Efficient Synthesis And Multisite Reactivity Of A Phosphinidene- Bridged Mo-Re Complex. A Platform Combining Nucleophilic And Electrophilic Features

The heterometallic complex [MoReCp(mu-PR*)(CO)(6)] (3) was prepared in 60% overall yield from syn- MoCp(PHR*)(CO)(2)] via a three-step procedure involving complexes syn-[MoCp(PCIR*)(CO)(2)] and [MoReCp(mu-PR*)(CO)(7)] as intermediate species (R* = 2,4,6-(C6H2Bu3)-Bu-t). The PR* ligand in 3 displays a novel asymmetric interaction with the dimetal center, involving a double bond with one atom (Mo) and a dative single bond with the other one (Re). Compound 3 underwent thermal isomerization involving a C-H bond cleavage to yield the hydride [MoReCp(mu-H){mu-P(CH2CMe2)(C6H2Bu2)-Bu-t}(CO)(6)] and reacted with I-2 to give [MoReCpI2(mu-PR*)(CO)(6)], which displays a symmetrical phosphinidene bridge. Its reaction with methyl propiolate at 293 K proceeded with [2 + 2] cycloaddition of the alkyne and decarbonylation to yield the phosphapropenylidene-bridged complex [MoReCp{mu-kappa(2)(p,c):eta(3)-PR*CHC(CO2Me)}(CO)(5)] as the major product, whereas its reaction with excess CN(4-C6H4OMe) at 273 K proceeded with formal [2 + 1] cycloaddition of the isocyanide and further isocyanide addition at the Re site to yield the complex [MoReCp{mu-eta(2)(P,C):kappa(pPR)-P-1*CN(4-C6H4OMe)}(CO)(6){CN(4-C6H4OMe)}], which displays an azaphosphaallene ligand in a novel bridging coordination mode.