Reactivity of amido ligands on a dinuclear Ru(II) center: Formation of imido complexes and C-N coupling reaction with alkyne

Article abstract of DOI:10.1021/ja047920s

Treatment of a dinuclear Ru(II) amido complex [Cp*Ru(μ₂-NHPh)]₂ (Cp* = η⁵-C₅Me₅) with small organic substrates including CO, tert-butyl isocyanide, a sulfur ylide Ph₂S=CH₂, and diphenylacetylene resulted in an unexpected disproportionation reaction of the bridging amido ligands to produce a free amine and a series of imido-bridged diruthenium complexes [(Cp*Ru)₂(μ₂-L)(μ₂-NPh)] (L = CO, t-BuNC, CH₂). In the case of diphenylacetylene, the bridging imido ligand underwent subsequent coupling reaction with the coordinated alkyne to form an iminoalkenyl complex [(Cp*Ru)₂(μ₂-PhNCPhCPh)]. Copyright

Full text of DOI:10.1021/ja047920s

Published on Web 08/14/2004
Reactivity of Amido Ligands on a Dinuclear Ru(II) Center: Formation of Imido
Complexes and C-N Coupling Reaction with Alkyne
Shin Takemoto,† Tomoharu Kobayashi,† and Hiroyuki Matsuzaka*,†,‡
Department of Chemistry, Faculty of Arts and Sciences, Osaka Prefecture UniVersity,
Sakai, Osaka 599-8531, Japan, and Coordination Chemistry Laboratories, Institute for Molecular Science,
Myodaiji, Okazaki 444-8585, Japan
Received April 10, 2004; E-mail: matuzaka@ms.cias.osakafu-u.ac.jp
Amido and imido complexes of low-valent late transition metals
have received considerable study recently,1 primarily because of
their implication in many important catalytic processes.2,3 Extensive
studies on isolable amido and imido complexes of group 8-10
metals have revealed diverse reactivities of such M-N bonds,
including insertion and metallcyclization with unsaturated C-C and
C-X bonds,2c,4,5 C-N bond-forming reductive elimination,6 imido
group transfer,7 and activation of H-H and C-H bonds.8,9 Still,
relatively little is known about how such ligands are incorporated
into chemical reactions when they are bound to multimetallic
centers,10 even though such polynuclear amido- and imidometal
species have been invoked in certain catalytic systems3 and offer
considerable prospect for new reaction sequences. In this context,
the dimeric Ru(II) anilido complex [Cp*Ru(µ2-NHPh)]2 (1; Cp*
) η5-C5Me5)11 originally reported by Don Tilley et al. is of
particular interest, since it contains two adjacent 16e Ru centers
that are not stabilized by additional π-donation from the amido
ligands as has been seen in many other 16e amido complexes12
and, therefore, is expected to show exceptionally high reactivity.
However, reactivity of 1 remains almost unexplored. Here we wish
to describe reactions of 1 with CO, t-butyl isocyanide, a sulfur ylide
Ph2SdCH2, and diphenylacetylene, which proceeded with an
unexpected disproportionation of the µ2-anilido ligands to form free
aniline and a series of new imidodiruthenium complexes. In the
case of diphenylacetylene, the imido fragment underwent subse-
quent coupling reaction with the alkyne to produce an iminoalkenyl
complex.
the formation of the imido carbonyl complex 3 with elimination of
1 equiv of aniline. A small amount of Ru(I) carbonyl complex
[Cp*Ru(CO)2]2 was also formed in this reaction. Complex 3 was
isolated as red plates in 63% yield after recrystallization from
1
hexanes and has been characterized by H NMR and IR spectros-
copy, elemental analysis, and single-crystal X-ray diffraction
(Scheme 1). Noteworthy aspects of the structure include the
presence of two five-coordinate Ru atoms, a very short Ru-Ru
distance (2.6013(9) Å), and a µ2-imido moiety that is planar at
nitrogen and exhibits very short Ru-N bond lengths (1.878 Å
(mean)).13 Existence of a Ru-Ru multiple bond is suggested by
electron counting and the short Ru-Ru distance that is close to
those of some other compounds with RudRu double bonds (2.417-
2.629 Å).14 Orbital analysis of a DFT-B3PW91 optimized model
compound [(CpRu)2(µ2-CO)(µ2-NH)] (3′) has provided insights into
the Ru-Ru bond in 3. Although the first six of HOMOs of 3′ are
predominantly metal-based orbitals and constitute a formally
nonbonded σ2σ*2δ4δ*4 configuration, the multiple bond order
between the Ru atoms can be rationalized by back-donation from
the filled Ru-Ru σ* orbital into a π* orbital of the CO ligand,15
and by donation from the imido and CO ligands into empty Ru-
Ru π-bonding orbitals.16
An intermediate in the above transformation was detected
spectroscopically during the course of the reaction (Scheme 2). This
Scheme 2
The chemistry we have observed is summarized in Scheme 1.
