Interconversion of quadruply and quintuply bonded molybdenum complexes by reductive elimination and oxidative addition of dihydrogen

Article abstract of DOI:10.1002/anie.201209064

Five plus H₂ gives four: UV irradiation of a bis(amidinate) complex with a [(H)Mo-Mo(H)] core induces reductive elimination of H₂ and formation of a known quintuply bonded Mo-Mo species (see scheme) that reacts back with H₂ to restore [(H)Mo-Mo(H)]. UV irradiation of the bis(hydride) species in benzene and toluene gives arene complexes in which the aromatic hydrocarbon bridges the molybdenum atoms. Dipp=2,6-diisopropylphenyl.

Full text of DOI:10.1002/anie.201209064

Angewandte
Chemie
DOI: 10.1002/anie.201209064
Metal–Metal Bonding
Interconversion of Quadruply and Quintuply Bonded Molybdenum
Complexes by Reductive Elimination and Oxidative Addition of
Dihydrogen**
Mario Carrasco, Natalia Curado, Celia Maya, Riccardo Peloso, Amor Rodrꢀguez, Eliseo Ruiz,
Santiago Alvarez,* and Ernesto Carmona*
Transition metal complexes that exhibit multiple metal–metal
bonding are of fundamental importance in chemistry.[1a]
Following decades of intense scrutiny of double, triple, and
quadruple metal–metal bonds, in 2005 Power and co-workers
made an outstanding discovery with the characterization of
the first stable molecule with fivefold bonding between two
chromium atoms.[2] This report encouraged the search for
further examples of quintuply bonded dimetal compounds[1b]
and was followed by numerous experimental[3–11] and compu-
tational studies.[12–18] By and large, these studies have focused
on chromium compounds.[1b,2–8,11] However, Tsai and co-
standing their bonding characteristics[12–18] and the chemical
À
reactivity of their central M M quintuple bond. So far, only
a few reports have appeared in the literature concerning
À
mainly the chemical properties of the Cr Cr quintuple bond.
Thus, these complexes feature interesting reactivity toward
unsaturated molecules like N2O,[19] alkenes, and alkynes,[20,21]
and are able to activate white phosphorous, yellow arsenic,
and AsP3.[22] Similar to carbon carbon double and triple
À
À
bonds, the Cr Cr quintuple bond of an aminopyridinate
complex undergoes facile carboalumination, to generate the
À
corresponding Cr Cr quadruple-bond derivative with for-
workers have extended their investigation of the Cr Cr
mally monoanionic bridging CH3 and AlMe2 groups.[23]
À
quintuple bond[6,7,11] to analogous molybdenum complexes
and have isolated two closely related compounds supported
by monoanionic amidinate ligands, N,N’-disubstituted with
2,6-diisopropylphenyl groups.[9] Recently, another compound
with the MoI2 central unit reinforced by three amidinate
ligands and a bridging lithium cation has also been reported
by the same group of researchers.[10]
Disproportionation of CrI to Cr0 and CrII induced by the
À
addition of [18]crown-6-ether to a Cr Cr quintuply bonded
complex has also been demonstrated.[11] During the prepara-
À
tion of this manuscript the reactivity of Mo Mo quintuply
bonded compounds with alkynes has been shown.[24]
The above results illustrate the potential of quintuply
bonded electron-rich MI2 centers for bimetallic activation.
Herein we describe that the quadruply bonded dimolybde-
num dihydride complex [Mo2(H)2{HC(N-2,6-iPr2C6H3)2}2-
(thf)2] 2 undergoes reductive elimination of H2 from its
Identification of the above complexes with fivefold metal-
metal bonding has prompted research directed toward under-
ꢀ
[(H)MoꢀMo(H)] core under UV irradiation (365 nm) to
afford the known [Mo2{HC(N-2,6-iPr2C6H3)2}2], 3,[9] with
[*] M. Carrasco, N. Curado, Dr. C. Maya, Dr. R. Peloso,
Dr. A. Rodrꢀguez, Prof. E. Carmona
À
fivefold
Mo Mo
bonding
(Scheme 1B).
