Indenyl ring slippage in crown thioether complexes [IndMo(CO)(2)L](+) and C-S activation of trithiacyclononane: Experimental and theoretical studies

The macrocycle 1,4,7-trithiacyclononane (ttcn) reacts with [(eta(5)-Ind)Mo(CO)(2)(NCMe)(2)](+) (or [(eta(5)-Ind)Mo(CO)(2)(kappa(2)-dme)](+)) to give [(eta(3)-Ind)Mo(CO)(2)(kappa(3)-ttcn)](+) as the BF4- salt (1), but its reaction with [(eta(5)-Ind)Mo(CO)(2)(C3H6)(FBF3)] affords the C-S bond cleavage product [(eta(5)-Ind)Mo(CO)(kappa(3)-1,4,7-trithiaheptanate)]BF4 (6), which has been characterised by X-ray crystallography (Ind = C9H7, indenyl). In contrast to ttcn, the macrocycles 1,3,5-trithiane (tt) and 1,4,7,10-tetrathiacyclododecane (ttcd) fail to induce changes in the coordination mode of indenyl: tt and ttcd react with [(eta(5)-Ind)Mo(CO)(2)(NCMe)(2)](+) (or [(eta(5)- Ind)Mo(CO)(2)(kappa(2)-dme)](+)) to give [(eta(5)-Ind)Mo(CO)(2)(kappa(2)-tt)](+) (2), characterised by X-ray crystallography, and [(eta(5)-Ind)Mo(CO)(2)(kappa(2)-ttcd)](+) (3), respectively. The cyclopentadienyl (Cp = C5H5) analogues [(eta(5)-CpMo(CO)(2)(kappa(2)-tt)](+) (4) and [(eta(5)-CpMo(CO)(2)(kappa(2)-ttcn)](+) (5) have also been synthesised and 5 characterised by X-ray crystallography. DFT calculations showed that the eta(5)-Ind/Cp coordination mode is always the most stable. However, a molecular dynamics study of the macrocycles conformations revealed that the major conformer of ttcn was a chair, which favoured kappa(3) coordination. As indenyl complexes undergo slippage with a small barrier (< 10 kcal mol(-1)), the kinetically preferred species [(eta(3)-Ind)Mo(CO)(2)(kappa(3)-ttcn)](+) (1) is the observed one. The conversion to 6 proceeds stepwise, with loss of ethylene followed by loss of CO, as calculated by DFT, with a barrier of 38.7 kcal mol(-1), consistent with the slow uncatalysed reaction.