Nickel and Palladium Complexes of Ferrocene-Backbone Bisphosphine-Borane and Trisphosphine Ligands

Reaction of a ferrocene-backbone bisphosphine-borane ligand, [Fe(eta(5)-C5H4PPh2)(eta(5)-(C5H4PBu)-Bu-t{C6H4(BPh2)-o})] (FcPPB), with [Ni(cod)(2)] (cod = 1,5-cydooctadiene) or 0.5 equiv of [Pd-2(dba)(3)] (dba = trans,trans-dibenzylideneacetone) afforded [Ni(FcPPB)] (1) and [Pd(FcPPB)] (2), respectively; compound 1 does not react with dba. The FcPPB ligand in complexes 1 and 2 is coordinated via both phosphine donors and an eta(BCC)-B-3-interaction with boron and the ipso- and ortho-carbon atoms of a B-phenyl group. The triphosphine analogue of the FcPPB ligand, [Fe(eta(5)-C5H4PPh2)(eta(5-C5H4PBu)-Bu-t{C6H4(PPh2)-o})] (FcPPP), was prepared by lithiation of [Fe(eta(5)-C5H4PPh2)(eta(5)-(C5H4PBu)-Bu-t(C6H4Br-o)] followed by addition of Ph2PCl, and reaction of FcPPP with [Ni(cod)(2)] provided Ni(FcPPP) (3), which exists as a mixture of isomers in which the FcPPP ligand is kappa(PPP)-P-3-coordinated. Attempts to obtain X-ray quality crystals of 3 were derailed by its propensity to react with traces of N-2 within an argon-filled glovebox, yielding rac-[{Ni(FcPPP)}(2)(mu-N-2)] (4), in which two nickel(0) centers are linked by an end-on-bridging N-2 unit. By contrast, reaction of FcPPP with 0.5 equiv of [Pd-2(dba)(3)] provided [Pd(eta(2)-dba)(FcPPP)] (5), in which the FcPPP ligand is kappa(PP)-P-2-coordinated, and 1 equiv of dba remains eta(CC)-C-2-coordinated to palladium. Complexes 3 and 4 also reacted with dba, forming a new compound tentatively assigned as [Ni(eta(2)-dba)(FcPPP)] (6). Complexes 1, 2, and 5 did not react with N-2.