Because
Instituto de Investigaciones Quꢀmicas-Departamento de Quꢀmica
Inorgꢁnica, Universidad de Sevilla-Consejo Superior de Investiga-
ciones Cientꢀficas
Avenida Amꢂrico Vespucio 49, 41092 Sevilla (Spain)
E-mail: guzman@us.es
a tetrahydrofuran (THF) solution of the latter reacts readily
with H2 to reform 2, our results demonstrate that quadruply
and quintuply bonded dimolybdenum complexes may inter-
convert by means of reductive elimination and oxidative
Prof. E. Ruiz, Prof. S. Alvarez
Departament de Quꢀmica Inorgꢃnica and Institut de Quꢀmica
Teꢄrica i Computacional, Universitat de Barcelona
Martꢀ i Franquꢅs 1–11, 08028 Barcelona (Spain)
[**] Financial support (FEDER contribution and Subprogramas Juan de
la Cierva) from the Spanish Ministry of Science and Innovation
(Projects CTQ2010-15833, CTQ2011-23862-C02-01 and Consolider-
Ingenio 2010 CSD2007-00006), the Generalitat de Catalunya
(Project 2009SGR-1459), and the Junta de Andalucꢀa (Grant FQM-
119 and Project P09-FQM-5117) is gratefully acknowledged. M.C.
and N.C. thank the Spanish Ministry of Education (AP-4193) and the
Spanish Ministry of Science and Innovation (BES-2011-047643) for
research grants. We also thank Prof. M. L. Poveda for helpful
discussions and advice, Dr. J. Lꢆpez-Serrano for assistance and
discussions on NMR analyses, and the Centre de Supercomputaciꢆ
de Catalunya (CESCA) for the allocation of computational resour-
ces.
Supporting information for this article (experimental details) is
available on the WWW under http://dx.doi.org/10.1002/anie.
201209064.
Scheme 1. A) Synthesis of the bis(hydride) complex 2 and B) its
interconversion with the quintuply bonded complex 3.
Angew. Chem. Int. Ed. 2013, 52, 3227 –3231
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3227

.
Angewandte
Communications
addition of dihydrogen, two ubiquitous reactions in transition
metal chemistry.[25] We also show in Scheme 2 that compound
3 reacts reversibly (thermally or with light irradiation) with
aromatic solvents like benzene and toluene, to yield the
corresponding adducts, [Mo2{HC(N-2,6-iPr2C6H3)2}2(C6H5R)]
(4; where R = H, 4·C6H6 or R = CH3, 4·C6H5CH3). The
electronic structure of the new complexes is discussed with
the help of density functional calculations.
quintuple bonds has not been investigated. Experimental and
theoretical studies on the mechanism of this reaction are in
progress and will be reported in due course.
Originally the photolysis of 3 was performed in benzene,
leading to a clean conversion into a new, multiply bonded
Mo2-arene complex, 4·C6H6 (Scheme 2). The corresponding
Reaction of Mo2(O2CCH3)4 and the lithium amidinate,
Li[HC(N-2,6-iPr2C6H3)2], in THF in a 1:2 molar ratio, resulted
in the formation of the complex [Mo2(O2CCH3)2{HC(N-2,6-
iPr2C6H3)2}2], 1, whose structural formula is depicted in
Scheme 1A. Solid-state magnetic susceptibility data revealed
that 1 is diamagnetic. 1H and 13C{1H} NMR data (see
Supporting Information) were in agreement with a trans
distribution of the ligands, which is otherwise expected on
steric grounds.[26] Methylation of 1 by LiMe gave rise to an
interesting set of methyl complexes of the quadruply bonded
[Mo2(amidinate)2] unit that will be discussed in a separate
publication. As shown in Scheme 1A and described in the
Supporting Information, a three-step, one-flask procedure
that involved LiMe and H2 as key reagents converted 1 into
the bis(hydride) complex 2, with the last hydrogenation step
liberating CH4. Hydride species with multiply bonded Mo
atoms are scarce.[27–29] Spectroscopic data were in agreement
with the hydride formulation proposed for 2, which feature
Scheme 2. Generation of 4·C6H6R from complexes 2 and 3.
toluene adduct, 4·C6H5CH3, was prepared similarly. Not
unexpectedly, these arene adducts could also be generated
by dissolving complex 3 in the corresponding aromatic
hydrocarbon (Scheme 2). At 258C, in the dark, these reac-
tions have half-life times, t1/2, of 0.25 hours for benzene and
4.5 hours for toluene. However, exposure of these solutions to
sunlight increases significantly the rate of the reaction.
Compounds like 4 that contain arene-bridged multiply
bonded M2 units are very rare, although recently Masuda and
co-workers reported the first examples of a quadruply bonded
À1
1
À
a Mo H IR stretching band at 1525 cm and a H NMR
hydride resonance with d = 5.67 ppm. These assignments have
been corroborated by deuteration experiments and, in the
case of the 1H NMR hydride signal, by a reaction in an NMR
tube with a slight excess of CHCl3 (Supporting Information).
