Dirhenium Complexes with S 2 CPR 3 Bridges Donating Four and Eight Electrons — X‐ray Structures of [Re 2 (CO) 8 {μ‐η 1 ;η 1 ‐S 2 CPCy 3 }] and {Re 2 (CO) 6 {μ‐η 3 ;‐S 2 CPCy 3 }] and [Re 2 (CO) 6 {μ‐η 2 ; η 3 ‐S 2 CPCy 3 }]

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 (RCy) 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 ReRe(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 )ReRe(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‐CHCH 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 (RCy), 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.