Investigation of Steric Factors Involved in the Formation of Terminal Cationic Platinum Arylborylene Complexes

The abstraction of halido ligands from Pt^II diphosphine boryl complexes has previously been shown to yield one of two isomeric products: either T-shaped cationic boryl complexes or square-planar cationic borylene complexes. However, the latter product has only been observed in one case, that of a mesitylboryl ligand, which converts to a mesitylborylene ligand upon halido abstraction. In an effort to test the efficacy of this reaction in the presence of different steric and electronic influences, Pt^II diphosphine boryl complexes were prepared with both 4-<i>tert</i>-butylphenyl and duryl (2,3,5,6-tetramethylphenyl) groups. Halide abstraction from the 4-<i>tert</i>-butylphenyl complex resulted in a T-shaped cationic boryl complex. However, subjecting the duryl-substituted complexes to the same conditions exclusively results in terminal cationic borylene complexes, a difference we attribute to the greater steric hindrance between the boron-bound bromide and the methyl groups at the 2- and 6-positions of the duryl group. This outcome indicates that the electronic effect of alkylation at the <i>para</i> position is not a factor for this borylene formation reaction