Further corroboration was provided by a single-crystal X-ray
experiment. The analysis of the structure of 2 confirmed the
À
existence of two terminal hydride ligands, with a Mo H
distance of approximately 1.71 ꢀ and a Mo Mo separation of
MoII species of this kind.[34,35] Solid-state magnetic-suscept-
À
2
2.089(1) ꢀ. The latter is in accord with a quadruply bonded
ibility measurements for 4·C6H6 confirmed its diamagnetic
nature (Supporting Information). 1H and 13C{1H} NMR
resonances owing to the amidinate ligands of 4·C6H6 are
consistent with C2 molecular symmetry (Supporting Informa-
tion). However, only one resonance was observed at 258C for
À
Mo Mo compound, which is further supported by computa-
tional studies (Supporting Information). Complex 2 is stable
toward loss of H2 at temperatures up to 608C, and upon
heating at higher temperatures, it undergoes extensive
decomposition. Nevertheless, UV irradiation (365 nm) of its
solutions in cyclohexane led to an approximately 1:1 mixture
of 2 and 3 (Scheme 1B).
1
the coordinated molecule of benzene (3.87 ppm in the H
NMR and 71.2 ppm in the 13C{1H} NMR), indicating that, at
À
this temperature, the coordinated and non-coordinated C C
To generate 3 cleanly, stirred solutions of 2 in cyclohexane
were irradiated for approximately 24 hours, with intermittent
vacuum/argon cycles to remove the liberated H2, permitting
the isolation of 3 in approximately 75% yield. 3 was
characterized by comparison of the NMR spectra with those
in the literature[9] and by X-ray analysis of a cyclohexane
solvate (Supporting Information). Complex 3 reacted readily
at 258C with H2 (1 bar, approximately 30 min, reacted in an
NMR tube) in [D8]THF to reform the bis(hydride) complex 2.
To our knowledge, this reactivity, whereby dinuclear oxida-
tive addition and reductive elimination of H2 interconvert
bonds undergo fast exchange. Cooling the sample to À858C
only caused broadening of these signals.
Benzene solutions of compound 4·C6H6 can be heated at
1208C in the dark without noticeable decomposition. In C6D6,
there is no observable reaction at 808C but at 1208C full
conversion into 4·C6D6 occurred after stirring for 24 hours.
Similarly, a C6D12 solution of 4·C6H6 in the dark, at room
temperature, showed no evidence for C6H6 dissociation and
generation of 3, but at 1208C, a 4:1 mixture of 4·C6H6:3 was
generated. However, under sunlight for a period of 0.5 hours
at ambient temperature, solutions of 4·C6H5CH3 in benzene,
and those of 4·C6H6 in toluene, transformed completely into
4·C6H6 and 4·C6H5CH3, respectively. In a kinetic competition
experiment, arene-free complex 3 reacted in the dark at room
temperature with an excess of an equimolar mixture of C6H6
and C6H5CH3 to afford mostly (approximately 95%) the
À
complexes with quintuple and quadruple M M bonds, has no
precedent in the literature. Oxidative addition and reductive
elimination in doubly and triply bonded M2 compounds (M =
Mo, W) are well-known reactions[30–32] but those involving H2
are rare.[33] Indeed, oxidative addition of H2 to known M M
À
3228
www.angewandte.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2013, 52, 3227 –3231

Angewandte
Chemie
benzene adduct. A thermodynamic preference for 4·C6H6
over 4·C6H5CH3 was also shown, as heating a solution of
4·C6H6 in the above mixture of solvents at 1208C in the dark
yielded solely 4·C6H6. Furthermore, treatment of 4·C6H5CH3
with an excess of the same mixture of benzene and toluene at
1208C for two days in the dark caused formation of 4·C6H6.
The solid-state molecular structure of 4·C6H6 presented in
would in principle be available for metal–metal bonding, as in
the parent complex 3. However, the strong electronic
interaction of the d and d* orbitals of the [Mo2(amidinate)2]
fragment with the p and p* orbitals of the arene results in
a smaller bond order, close to a quadruple bond (see below).
For the sake of simplicity, and keeping in mind Cottonꢁs
qualitative definition of bond order,[1a] compounds 4 are
represented in Scheme 2 as MoI2 derivatives with fivefold
bonding between their metal atoms.
