Formation of P-H, P-C, and C-H bonds by hydride attack on a electrophilic phosphide-bridged dimolybdenum complex.: Trapping the phosphinidene ligand with borane

The phosphide-bridged complex [Mo2Cp2(mu-P)(CO)(2)(eta(6)-HR*)][BAr'(4)] (1) [Cp = eta(5)-C5H5; R* = 2,4,6-(C6H2Bu3)-Bu-t, Ar' = 3,5-C6H3(CF3)(2)] is deprotonated by KH in THF at 293 K to give the (cyclopentadienylidene)phosphinidene derivative [Mo2Cp(mu-kappa(1):kappa(1),eta(5)-PC5H4)(eta(6)-HR*)(CO)(2)]. In contrast, reaction with K[(BHBu3)-Bu-s] at 213 K gives the cyclopentadiene complex [Mo2Cp(mu-P)(CO)(2)(eta(6)-HR*)(eta(4)-C5H6)], resulting from hydride attack at a carbon atom. This compound undergoes spontaneous C-H bond cleavage above 253 K to give the phosphinidene complex [Mo2Cp2(mu-PH)(CO)(2)(eta(6)-HR*)], which turns out to be the direct product of the reaction of 1 with Li[BHEt3] in THF at 213 K. This thermally unstable species can be stabilized through reaction with BH3 center dot THF, to give [Mo2Cp2{mu-kappa(1):kappa(1),eta(2)-HPBH3}(CO)(2)(eta(6)-HR*)], the first complex reported to have the phosphinidene-borane (HPBH3) ligand.