P-C bond scission at the TRIPHOS ligand and C-CN bond cleavage in 2-methyl-3-butenenitrile with [Ni(COD)2]

Article abstract of DOI:10.1021/om7011425

The use of catalytic amounts of [Ni(COD)₂] and TRIPHOS (bis(2-diphenylphosphinoethyl)phenylphosphine) allows the isomerization of 2-methyl-3-butenenitrile (2M3BN) at 100°C, to yield Z- and E-2-methyl-2-butenenitrile (2M2BN) (57% and 31%, respectively), small amounts of 3-pentenenitrile (3PN) (5%), along with a mixture of nickel complexes, consisting of cis- and trans- [Ni₂(μ-P(CH₂CH ₂PPh₂)₂)₂(CN)₂] (1, 2), cis- and irans-[Ni(TRIPHOS)(CN)₂] (3, 4), [Ni(TRIPHOS)] (5), and [Ni₂(μ-P(CH₂CH₂PPh₂) ₂)₂] (6), where compounds 1-4 and 6 are the C-CN and P-C bond cleavage products, respectively. The persistent presence of benzene in the reaction mixture was confirmed by GC-MS. The use of stochiometric amounts of the reagents led to the isomerization of 2M3BN to Z- and E-2M2BN (47% and 44%, respectively) and 3PN (9%); the formation of complexes 2, 5, and 6 has been confirmed to take place, in addition to benzene and 1,3-butadiene. Complexes 1 and 3 were characterized by single-crystal X-ray determinations.

Full text of DOI:10.1021/om7011425

1834
Organometallics 2008, 27, 1834–1840
P-C Bond Scission at the TRIPHOS Ligand and C-CN Bond
Cleavage in 2-Methyl-3-butenenitrile with [Ni(COD)2]
Alberto Acosta-Ramírez,† Marcos Flores-Álamo,† William D. Jones,‡ and
Juventino J. García†,*
Facultad de Química, UniVersidad Nacional Autónoma de México, México City, México D.F. 04510, and
Department of Chemistry, UniVersity of Rochester, Rochester, New York, 14627
ReceiVed NoVember 13, 2007
The use of catalytic amounts of [Ni(COD)2] and TRIPHOS (bis(2-diphenylphosphinoethyl)phe-
nylphosphine) allows the isomerization of 2-methyl-3-butenenitrile (2M3BN) at 100 °C, to yield Z- and
E-2-methyl-2-butenenitrile (2M2BN) (57% and 31%, respectively), small amounts of 3-pentenenitrile
(3PN) (5%), along with a mixture of nickel complexes, consisting of cis- and trans-[Ni2(µ-
P(CH2CH2PPh2)2)2(CN)2] (1, 2), cis- and trans-[Ni(TRIPHOS)(CN)2] (3, 4), [Ni(TRIPHOS)] (5), and
[Ni2(µ-P(CH2CH2PPh2)2)2] (6), where compounds 1–4 and 6 are the C-CN and P-C bond cleavage
products, respectively. The persistent presence of benzene in the reaction mixture was confirmed by
GC-MS. The use of stochiometric amounts of the reagents led to the isomerization of 2M3BN to Z- and
E-2M2BN (47% and 44%, respectively) and 3PN (9%); the formation of complexes 2, 5, and 6 has been
confirmed to take place, in addition to benzene and 1,3-butadiene. Complexes 1 and 3 were characterized
by single-crystal X-ray determinations.
monophosphine ligands, and their activation has been reported
to take place in the presence of clusters,3 as well as in the
presence of homo-4 and heterobimetallic complexes.5 Also,
PsC bond cleavage has been observed when the complexes
are in the presence of OH and water, under which conditions
the reaction is favored by the formation of PsOH6 or PdO
bonds.7
Examples of the latter type of reactivity involving the
cleavage of PsC bonds of chelating diphosphines bearing
perfluoro aromatic substituents,8as well as those in which the
Introduction
The development of organometallic chemistry and homo-
geneous catalysis with transition metals has long been assisted
by the use of omnipresent phosphine ligands, providing their
great versatility and capability to stabilize a variety of metal
centers in different oxidation states and geometries. The
applicability of phosphine ligands has been particularly
highlighted as a result of the possibilities offered by these
ligands to assist in a wide variety of metal-mediated and
metal-catalyzed bond cleavage and formation reactions
involving different substrates,1 and in many cases, some
rather complicated transformations have been achieved.