À
Figure 1 features a Mo Mo quintuple bond length of
2.106(1) ꢀ (2.105(1) ꢀ for 4·C6H5CH3; Supporting Informa-
Geometry optimization of complex 4·C6H6 yields a struc-
ture that is in excellent agreement with the experimental one
À
À
À
in the Mo Mo (2.134 ꢀ) and Mo C bond distances, in the C
C bond distance distribution pattern of the benzene ring, and
À
À
in the N Mo N hinge angles. A significant HOMO–LUMO
gap attests to the thermodynamic stability of the benzene
adduct and indicates the monoconfigurational character of its
electronic structure. The coordination of benzene to the
dimolybdenum unit brings about a remarkable reorganization
of its electronic structure that can be understood with the help
of the Dewar–Chatt–Duncanson model and of the symmetry
properties of the molecular orbitals of the interacting benzene
and Mo2 fragments in the idealized C2v point group.
Two donor–acceptor interactions involve the occupied p
orbitals of benzene belonging to the A1 and B1 irreducible
representations and the in-phase and out-of-phase combina-
tions of the sp2 hybrid orbitals of the Mo atoms (not shown).
However, the purported back-bonding interactions must
involve the d(B2) and d*(A2) orbitals of the Mo2 moiety and
benzene p orbitals of the same symmetries (Figure 3). Notice
that both orbitals of A2 symmetry are empty in the quintuply
bonded Mo2 and neutral benzene fragments, which in
principle, prevents back-bonding. Moreover, the fragment
orbitals of B2 symmetry are both occupied and should
produce four-electron repulsion rather than bonding. But
the strong overlap between the orbitals of the two fragments
stabilizes the A2 bonding MO below the antibonding B2 one
Figure 1. Solid-state molecular structure of 4·C6H6, with thermal ellip-
soids set at 50% probability.
tion). This bond is longer than that of 3 (approximately
2.02 ꢀ)[9] but it is in the upper part of the 2.02–2.12 ꢀ range
[14]
À
predicted theoretically for Mo Mo quintuple bonds. The
two Mo atoms are symmetrically bound to their respective
À
carbon atoms, with a Mo C distance of approximately 2.22 ꢀ
À
À
(Figure 2). The Mo C(52) and Mo C(55) separation varies
between approximately 2.62 ꢀ and 2.73 ꢀ (Figure 2) and may
therefore be viewed as non-bonding. There is a small arene
distortion upon coordination, which is evidenced mainly in
À
the lengthening of the arene C C bonds, with the coordinated
À
À
C(53) C(54) and C(51) C(56) being the longest at 1.45 ꢀ
(Figure 2). These structural data and the arene substitution
chemistry outlined above for complexes 4 are more consistent
with their formulation as MoI2 species with a coordinated
neutral molecule of C6H5R rather than as MoII2 derivatives of
an arene dianion,[36–38] C6H5R2À. Thus, five pairs of d electrons
Figure 3. Partial orbital-interaction diagram showing the electronic
reorganization associated with back-bonding of the Mo2L2 fragment to
C6H6.
Figure 2. Selected bond lengths taken from Figure 1.
Angew. Chem. Int. Ed. 2013, 52, 3227 –3231
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3229

.
Angewandte
Communications
and induces the transfer of an electron pair from the B2 to the
A2 set.
[1] a) F. A. Cotton, C. A. Murillo, R. A. Walton, Multiple Bonds
Between Metal Atoms, 3rd ed., Springer Science and Business
Media, New York, 2005;b) F. R. Wagner, A. Noor, R. Kempe,
Nat. Chem. 2009, 1, 529 – 536.
[2] T. Nguyen, A. D. Sutton, M. Brynda, J. C. Fettinger, G. J. Long,
P. P. Power, Science 2005, 310, 844 – 847.
[3] R. Wolf, C. Ni, T. Nguyen, M. Brynda, G. J. Long, A. D. Sutton,
R. C. Fischer, J. C. Fettinger, M. Hellman, L. Pu, P. P. Power,
Inorg. Chem. 2007, 46, 11277 – 11290.
[4] K. A. Kreisel, G. P. A. Yap, O. Dmitrenko, C. R. Landis, K. H.
Theopold, J. Am. Chem. Soc. 2007, 129, 14162 – 14163.
[5] A. Noor, F. R. Wagner, R. Kempe, Angew. Chem. 2008, 120,
7356 – 7359; Angew. Chem. Int. Ed. 2008, 47, 7246 – 7249.
