Inorganic rings, intact and cleaved, between two metal fragments

Abstract

The electronic structure of CpME,MCp (M = Cr, Mo; E = P, As) triple-decker complexes is explored, where the middle deck contains a fiveor six-membered ring of group 15 E atoms. From another point of view, the metal and group 15 atoms form a polynuclear cluster. All hitherto known compounds possess short metal-metal distances across the central ring, are electron deficient, and do not follow the triple-decker 30 electron or Wade-Mingos skeletal electron counting rules. In addition, the complex CpMoAsSMoCp exhibits a substantial distortion from idealized 5-fold symmetry; the middle deck shows a partitioning into As, and As, fragments. By making use of the frontier orbitals of the CpMo and E, fragments the electronic structure of these “inorganic” triple-decker compounds is analyzed. The short metal-metal distances in these systems are responsible for their apparent electron deficiency. The distortion of the central As, ring in CpMoAs,MoCp is traced to the simultaneous working of firstand second-order Jahn-Teller effects. Some remarkable compounds containing homoatomic rings of main group elements stabilized by coordination to transition-metal fragments have been synthesized.I Sacconi and co-workers described a number of “double sandwich” compounds [(triphos)M’-(p-(q3-E3)M’’(triphos)]”+ (1) containing cyclo-triphosphorus $-P3 or cyclo-triarsenic $-As3 groups sandwiched between two ML3 fragments.* Rheingold, Scherer, and their co-workers added