
dtbpe (1,2-bis(di-tert-butylphosphino)ethane), reacts with the cyano-olefins involved in the isomerization
process of 2-methyl-3-butenenitrile (2M3BN), producing the corresponding complex [(P-P)Ni(η2-C,C-
cyano-olefin)]. In the case of 2M3BN and 3-pentenenitrile (3PN), the π-methylallyl metal complex was
observed in solution. All of the intermediates in the catalytic cycle were detected and characterized by
heteronuclear NMR spectroscopy; some of these were also characterized by single-crystal X-ray diffraction
studies. The initial catalytic behavior of this system for the isomerization of 2M3BN was studied also.
Introduction
Ever since the discovery of Nylon-66 (poly(hexamethylene
adipamide)),1 the large-scale production of adiponitrile (AdN)s
a precursor of 1,6-hexanediamineshas been a very important
industrial process.2 The catalytic industrial process requires the
double hydrocyanation of butadiene, with Ni(0)-phosphite
complexes typically being added as catalysts to drive this
process. The first HCN addition produces a kinetic mixture of
isomers, composed of the desirable linear isomer 3-pentenenitrile
(3PN) and the undesirable branched isomer 2-methyl-3-
butenenitrile (2M3BN); the latter is converted in situ into 3PN
by means of a catalytic C-CN bond breaking/forming reaction,
driven by a Ni(II) allyl cyanide complex. Once formed, 3PN is
catalytically isomerized further to the terminal olefin derivative
4-pentenenitrile (4PN). The process is carried out in the presence
of a Ni(0) complex and Lewis acids (LA), which are used as
cocatalysts. The addition of a second HCN to the olefin in this
linear nitrile ultimately takes place, producing AdN.3
2M3BN and 3PN may also undergo a rearrangement of the
CdC bond through a C-H bond activation reaction to produce
other stable products, such as Z- or E-2-methyl-2-butenenitrile
(2M2BN) and the linear 2-pentenenitrile (2PN) isomer, the
stability of these isomers being associated with the conjugation
of the CdC bond in these compounds with the CtN moiety.
All eight possible isomers are shown in Figure 1.
Figure 1. Isomerization of 2-methyl-3-butenenitrile catalyzed by
Ni(0).
Several mechanistic studies have been made using [(phos-
phite)Ni(0)] complexes, cyano-olefins, and HCN, to yield
additions to CdC bonds, including the use of Lewis acids in
such processes.4-6 More recently, the use of [Ni(COD)2] as
catalytic precursor, in combination with P-donor-bidentate
ligands such as phosphines, 7-11 phosphonites,8 and phosphites,12
has been reported to achieve the transformation from the
(4) Tolman, C. A.; Seidel, W. C.; Druliner, J. D.; Domaille, P. J.
Organometallics 1984, 3, 33.
(5) Druliner, J. D. Organometallics 1984, 3, 205.
(6) Ba¨ckvall, J. E.; Andell, O. S. Organometallics 1986, 5, 2350.
(7) Chaumonnot, A.; Lamy, F.; Sabo-Etienne, S.; Donnadieu, B.;
Chaudret, B.; Barthelat, J. C.; Galland, J. C. Organometallics 2004, 23,
3363.
(8) Van der Vlugt, J. I.; Hewat, A. C.; Neto, S.; Sablong, R.; Mills, A.
M.; Lutz, M.; Spek, A. L.; Mu¨ller, C.; Vogt, D. AdV. Synth. Catal. 2004,
346, 993.
(9) Wilting, J.; Mu¨ller, C.; Hewat, A. C.; Ellis, D. D.; Tooke, D. M.;
Spek, A. L.; Vogt, D. Organometallics 2005, 24, 13.
(10) Chamard, A.; Galland, J. C.; Didillon, B. Method for transforming
ethylenically unsaturated compounds into nitriles and branched nitriles into
linear nitriles. Pat. WO 03/031392, 2002.
* To whom correspondence should be addressed. E-mail: juvent@
servidor.unam.mx.
† Universidad Nacional Auto´noma de Me´xico.
§ Universidad Auto´noma del Estado de Morelos.
‡ University of Rochester.
(1) (a) Kohan, M. I. In Ullmann’s Encyclopedia of Industrial Chemis-
try: Polyamides, 6th ed.; Wiley-VCH: Weinheim, 2003; Vol. 28, pp 25-
53. (b) Estes, L. L. In Ullmann’s Encyclopedia of Industrial Chemistry:
Fibers, 4. Synthetic Organic, 6th ed.; Wiley-VCH: Weinheim, 2003; Vol.
13, pp 467-479.
(2) van Leeuwen, P. W. N. M. Homogeneous Catalysis: Understanding
the Art; Kluwer Academic Publishers: Dordrecht, The Netherlands, 2004;
pp 229-233.
(3) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 3rd ed.; John Wiley & Sons: New York, 2001; pp 244-247.
(11) Acosta-Ram´ırez, A., Mun˜oz-Herna´ndez, M.; Jones, W. D.; Garc´ıa,
J. J. J. Organomet. Chem. 2006, 691, 3895.
(12) (a) Bartsch, M.; Bauman, R.; Kunsmann-Keietel, D. P.; Haderlein,
G.; Jungkamp, T.; Altmayer, M.; Seigel, W. Catalyst system containing,
Ni(0) for hydrocyanation. US 0176622, 2004. (b) Bartsch, M.; Kunsmann-
Keietel, D. P.; Bauman, R.; Haderlein, G.; Seigel W. (BASF) Zur
Herstellung von Nitrilen, geeigneter katalysator und verfahren zur herstellung
von nitrien. 10038037, 2002.
10.1021/om061037g CCC: $37.00 © 2007 American Chemical Society
Publication on Web 02/20/2007

Ni Complexes and the Isomerization of 2-Methyl-3-butenenitrile
Organometallics, Vol. 26, No. 7, 2007 1713
on the substituent that is present (except for adamantyl-nitrile,
which is stable to further reaction13), these η2-nitrile complexes
undergo oxidative addition of the C-CN bond to the nickel(0)
center, producing the nickel(II) derivatives of the type [(P-P)-
Ni(CN)(R)]. The latter results have prompted us to study the
reactivity of nickel complexes containing the moiety [(P-P)-
Ni] in reactions using unsaturated nitriles. In particular, the
catalytic isomerization of 2M3BN to 3PN using the [(dppf)Ni]
species (dppf ) 1,2-bis(diphenylphosphino)ferrocene) has re-
cently been reported.11 The catalytic isomerization of 2M3BN
was achieved with 100% conversion using [(dppf)Ni], and the
1
yield of 3PN was found to be 83% by both GC-MS and H
NMR spectroscopy.11 In this study, the methodology for the
characterization and quantification of products was rigorously
demonstrated, the available literature addressing the mechanistic
details of such process being very limited,7-10 and a lack of
hard analytical data being cited to permit reproduction of the
reported results (see ref 11). Recently, Jones and co-workers
have extended the chemistry of the [(dippe)Ni] moiety to the
C-CN activation of allylnitrile in order to investigate the C-H
and C-CN cleavage reaction in this substrate. The reaction of
[(dippe)NiH)]2 with allyl cyanide at low temperature quantita-
tively generated the η2-olefin complex [(dippe)Ni(η2-C,C-
CH2dCHCH2CN)], which at ambient temperature or above was
converted to a mixture of the C-CN cleavage product [(dippe)-
Ni(η3-allyl)(CN)] and the olefin-isomerization products cis- and
trans-[(dippe)Ni(η2-C,C-crotononitrile)], formed via C-H ac-
tivation.15 Ultimately, only the latter products were observed,
as they represent the thermodynamic sink for the reaction.