Among the diversity of possible combinations that phosphine
ligands offer for such transformations, PPh3 is by far the most
frequently used. However, under certain circumstances it has
been reported that both triaryl and trialkyl phosphine ligands
may react with metal centers upon coordination, the sto-
ichiometric cleavage of both C-H and P-C bonds of the
ligands having been reported to take place effectively: C-H
ortho-metallated complexes been reported to form in the case
of some aryl phosphines, while phosphido-bridged derivatives
have been found in the case of other trialkyl phosphine
ligands. The latter processes have been associated with the
deactivation of the catalytic species in homogeneous pro-
cesses and a wealth of examples have been provided in the
literature.2 In the case of P-C bond cleavage reactions, the
vast majority of the documented data involves aryl and alkyl
(3) (a) Watson, W. H.; Wu, G.; Richmond, M. G. Organometallics 2006,
25, 930. (b) Kabir, S.; Miale, M. A.; Sarker, N. C.; Husain, G. M. G.;
Hardcastle, K. I.; Nordlaner, E.; Rosenber, E. Organometallics 2005, 24,
3315. (c) Bruce, M. I.; Humphrey, P. A.; Schmutzler, R.; Skelton, B. W.;
White, A. H. J. Organomet. Chem. 2004, 689, 2415. (d) Bruce, M. I.;
Humphrey, P. A.; Okucu, S.; Schmutzler, R.; Skelton, B. W.; White, A. H.
Inorg. Chim. Acta 2004, 357, 1805. (e) Pereira, R. M. S.; Fujiwara, F. Y.;
Vargas, M. D.; Braga, D.; Gripioni, F. Organometallics 1997, 16, 4833.
(f) Briard, P.; Cabeza, J. A.; Llamazares, A.; Ouahab, L.; Riera, V.
Organometallics 1993, 12, 1006.
(4) (a) Alvarez, M. A.; García, M. E.; Martínez, M. E.; Ramos, A.; Ruiz,
M. A.; Saéz, D.; Vaisserman, J. Inorg. Chem. 2006, 45, 6965. (b) Tschan,
M-J.-L; Chérioux, F.; Karmazin-Brelot, L.; Süss-Fink, G. Organometallics
2005, 24, 1974. (c) Kawano, H.; Narimatsu, H.; Yamamoto, D.; Tanaka,
K.; Hiraki, K.; Onishi, M. Organometallics 2002, 21, 5526. (d) Bender,
R.; Bouaound, S.-E.; Braunstein, P.; Dusausoy, Y.; Merabet, N.; Raya, J.;
Rouag, D. J. Chem. Soc., Dalton Trans. 1999, 735. (e) Bender, P.;
Braunstein, P.; Dedieu, A.; Ellis, P. D.; Higgins, B.; Harvey, P. D.; Sappa,
E.; Tiripicchio, A. Inorg. Chem. 1996, 35, 1223. (f) Taylor, N. J.; Chieh,
P. C.; Carty, A. J. J. Chem. Soc., Chem. Commun. 1975, 448.
(5) Nakajima, T.; Shimizu, I.; Kobayashi, K.; Koshino, H.; Wakatsuki,
Y. Inorg. Chem. 1997, 36, 6440.
(6) (a) Kohl, S. W.; Heinemann, F. W.; Hummert, M.; Bauer, W.;
Grohman, A. Dalton 2006, 5583. (b) Quesada, R.; Ruiz, J.; Riera, V.; García-
Granada, S.; Díaz, R. Chem. Commun. 2003, 1942. (c) Lin, I. J. B.; Lai,
J. S.; Liu, C. W Organometallics 1990, 9, 530.
* To whom correspondence should be addressed. E-mail: juvent@
servidor.unam.mx.
† Universidad Nacional Autónoma de México.
‡ University of Rochester.
(7) Bergamini, P.; Sostero, S.; Traverso, O.; Kemp, T. J.; Pringle, P.
Dalton 1989, 2017.
(1) Murai, S., Ed. ActiVation of UnreactiVe Bonds and Organic Synthesis;
Springer-Verlag: Berlin, Germany, 1999.
(2) (a) Garrou, P. E. Chem. ReV. 1985, 85, 171. (b) van Leewen,
P. W. N. M. Appl. Catal. A: Gen. 2001, 212, 61. (c) Parkins, A. W. Coord.
Chem. ReV. 2006, 250, 449.
(8) Heyn, R.; Görbitz, C. H. Organometallics 2002, 21, 2781.
(9) (a) Shiu, K.-B.; Jean, S.-W.; Wang, H.-J.; Wang, S.-L.; Liao, F.-L.;
Wang, J.-C.; Liou, L.-S. Organometallics 1997, 16, 114. (b) Cotton, F. A.;
Canich, J. A.; Luck, R. L.; Vidyassager, K. Organometallics 1991, 10, 352.
(c) Lin, I. J. B.; Lai, J. S.; Liu, C. W. Organometallics 1990, 9, 530.
