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

Reaction of a ferrocene-backbone bisphosphine-borane ligand, [Fe­(η5-C5H4PPh2)­(η5-C5H4P t Bu­{C6H4(BPh2)-o})] (FcPPB), with [Ni­(cod)2] (cod = 1,5-cyclooctadiene) or 0.5 equiv of [Pd2(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 η3 BCC-interaction with boron and the ipso- and ortho-carbon atoms of a B-phenyl group. The triphosphine analogue of the FcPPB ligand, [Fe­(η5-C5H4PPh2)­(η5-C5H4P t Bu­{C6H4(PPh2)-o})] (FcPPP), was prepared by lithiation of [Fe­(η5-C5H4PPh2)­(η5-C5H4P t Bu­(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 κ3 PPP-coordinated. Attempts to obtain X-ray quality crystals of 3 were derailed by its propensity to react with traces of N2 within an argon-filled glovebox, yielding rac-[{Ni­(FcPPP)}2(μ-N2)] (4), in which two nickel(0) centers are linked by an end-on-bridging N2 unit. By contrast, reaction of FcPPP with 0.5 equiv of [Pd2(dba)3] provided [Pd­(η2-dba)­(FcPPP)] (5), in which the FcPPP ligand is κ2 PP-coordinated, and 1 equiv of dba remains η2 CC-coordinated to palladium. Complexes 3 and 4 also reacted with dba, forming a new compound tentatively assigned as [Ni­(η2-dba)­(FcPPP)] (6). Complexes 1, 2, and 5 did not react with N2.