Herein, we report the isolation of the key intermediates involved
in the isomerization of 2M3BN to the linear 3- and 4-PN
products using nickel(0) complexes, the [(dcype)Ni] moiety
being particularly useful for such ends. Spectroscopic charac-
terization of Ni(0) complexes of all eight isomers of 2M3BN
is provided, as well as characterization of σ- and π-allyl cyanide
intermediates in the isomerizations.
Figure 2. Catalytic cycle proposed for the isomerization of 2M3BN
to 3PN.7
branched nitrile (2M3BN) to the linear nitrile (3PN). Although
some mechanistic details are still unknown, Sabo-Etienne
recently disclosed a proposal for the catalytic isomerization of
2M3BN to 3PN on the basis of DFT calculations (see Figure
2),7 in which the substitution of COD ligands by phosphines in
[Ni(COD)2] produces the reactive intermediate [Ni(PH3)2] (A).
The latter was proposed to react with a molecule of 2M3BN to
give an η2-C,C bound olefin complex of the formula [(PH3)2-
Ni(η2-C,C-2M3BN)] (B), in which the C-CN bond oxidative
cleavage by nickel(0) occurs producing a σ-allyl nickel(II)
complex of the type [(PH3)2Ni(η1-allyl)(CN)] (D). A transition
state metallacycle of the type [(PH3)2Ni(η1-C-allyl,η1-C-CN)]
(C), resulting from the rearrangement of the nitrile ligand, was
proposed to exist prior to the oxidative addition of the C-CN
bond to form complex D. This species was then proposed to
isomerize into a π-allyl complex, [(PH3)2Ni(η3-1-methylallyl)-
(CN)] (E), which evolved into a second σ-allyl complex, [(PH3)2-
Ni(η1-allyl)(CN)] (F), with the inner skeleton of the allyl now
bound to the nickel(II) center, proximal to the -CN ligand.
From this intermediate, re-formation of the C-CN bond through
another metallacycle transition state (G) leads to the η2-C,C
linear bound 3PN nickel(0) complex (H), from which 3PN could
be obtained along with the original catalyst species A, thereby
continuing the catalytic cycle.
For a number of years, our group has been interested in the
activation of C-CN bonds of aryl-, heteroaryl-, and alkyl-nitriles
using nickel(0) complexes of the general formula [(P-P)Ni(µ-
H)]2, in which (P-P) is a chelating diphosphine ligand such
as dcype (1,2-bis(dicyclohexylphosphino)ethane), dtbpe (1,2-
bis(di-tert-butylphosphino)ethane), or dippe (1,2-bis(diisopro-
pylphosphino)ethane).13,14 The reactions that occur result in
the immediate formation of nickel(0) complexes of the type
[(P-P)Ni(η2-C,N-R)] (R ) aryl, heteroaryl,14 alkyl13), in which
the nitrile is side-on coordinated to the [(P-P)Ni] moiety. Under
certain conditions (thermal14 or photochemical13) and depending
Results and Discussion
Reactions of 2M3BN and 3PN. The in situ reaction of
[(dcype)Ni(COD)]16 with a 2-fold excess of 2M3BN in toluene-
d8 solution produces an instantaneous color change from brown-
red to brown-yellow. After 15 min of stirring, the 31P{1H} NMR
spectrum showed two doublets centered at δ 58.3 and 61.9 (2JP-P
) 52 Hz), the magnitude of the coupling constant being
indicative of a nickel(0) complex with two distinct phosphorus
environments.13,14 This initial complex was assigned as [(dcype)-
Ni(η2-C,C-2M3BN)], 1 (Figure 3a). After 6 h at room temper-
ature, four new species were observed to form gradually, the
evolution of reaction intermediates being determined by the
corresponding 31P{1H} NMR spectrum at different reaction
times (15 min, 6 h, and 12 h, see Figure 3). The new species
can be described in these spectra as follows: (1) two doublets
at δ 63.5 and 59.1, with 2JP-P ) 52.2 Hz, attributed to [(dcype)-
Ni(η2-C,C-trans-3PN)], 3, (2) a broad signal centered at δ 66.0
indicative of an exchange process, assigned as a fluxional η3-
1-methylallyl complex, 2, (3) a singlet at δ 85.8 ppm due to
(15) (a) Brunkan, N. M.; Brestensky, D. M.; Jones, W. D. J. Am. Chem.
Soc. 2004, 126, 3627. (b) Brunkan, N. M.; Jones, W. D. J. Organomet.
Chem 2003, 683, 77.
(16) The reaction of [Ni(COD)2] with 1 equiv of dcype in a toluene
solution produced an instantaneous color change from yellow to brown-
red. The 31P{1H} NMR spectrum in toluene-d8 revealed the presence of a
singlet at 67.3 ppm, assigned to the complex [(dcype)Ni(COD)].
(13) Garc´ıa, J. J.; Are´valo, A.; Brunkan, N. M.; Jones, W. D. Organo-
metallics 2004, 23, 3997.
(14) (a) Garc´ıa, J. J.; Brunkan, N. M.; Jones, W. D. J. Am. Chem. Soc.
2002, 124, 9545. (b) Garc´ıa, J. J.; Jones, W. D. Organometallics 2000, 19,
5544.

1714 Organometallics, Vol. 26, No. 7, 2007
Acosta-Ramirez et al.
Scheme 1
on using trans-3PN. Consequently complex [ may be the
analogue of complex D in Figure 2 and complex + may be the
analogue of complex F in Figure 2. Similar reactions were
performed using [(dcype)Ni(µ-H)]2 as nickel source, giving
similar behavior, ruling out the involvement of COD in these
species. The above assignment requires that the broadness of
π-allyl cyanide 2 be attributed to hindered rotation of the allyl
group, not π f σ interconversion.