10.1021/om7011425 CCC: $40.75
2008 American Chemical Society
Publication on Web 03/05/2008

P-C Bond Scission at the TRIPHOS Ligand
Organometallics, Vol. 27, No. 8, 2008 1835
Scheme 1
cleavage was observed to take place over the bridging hydro-
carbon chain, are also known.9 Reversibility of the PsC bond
cleavage reaction in the case of palladium complexes has also
been reported.10 Formation of biphenyls as a consequence of
successive PsC bond cleavage and CsC coupling has been
documented for aryl phosphines such as PPh3;11 the additional
presence of hydride sources been observed to promote the
formation of benzene.4b,11a,12 Related to this, compounds bearing
CO ligands have been found to favor the formation of
benzaldehyde.11a,13 Also of note, phenyl moieties resulting from
the PsC bond scission of PPh3 have been reported to remain
bound to metal centers in a number of cases, displaying
η1-,3a3e µ-η1-,3f,4b η1:η2-,3c,3d and µ-η2:η2-coordinations.14 In
the case of carbonyl-substituted compounds, an acyl
complex,3e,3f and in the case of cluster systems, one example
showing the phenyl moiety that remains coupled to a ring-
opened thiophene have also been described.4c
Results and Discussion
Study of the Isomerization Reaction under Catalytic
Conditions. The catalytic isomerization reaction of neat 2M3BN
in the presence of [Ni(COD)2], used as a catalytic precursor,
and the TRIPHOS ligand at a 110-fold excess of the substrate
and 100 °C, yielded 100% conversion of the substrate producing
Z- and E-2M2BN (57% and 31%, respectively) within 24 h; a
poor yield of 3PN (5%) was also observed18 (see Scheme 1).
A crop of air-stable red crystals, namely trans-[Ni2(µ-
P(CH2CH2PPh2)2)2(CN)2] (1), was obtained from the reaction
mixture (see the Experimental Section). The crystals were
suitable for X-ray diffraction studies, the structure of the latter
compound being shown in Figure 1. Relevant crystallographic
data for this compound are summarized in Table 1.
(10) (a) Morita, D. K.; Stille, J. K.; Norton, J. R. J. Am. Chem. Soc.
1995, 117, 8576. (b) Kong, K. C.; Cheng, C.-H. J. Am. Chem. Soc. 1991,
116, 16–6313.
(11) (a) Dubuis, R.; Garrou, P. E.; Javin, K. D.; Allcock, H. R.
Organometallics 1986, 5, 466. (b) Levine, M.; Aizenshtat, Z.; Blum, J. J.
Organomet. Chem. 1980, 184, 255.
The chemistry related to phosphido ligands has been widely
studied, the latter being useful ligands for the stabilization of
single4d-4f and multiple metal-metal bonds.4a,4b Phosphido
ligands are able to act as both bridging and terminal ligands,
extremes that have been observed particularly in the case Pt
complexes.15
(12) Sabo-Etienne, S.; Chaudret, B.; Gervais, D. J. Organomet. Chem.
1983, 258, C19.
(13) (a) Lugan, N.; Lavigne, G.; Bonnet, J. J.; Réau, R.; Neibecker, D.;
Tkatchenko, I. J. Am. Chem. Soc. 1988, 110, 5369. (b) Abatjoglou, A. G.;
Billing, E.; Bryant, D. R. Organometallics 1984, 3, 923.
(14) Omori, H.; Suzuki, H.; Take, Y.; Moro-oka, Y. Organometallics
1989, 8, 2270.
Currently, as a result of our growing interest in the CsCN
bond activation reactions16 and the isomerization of cyano
olefins using Ni(0) complexes,17 we have moved to the use of
Ni(TRIPHOS) complexes for the isomerization of 2M3BN. We
find that contrary to other P-donor ligands already used, the
TRIPHOS ligand suffers a PsC bond cleavage that accompanies
the additional cleavage of the CsCN bond at the cyanoolefin,
both under catalytic and stochiometric conditions. In addition,
this catalyst does not show similar selectivity for 3-PN as seen
with the commercial catalyst. Details of these studies are
presented in this paper.
(15) Scriban, C.; Wicht, D. K.; Glueck, D. S.; Zakharov, L. N.; Golen,
J. A.; Rheingold, A. L. Organometallics 2006, 24, 3370.
(16) (a) García, J. J.; Arévalo, A.; Brunkan, N. M.; Jones, W. D.
Organometallics 2004, 23, 3997. (b) García, J. J.; Brunkan, N. M.; Jones,
W. D. J. Am. Chem. Soc. 2002, 124, 9545. (c) García, J. J.; Jones, W. D.
Organometallics 2000, 19, 5544.
