Synthesis and characterization of isomeric 4- and 8-(σ–CHdouble bond; length as m-dashCHPh)-closo-ruthenacarboranes with η3:η2-phosphacarbocyclic ligand

Reactions of [3,3-(PPh3)2-3-Cl-3-H-3,1,2-closo-RuC2B9H11] (1) and its exo-nido isomer [exo-5,6,10-{Ru(Ph3P)2Cl}-5,6,10-(μ-H)3-10-H-7,8-nido-C2B9H8] (2) with NH4PF6 in methanol or ethanol solution followed by heating in the presence of an excess of phenylacetylene (3) affords a mixture of two isomeric closo species [3,3-{(1′-3′-η3):(5′,6′-η2)-ortho-C6H4PPh2CHC(Ph)CHCHPh}-8-(σ–CHdouble bond; length as m-dashCHPh)-3,1,2-closo-RuC2B9H10] (4) and [3,3-{(1′-3′-η3):(5′,6′-η2)-ortho-C6H4PPh2CHC(Ph)CHCHPh}-4-(σ–CHdouble bond; length as m-dashCHPh)-3,1,2-closo-RuC2B9H10] (5) in which boron vertexes in β- and α-sites with respect to the cage carbons bear the (E)–CHdouble bond; length as m-dashCHPh group. The X-ray diffraction study of 4 together with the multinuclear NMR data for 4 and 5 revealed that such an unusual η3:η2-phosphacarbocyclic ligand in both isomeric complexes is formed by specific insertion of the initially metal-bound PPh3 group into the chain of two alkyne molecules coupled in a “head-to-tail” fashion around the metal vertex.