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(μ-P)(CO)2(η6-HR*)][BAr‘4] (1) [Cp = η5-C5H5; R* = 2,4,6-C6H2tBu3,
Ar‘ = 3,5-C6H3(CF3)2] is deprotonated by KH in THF at 293
K to give the (cyclopentadienylidene)phosphinidene derivative
[Mo2Cp(μ-κ1:κ1,η5-PC5H4)(η6-HR*)(CO)2]. In contrast, reaction
with K[BHsBu3] at 213 K gives the cyclopentadiene complex
[Mo2Cp(μ-P)(CO)2(η6-HR*)(η4-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(μ-PH)(CO)2(η6-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·THF, to give [Mo2Cp2{μ-κ1:κ1,η2-HPBH3}(CO)2(η6-HR*)], the first complex reported to have the
phosphinidene−borane (HPBH3) ligand.