VOLTAMMETRY OF CARBOCATIONS STABILIZED BY COORDINATION WITH TETRAHEDRAL MOLYBDENUM AND TUNGSTEN CARBON CLUSTERS - CO)(4)-MU-ETA(2)ETA(3)-(HCCCR(1)R(2))](BF4-)-B(-I) COMPLEXES() (M=MO, W, R(1), R(2)=H, ME, AND PR)

The electrochemical reduction of the carbocationic complexes [CP(2)M(2 )(CO)(4)-mu-eta(2) 2:eta(3) (HCCCR(1) R(2))](BF4-)-B-+ where M/R(1), R (2) = Mo/H, H (1(+)), Mo/H, Me (2(+)), Mo/Me, Me (3(+)), Mo/H, Pr-i (4 (+)), has been studied by polarography and cyclic voltammetry on a Hg- electrode in THF solution. It has been suggested that carbocationic ce nter-directed reversible two-electron reduction of 1(+)-4(+) takes pla ce according to an ECE-mechanism and results in the carbanionic comple xes [Cp(2)M(2)(CO)(4)-mu-eta(2):eta(3)-(HCCCR(1)R(2))] (1(-)-4(-)) as final products via carbon-centered radicals as intermediates. Anions 1 (-)-4(-) are capable of irreversible two-electron reduction at more ne gative potentials or protonation resulting in their transformation int o the corresponding acetylene complexes [Cp(2)M(2)(CO)(4)(HCCCHR(1)R(2 ))], which are also capable of irreversible two-electron reduction. An ions 1(-)-4(-) and their protonated forms are reduced with cleavage of the Mo-Mo bond. The reduction pathways of complexes 1(+), 2(+), and 4 (+) with C-H bonds at the carbon atom of the carbocationic center are different on a Pt-electrode. It is suggested that this difference is d ue to the abstraction of a H-atom from the intermediate radical specie s by platinum.