Addition of primary and secondary phosphines to dinuclear tantalum hydrides: Synthesis of phosphides and phosphinidenes via P-H bond activation

The dinuclear complex ((RPh)[NPN]Ta)(2)(mu-H)(4) (where (RPh)[NPN] = [RP(CH2SiMe2NPh)(2)] and R = Ph, Cy) shows remarkable reactivity with molecular nitrogen, producing the side-on end-on bound dinitrogen complex ((RPh)[NPN]Ta)(2)(mu-eta(1):eta(2)-N-2)(mu-H)(2.) This tantalum tetrahydride also promotes other small molecule activation. Addition of secondary phosphines HPR'(2) (R' = Ph, Cy) to ((RPh)[NPN]Ta)(2)(mu-H)(4) accesses trihydride phosphide systems ((RPh)[NPN]Ta)(2)(mu-H)(3)(mu-PR'(2)). Addition of primary phosphines H2PR" (R" = Cy, Ad) gives bridging phosphinidene tantalum complexes ((RPh)[NPN]Ta)(2)(mu-H)(2)(mu-PR"). Molecular structures as determined by X-ray crystallography for the complexes ((PhPh) [NPN]Ta)(2)(mu-H)(3)(mu-PCy2) and ((CyPh)[NPN]Ta)(2)(mu-H)(2)(mu 1-PAd) are presented. Isotopic labeling studies offer mechanistic insights into the reactivity of this tetrahydride system. Reaction Of Cy2PH with ((CyPh)[NPN]Ta)(2)(mu-D)(4), for instance, gives solely the monchydride dideuteride complex ((CyPh)[NPN]Ta)(2)(Y-H)(mu-D)(2)(mu-PCy2). This labeling study indicates that D-2 loss forms the reactive species, ((CyPh) [NPN]Ta)(2)(mu-D)(2), which promotes small molecule activation. Addition of CyPH2 to ((CyPh)[NPN]Ta)(2)(AtD)(4) gives a series of isotopomers, with an average composition of 0.67 H and 1.33 D, supporting a 1,2-H-2 elimination step to form the tantalum phosphinidenes. These results are tied into the general reactivity of ((RPh)[NPN]Ta)(2)(mu-H)(4).