Addition of 1.5 equiv of CO into a THF solution of 1 resulted in
Scheme 1
species could not be isolated, but its formulation as a µ2-carbonyl
adduct of 1, [(Cp*Ru)2(µ2-CO)(µ2-NHPh)2] (2), is supported by
1
its H and 13C{1H} NMR, IR, and FAB-MS spectra. Complex 2
cleanly afforded 3 and aniline within 15 h at room temperature.
The reverse reaction, addition of aniline to the imido complex 3,
did proceed and gave 2 although the conversion was very low (ca.
1% in the presence of 20 equiv of aniline). Since 2 is a
coordinatively saturated species, dissociation of a Ru-N bond in
2 would be a facile process. This generates a basic terminal amido
ligand capable of deprotonating the bridging amido ligand to form
the imido complex 3 (Scheme 2). The disproportionation of amido
ligands into amine and an imido ligand has been observed in some
monomeric poly(amido) complexes and has been recognized as a
useful method for the generation of reactive low-coordinate
imidometal species.17 However, such a reaction is unprecedented
for bridging amido systems.
Treatment of 1 with 1 equiv of tert-butyl isocyanide or a sulfur
ylide Ph2SdCH218 afforded analogous dinuclear imido complexes
4 (40%) and 5 (81%) containing µ2-isocyanide or µ2-methylene
† Osaka Prefecture University.
‡ Institute for Molecular Science.
9
10802
J. AM. CHEM. SOC. 2004, 126, 10802-10803
10.1021/ja047920s CCC: $27.50 © 2004 American Chemical Society

C O M M U N I C A T I O N S
M. D.; Montgomery, C. D. Coord. Chem. ReV. 1989, 95, 1-40. (e) Fulton,
J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem. Res. 2002,
35, 44-56.
ligands, respectively (Scheme 1), whose structures were also
determined by X-ray crystallography. While complexes 3-5 show
quite similar overall structures, the Ru-Ru distances vary in the
order 5 (2.5728(11) Å) < 3 (2.6013(9) Å) < 4 (2.6594(5) Å),19
with decrease in the π-acceptor strength of the bridging ligands
CH2 > CO > t-BuNC. This trend is consistent with the above MO
consideration, which concluded that back-bonding to the bridging
π-acid ligands is crucial in the formation of the Ru-Ru bond. The
methylene derivative 5 represents, to our knowledge, the first late
transition-metal complex containing imido and carbene ligands.
The new imidodiruthenium fragment {(Cp*Ru)2(µ2-NPh)} de-
rived from 1 can not only bind various organic ligands as described
above, but also induce subsequent transformation at the bimetallic
center. Thus, treatment of the bis(amido) complex 1 with diphen-
ylacetylene resulted in the formation of a dinuclear iminoalkenyl
complex [(Cp*Ru)2(µ2-η3:η3-PhNCPhCPh)] (6) with elimination of
1 equiv of aniline (Scheme 1).20 Complex 6 was isolated in 53%
yield as dark red prisms and has been characterized by spectro-
scopic, analytical, and crystallographic methods. The molecule
contains a crystallographic C2 axis passing through the central
iminoalkenyl carbon atom. This makes the terminal iminoalkenyl
carbon and nitrogen atoms symmetrically related to each other, and
the C-C and C-N bond lengths in the iminoalkenyl moiety are
essentially identical (1.439(5) Å). The iminoalkenyl ligand is η3-
bonded to each of the Ru atoms. The Ru-C bond length for the
central carbon atom is 2.259(5) Å, which is longer than the Ru-C
and Ru-N bond lengths for the terminal carbon and nitrogen atoms
(2.016(3), 2.066(3) Å). Complex 6 was most likely formed by
coupling of the imido and alkyne ligands via a transient µ2-imido
µ2-η2:η2-alkyne complex [(Cp*Ru)2(µ2-NPh)(µ2-η2:η2-PhCCPh)]
(6′). This assumption is reinforced by the reaction of the isolated
imido isocyanide complex 4 with diphenylacetylene, which also
afforded 6 with liberation of the isocyanide ligand (Scheme 1). The
coupling reaction between imido and alkyne ligands is relevant to
catalytic hydroamination and has been well-established for mono-
nuclear terminal imido derivatives of group 4 metals.21 However,
such a reaction is uncommon for late transition-metal complexes5a
and has rarely been observed for polynuclear imido complexes
where imido ligands tend to be stabilized by bridging coordination.10b
In summary, we have demonstrated that the dimeric Ru(II)
anilido complex 1 serves as an excellent precursor for a new
dinuclear imidoruthenium fragment {(Cp*Ru)2(µ2-NPh)} that is
capable of binding various organic ligands and promoting C-N
bond formation with alkyne. The results disclosed here would
broaden the scope of the reactions of bridging amido and imido
complexes. Further studies on the reactivity of 1 and the new
complexes 3-6 are now in progress.