Characterization of the Complexes [(dcype)Ni(η2-C,C-
2M3BN)] (1) and [(dtbpe)Ni(η2-C,C-2M3BN)] (1′). The reac-
tion of the nickel(I) dimer [(dcype)Ni(µ-H)]2 in toluene-d8 with
2M3BN immediately yielded the olefinic complex 1 with
evolution of H2 gas (color change of the solution from dark red
to yellow). The 31P{1H} NMR spectrum displayed the signals
mentioned above for this complex, located at δ 58.3 and 61.9
1
(2JP-P ) 52 Hz). In the H NMR spectrum the resonances
assigned to the coordinated olefinic protons were shifted upfield
from those in free 2M3BN (δ 5.80 and 5.28) and overlapped
with the signals rising from the alkylphosphine ligand, consistent
with the side-on coordination of the CdC bond to the nickel
center (Scheme 1). No 13C{1H} is available for 1 due to the
reactivity of the sample at room temperature during the
acquisition process. The presence of two 31P resonances indicates
that the olefin lies in the NiP2 plane and is not rotating rapidly.
Figure 3. 31P{1H} NMR spectra in toluene-d8 at different times,
for the isomerization of 2M3BN using nickel complexes: (a) 15
min, (b) 6 h, (c) starting from trans-3PN, 12 h.
On using a bulkier diphosphine as dtbpe, the analogous
the nickel(II) complex [(dcype)Ni(CN)2], 10 (confirmed further
by X-ray structure analysis, Vide infra; the latter being analogous
with the complex [(dippe)Ni(CN)2]),13 and (4) two small
doublets centered at δ 73.6 and 71.3 with JP-P ) 16.3 Hz
characteristic of a nickel(II) complex.
Confirmation of the new nickel(0) and nickel(II) intermediates
was obtained by using pure trans-3PN. (These intermediates
are labeled in Figure 3b as 3 and [, respectively.) The reaction
of [(dcype)Ni(COD)] with a 2-fold excess of trans-3PN at
ambient temperature in toluene-d8 gave rise after 15 min to
signals in the 31P{1H} NMR spectrum at δ 63.5 and 59.1 with
2JP-P ) 52.2 Hz, the same as observed in the reaction using
2M3BN after 6 h of reaction and thereby assigned to [(dcype)-
Ni(η2-C,C-trans-3PN)]. The same reaction with pure trans-3PN
was also examined after 12 h at room temperature (Figure 3c).
The 31P{1H} NMR spectrum displayed some of the signals
observed in the reaction starting with 2M3BN after 6 h, as well
complex 1′ was obtained. The 31P{H} NMR spectrum displayed
2
two sharp doublets at 89.5 and 91.7 ppm, with JP-P ) 64.7
1
2
Hz. The H NMR spectrum depicted no signals for the free
olefin, and only slightly broad multiplets between δ 2.4 and
0.8 were observed. The 13C{1H} NMR spectrum was more
informative, the olefinic carbons appearing as doublets of
doublets at δ 47.7 (J1 ) 25.7 Hz, J2 ) 2.7 Hz) and δ 32.9 ppm
(J1 ) 20.8 Hz, J2 ) 2.6 Hz), the two chemical shifts for these
carbons shifted substantially upfield from those of the free ligand
(δ 135.2 for CHRd and δ 117.4 ppm for CH2d), which appear
as singlets. The -CN signal was located at δ 123.8, close to
the resonance of this moiety in the free ligand in the same
solvent (121.4 ppm), thereby indicating no η2-CN coordination
to the nickel(0) center. In both cases (1 and 1′) only one isomer
1
was detected at room temperature in the NMR spectra for H,
13C{1H}, and 31P{1H}, despite the fact that the double bond in
2M3BN has two distinct faces. This may be due to small NMR
differences between the diastereomers not resolved or to the
nickel preferentially binding to one particular face of the olefin.
as some additional signals that were assigned as follows: (a)
2
two small doublets centered at δ 82.2 and 69.5 with JP-P
)
25.9 Hz, assigned to a nickel(II) complex, (b) two small doublets
at δ 62.5 and 55.8 with 2JP-P ) 57.9 Hz, attributed to the nickel-
(0) complex [(dcype)Ni(η2-C,C-E-2M2BN)], 6 (Vide infra), and
(c) two signals at δ 63.3 and 58.9 with 2JP-P ) 52.1 Hz, which
were assigned to [(dcype)Ni(η2-C,C-cis-3PN)], 4 (Vide infra).
The above nickel(II) complexes were tentatively assigned to
Ni-σ-allyl species depicted in Figure 2 as D and F, respectively,
the small coupling constants of 16.3 and 25.9 Hz being
consistent with this formulation. The compound labeled as [
in Figure 3 was observed on using 2M3BN or starting from
trans-3PN, whereas the complex labeled as + was formed only
Characterization of Complexes [(dcype)Ni(η3-1-methyla-
llyl)(CN)] (2), [(dcype)Ni(η2-C,C-trans-3PN) (3), and [Ni-
(dcype)(η2-C,C-cis-3PN)] (4). The reaction of [(dcype)Ni(µ-
H)]2 with trans-3PN produces a mixture of the complexes 2, 3,
and 4 (Scheme 2); complex 3 forms first and isomerizes into
complexes 2 and 4 after 12 h.
Complex 2 was separated from the other two by column
chromatography over silica gel and was characterized separately;
separation of complexes 3 and 4 was not possible, and the two
complexes were characterized in the mixture. In the case of 2,

Ni Complexes and the Isomerization of 2-Methyl-3-butenenitrile
Scheme 2
Organometallics, Vol. 26, No. 7, 2007 1715
Scheme 3
The formation of the cis- and trans-3PN isomers can be
explained on the basis of the coexistence of syn- and anti-
conformers within the 1-methylallyl complex, arising from
π-σ-π isomerization.17 Reductive elimination of the -CN
moiety in the syn-isomer will produce the trans-3PN isomer 3,
while reductive elimination in the anti-allyl conformer will
produce the corresponding nickel(0) cis-3PN complex 4.
Alternatively, these reductive eliminations might proceed through
a transition state similar to that in G. This type of reactivity
has already been established for closely related allyl-palladium
complexes.18
Reactions of [(dcype)Ni(µ-H)]2 with 4PN, E-2M2BN,
Z-2M2BN, and cis-2PN. Given that 2M3BN not only isomer-
izes to 3PN and 4PN but also produces E- and Z-2M2BN and
2PN, the reactions of the nickel(I) hydride dimer [(dcype)Ni-
(µ-H)]2 were also studied with these nitriles under stoichiometric
conditions (Scheme 4). In all cases, the reactions occurred
instantaneously upon addition of the corresponding nitrile (two
per nickel center), resulting in the immediate change of color
from the solution from dark red to yellow and the sudden
evolution of H2 gas. After 15 min, complexes 5-7 and 9 were
obtained. These compounds were characterized by heteronuclear
NMR and in the case of 6′ and 7′ by single-crystal X-ray
diffraction studies (Vide infra). None of the complexes derive
from C-CN bond cleavage. On using a 2-fold excess of cis-
2PN, the isomerization from cis- to trans-isomer on the olefin
was observed, giving rise to complex 8, a feature that can be
explained by a reversible C-H breaking/forming reaction (Vide
infra).
