Conformational preferences of heteronuclear Fischer carbene complexes of cymantrene and cyclopentadienyl rhenium tricarbonyl

摘要

Homo- and heteronuclear bimetallic carbene complexes of group VIItransition metals (Mn and Re), with cymantrene or cyclopentadienylrhenium tricarbonyl as the starting synthon, have been synthesizedaccording to classic Fischer methodology. Crystal structures of the carbenecomplexes with general formula [RC5H4 M'(CO)2{C(OEt)(C5H4 M(CO)3)}], whereM = M′ = Mn, R = H (1), R = Me (2); M = Mn, M′ = Re, R = H (3); M = M′ = Re,R = H (4); and M = Re, M′ = Mn, R = H (5), are reported. A density functionaltheory (DFT) study was undertaken to determine natural bonding orbitals(NBOs) and conformational as well as isomeric aspects of the binuclearcomplexes. Application of second-order perturbation theory (SOPT) ofthe NBO method revealed stabilizing interactions between the methyleneC–H bonds and the carbonyl ligands of the carbene metal moiety. Energycalculations in the gas phase of the cis and trans conformations of the Cprings relative to one another are comparable, with the trans conformationslightly lower in energy. The theoretical findings have also been confirmedwith single-crystal X-ray diffraction, and all solid-state structures are foundin the trans geometry.