(2) (a) Mu¨ller, T. E.; Beller, M. Chem. ReV. 1998, 98, 675-703. (b) Uchimaru,
Y. Chem. Commun. 1999, 1133-1134. (c) Casalnuovo, A. L.; Calabrese,
J. C.; Milstein, D. J. Am. Chem. Soc. 1988, 110, 6738-6744. (d) Brunet,
J.-J.; Commenges, G.; Neibecker, D.; Philippot, K. J. Organomet. Chem.
1994, 469, 221-228. (e) Hartwig, J. F. Acc. Chem. Res. 1998, 31, 852-
860. (f) Muci, A. R.; Buchwald, S. L. Top. Curr. Chem. 2001, 219, 131-
209. (g) Noyori, R.; Ohkuma, T. Angew. Chem., Int. Ed. 2001, 40, 40-
73. (h) Watanabe, M.; Murata, K.; Ikariya, T. J. Am. Chem. Soc. 2003,
125, 7508-7509.
(3) (a) Alper, H.; Hashem, K. E. J. Am. Chem. Soc. 1981, 103, 6514-6515.
(b) Andrews, M. A.; Kaesz, H. D. J. Am. Chem. Soc. 1979, 101, 7255-
7259. (c) Bernhardt, W.; Von Schnering, C.; Vahrenkamp, H. Angew.
Chem., Int. Ed. Engl. 1984, 23, 381-381. (d) Holm, R. H.; Solomon, E.
I. Chem. ReV. 1996, 96, 2239-2314.
(4) (a) Bryndza, H. E.; Fultz, W. C.; Tam, W. Organometallics 1985, 4, 939-
940. (b) Joslin, F. L.; Johnson, M. P.; Mague, J. T.; Roundhill, D. M.
Organometallics 1991, 10, 2781-2794. (c) Cowan, R. L.; Trogler, W.
C. J. Am. Chem. Soc. 1989, 111, 4750-4761.
(5) (a) Glueck, D. S.; Wu, J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem.
Soc. 1991, 113, 2041-2054. (b) Danopoulos, A. A.; Wilkinson, G.; Sweet,
T. K. N.; Hurthouse, M. B. J. Chem. Soc., Dalton Trans. 1996, 3771-
3778.
(6) Driver, M. S.; Hartwig, J. F. J. Am. Chem. Soc. 1997, 119, 8232-8245.
(7) (a) Waterman, R.; Hillhouse, G. L. J. Am. Chem. Soc. 2003, 125, 13350-
13351. (b) Jenkins, D. M.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc.
2002, 124, 11238-11239. (c) Leung, S. K.-Y.; Huang, J.-S.; Liang, J.-
L.; Che, C.-M.; Zhou, Z.-Y. Angew. Chem., Int. Ed. 2003, 42, 340-342.
(8) (a) Fryzuk, M. D.; Montgomery, C. D.; Rettig, S. J. Organometallics 1991,
10, 467-473. (b) Abdur-Rashid, K.; Clapham, S. E.; Hadzovic, A.;
Harvey, J. N.; Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 2002, 124,
15104-15118.
(9) (a) Fulton, J. R.; Sklenak, S.; Bouwkamp, M. W.; Bergman, R. G. J. Am.
Chem. Soc. 2002, 124, 4722-4737. (b) Conner, D.; Jayaprakash, K. N.;
Wells, M. B.; Manzer, S.; Gunnoe, T. B.; Boyle, P. D. Inorg. Chem. 2003,
42, 4759-4772. (c) Murata, K.; Konishi, H.; Ito, M.; Ikariya, T.;
Organometallics 2002, 21, 253-255. (d) Thyagarajan, S.; Shay, D. T.;
Incarvito, C. D.; Rheingold, A. L.; Theopold, K. H. J. Am. Chem. Soc.
2003, 125, 4440-4441.
(10) (a) Ge, Y.-W.; Sharp, P. R. Organometallics 1988, 7, 2234-2236. (b)
Song, J.-S.; Han, S.-H.; Nguyen, S. T.; Geoffroy, G. L. Organometallics
1990, 9, 2386-2395. (c) Dobbs, D. A.; Bergman, R. G. Organometallics
1994, 13, 4594-4605. (d) Cabeza, J. A.; del R´ıo, I.; Garc´ıa-Granda, S.;
Moreno, M.; Riera, V.; Rosales-Hoz, M. d. J.; Sua´rez, M. Eur. J. Inorg.