[6] Y.-C. Tsai, C.-W. Hsu, J.-S. K. Yu, G.-H. Lee, Y. Wang, T.-S. Kuo,
Angew. Chem. 2008, 120, 7360 – 7363; Angew. Chem. Int. Ed.
2008, 47, 7250 – 7253.
[7] C.-W. Hsu, J.-S. K. Yu, C.-H. Yen, G.-H. Lee, Y. Wang, Y.-C.
Tsai, Angew. Chem. 2008, 120, 10081 – 10084; Angew. Chem. Int.
Ed. 2008, 47, 9933 – 9936.
[8] A. Noor, G. Glatz, R. Mꢂller, M. Kaupp, S. Demeshko, R.
Kempe, Z. Anorg. Allg. Chem. 2009, 635, 1149 – 1152.
[9] Y.-C. Tsai, H.-Z. Chen, C.-C. Chang, J.-S. K. Yu, G.-H. Lee, Y.
Wang, T.-S. Kuo, J. Am. Chem. Soc. 2009, 131, 12534 – 12535.
[10] S.-C. Liu, W.-L. Ke, J.-S. K. Yu, T.-S. Kuo, Y.-C. Tsai, Angew.
Chem. 2012, 124, 6500 – 6503; Angew. Chem. Int. Ed. 2012, 51,
6394 – 6397.
[11] Y.-L. Huang, D.-Y. Lu, H.-C. Yu, J.-S. K. Yu, C.-W. Hsu, T.-S.
Kuo, G.-H. Lee, Y. Wang, Y.-C. Tsai, Angew. Chem. 2012, 124,
7901 – 7905; Angew. Chem. Int. Ed. 2012, 51, 7781 – 7785.
[12] M. Brynda, L. Gagliardi, P.-O. Widmark, P. P. Power, B. O. Roos,
Angew. Chem. 2006, 118, 3888 – 3891; Angew. Chem. Int. Ed.
2006, 45, 3804 – 3807.
Such an electron reshuffling can be simply described in
terms of two two-electron donor–acceptor interactions by
considering several alternative ways of assigning the four
electrons, considering the Mo2 and benzene fragments. As an
example, we may consider an initial electron transfer from
d(B2) to p*(A2) that would allow for two back-bonding
interactions and implies a formal oxidation of the Mo atoms
to MoII and the corresponding reduction of benzene to
a dianionic form. These canonical Lewis structures of 4·C6H6
À
coincidentally predict a decreased Mo Mo bond order and
a partial loss of the aromatic character of benzene, in
agreement with the structural data (Figure 2). A small but
non-negligible anionic character of the benzene ring is shown
by its negative calculated charge (À0.20), as compared to
a neutral benzene ring in the analogous MoII2 adduct reported
by Masuda and co-workers.[34] In summary, as expected the
À
back-bonding interactions provide Mo C bonding at the
À
À
expense of weakening the C C and Mo Mo bonds.
À
Comparison of the Mo Mo bond distance and calculated
Meyer bond order for the benzene adduct reported herein
with those of the undisputed quintuple bond of Tsai et al.
(3)[9] and with the related MoII benzene adduct of Masuda
2
and co-workers (Figure 4),[34] indicates that compound 4·C6H6
[13] C. R. Landis, F. Weinhold, J. Am. Chem. Soc. 2006, 128, 7335 –
7345.
[14] G. Merino, K. J. Donald, J. S. DꢁAcchioli, R. Hoffmann, J. Am.
Chem. Soc. 2007, 129, 15295 – 15302.
[15] B. O. Roos, A. C. Borin, L. Gagliardi, Angew. Chem. 2007, 119,
1491 – 1494; Angew. Chem. Int. Ed. 2007, 46, 1469 – 1472.
[16] G. La Macchia, L. Gagliardi, P. P. Power, M. Brynda, J. Am.
Chem. Soc. 2008, 130, 5104 – 5114.
[17] G. La Macchia, G. Li Manni, T. K. Todorova, M. Brynda, F.
Aquilante, B. O. Roos, L. Gagliardi, Inorg. Chem. 2010, 49,
5216 – 5222.
[18] L.-C. Wu, C.-W. Hsu, Y.-C. Chuang, G.-H. Lee, Y.-C. Tsai, Y.
Wang, J. Phys. Chem. A 2011, 115, 12602 – 12615.
[19] C. Ni, B. D. Ellis, G. J. Long, P. P. Power, Chem. Commun. 2009,
2332 – 2334.
[20] J. Shen, G. P. A. Yap, J.-P. Werner, K. H. Theopold, Chem.
Commun. 2011, 47, 12191 – 12193.