(17) (a) Acosta-Ramírez, A.; Muñoz-Hernández, M.; Jones, W. D.;
García, J. J. Organometallics 2007, 26, 5766. (b) Acosta-Ramírez, A.;
Flores-Gaspar, A.; Muñoz-Hernández, M.; Arévalo, A.; Jones, W. D.;
García, J. J. Organometallics 2007, 26, 1712. (c) Acosta-Ramírez, A.;
Muñoz-Hernández, M.; Jones, W. D.; García, J. J. J. Organomet. Chem.
2006, 691, 3895.
(18) The presence of the nitriles was analyzed by GC-MS and 1H NMR
in toluene-d8 solution.

1836 Organometallics, Vol. 27, No. 8, 2008
Acosta-Ramírez et al.
Figure 1. ORTEP drawing of complex 1 at 50% probability. Selected bond distances (Å): Ni1-P1 (2.2063(7)), Ni1-P2 (2.2452(6)),
Ni1-P3 (2.2018(6)), Ni2-P3 (2.1987(6)), Ni1-C29 (1.885(2)), C29-N2 (1.154(3)). Selected angles (deg): P1-Ni-C29 (97.34(8)),
P2-Ni-C29 (102.17(8)), P3-Ni-C29 (164.62(8)), P1-Ni-P2 (114.10(2)), P2-Ni-P3 (88.56(2)).
Table 1. Summary of Crystallographic Results for 1 and 3
1
3
empirical formula
fw
C58H56N2Ni2P6
1084.29
C36H33N2NiP3
645.26
temp
298(2) K
298(2) K
wavelength
cryst system
space group
unit cell dimensions
0.71073 Å
P2(1)/n
monoclinic
a ) 12.9870(13) Å, R ) 90°
b ) 14.4380(14) Å, ꢀ) 92.250(8)°
c ) 13.7690(11) Å, γ)90° γ ) 90°
2579.8(4) Å3
0.71073 Å
P2(1)2(1)2(1)
orthorhombic
a ) 7.6630(18) Å, R ) 90°
b ) 19.375(5) Å, ꢀ ) 90°
c ) 21.757(7) Å, γ ) 90°
3230.3(15) Å3
volume
Z
2
4
density (calcd)
abs coeff
1.396 Mg/m3
1.327 Mg/m3
0.957 mm-1
0.777 mm-1
F(000)
crystal size
θ range for data collection
index ranges
no. of reflns collected
no. of independent reflns
completeness to θ
refinement method
data/restraints/parameters
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole
1128
1344
0.6 × 0.6 × 0.53 mm3
0.3 × 0.2 × 0.1 mm3
2.04 to 25.99°
-1 e h e 16, –1 e k e 17, –16 e l e 16
6200
1.41 to 27.99°
-1 e h e 10, –1 e k e 25, –1 e l e 28
5523
5041 [R(int) ) 0.0199]
5268 [R(int) ) 0.0262]
99.8% (25.99°)
100% (27.99°)
full-matrix least-squares on F2
5041/0/259
full-matrix least-squares on F2
5268/0/379
1.056
1.035
R1 ) 0.0344, wR2 ) 0.0897
R1 ) 0.0430, wR2 ) 0.0935
0.565 and –0.233 e · Å-3
R1 ) 0.0482, wR2 ) 0.0925
R1 ) 0.0797, wR2 ) 0.1051
0.294 and –0.257 e · Å-3
The structure of complex 1 can be envisaged as the result
of a PsC bond cleavage of the TRIPHOS ligand, losing the
phenyl group attached to the central phosphorus atom of the
tridentate ligand, thereby resulting in the formation of a
binuclear compound with a phosphido bridge. The structure
of this compound also displays two CN ligands, one
coordinated to each metal center. As such, they provide ev-
idence for CsCN bond cleavage taking place in the substrate,
2M3BN. Each nickel center shows a distorted trigonal
bipyramidal geometry, where the apical positions are oc-
cupied by -CN and phosphido moieties, the equatorial
positions around each metal center being occupied by PPh2
and a second phosphido moiety. The NisP bond distances
in the phosphido bridge complex 1are 2.2018(6) and 2.1987(6)

P-C Bond Scission at the TRIPHOS Ligand
Organometallics, Vol. 27, No. 8, 2008 1837
Å, which are slightly longer than those observed in the related
compound [(η5-Cp)Ni(µ-CO)(µ-PMe2)(η5-Cp)W(Me)(PMe3)],
2.114(2) Å.
