Unusual reactivity of the unsaturated dimolybdenum complex [Mo2(η5-C5H5)2{μ-OP(OEt)2}{μ-P(OEt)2}(CO)2]

Reaction of the doubly metal-metal bonded compound [Mo2Cp2{mu-OP(OEt)(2)}{mu-P(OEt)(2)}-(CO)(2)] with [Fe-2(CO)(9)] leads to the 46 e(-) cluster [(FeMoCp2)-Cp-2{mu-OP(OEt)(2)}{mu-P(OEt)(2)}(CO)(5)]. By contrast, reaction of Mo2Cp2{mu-OP(OEt)(2)}{mu-P(OEt)(2)](CO)(2)] with SnCl2 leads to the incorporation of two molecules of reagent: one molecule inserts into the Mo-O bond, and the other one adds to the Mo=Mo double bond to finally yield the tetranuclear compound [Mo2CP2{mu-(EtO)(2)POSnCl2}{mu-P(OEt)(2)}(mu-SnCl2)(CO)(2)] as confirmed by an X-ray diffraction study. Complex [Mo2Cp2]{mu-OP(OEt)(2)]{mu-P(OEt)(2)}(CO)(2)] reacts with HCC(p-C6H4Me) to give a mixture of the alkyne-bridged compound [Mo2Cp2{mu-eta(2):eta(2)-HCC(p-C6H4Me)}{mu-(EtO)(2)POP-(OEt)(2)}(CO)(2)] and the alkenyl-bridged {Mo2Cp2{mu-eta(1),k(1):eta(2)-OP(OEt)(2)CH=C(p-C6H4Me)}{mu-P(OE)(2)(CO)(2)] (structure confirmed through an X-ray diffraction study). This requires either P-O reductive elimination between phosphonate and phosphido ligands or insertion of the incoming alkyne into the Mo-P (phosphonate) bond, all these uncommon processes occurring at room temperature. The solution structure of the new compounds is analyzed on the basis of their IR and NMR data and X-ray diffraction studies, and the reaction pathways prevalent for the title compound are discussed on the basis of the data available.