Reactivity of Boryl Complexes: Synthesis and Structure of New Neutral and Cationic Platinum Boryls and Borylenes

A reactivity study on a series of platinum boryl complexes
was
performed. The first stable base adducts of cationic haloboryl complexes
of the form trans-[Pt­{B­(Br)­(NMe2)}­(NCMe)­(PCy3)2]+ were isolated and fully characterized.
The dianion [B12Cl12]2– was
introduced as a weakly coordinating anion to complex chemistry forming
a A2X salt. Through the reaction of trans-[Pt­{B­(Br)­(tBu)}­Br­(PCy3)2]
with BBr2tBu, the first highly soluble
dinuclear platinum boryl complex, [Pt­{B­(Br)­(tBu)}­(μ-Br)­(PCy3)]2, could be synthesized with concomitant buildup
of the corresponding phosphine-borane adduct. In contrast to this
observation, reaction of trans-[Pt­{B­(Br)­(Mes)}­Br­(PCy3)2] with BBr3 leads to the formation
of the cationic borylene complex trans-[Pt­(BMes)­Br­(PCy3)2]+ by abstraction of the bromo ligand
bound mutually trans to the boryl ligand in the precursor
and concomitant buildup of [BBr4]−. Reaction
of [Pt­(PCy3)2] with BCl3 and subsequent
abstraction of the platinum-bound chloro ligand enabled the structural
characterization of trans-[Pt­(BCl2)­(PCy3)2]+, which is isoelectronic with the
metal-only Lewis pair trans-[Pt­(BeCl2)­(PCy3)2]. The bonding situation in both systems was
investigated in detail using quantum chemical calculations. A T-shaped
cationic complex, trans-[Pt­{B­(Br)­(Fc)}­(PiPr3)2]+, and its precursor trans-[Pt­{B­(Br)­(Fc)}­Br­(PiPr3)2], both with reduced steric bulk at the phosphine ligands
compared with their PCy3 derivatives, were fully characterized.