The reaction mixture was analyzed by GC-MS and, in
addition to the isomerized nitriles described above, a significant
amount of benzene and butadiene were also confirmed to be
present after 24 h reflux. Our interpretation of the transforma-
tions that take place is summarized in Scheme 1. The 31P{1H}
NMR spectrum of an aliquot of the reaction mixture in CDCl3
displayed a number of different signals, those for complex 1
2
being observed at 44.1 ppm (dd, JP-P ) 48.0 and 38.5 Hz),
assigned to the phosphido bridge, and an additional pair of
doublets at 54.8 (2JP-P ) 48.0 Hz) and 23.8 ppm (2JP-P ) 38.5
Hz) for the PPh2 moieties. A similar set of minor signals was
observed at 53.1 (dd, 2JP-P ) 53.7 and 32.1 Hz), 50.2 (d, 2JP-P
2
) 53.7 Hz), and 25.3 ppm (d, JP-P ) 32.1 Hz). The two sets
of signals were attributed to the presence of two isomers, namely
the trans- and cis-isomers of [Ni2(µ-P(CH2CH2PPh2)2)2(CN)2],
compounds 1 and 2, respectively (Scheme 1). Additional species
present in the crude reaction mixture, compounds 3-6 (vide
infra), could also be isolated and characterized further upon
workup. Evaporation of solvent followed by extraction with THF
left behind a red residue, whose 31P{1H} NMR spectrum in
CDCl3 showed the presence of two isomers in a 7:1 ratio,
assigned as cis- and trans-[Ni(TRIPHOS)(CN)2] (3 and 4). Of
these, the compound in the higher proportion, complex 3,
displayed a doublet centered at 37.9 ppm (2JP-P ) 29.3 Hz)
and a broad triplet at 98.4 ppm (2JP-P ) 29.3 Hz), while the
second compound, complex 4, showed a doublet at 39.5 ppm
(2JP-P ) 30.1 Hz) and a triplet at 103.5 ppm (2JP-P ) 30.1
Hz). The coupling constants for such species are consistent with
those of Ni(II) complexes. The 1H NMR spectrum of the same
pair of species displayed a multiplet between 6.97 and 7.9 ppm
(25H) for the aromatic protons of the TRIPHOS ligand and a
multiplet centered at 2.36 ppm (8H) for the methylene groups
within the same ligand. The 13C{1H} NMR spectrum displayed
two multiplets at 28.0 and 29.4 ppm that were assigned to the
methylene carbons of the major species, 3, and two other
multiplets at 25.8 and 33.4 ppm for the minor species, 4. The
aromatic carbons appeared as overlapping multiplets between
128.7 and 134.7 ppm. The resonance for the -CN ligand
appeared overlapped with those of the aromatic signals;
however, the IR allowed us to confirm the presence of such
Figure 2. ORTEP drawing of complex 3 at 50% probability.
Selected bond distances (Å): Ni1-P1 (2.1932(14)), Ni1-P2
(2.2149(14)), Ni1-P3 (2.2425(13)), Ni1-C35 (1.947(5)), Ni1-C36
(1.894(5)).Selectedangles(deg):P1-Ni1-P2(85.77(6)),P2-Ni1-P3
(120.01(5)), P3-Ni1-P1 (87.53(5)), P1-Ni1-C35 (94.14(13)),
P1-Ni1-C36(176.53(16)),P2-Ni1-C35(123.89(14)),P2-Ni1-C36
(91.20(16)).
(6). The 31P{1H} NMR for the less polar fraction, complex 5
(Scheme 1), displayed a doublet at 45.9 ppm (2JP-P ) 48.5 Hz)
1
and a triplet at 108.3 ppm (2JP-P ) 48.5 Hz). The H NMR
spectrum of this compound showed several signals between 1.6
and 3.07 ppm (8H) and a broad multiplet for the aromatic
protons between 6.9 and 8.6 ppm (25H). The 13C{1H} NMR
spectra displayed multiplets for the methylene carbons at 25.3
and 28.3 ppm only; the aromatic carbons were detected in the
range of 125–134.7 ppm. No signals in either the 13C{1H} NMR
or the IR spectrum of this compound were found for a -CN
ligand, suggesting the presence of a vacant site as proposed for
compound 5. Additional evidence for this formulation comes
from the addition of PPh3, which produces the known complex
[Ni(TRIPHOS)(PPh3)].20
The more polar fraction containing complex 6 displayed a
doublet centered at 28.5 ppm, (2JP-P ) 51.7 Hz, PPh2) and a
triplet centered at 37.8 ppm (2JP-P ) 51.7 Hz, µ-P) in the
31P{1H} NMR spectrum. The pattern is consistent with that of
a phosphido bridge compound as in the case of 1, and thus it
was assigned as having the formulation [Ni2(µ-P(CH2CH2-
PPh2)2)2]. A related dimeric compound [Ni2(µ-PCy2)2(PCy2-
Me)2] with similar chemical shift and multiplicity assigned to
the resonance for the phosphido bridge is in agreement with
ligand at 2199 and 2095 cm-1
.
