Reactivity of a Borane-Appended 1,1′-Bisphosphinoferrocene Ligand: Transition Metal and Lewis Acid Coordination, Cyclopentadienyl Ring Borylation, and Boronium Cation Generation

Abstract

The reaction of a borane-appended analogue of 1,1′-bis(phosphino)ferrocene, [Fe(η5-C5H4PPh2)(η5-C5H4PtBu{(o-BPh2)C6H4})] (FcPPB), with [W(CO)6] under photochemical conditions lead to [W(CO)4(FcPPB*)] (1) (FcPPB* = [Fe(η5-C5H4PPh2){η5-C5H3P(tBu)C6H4-o-BPh}]), in which the borane has added to a cyclopentadienyl ring of the ligand backbone and benzene has been eliminated. Formation of 1 did not occur under thermal conditions, and benzene solutions of the free FcPPB ligand were unreactive under both photochemical and refluxing conditions. Boranes of greater Lewis acidity than the pendent triarylborane of FcPPB were introduced to free FcPPB in an effort to promote intramolecular electrophilic borylation of the ferrocene backbone by eliminating the borane–phosphine interaction in FcPPB. However, addition of B(C6F5)3 provided [Fe(η5-C5H4PPh2{B(C6F5)3})(η5-C5H4PtBu{C6H4(BPh2)-o})], FcPPB{B(C6F5)3} (2), in which B(C6F5)3 forms an adduct with the −PPh2 group, and the intramolecular phosphine–borane interaction pres...