Synthesis and reactivity of triruthenium carbonyl cluster complexes containing a bridging 1-azavinylidene ligand derived from benzophenone imine

The reaction of [Ru-3(CO)(12)] with the lithium salt of benzophenone imine (LiN=CPh(2)) followed by protonation with trifluoroacetic acid leads to the eta(1)-1-azavinylidene cluster complex [Ru-3(mu-H)(mu-N=CPh(2))(CO)(10)] (1). Compound 1 cannot be prepared by direct reaction of [Ru-3(CO)(12)] with benzophenone imine under thermal conditions. Carbonyl substitution and thermolysis reactions on compound 1 and on some of its derivatives are described. Complex 1 reacts with 1 and 2 equiv of bis(diphenylphosphino)methane (dppm) at room temperature to give the substituted derivatives [Ru-3(mu-H)(mu-N=CPh(2))(mu-dppm)(CO)(8)] (2) and [Ru-3(mu-H)(mu-N=CPh(2))(mu-dppm)(dppm)(CO)(7)] (3), respectively. In both complexes the three bridging Ligands span the same Ru-Ru edge; in addition, complex 3 contains an yl-dppm ligand occupying an equatorial site on the unique Ru atom. An X-ray structure analysis of 3 . 0.5CH(2)Cl(2) is reported. Thermolysis of complex 2 in THF at reflux temperature leads to [Ru-3(mu-H)(mu(3)-N=CPh(2))(mu-dppm)(CO)(7)] (4), a compound which contains a bridging eta(2)-1-azavinylidene ligand interacting with the three Ru atoms. Complex 4 reacts with CO (1 atm, 18 degrees C) reverting to complex 2. The reaction of compound 1 with PPh(3) at room temperature gives the monosubstituted derivative [Ru-3(mu-H)(mu-N=CPh(2))(PPh(3))(CO)(9)] (5), in which the P-donor ligand is attached to one of the two bridged Ru atoms. Thermolysis of 5 in THF at reflux temperature leads to [Ru-3(mu-H)(mu(3)-N=CPh(2))(PPh(3))(CO)(8)] (6), which, as complex 4, contains a face-bridging eta(2)-1-azavinylidene ligand. The reaction of complex 5 with PPh(3) occurs only at higher temperatures (40-70 degrees C) to give the asymmetrically disubstituted derivative [Ru-3(mu-H)(mu-N=CPh(2))(PPh(3))(2)(CO)(8)] (7), which has the additional PPh(3) ligand attached to the unbridged Ru atom. Compound 7 is thermally unstable, undergoing an easy (40-70 degrees C) orthometalation reaction of a phenyl ring of the azavinylidene ligand to give the derivative [Ru-3(mu-H)(2)(mu-N=CPhC(6)H(4))(PPh(3))(2)(CO)(7)] (8). This compound reacts with CO (1 atm, 18 degrees C) to regenerate complex 7.