the 31P{1H} NMR spectrum of this complex showed only a
broad signal centered at δ 66.0 ppm, indicative of an exchange
process consistent with the hindered rotation of the π-allyl ligand
(syn- and anti-conformers illustrated in Scheme 3, Vide infra).17
The same kind of spectrum has been observed in closely related
compounds such as [(dppb)Ni(η3-1-methylallyl)(CN)]7 and
[(dppf)Ni(η3-1-methylallyl)(CN-BEt3)].11 The 1H NMR spec-
trum displayed one resonance for each allylic proton in the
complex, the latter being located at δ 4.93 (s, br, CH central),
4.41 (q, 3JH-H ) 9.6 Hz, CHMe), and 3.35 (d, 3JH-H ) 9.6 Hz,
CH2). The resonance for the methyl group was obscured by the
resonances of the cyclohexyl groups from the phosphine. The
13C{1H} spectrum of complex 2 displayed the expected signals
for the allylic ligand at δ 107.8 (br, CH central), 83.7 (pt,
CHMe), and 51.2 (pt, CH2). The signal for the -CN moiety in
the same spectrum appeared as a broad signal centered at 146.5
ppm.
Characterization of [(dcype)Ni(η2-C,C-4PN)] (9). As in all
other nickel complexes containing the [(dcype)Ni] moiety, the
31P{1H} NMR spectrum of complex 9 displayed two sharp
doublets at δ 62.0 (2JP-P ) 65.5 Hz) and 57.5 (2JP-P ) 65.5
The 31P{1H} spectrum of the mixture of 3 and 4 showed two
slightly asymmetric doublets with coupling constants of 52 Hz,
consistent with the presence of nickel(0): in the case of 3, at δ
63.5 (2JP-P ) 52.2 Hz) and 59.1 (2JP-P ) 52.2 Hz), and in the
case of 4, at δ 63.3 (2JP-P ) 52.1 Hz) and 58.9 (2JP-P ) 52.1
Hz). The 13C{1H} spectrum of this mixture displayed signals
for the olefinic carbons in both complexes shifted upfield from
those in the free ligand (δ 130.6, dCHCH2CN and δ 120.7,
dCHMe): at δ 52.6 (2JC-P ) 26.8 Hz) and 35.3 (2JC-P ) 15.5
Hz) for 3, and at δ 50.1 (2JC-P ) 26.9 Hz) and 35.1 ppm (2JC-P
) 15.5 Hz) for 4. The uncoordinated -CN moieties were located
at δ 125.9 and 124.6 for 3 and 4, respectively. In both cases,
the chemical shifts appear slightly downfield from that of free
trans-3PN (δ 118.5, s), due to coordination through the double
bond to the metal center. The 1H NMR spectrum of the mixture
was also obtained, showing two slightly broad multiplets at δ
3.37 and 2.55, attributed to olefinic proton resonances. The two
resonances overlap partially with those of the phosphine ligand
and are shifted upfield from those of the free 3PN ligand (δ
5.78 (dHCH2CN) and δ 5.38 (dHMe)).
1
Hz), characteristic of nickel(0). The H NMR spectrum of 9
was indicative of η2-coordination of the CdC bond in 4PN,
showing two multiplets at δ 2.57 and 2.35 (overlapping with
the resonances for the dcype ligand). Both sets of signals are
shifted upfield from those in the free ligand (δ 6.0 and 5.22).
The 13C{1H} NMR spectrum is consistent with η2-C,C coor-
dination of the CdC bond, with signals being observed at δ
47.7 (d, 2JC-P ) 21.2 Hz, CH) and δ 35.1 (d, 2JC-P ) 18.5 Hz,
CH2). The signal for the uncoordinated -CN moiety in 9 was
located at δ 120.9. For comparison, the signals for the free ligand
appear as singlets at δ 135.5 (CH), 117.3 (CH2), and 121.2 (CN).
Characterization of Complexes [(dcype)Ni(η2-C,C-Z-
2M2BN)] (5), [(dcype)Ni(η2-C,C-E-2M2BN)] (6), and [(dtb-
pe)Ni(η2-C,C-E-2M2BN)] (6′). Complexes 5 and 6 exhibit
similar spectroscopic features in THF-d8 solution. Complex 5
has 31P resonances at 61.0 and 54.1 ppm (2JP-P ) 58.3 Hz),
while complex 6 has resonances at 62.5 and 55.8 ppm (2JP-P
1
) 57.9 Hz). The H NMR spectra for both compounds reveal
(18) van Haaren, R. J.; Oevering, H.; Coussens, B. B.; van Strijdonck,
G. P. F.; Reek, J. N. H.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. Eur.
J. Inorg. Chem. 1999, 1237.
(17) Trost, B. M. Chem. ReV. 1996, 96, 395.

1716 Organometallics, Vol. 26, No. 7, 2007
Acosta-Ramirez et al.
Scheme 4
that the signal for the single olefinic proton was shifted from
its free ligand position (δ 6.3 for Z-2M2BN and 6.4 for
E-2M2BN) to overlap with the phosphine signals. The 13C{1H}
NMR spectra provided better evidence for the η2-coordination
of the olefin moiety. The signal for the CH olefinic carbon
shifted significantly upfield from δ 143.24 (free Z-2M2BN) to
Characterization of Complexes [(dcype)Ni(η2-C,C-cis-
2PN)] (7), [(dtbpe)Ni(η2-C,C-cis-2PN)] (7′), and [(dcype)Ni-
(η2-C,C-trans-2PN)] (8). Complex 7 was formed by the reaction
of [(dcype)Ni(µ-H)]2 and cis-2PN. The 31P{1H} NMR spectum
of this complex depicts two large doublets at δ 61.8 and 65.4,
with coupling constants of 52.8 Hz, confirming the formation
of a Ni(0) complex. Two additional small doublets were ob-
served at δ 65.6 (2JP-P ) 52 Hz) and δ 62.0 (2JP-P ) 52 Hz).
The 13C{1H} NMR spectrum of 7 permitted further character-
ization of the η2-C,C-coordinated CdC bond to the nickel(0)
center. The signals for the olefinic carbons appear at δ 49.8 (d,
2
δ 47.9 ppm (d, JC-P ) 26.4 Hz) in 5. The same effect was
observed in the case of 6 with the resonance shifting from δ
143.27 (E-2M2BN) to δ 47.9 (d, 2JC-P ) 26.5 Hz) for complex
6. The methyl groups in 5 give resonances at δ 17.9 ppm (d,
2JC-P ) 3 Hz, Me- cis to CN) and δ 16.3 ppm (bs, Me gem to
CN). The corresponding resonances in 6 appear at δ 17.9 (s,
br, Me trans to CN) and δ 16.3 (s, br, Me gem to CN). An
interesting feature in complexes 5 and 6 is that the signal for
the -CN moiety is shifted downfield to δ 128.6 in both
complexes (from δ 120.9 in Z-2M2BN and δ 118.2 in
E-2M2BN). This observation may be due to a weak interaction
between the Ni center and the CtN moiety.15a
2
2JC-P ) 27.3 Hz, EtCHd) and δ 18.7 (d, JC-P ) 19.7 Hz,
dCHCN), downfield from the free ligand (δ 157.8 and 101.2).
