MIXED-METAL CLUSTER CHEMISTRY .5. SYNTHESES AND X-RAY CRYSTAL-STRUCTURE OF CP2MO2IR2(MU(3)-CO)(MU-CO)(5)(CO)(4)

The mixed-metal cluster Cp2Mo2Ir2(CO)(10) has been synthesized by two procedures, namely reacting CpMo(CO)(3)H with IrCl(CO)(2)( p-toluidine ) under a CO atmosphere in the presence of zinc (23%), and by combinin g [CpMo(CO)(3)](-) with IrCl(CO)(2)(p-toluidine) (78%). A structural s tudy reveals that, in contrast to the analogous Cp2W2Ir2(CO)(10) it is a rare example of a tetrahedral cluster with all edges bridged by CO, and that it possesses an unusual 'semi-face-capping' carbonyl ligand. Carbonyl bridging and hence steric crowding increase on proceeding fr om tungsten to molybdenum, rendering the title complex amongst the mos t crowded of metal clusters. (C) 1997 Elsevier Science S.A.