Metal–metal interactions across bridging elemental carbon chains: a computational study of odd-carbon complexes
Structure, bonding and metal–metal interactions in complexes [LyMCxM′Ly′′]z+ with odd-carbon chains, and monometallic reference compounds, are investigated at the B3LYP density functional level of theory. The data show strong rhenium–manganese interactions in [(η5-C5H5)(NO)(PH3)ReCxMn(CO)2(η5-C5H5)]+ (x = 3, 5, 7, 9), as evidenced by bond lengths and orders, charge distributions, and negative homodesmotic energies (which diminish with chain length). Natural bond orbital (NBO) analyses give ground states with highly polarized Re–C bonds, and suggest dominant +Re–(CC)nCMn as opposed to +Re(CC)nCMn character. The corresponding dirhenium complexes are similar but with dominant Re(–CC)n–CRe+ character. The more symmetrical uncharged complexes (η5-C5H5)(CO)2M(1)CxM(2)(CO)2(η5-C5H5) [x = 3, 5; M(1), M(2) = Re or Mn] exhibit analogous geometric, electronic and homodesmotic energy trends, but have dominant M(CC)nCM character. In contrast, (η5-C5H5)(NO)(PH3)ReC3W(OMe)3 which has a ReCCCW linkage, shows no significant (net) rhenium–tungsten interactions. All geometric and electronic properties are very close to those of monometallic reference compounds. Homodesmotic energies are near zero, although related triple bond metatheses used preparatively are exothermic. The dimerization of (MeO)3WCH is exothermic (−14.6 kcal mol−1), giving a methoxy-bridged structure closely resembling literature compounds.