Investigation of Steric Factors Involved in the Formation
of Terminal Cationic Platinum Arylborylene Complexes
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Abstract
The
abstraction of halido ligands from Pt<sup>II</sup> 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<sup>II</sup> 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