Metal-metal interactions across bridging elemental carbon chains: a computational study of odd-carbon complexes

Structure, bonding and metal-metal interactions in complexes [LyMCxM'L'(y)] (z+) with odd-carbon chains, and monometallic reference compounds, are inve stigated at the B3LYP density functional level of theory. The data show str ong rhenium-manganese interactions in [(eta (5)-C5H5)(NO)(PH3)ReCxMn(CO)(2) (eta (5)-C5H5)](+) (x = 3, 5, 7, 9), as evidenced by bond lengths and order s, 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+-(C=C)(n)=C=Mn a s opposed to Re+=(C=C)(n)=C=Mn character. The corresponding dirhenium compl exes are similar but with dominant Re(-C=C)(n)-C=Re+ character. The more sy mmetrical uncharged complexes (eta (5)-C5H5)(CO)(2)M(1)CxM(2)(CO)(2)(eta (5 )-C5H5) [x = 3, 5; M(1), M(2) = Re or Mn] exhibit analogous geometric, elec tronic and homodesmotic energy trends, but have dominant M=(C=C)(n)=C=M: ch aracter. In contrast, (eta (5)-C5H5)(NO)(PH3)ReC3W(OMe)(3) which has a ReC= CC=W linkage, shows no significant (net) rhenium-tungsten interactions. All geometric and electronic properties are very close to those of monometalli c reference compounds. Homodesmotic energies are near zero, although relate d triple bond metatheses used preparatively are exothermic. The dimerizatio n of (MeO)(3)W=CH is exothermic(- 14.6 kcal mol(-1)), giving a methoxy-brid ged structure closely resembling literature compounds.