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

The abstraction of halido ligands from PtII 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, PtII diphosphine boryl complexes were prepared with both 4-tert-butylphenyl and duryl (2,3,5,6-tetramethylphenyl) groups. Halide abstraction from the 4-tert-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 para position is not a factor for this borylene formation reaction.