The -CN resonance was located at δ 124.5 as a slightly broad
singlet, again indicating an interaction of the nickel(0) center
with the -CN moiety (cf. the free ligand at δ 117.6).
Addition of a 2-fold excess of cis-2PN to the THF-d8 solution
of 7 resulted in the increase of the two small signals in the 31P-
{1H} NMR spectum after 30 min at room temperature. The 1H
NMR spectrum permitted confirmation of the presence of free
trans-2PN, therefore suggesting that this second species corre-
sponds to the nickel(0) complex [(dcype)Ni(η2-C,C-trans-2PN)]
(8). After 12 h at room temperature, the 7/8 ratio had increased
to 2:1, as indicated by 1H and 13C{1H} NMR spectroscopy. The
key signals establishing the presence of a bound olefin in 8 in
On using a bulkier diphosphine such as dtbpe, the analogous
complex 6′, [(dtbpe)Ni(η2-C,C-E-2M2BN)],19 was isolated and
characterized by single-crystal X-ray diffraction. A summary
of crystallographic results and the molecular structure for 6′
are shown in Table 1 and Figure 4, respectively. The Ni center
in 6′ adopts a pseudo-square-planar geometry, as observed in
other related Ni-cyano-olefin complexes.15a The bond distances
in complex 6′ are in agreement with those found in closely
related structures where cis- and trans-crotonitrile were used.
No significant differences in the CdC bond distance in the three
complexes were detected, the latter being 1.442(3) Å in complex
6′, 1.441(4) Å in [(dippe)Ni(η2-C,C-trans-crotonitrile)], and
1.442(5) Å in [(dippe)Ni(η2-C,C-cis-crotonitrile-BPh3)]. As
mentioned above, the interaction between the nickel center and
the -CN moiety was also corroborated in the solid state. The
Ni1-C21 distance is 2.885 Å, where the sum of the van der
Waals radii is 3.33 Å, indicative of this interaction.14a,15a
2
the 13C NMR spectrum were at δ 52.4 (d, JC-P ) 27.3 Hz,
2
CHCN) and 19.0 (d, JC-P ) 15.2 Hz, CHEt), with the
uncoordinated -CN moiety appearing at δ 125.8.
The cis-trans isomerization reaction can be described as
occurring via a C-H activation reaction to form a π-allyl
hydride species, although no hydride species was detected by
1H NMR spectroscopy (see Scheme 5).
X-ray Structure of [(dtbpe)Ni(η2-C,C-cis-2PN)] (7′). Com-
plex 7′ was prepared following the same methodology used for
7,20 providing crystals suitable for X-ray diffraction. A summary
(19) Complex 6′ displays in the 31P{1H} NMR two sharp doublets at δ
(20) Complex 7′ displays in the 31P{1H} NMR two sharp doublets at δ
2
2
83.5 and 80.9 with JP-P ) 61.4 Hz.
90.2 and 86.6 with JP-P ) 57.3 Hz.

Ni Complexes and the Isomerization of 2-Methyl-3-butenenitrile
Organometallics, Vol. 26, No. 7, 2007 1717
Table 1. Summary of Crystallographic Data for 6′, 7′, and 10
6′ 7′
10
empirical formula
fw
temperature
wavelength
cryst syst
space group
unit cell dimens
C23H47NNiP2
458.27
100 (2) K
0.71073 Å
monoclinic
P2(1)/n
C23H46NNiP2
457.23
100(2) K
0.71073 Å
monoclinic
C2/c
C28H48N2NiP2
533.33
100(2) K
0.71073 Å
triclinic
P1h
a ) 11.1322(15) Å
b ) 14.1435(19) Å
c ) 16.532(2) Å
R ) 90°
a ) 18.886(4) Å
b ) 10.536(2) Å
c ) 12.667(3) Å
R ) 90°
a ) 7.4217(18) Å
b ) 9.326(2) Å
c ) 10.718(3) Å
R ) 93.263(4)°
â ) 108.721(4)°
γ ) 101.016(4)°
1.295(3) Å3
1
â)102.732(2)°
γ ) 90°
â ) 91.843(4)°
γ ) 90°
volume
Z
density (calcd)
absorp coeff
F(000)
cryst size
θ range for data collection
index ranges
2539.0(6) Å3
2519.2(10) Å3
4
4
1.199 Mg/m3
1.206 Mg/m3
0.906 mm-1
996
1.295 Mg/m3
0.845 mm-1
288
0.899 mm-1
1000
0.31 × 0.23 × 0.17 mm3
0.2 × 0.14 × 0.1 mm3
2.16 to 28.27°.
-25 e h e 24,
-13 e k e 13,
-16 e l e 16
11 295
0.08 × 0.14 × 0.17 mm3
2.02 to 28.28°.
-9 e h e 9,
-12 e k e 12,
-12 e l e 13
4747
1.92 to 24.99
-5 e h e 12,
-11 e k e 16,
-19 e l e 19
6320
no. of reflns collected
no. of indep reflns
completeness to θmax
refinement method
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
4050 [R(int) ) 0.0198]
2993 [R(int) ) 0.0604]
4180 [R(int) ) 0.0220]
90.6%
95.7%
83.1%
full-matrix least-squares on F2
4050/0/258
full-matrix least-squares on F2
2993/0/154
full-matrix least-squares on F2
4180/3/298
0.679
1.000
1.062
R1 ) 0.0311, wR2 ) 0.0856
R1 ) 0.0349, wR2 ) 0.0896
0.563 and -0.252 e‚Å-3
R1 ) 0.0562, wR2 ) 0.1322
R1 ) 0.0808, wR2 ) 0.1430
0.466 and -0.304 e‚Å-3
R1 ) 0.0346, wR2 ) 0.0833
R1 ) 0.0353, wR2 ) 0.0837
0.826 and -0.548 e‚Å-3
largest diff peak and hole
Table 2. Isomerization of 2M3BN Using Ni(0) Complexesa
conversion
(%)
yield of
3-PN (%)
yield of
4-PN (%)
yield of
E-2M2BN (%)
other
nitriles (%)
entry
precursor
t (h)
1
2
3
4
[(dcype)Ni(H)]2
[(dtbpe)Ni(H)]2
complex 9b
1
1
192
24
68
100
100
77
0
0
39
66
0
0
22
2
57
85
36
2
11
15
3
complex 9
7
1
a Neat substrate:precursor ) 110:1. T ) 25 °C. 2M3BN conversion % and yields were obtained by GC-MS and confirmed by H NMR spectroscopy.
bThis reaction was evaluated using a substrate:precursor ratio of 2:1 and THF as solvent (1 mL).
Figure 5. Molecular structure of complex 7′ at 50% probability.