Suitable crystals for X-ray diffraction studies of complex 3
were obtained by vapor diffusion of a THF/CH2Cl2 system. The
molecular structure of complex 3 is depicted in Figure 2, and a
summary of the relevant crystallographic data for this compound
is included in Table 1. The geometry around the Ni center in 3
is trigonal bipyramidal with the cyanide ligands occupying both
axial and equatorial positions. The PsNi bond distances of
2.1932(4), 2.2149(14), and 2.2425(13) Å, for the chelate are
similar to those found in closely related compounds such as
[Ni(TRIPHOS)(η3-C3H3)]+:19 2.2463(13), 2.2475(13), and
2.2501(12) Å; the NisCN bond distances in compound 3 are
in agreement with those found in other compounds of
nickel(II).16a
1
the proposed structure (δ 23.6).21 The H NMR spectrum for
compound 6 displayed two broad signals at δ 2.30 and 2.07
ppm (8H) for the methylene protons and a multiplet centered
at 7.54 ppm for the aromatic protons. The 13C{1H} NMR
spectrum of 6 showed resonances for the methylene groups as
1
2
doublets of doublets at δ 22.4 (dd, JC-P ) 66.5 and JC-P
)
4.0 Hz) and δ 21.5 (dd, 1JC-P ) 70.2 and 2JC-P ) 4.3 Hz); the
aromatic carbons appeared between 129.1 and 133.9 ppm.
Again, no signals either in the 13C{1H} NMR or IR spectrum
of the compound were found for potential -CN moieties, and
therefore a structure lacking such entities, as depicted in Scheme
1, was proposed.
After having separated compounds 3 and 4 from the reaction
mixture the remaining mother liquors produced two more
compounds following chromatography, tentatively assigned on
the basis of spectroscopic and reactivity data as [Ni(TRIPHOS)]
(5) (still containing traces of 2) and [Ni2(µ-P(CH2CH2PPh2)2)2]
(20) Eckert, N. A.; Dougherty, W. G.; Yap, G. P. A.; Riordan, C, G
J. Am. Chem. Soc. 2007, 129, 9286.
(19) Clegg, W.; Cropper, G.; Henderson, R. A.; Strong, C.; Parkinson,
B. Organometallics 2001, 20, 2579.
(21) Kriley, C E.; Woolley, C. J; Krepps, M. K.; Popa, E. M.; Fanwick,
P. E.; Rothwell, I. P. Inorg. Chim. Acta 2000, 300–302, 200.

1838 Organometallics, Vol. 27, No. 8, 2008
Acosta-Ramírez et al.
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 CDCl3. 1H chemical shifts (δ) are reported
relative to the residual proton resonances in the deuterated
solvent. 13C{1H} NMR chemical shifts (δ) are reported relative
to resonance of the deuterated solvent. All 31P{1H} NMR spectra
were recorded relative to external 85% H3PO4. All NMR spectra
and catalytic reactions were carried out with thin wall (0.38 mm)
WILMAD NMR tubes with J. Young valves. A Siemens P4 four-
cycle diffractometer at room temperature with monochromatized
Mo KR radiation (λ ) 0.71073 Å) was used for the X-ray
structure determinations. Infrared spectra were obtained on a
Perkin-Elmer 1600 FT spectrophotometer. Elemental analyses
were carried out by USAI-UNAM, using an EA 1108 FISONS
Instrument analyzer. Reproducible elemental analyses could not
be obtained for complexes 5 and 6 due to the high air sensitivity
of these samples (they are Ni0). Mass determinations were made
on a JEOL SX-102A (FAB+), using nitrobenzilic alcohol matrix
and GC-MS determinations on a Varian Saturn 3 with a 30 m
DB-5MS capillary column.
Catalytic Isomerization of 2M3BN. A suspension of 2M3BN
(0.4 mL, 4.00 mmol) and TRIPHOS (19.2 mg, 0.036 mmol) was
added to crystalline [Ni(COD)2] (10 mg, 0.036 mmol), which
rendered an orange suspension after 15 min of stirring. The mixture
was transferred to an NMR tube with a J. Young valve and the
tube was heated at 100 °C in an oil bath with stirring, producing a
red solution. After cooling to room temperature, a sample of the
reaction mixture was taken and dissolved in THF inside the drybox
and analyzed by GC-MS. A second sample was dissolved in
toluene-d8 and analyzed by 1H NMR spectroscopy. The latter
sample displayed resonances characteristic of E- and Z-2M2BN
and trans-3PN. The use of catalytic amounts of 5 gave similar
activity.
Study of the Isomerization Reaction under Stoichiomet-
ric Conditions. After having established the distribution of
products under catalytic conditions, the isomerization reaction
of 2M3BN was studied under stoichiometric conditions. This
particular reaction was carried out with THF or THF-d8 at 100
°C. The formation of the organic products E- and Z-2M2BN,
along with a small amount of 3PN and benzene, as in the
catalytic case, was detected by GC-MS. Examination of the 1H
NMR of the mixture confirmed in addition the presence of 1,3-
butadiene. The production of complexes 2, 5, and 6 was also
established by means of 31P{1H} NMR spectroscopy of the same
mixture, dissolved in THF-d8.
