COORDINATION AND REDUCTION OF ISOCYANIDE LIGANDS IN HYDRIDO-CARBONYL RHENIUM CLUSTER CHEMISTRY - SYNTHESIS AND CHARACTERIZATION OF THE ANION [RE3(MU-H)4(CO)9(CNR)]- AND OF THE FORMIMIDOYL DERIVATIVE [RE3(MU-H)3(CO)9(MU-ETA-2-C(H)=NC6H11)(PME2PH)]-

The reaction of the unsaturated anion [Re3(mu-H)4(CO)9(NCMe)]- with cyclohexylisocyanide gives the novel unsaturated anion [Re3(mu-H)4(CO)9(CNC6H11)]-. By reaction of this species with dimethylphenylphosphine a saturated compound is obtained, [Re3(mu-H)3(CO)9(mu-eta-2-C(H) = NC6H11)-(PMe2Ph)]-, containing a bridging formimidoyl ligand, Two isomers of this anion have been identified and the structure of one of them has been elucidated by X-ray analysis. The anion contains an isosceles triangle of Re atoms with two longer hydrogen-bridged edges [mean 3.255 angstrom] and one shorter edge [3.164(1) angstrom], doubly bridged by the formimidoyl ligand and the third hydride. The phosphine ligand is coordinated in the axial direction with respect to the Re3 plane, with a Re-P bond length of 2.454(7) angstrom.