Selected bond distances (Å): Ni-P1 (2.1792(18)), Ni1-P1A
(2.1945(18)), C11-C12 (1.441(9)), C10-N1 (1.17(3)), Ni1-C11
(1.968(6)), Ni1-C12 (1.954(6)). Selected angles (deg): P1-Ni1-
P1A (92.49(4)), C11-Ni1-C12 (43.1(3)).
Figure 4. Molecular structure of complex 6′ at 50% probability.
Selected bond distances (Å): Ni1-P1(2.1930(6)), Ni1-P2 (2.2072-
(6)), C19-C20 (1.442(3)), C21-N1 (1.150(3)), Ni1-C19 (1.9590-
(19)), Ni1-C20 (1.9936(18)), Ni1-C21 (2.885). Selected angles
(deg): P1-Ni1-P1A (92.49(4)), C11-Ni1-C12 (43.1(3)).
axis, which generates a second nickel (population 50%) and a
second orientation of the nitrile and ethyl groups (population
50%).
of crystallographic results and the molecular structure for 7′
are shown in Table 1 and Figure 5, respectively. The ethyl group
and the nitrile ligand are disordered. In the crystallographic
model, the nickel lies slightly off of the crystallographic 2-fold
The structure is rather similar to that reported for [(dippe)-
Ni(η2-C,C,-trans-crotylnitrile)] and [(dippe)Ni(η2-C,C,-cis-cro-

1718 Organometallics, Vol. 26, No. 7, 2007
Acosta-Ramirez et al.
analogous structure of [(dippe)Ni(CN)2] reported previously.13
10 is believed to form in these reactions when butadiene is lost
to produce small amounts of (dcype)Ni(CN)2 and (dcype)NiH2.
The latter loses H2 and continues in the reaction with 2M3BN.
Isomerization of 2M3BN. Since the [(dcype)Ni] moiety can
isomerize 2M3BN to 3PN under stoichiometric conditions, such
isomerization using catalytic amounts of [(dcype)Ni(µ-H)]2 or
[(dtbpe)Ni(µ-H)]2 as catalyst precursors was also examined. The
results using a 110-fold excess of the 2M3BN substrate are
summarized in Table 2.
In sharp contrast with the results observed in the stochiometric
reaction with the [(dcype)Ni] moiety, the reaction under catalytic
conditions using neat substrate showed that the selectivity for
linear 3PN decreased significantly, producing E-2M2BN instead,
the latter being obtained as the major product. The use of the
bulkier dtbpe ligand resulted in a more active catalytic system,
producing mainly E-2M2BN. In the case of 9 as a convenient
precursor to [(dcype)Ni], the use of catalytic conditions resulted
in increased catalyst activity, with equilibrium being been
reached after 24 h (entry 4), giving 77% conversion with a
modest selectivity for 3PN (66%) and a small amount of 4PN,
implying a better performance of complex 9 under the catalytic
conditions than those observed in the stoichiometric situation
(entry 3).
Figure 6. Molecular structure of complex 10 at 50% probability.
Selected bond distances (Å): Ni1-C27 (1.871(4)), Ni1-C28
(1.879(4), Ni-P1 (2.1693(10)), Ni-P2 (2.1657(11)), C27-N1
(1.151(5)), C28-N2 (1.144(4)). Selected angles (deg): C27-Ni1-
C28 (93.30(16)), C28-Ni1-P2 (89.72(12)), C27-Ni1-P1 (88.72-
(11)), P1-Ni-P2 (88.38(4)).
Scheme 5
Conclusions
The use of σ-donor P-ligands as dcype and dtbpe has allowed
the detection and in some cases isolation of the nickel complexes
involved in the isomerization of 2M3BN to 3PN. The two
nickel(0) moieties [(dcype)Ni] and [(dtbpe)Ni] convert 2M3BN
under catalytic conditions in high efficiency, although the
selectivity for the branched E-2M2BN isomeric product was
preferred, in a sharp contrast to the stochiometric reaction in
which the opposite occurs. The use of [(dcype)Ni(η2-C,C-4PN)]
(9) resulted in a different outcome, a moderate yield of the linear
3PN isomer been obtained under both stochiometric and catalytic
conditions.
Comparison of the current report with previous results from
our group11 allowed us to conclude that the use of bulky,
electron-rich ligands (σ-donor ligands) in the isomerization
reaction of 2M3BN yields much more 2M2BN and therefore
favors net H- transfer rather than CN- transfer, relative to dppf
(σ-donor, π-aceptor ligand), a general statement that is probably
appliable to other similar ligands. Further studies are currently
underway to extend the scope of this research to other closely
related bis(phosphino)ferrocenes.
tylnitrile-B(Ph)3].15a All of these complexes present a pseudo-
square-planar geometry around the nickel(0) center. Bond
distances are in agreement with these related structures, the Cd
C bond distance being the same in the three cases: 1.441(9) Å,
complex 7′; 1.441(4) and 1.442(5) Å in the complexes with
trans- and cis-crotonitrile, respectively. The Ni-C bond dis-
tances are also very similar between complex 7′ (1.959(2) Å)
and [(dippe)Ni(η2-C,C,-trans-crotylnitrile) (1.949(2) Å).
X-ray Structure of [(dcype)Ni(CN)2] (10). Yellow crystal-
line cubes of complex 10, suitable for X-ray determination, were
obtained during the isomerization reaction of 2M3BN with
[(dcype)Ni(µ-H)]2 (the product of this reaction confirmed by
an independent reaction of [(dcype)NiCl2] with NaCN). The
molecular structure is depicted in Figure 6, and crystallographic
data are summarized in Table 1. The structure shows a square
planar geometry around the nickel(II) center, the distances and
angles within the structure being in agreement with the
Experimental Section
All manipulations were carried out using standard Schlenk and
glovebox techniques under argon (Praxair 99.998). THF (J. T.
Baker) was dried and distilled from dark purple solutions of sodium/
benzophenone ketyl. Deuterated solvents were purchased from
Cambridge Isotope Laboratories and stored over 3 Å molecular
sieves in an MBraun glovebox (<1 ppm H2O and O2). [Ni(COD)2]
was purchased from Strem and purified from a THF solution,
filtered through Celite, and vacuum-dried to yield yellow, crystalline
[Ni(COD)2], which was further dried for 3 h in Vacuo. dcype was
purchased from Strem and was used as received. dtbpe was prepared
according to the previously reported procedure.21 The synthesis of
[(dcype)Ni(µ-H)]2 and [(dtbpe)Ni(µ-H)]2 was carried out using the
(21) Po¨rschke, K. R.; Pluta, C.; Prof., B.; Lutz, F.; Kru¨ger, C. Natur-
forsch. B. Anorg. Chem. Org. Chem. 1993, 48, 608.

