Dirhenium Complexes with S₂CPR₃ Bridges Donating Four and Eight Electrons — X‐ray Structures of [Re₂(CO)₈{μ‐η¹;η¹‐S₂CPCy₃}] and {Re₂(CO)₆{μ‐η³;‐S₂CPCy₃}] and [Re₂(CO)₆{μ‐η²; η³‐S₂CPCy₃}]

Abstract

Abstract The reaction of fac ‐[Re(CO) 3 (S 2 CPR 3 )Br] with [Rc(CO) 5 ] − affords the dinuclear octacarbonyl compounds [Re 2 (CO) 8 (μ‐S 2 CPR 3 )] ( 3a  b ), which have been isolated and characterized by spectroscopic methods. An X‐ray crystal‐structure determination of the derivative 3a (RCy) shows that the S 2 CPCY 3 ligand acts as an η 1 (S);η 1 (S′) bridge donating two electrons to each metal atom of a symmetrical (CO) 4 ReRe(CO) 4 unit. This unit is presumably formed through a concerted process involving carbonyl/sulfur exchange in the nonsymmetrical octacarbonyl (CO) 3 (S 2 CPR 3 )ReRe(CO) 5 generated after the coupling of the bromo derivative with the carbonyl anion. Complexes 3a  b can be obtained more directly by adding S 2 CPR 3 to [Re 2 (CO) 8 (μ‐H)(μ‐CHCH n Bu)], which is formed by irradiation of Re 2 (CO) 10 with 1 ‐hexene. Hydride addition to the central carbon atom of the S 2 CPR 3 ligand of 3a – b occurs with loss of PR 3 , to give the anion [Re 2 (CO) 8 (μ‐S 2 CH)] − which may be isolated as a salt with the PPN + cation. The octacarbonyl compounds 3a – b can be converted into hexacarbonyl complexes [Re 2 (CO) 6 (μ‐S 2 CPR 3 )] ( 5a – b ) by heating in toluene or octane at reflux temperature. According to an X‐ray crystal‐structure determination of the derivative 5a (RCy), the loss of one carbonyl ligand from each rhenium atom is accompanied by the rearrangement of the S 2 CPR 3 ligand which changes its bonding mode from η 1 (S);η 1 (S′) donating four electrons to η 3 (S,C,S′);η 2 (S,S′) donating eight electrons.