Remarkably, a catalytic run with 3 as catalytic precursor
was carried out to establish its participation in the PsC bond
cleavage reaction that is related to the formation of benzene.
Only cyanoolefins (Z-2M2BN (77%), E-2M2BN (15%), and
cis-2PN (8%)) were detected from this experiment by means
of GC-MS at the end of the reaction and as a result, we have
speculated on a possible mechanistic pathway (see Scheme
2). We propose the isomerization reaction of 2M3BN into
2M2BN to occur initially by the formation of [Ni-
(TRIPHOS)(η2-C,C-2M3BN)] (A), followed by the formation
of a nickel(II) allyl-hydride complex (B), which promotes
a CsH bond breaking/forming step and evolves into a
rearranged alkene complex (C). This is thought to be followed
by the release of the isomerized olefin with the concurrent
formation of complex 5. Additionally, A can participate in a
CsCN breaking/forming catalytic cycle, from which the
isomerization of 2M3BN to the linear 3PN, through the
formation of a nickel(II) allyl-cyanide complex (D), can also
take place. At this point, ꢀ-elimination can occur to yield
1,3-butadiene, producing a Ni(II)-hydride-cyanide complex
as well. The latter hydride intermediate is likely involved in
the PsC bond scission of the TRIPHOS ligand that precedes
the formation of benzene. The cleavage can take place by at
least two pathways involving a hydride transfer:2a the first
leading to the formation of compounds 1 and 2 and the second
to compound 6, along with 3 or 4.
Preparation of cis- and trans-[Ni2(µ-P(CH2CH2PPh2)2)2(CN)2]
(1, 2), cis- and trans-[Ni(TRIPHOS)(CN)2] (3, 4), [Ni(TRIPH-
OS)] (5), and [Ni2(µ-P(CH2CH2PPh2)2)2] (6). A suspension of
2M3BN (1.6 mL, 16.0 mmol) and TRIPHOS (76.8 mg, 0.144
mmol) was added to yellow crystalline [Ni(COD)2] (40 mg, 0.144
mmol), which after 15 min of stirring produced an orange
suspension. The mixture was transferred to an NMR tube with
a J. Young valve, and the tube was heated at 100 °C in an oil
bath with stirring during 24 h. After this time, complex 1
precipitated as a red crystalline solid, and was filtered out and
dried in vacuo for 3 h. The filtrate was evaporated to dryness
and dried in vacuo for 3 h. The residue was washed with THF
leaving behind a mixture of complexes 3 and 4 as a red powder,
which were filtered and further dried in vacuo. The mother
liquors were then reduced in volume and separated by column
chromatography on silica gel, eluting first with hexane and then
increasing the polarity to hexane/ethanol 1:1 (v/v). The less polar
fraction contained mainly complex 5 (yellow powder containing
traces of 2) and the more polar fraction contained complex 6
(dark brown). The spectroscopic and analytical details are as
follows: trans-[Ni2(µ-P(CH2CH2PPh2)2)2(CN)2] (1): 10 mg, 13%
(isolated). Anal. Calcd for C58H56N2Ni2P6: C 64.20, H 5.16, N
2.58. Found (crystals): C 64.10, H 5.13, N 2.50. MS-FAB+ )
1084 (M+). 1H NMR (299.7 MHz): δ 2.5 (m, 8H, CH2), 6.91–7.8
(m, 25H, aromatic). 13C{1H} NMR: δ 135.6–128.2 (CN and
aromatic carbons), 27.2 and 24.4 (CH2P). 31P{1H} NMR (121.3
Conclusions
The reactivity of “Ni(TRIPHOS)” complexes with 2M3BN
yields CsH bond activation products that promote the formation
of the stable branched isomers E- and Z-2M2BN, along with
CsCN activation products that enable the formation of 3PN,
although only in low yields. The low yields for the linear 3PN
are attributed to the occurrence of CsP bond cleavage reactions
taking place over the TRIPHOS ligand that result in the
formation of very stable µ-phosphide nickel dinuclear complexes
that deactivate the catalytic process.
