REACTIVITY PATTERNS OF THE UNSATURATED TETRAHEDRAL CLUSTER [RE-4(MU(3)-H)(4)(CO)(12)] - EASY ADDITION OF 4 MECN MOLECULES AND IONIC OR NEUTRAL FRAGMENTATION PATHWAYS OF THE SPIKED-TRIANGLE INTERMEDIATE [RE-4(MU-H)(4)(CO)(12)(NCME)(4)]

The unsaturated (56 valence electrons, v.e.s) tetrahedral cluster [Re- 4(mu(3)-H)(4)(CO)(12)] 1 readily added four acetonitrile molecules, af fording two isomers 2a and 2b of the 64 v.e.s [Re-4(mu-H)(4)(CO)12- (N CMe)(4)] derivative, containing a spiked-triangle metallic skeleton. T hese isomers at room temperature rapidly underwent an ionic fragmentat ion to the known unsaturated triangular cluster anion [Re-3(mu-H)(4)(C O)(9)(NCMe)](-) and to the cation [Re(CO)(3)(NCMe)(3)](+). The rate of decomposition significantly increased at low [MeCN] concentration. Tr eatment of compounds 2a and 2b with the pi-acidic ligand CO, in the ab sence of free acetonitrile, gave only neutral products. Monitoring by NMR spectroscopy has revealed the rapid stepwise substitution of the n itrile ligands, accompanied by fragmentation to the known saturated tr iangular clusters [Re-3(mu-H)(3)(CO)(12-n)(NCMe)(n)] (n = 1-3) and to the mononuclear complexes [ReH(CO)(5-n)(NCMe)(n)] (n = 0 or 1). The no vel, unstable. mononuclear hydride [ReH(CO)(4)(NCMe)] has been obtaine d by treatment of [ReH(CO)(5)] with Me(3)NO in acetonitrile and by rea ction of [ReH2(CO)(4)](-) with CF3SO3H. in acetonitrile. In the presen ce of free acetonitrile, compounds 2a and 2b reacted with CO more slow ly and gave both anionic and neutral triangular clusters.