Methylidyne Transfer Reactions with Niobium

The mononuclear niobium methylidyne
[(PNP)­(ArO)­NbCH] (1; PNP– =
N­[2-PiPr2-4-methylphenyl]2–, Ar
= 2,6-iPr2C6H3) reacts with the isocyanate OCNtBu to form a mononuclear niobium oxo species with
a rare example of an azaallenyl ligand, namely [(PNP)­(ArO)­NbO­(CHCNtBu)] (2). When 1 is treated with the phosphaalkyne PCAd (Ad = 1-adamantyl),
PC bond cleavage occurs to form a mononuclear complex where
P–P coupling has occurred between the formal phosphaalkyne
phosphorus atom and one phosphine arm from the PNP ligand, namely
[(PNPP)­(ArO)­Nb­(η2-AdCCH)] (3). Solid-state
structural studies and isotopic labeling experiments confirm C–C
bond formation of the methylidyne group as well as provide conclusive
evidence for the oxo ligand in 2 being terminal and the
fate of the phosphorus atom from PCAd in complex 3. Computational studies have been applied to understand the pathway
involving the P–P bond forming reaction of 1 and
PCAd.