Efficient Synthesis and Multisite Reactivity of a Phosphinidene-Bridged Mo-Re Complex. A Platform Combining Nucleophilic and Electrophilic Features.

The heterometallic complex [MoReCp(μ-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(PClR*)(CO)2] and [MoReCp(μ-PR*)(CO)7] as intermediate species (R* = 2,4,6-C6H2tBu3). 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(μ-H){μ-P(CH2CMe2)C6H2tBu2}(CO)6] and reacted with I2 to give [MoReCpI2(μ-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{μ-κ2P,C:η3-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{μ-η2P,C:κ1P-PR*CN(4-C6H4OMe)}(CO)6{CN(4-C6H4OMe)}], which displays an azaphosphaallene ligand in a novel bridging coordination mode.