À
Figure 4. Scatter plot of experimental Mo Mo bond distances and
calculated Meyer bond orders for compounds with quadruple and
quintuple bonds discussed in this paper (see Ref. [9] and [34] for 3 and
MoII·C6H6, respectively).
[21] A. Noor, E. S. Tamne, S. Qayyum, T. Bauer, R. Kempe, Chem.
Eur. J. 2011, 17, 6900 – 6903.
[22] C. Schwarzmaier, A. Noor, G. Glatz, M. Zabel, A. Y. Timoshkin,
B. M. Cossairt, C. C. Cummins, R. Kempe, M. Scheer, Angew.
Chem. 2011, 123, 7421 – 7424; Angew. Chem. Int. Ed. 2011, 50,
7283 – 7286.
[23] A. Noor, G. Glatz, R. Mꢂller, M. Kaupp, S. Demeshko, R.
Kempe, Nat. Chem. 2009, 1, 322 – 325.
is somewhere in-between a quintuple and a quadruple bond,
À
albeit closer to a quadruple Mo Mo bond, in agreement with
the description of the electronic structure just discussed. This
situation is comparable to that of compound 2, which should
be considered formally as a hydrido-MoII species, with
2
À
[24] H.-Z. Chen, S.-C. Liu, C.-H. Yen, J.-S. K. Yu, Y.-J. Shieh, T.-S.
Kuo, Y.-C. Tsai, Angew. Chem. 2012, 124, 10488 – 10492; Angew.
Chem. Int. Ed. 2012, 51, 10342 – 10346.
[25] G. J. Kubas, Metal Dihydrogen and s-Bond Complexes, Kluwer/
Plenum, New York, 2001.
similar Mo Mo distances and Meyer bond orders.
Received: November 12, 2012
Revised: December 4, 2012
Published online: February 1, 2013
[26] D. J. Brown, M. H. Chisholm, J. C. Gallucci, Dalton Trans. 2008,
1615 – 1624.
Keywords: density functional calculations · hydrides ·
metal arene · molybdenum · multiple bonds
[27] K. W. Chiu, R. A. Jones, G. Wilkinson, A. M. R. Galas, M. B.
Hursthouse, J. Chem. Soc. Dalton Trans. 1981, 1892 – 1897.
.
3230
www.angewandte.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2013, 52, 3227 –3231

Angewandte
Chemie
[28] a) F. A. Cotton, P. C. W. Leung, W. J. Roth, A. J. Schultz, J. M.
Williams, J. Am. Chem. Soc. 1984, 106, 117 – 120; b) F. A. Cotton,
J. P. Donahue, P. Huan, C. A. Murillo, D. Villagrꢃn, Z. Anorg.
Allg. Chem. 2005, 631, 2606 – 2612.
[33] A. P. Sattelberger, R. B. Wilson, Jr., J. C. Huffman, Inorg. Chem.
1982, 21, 4179 – 4184.
[34] Y. Kajita, T. Ogawa, J. Matsumoto, H. Masuda, Inorg. Chem.
2009, 48, 9069 – 9071.
[29] M. E. Garcꢄa, A. Ramos, M. A. Ruiz, M. Lanfranchi, L. Marchio,
Organomet. 2007, 26, 6197 – 6212.
[35] T. Ogawa, Y. Kajita, H. Masuda, Jpn. J. Appl. Phys. 2011, 50,
01AK05-1.
[30] M. H. Chisholm in Reactivity of Metal – Metal Bonds, Vol. 155
(Ed.: M. H. Chisholm), ACS Synposium Series, New York, 1981,
pp. 17 – 39.
[31] M. H. Chisholm, Acc. Chem. Res. 1990, 23, 419 – 425.
[32] M. D. Curtis, L. Messerle, N. A. Fotinos, R. F. Gerlach in
Reactivity of Metal-Metal Bonds, Vol. 155 (Ed.: M. H. Chis-
holm), ACS Synposium Series, New York, 1981, pp. 221 – 257.
[36] A. Sekiguchi, K. Ebata, C. Kabuto, H. Sakurai, J. Am. Chem.
Soc. 1991, 113, 1464 – 1465.
[37] M. C. Cassani, D. J. Duncalf, M. F. Lappert, J. Am. Chem. Soc.
1998, 120, 12958 – 12959.
[38] A. Sattler, G. Parkin, J. Am. Chem. Soc. 2012, 134, 2355 – 2366.
Angew. Chem. Int. Ed. 2013, 52, 3227 –3231
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3231