Chem. 2001, 2899-2906. (e) Tejel, C.; Ciriano, M. A.; Bordonaba, M.;
Lo´pez, J. A.; Lahoz, F. J.; Oro, L. A. Inorg. Chem. 2002, 41, 2348-
2355.
(11) Blake, R. E., Jr.; Heyn, R. H.; Tilley, T. D. Polyhedron 1992, 11, 709-
710. For related amido-, alkoxo-, and thiolato-bridged diruthenium
complexes, see: (a) Koelle, U. Chem. ReV. 1998, 98, 1313-1334. (b)
Hidai, M.; Mizobe, Y.; Matsuzaka, H. J. Organomet. Chem. 1994, 473,
1-14. (c) Takemoto, S.; Oshio, S.; Kobayashi, T.; Matsuzaka, H.; Hoshi,
M.; Okimura, H.; Yamashita, M.; Miyasaka, H.; Ishii, T.; Yamashita, M.
Organometallics 2004, 23, 3587-3589.
(12) (a) Caulton, K. G. New J. Chem. 1994, 18, 25-41. (b) Mayer, J. M.
Comments Inorg. Chem. 1988, 8, 125-135.
(13) Examples of structurally characterized imidoruthenium complexes: (a)
Kee, T. P.; Park, L. Y.; Robbins, J.; Schrock, R. R. J. Chem. Soc., Chem.
Commun. 1991, 121-122. (b) Burrell, A. K.; Steedman, A. J. Organo-
metallics 1997, 16, 1203-1208. (c) Nakajima, Y.; Suzuki, H. Organo-
metallics 2003, 22, 959-969.
(14) (a) Cotton, F. A.; Feng, X. J. Am. Chem. Soc. 1997, 119, 7514-7520.
(b) Lin, W.; Wilson, S. R.; Girolami, G. S. Organometallics 1994, 13,
2309-2319. (c) Eisenberg, R.; Gaughan, A. P., Jr.; Pierpont, C. G.; Reed,
J.; Shultz, A. J. J. Am. Chem. Soc. 1972, 94, 6240-6241.
(15) A similar metal-metal bond has been proposed for Fe2(CO)9: Reinhold,
J.; Hunstock, E. New J. Chem. 1994, 18, 465-471.
(16) See Supporting Information for details.
Acknowledgment. This work was supported by a Grant-in-Aid
for Scientific Research from the Ministry of Education, Science,
Sports, and Culture of Japan. We are also grateful to the Mitsubishi
Foundation, the UBE Foundation, and The Japan Securities
Scholarship Foundation for financial support.
(17) (a) Chan, D. M.-T.; Fultz, W. C.; Nugent, W. A.; Roe, D. C.; Tulip, T.
H. J. Am. Chem. Soc. 1985, 107, 251-253. (b) Walsh, P. J.; Hollander,
F. J.; Bergman, R. G. J. Am. Chem. Soc. 1988, 110, 8729-8731. (c)
Zambrano, C. H.; Profilet, R. D.; Hill, J. E.; Fanwick, P. E.; Rothwell, I.
P. Polyhedron 1993, 12, 689-708. (d) Schaller, C. P.; Cummins, C. C.;
Wolczanski, P. T. J. Am. Chem. Soc. 1996, 118, 591-611.
(18) Gandelman, M.; Rybtchinski, B.; Ashkenazi, N.; Gauvin, R. M.; Milstein,
D. J. Am. Chem. Soc. 2001, 123, 5372-5373.
Supporting Information Available: Experimental, crystallographic,
and computational details (CIF, PDF). This material is available free
of charge via the Internet at http://pubs.acs.org.
(19) This trend is reproduced in the DFT calculation of model complexes.
(20) The diruthenium complexes containing isoelectronic η3-amidinate ligands
have been reported: Kondo, H.; Matsubara, K.; Nagashima, H. J. Am.
Chem. Soc. 2002, 124, 534-535.
(21) (a) Walsh, P. J.; Baranger, A. M.; Bergman, R. G. J. Am. Chem. Soc.
1992, 114, 1708-1719. (b) Shi, L. Y.; Odom, A. L. J. Am. Chem. Soc.
2004, 126, 1794-1803. (c) Pohlki, F.; Doye, S. Chem. Soc. ReV. 2003,
32, 104-114.
References
(1) (a) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239-482. (b) Nugent,
W. A.; Haymore, B. L. Coord. Chem. ReV. 1980, 31, 123-175. (c)
Bryndza, H. E.; Tam, W. Chem. ReV. 1988, 88, 1163-1188. (d) Fryzuk,
JA047920S
9
J. AM. CHEM. SOC. VOL. 126, NO. 35, 2004 10803