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

Abstract

Structure, bonding and metal–metal interactions in complexes [L_yMC_xM′L_y′^′]^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)ReC_xMn(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)C_xM(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.