Experimental Section
All manipulations were carried out with standard Schlenk and
glovebox techniques under argon (Praxair 99.998). THF and
hexane (J. T. Baker) were dried and distilled from sodium/
benzophenone ketyl solutions. Ethanol (J. T. Baker) was dried
over 3Å molecular sieves and deoxygenated with argon. Deu-
terated solvents were purchased from Cambridge Isotope Labo-
ratories and stored over 3Å 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 vaccuum dried to yield yellow crystalline [Ni(COD)2],
which was further dried for 3 h in vacuo. TRIPHOS was
purchased from Strem and was used as received. 2M3BN (86.5%
by GC-MS) was purchased from TCI America, purged, and
2
2
MHz): δ 54.8 (d, JP-P ) 48.0 Hz, P(Ph)2R), 44.1 (dd, JP-P
)
2
48.0 and 38.5 Hz, phosphido bridge), 23.8 (d, JP-P) 38.5,
P(Ph)2R).IR:ν)2108cm-1,-CN.cis-[Ni2(µ-P(CH2CH2PPh2)2)2-
(CN)2] (2): 31P{1H} NMR (121.3 MHz): δ 53.1 (dd, JP-P
)
2
2
53.7 and 32.1 Hz, phosphido bridge), 50.2 (d, JP-P) 50.2 Hz,
P(Ph)2R), 25.2 ppm (d, 2JP-P) 32.1 Hz, P(Ph)2R). cis- and trans-
[Ni(TRIPHOS)(CN)2] (3 and 4, respectively): 30.2 mg, 32.5%
(isolated). Anal. Calcd for C36H33N2NiP3: C 66.97, H 5.12, N

P-C Bond Scission at the TRIPHOS Ligand
Organometallics, Vol. 27, No. 8, 2008 1839
Scheme 2
1
4.34. Found: C 68.14, H 5.28, N 4.08. MS-FAB+ ) 645 (M+),
analysis. H NMR (299.7 MHz): δ 8.6–6.9 (m, 25H, aromatic
protons), several multiplets at 3.07–3.01, 2.89–2.8, 2.7–2.55,
2.4–2.27, 2.17–2.00, 1.87–1.6 (8H for all, CH2). 13C{1H} NMR
1
620 (M+ - CN). H NMR (299.7 MHz): δ 2.36 (m, 8H, CH2),
6.97–7.9 (m, 25H, aromatic). 13C{1H} NMR (75.4 MHz): δ
134.7–128.7 (multiplets, aromatic carbons), 33.4–25.8 (m, CH2,
one isomer), 29.4–28.0 (m, CH2 one isomer) . 31P{1H} NMR
(75.4 MHz): δ 134.7–125 (aromatic carbons), 28.3 (m, CH2),
25.3 (m, CH2). 31P{1H} NMR (121.3 MHz) δ 108. 3 (t, JP-P
)
2
2
2
2
(121.3 MHz): δ 103.5 (t, JP-P) 30.1 Hz), 98.4 (t, JP-P) 29.3
48.5 Hz), 45.9 (d, JP-P) 48.5 Hz). The addition of PPh3 gave
the same spectra as reported for [Ni(TRIPHOS)PPh3. [Ni2(µ-
P(CH2CH2PPh2)2)2] (6): 20 mg, 13.5%. The high air sensitivity
of the sample did not allow reproducible elemental analysis. 1H
NMR (299.7 MHz): δ 7.54 (m, 20H, aromatic protons),
2
2
Hz), 39.5 (d, JP-P) 30.1 Hz), 37.9 (d, JP-P) 29.3 Hz). IR: ν
) 2199 and 2095 cm-1, -CN. [Ni(TRIPHOS)] (5): 16 mg,
18.5%. FAB+: 597 (M+), the air sensitivity of the sample and
presence of traces of 2 did not allow reproducible elemental

1840 Organometallics, Vol. 27, No. 8, 2008
Acosta-Ramírez et al.
2.30–2.07 (m, 8H, CH2). 13C{1H} NMR (75.4 MHz): δ
133.9–129.1 (aromatic carbons), 22.4 (dd, 1JC-P ) 66.5 and 2JC-P
) 4.0 Hz, CH2-P), 21.5 (dd, 1JC-P ) 70.2 and 4.3 Hz, CH2-P).
graduate studies grant. The authors also thank Dr. A. Arévalo
for technical assistance. W.D.J. acknowledges support from
the U.S. Department of Energy, grant no. FG02-86ER13569.
2
31P{1H} NMR (121.3 MHz) δ 37.8 (t, JP-P) 51.7 Hz), 28.5
2
ppm (d, JP-P) 51.7 Hz). The reactión of 1 (10 mg) with an
Supporting Information Available: Detailed GC-MS determi-
nations and tables of complete crystallographic data for 1 and 3.
This material is available free of charge via the Internet at
http://pubs.acs.org.
excess of sodium allow the formation of the same signals above
quoted for 6.
Acknowledgment. We thank CONACyT (grant 42467-
Q) and DGAPA-UNAM (grant IN202907-3) for financial
support for this work. A.A.-R. also thanks CONACyT for a
OM7011425