Ni Complexes and the Isomerization of 2-Methyl-3-butenenitrile
Organometallics, Vol. 26, No. 7, 2007 1719
previously reported procedure.22 2M3BN and E- and Z-2M2BN
were purchased from TCI America, purged, and stored in the
glovebox. trans-3PN, cis-2PN, and 4PN were purchased from
Aldrich, purged, and stored in the glovebox. 1H, 13C{1H}, and 31P-
{1H} NMR spectra were recorded at room temperature on a 300
MHz Varian Unity spectrometer in THF-d8, toluene-d8, or CDCl3.
1H and 13C{1H} chemical shifts (δ) are reported relative to the
residual proton resonances in the deuterated solvent. All 31P{1H}
NMR spectra were recorded relative to external 85% H3PO4. All
NMR spectra and catalytic reactions were carried out using thin-
wall (0.38 mm) WILMAD NMR tubes with J. Young valves.
Elemental analyses were carried out by USAI-UNAM using an EA
1108 FISONS Instruments analyzer; reproducible elemental analy-
ses could not be obtained due to the samples’ high instability. A
Bruker APEX CCD diffractometer with monochromatized Mo KR
radiation (λ ) 0.71073 Å) was used for the X-ray structure
determinations. Crystals of 6′, 7′, and 10 were mounted under
Paratone 8277 on a glass fiber and immediately placed under a
cold stream of nitrogen.
{1H} NMR (THF-d8): δ 50.1 (d, 2JC-P ) 26.9 Hz, CNCH2CHd),
2
35.1 (d, JC-P ) 15.5 Hz, MeCHd), 124.6 (s, CN).
Preparation of [(dcype)Ni(η2-C,C-4PN) (9). To a stirred
solution of [(dcype)Ni(µ-H)]2 (100 mg 0.104 mmol) in 10 mL of
THF was added 20.5 µL (0.208) of 4PN to give an instantaneous
color change from dark wine to brown-yellow along with a strong
effervescence; all the gas vented into the box. After 15 min the
solvent was removed in Vacuo and the residue was dried for 3 h to
1
give a red solid (111 mg, 95%). H NMR (299.7 MHz, THF-d8):
δ 0.8-2.2 (br, m), 2.57 (m, 1H, CHHd), 2.35 (m, 1H, CHHd).
31P{H} NMR (121.3 MHz, THF-d8): δ 62.0 (d, 2JP-P ) 65.5 Hz),
57.5 (d, 2JP-P ) 65.5 Hz). 13C{H} NMR (THF-d8): δ 47.7 (d, 2JC-P
2
) 21.2,CHd), 35.1 (d, JC-P ) 18.5 Hz, CH2d), 120.9 (s, CN).
Preparation of Complexes [(dcype)Ni(η2-C,C-Z-2M2BN)] (5),
[(dcype)Ni(η2-C,C-E-2M2BN)] (6), and [(dtbpe)Ni(η2-C,C-E-
2M2BN)] (6′). Complexes 5 and 6 were prepared using the same
procedure as described above for complex 4, using 25 mg of
[(dcype)Ni(µ-H)]2 (0.026 mmol) and 5.1 µL of Z-2M2BN or
E-2M2BN (0.052 mmol), obtaining in both cases yellow-brown
solutions and after evaporation brown solids (5 25.7 mg, 88% and
6 26.8 mg, 92%). Complex 6′ was prepared using the same
procedure as used for complex 1′, using 30 mg of [(dtbpe)Ni(µ-
H)]2 (0.04 mmol) and 8 µL of E-2M2BN (0.08 mmol), obtaining
a red-brown solution and dark red solid after solvent evaporation
(31.8 mg, 87%). Suitable crystals for X-ray diffraction of 6′ were
obtained by slow diffusion of hexane in a THF solution of the
complex. 5: 1H NMR (299.7 MHz, THF-d8): δ 0.8-2.5 (br, m),
2.58 (m, 1H, MeCHd). 31P{1H} NMR (121.3 MHz, THF-d8): δ
61.0 (d, 2JP-P ) 58.3 Hz), 54.1 (d, 2JP-P ) 58.3 Hz). 13C{1H} NMR
Isomerization of 2M3BN to 3PN. A solution of dcype (46 mg,
0.109 mmol) in toluene-d8 was added to the yellow, crystalline [Ni-
(COD)2] (30 mg, 0.109 mmol), producing a brown-red solution.
The mixture was transferred to an NMR tube with a J. Young valve,
and 2M3BN was added (10 µL, 0.109 mmol). The reaction was
1
followed by H and 31P{1H} NMR spectroscopy.
Preparation of [(dcype)Ni(η2-C,C-2M3BN)] (1) and [(dtbpe)-
Ni(η2-C,C-2M3BN)] (1′). To a stirred solution of [(dcype)Ni(µ-
H)]2 or [(dtbpe)Ni(µ-H)]2 (0.08 mmol) in 10 mL of THF was added
16 µL (0.16 mmol) of 2M3BN. On using [(dcype)Ni(µ-H)]2 an
instantaneous color change from dark red to brown was observed,
while on using [(dtbpe)Ni(µ-H)]2 the solution turned orange-yellow
but only after overnight reaction at room temperature. In both cases,
the solvent was removed in Vacuo and the residue was dried for 3
h to give red solids (1, 80.9 mg, 90% and 1′, 62.5 mg, 89%). 1: 1H
NMR (299.7 MHz, THF-d8): δ 0.8-2.5 (br, m). 31P{H} (121.3
MHz, toluene-d8): δ 58.3 (d, 2JP-P ) 52 Hz), 61.9 (d, 2JP-P ) 52
Hz). 1′: 1H NMR (299.7 MHz, THF-d8): δ 0.8-2.1 (br, m), 2.3
(m, 1H, CHd), 2.06 (m, 2H, CH2d). 31P{1H} NMR (121.3 MHz,
THF-d8): δ 89.5 (d, 2JP-P ) 64.7 Hz), 91.7 (d, 2JP-P ) 64.7 Hz).
2
2
(THF-d8): δ 47.9 (d, JC-P ) 26.4, MeCHd), 17.9 (d, JC-P ) 3
Hz, Me cis to CN), 16.3 (bs, Me gem to CN), 128.6 (CN). 6: 1H
NMR (299.7 MHz, THF-d8): δ 0.8-2.5 (br, m), 2.59 (m, 1H,
MeCHd). 31P{H} NMR (121.3 MHz, toluene-d8): δ 62.5 (d, 2JP-P
2
) 57.9 Hz), 55.8 (d, JP-P ) 57.9 Hz). 13C{H} NMR (THF-d8):
2
δ 47.9 (d, JC-P ) 26.5, MeCHd), 17.9 (bs, Me trans to CN),
16.3 (bs, Me gem to CN), 128.6 (s, CN). 6′: 1H NMR (299.7 MHz,
THF-d8): δ 0.8-2.0 (br signals) and 2.65 (br). 13C{1H} NMR
(THF-d8): 17.2 (Me, gem CN), 19.3 (Me trans to CN), 28.4 (dd,
2
2JC-P ) 22.8 Hz C), 47.2 (dd, JC-P ) 26.5 Hz, dCHMe), 128.6
1
13C{1H} NMR (THF-d8): δ 47.7 (dd, JC-P ) 25.7 Hz and 2.7
2
(CN). 31P{1H} NMR (121.3 MHz, THF-d8): δ 84.7 (d, JP-P
61.4 Hz), 87.4 (d, JP-P ) 61.4 Hz).
)
1
2
Hz, CHd), 32.9 (dd, JC-P ) 20.8 and 2.6 Hz, CH2d), 123.8 (s,
CN). Crystallization of [(dcype)Ni(CN)2] (10) was achieved from
the above reaction mixture after 2 days at room temperature. 31P-
{1H} NMR (toluene-d8) at 85.8 ppm (s).
