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.