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

Reaction of a ferrocene-backbone
bisphosphine-borane ligand, [Fe­(η5-C5H4PPh2)­(η5-C5H4PtBu­{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 η3BCC-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-C5H4PtBu­{C6H4(PPh2)-o})] (FcPPP), was prepared by
lithiation of [Fe­(η5-C5H4PPh2)­(η5-C5H4PtBu­(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 κ3PPP-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 κ2PP-coordinated, and 1 equiv of dba remains η2CC-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.