Preparation of Complexes [(dcype)Ni(η2-C,C-cis-2PN)] (7)
and [(dtbpe)Ni(η2-C,C-cis-2PN)] (7′), and [(dcype)Ni(η2-C,C-
trans-2PN)] (8). Complex 7 was prepared using the same procedure
used for complex 4, using 30 mg of [(dcype)Ni(µ-H)]2 (0.031 mmol)
and 6 µL of cis-2PN (0.062 mmol), obtaining a yellow-brown
solution and brown solid after solvent removal (7 31.1 mg, 95%).
Complex 7′ was prepared using the same procedure as used for
complex 1′, using 30 mg of [(dtbpe)Ni(µ-H)]2 (0.04 mmol) and 8
µL of cis-2PN (0.08 mmol), to yield a red-brown solution and dark
red solid (7′ 34.4 mg, 94%). Complex 8 was prepared by adding a
2-fold excess of cis-2PN to a solution of 7 in THF-d8 solution.
After 12 h at room temperature complex 8 was obtained. On cooling
to -35 °C in the drybox, crystals of 7′ suitable for X-ray diffraction
were obtained. 7: 1H NMR (299.7 MHz, THF-d8): δ 0.8-2.35
(br, m), (m, 1H, CNCHd), 2.10 (m, 1H, EtCHd). 31P{1H} NMR
(121.3 MHz, THF-d8): δ 61.8 (d, 2JP-P ) 52.8 Hz), 65.4 (d, 2JP-P
) 52.8 Hz). 13C{1H} NMR (THF-d8): δ 49.8 (d, 2JC-P ) 27.3 Hz,
CNCHd), 18.7 (d, 2JC-P ) 19.7 Hz, EtCHd), 124.5 (CN). 7′: 1H
NMR (299.7 MHz, THF-d8): δ 0.8-2.4 (br signals). 13C{1H} NMR
Preparation of [(dcype)Ni(η3-1-methylallyl)(CN)] (2), [(dcype)-
Ni(η2-C,C-trans-3PN) (3), and [(dcype)Ni(η2-C,C-cis-3PN)] (4).
To a stirred solution of [(dcype)Ni(µ-H)]2 (110 mg 0.114 mmol)
in 10 mL of THF was added 22 µL (0.224 mmol) of trans-3PN.
An instantaneous color change from red-wine to brown-yellow and
a strong effervescence were observed, and all the gas vented into
the box. After 15 min, the solvent was removed in Vacuo and the
residue was dried for 3 h to give a red solid. Complexes 3 and 4
were separated as a mixture from complex 2 by column chroma-
tography on silica gel (complexes 3 and 4 with hexane/THF ) 10:1
and complex 2 with THF). 2: 1H NMR (299.7 MHz, THF-d8): δ
4.93 (pq, 1H, CH central), 4.41 (m, 1H, CHMe), 3.35(m, 1H, CHH).
13C{1H} NMR (75.4 MHz, THF-d8): δ 146.5 (s, CN), 107.8 (pt,
CH central), 83.7 (pt, CHMe), 51.2 (CH2). 31P{1H} NMR (toluene-
d8): δ 66.0 (br). 3: 1H NMR (299.7 MHz, THF-d8): δ 0.8-2.5
(br, m), 3.37 (m, 1H, CNCH2CHd), 2.55 (m, 2H, MeCHd). 31P-
{1H} NMR (121.3 MHz, toluene-d8): δ 63.5 (d, 2JP-P ) 52.2 Hz),
2
(THF-d8): 14.6 (CH3), 18.0 (CH2), 20.7 (dd, JC-P ) 19.8 Hz,
2
59.1 (d, JP-P ) 52.2 Hz). 13C{1H} NMR (THF-d8): δ 52.5
2
CH2Et), 50.6 (dd, JC-P ) 27.8 Hz, CHCN), 125.1(CN). 31P{1H}
2
2
NMR (121.3 MHz, THF-d8): δ 90.2 (d, 2JP-P ) 57.3 Hz), 86.6 (d,
2JP-P ) 57.3 Hz). 8: 31P{H} NMR (121.3 MHz, THF-d8): δ 65.6
(d, 2JP-P ) 52 Hz), 62.0 (d, 2JP-P ) 52 Hz). 13C{1H} NMR (THF-
(d, JC-P ) 26.8 Hz, CNCH2CHd), 35.3 (d, JC-P ) 15.5 Hz,
MeCHd), 125.9 (s, CN). 4: 31P{1H} NMR (121.3 MHz, toluene-
d8): δ 63.3 (d, JP-P ) 52.1 Hz), 58.9 (d, JP-P ) 52.1 Hz). 13C-
2
2
2
2
d8): δ 52.4 (d, JC-P ) 27.3 Hz, CNCHd), 19 (d, JC-P ) 15.2
Hz, EtCHd), 125.9 (CN).
(22) Vicic, D. A.; Jones, W. D. J. Am. Chem. Soc. 1997, 119,10855.

1720 Organometallics, Vol. 26, No. 7, 2007
Acosta-Ramirez et al.
Catalytic Isomerization of 2M3BN. 2M3BN (0.4 mL, 4.00
mmol) was added to the precursor [(dcype)Ni(µ-H)]2, [(dtbpe)Ni-
(µ-H)]2, or complex 4 (0.036mmol), producing red-colored solu-
tions. The mixture was stirred at room temperature and was
analyzed by GC-MS taking a sample from the reaction mixture
and dissolved in THF inside the drybox. Simultaneously, a second
sample was taken and dissolved in toluene-d8 and analyzed by 1H
NMR spectroscopy.
A.A.-R. also thanks CONACyT for a graduate studies grant.
A.F.-G. thanks Subprograma 127-FQ-UNAM. W.D.J. thanks
NSF INT-0102217 for travel support.
Supporting Information Available: Detailed GC-MS deter-
minations and tables of complete crystallographic data for 6′, 7′,
and 10. NMR spectra are included for the compounds lacking
elemental analyses. This material is available free of charge via
the Internet at http://pubs.acs.org.
Acknowledgment. We thank CONACyT (grant 42467-Q)
and DGAPA-UNAM (grant IN205603) for the financial support
for this work and Marco G. Crestani for technical assistance.
OM061037G