ELECTROCHEMICAL DEPROTECTION OF A SUBSTRATE-BINDING SITE IN [MO-2(CP)(2)(MU-SME)(3)(MU-CL)] (CP=ETA(5)-C5H5) VIA CHLORIDE-BRIDGE OPENING - KINETICS OF MECN AND BU(T)NC BINDING AT THIS SITE

The access to a co-ordination site in the quadruply bridged complex [M o-2(cp)(2)(mu-SMe)(3)(mu-Cl)] (cp = eta(5)-C5H5) has been found to be redox controlled. Electrochemical one-electron oxidation of the comple x unlocks the chloride bridge but the radical cation retains the quadr uply bridged geometry of the neutral parent as indicated by cyclic vol tammetry and EPR spectroscopy. The chloride bridge opens up in the pre sence of a substrate (Y=Z = MeCN, Bu(t)NC, Me(2)C(6)H(3)NC or CO), lea ding to the formation of [Mo-2(cp)(2)(mu-SMe)(3)Cl(Y=Z)](.+) derivativ es. The site is sensitive to the electronic properties of the substrat e, and kinetic studies of the substrate-binding step demonstrated that Bu(t)NC reacts faster and is bound more tightly at [Mo-2(cp)(2)(mu-SM e)(3)Cl](.+) than is MeCN. The reduction of [Mo-2(cp)(2)(mu-SMe)(3)Cl( Y=Z)](.+) is reversible for Y=Z = CO and RNC (R = Bu(t) or C(6)H(3)Me( 2)) whereas MeCN is lost on reduction. In this case the fact that the chloride ligand is still present at the neighbouring molybdenum centre allows regeneration of the parent complex via bridge reclosure. The r eactivity of [Mo-2(cp)(2)(mu-SMe)(3)(mu-Cl)] in MeCN has also been inv estigated: instead of the bridge-opening process of the radical cation , the neutral parent loses the chloride bridge in MeCN; the resulting bis(acetonitrile) cation, [Mo-2(cp)(2)(mu-SMe)(3)(MeCN)(2)](+), has be en isolated and characterized.