Control of Olefin Hydroarylation Catalysis via a Sterically and Electronically Flexible Platinum(II) Catalyst Scaffold

PtII complexes supported by dipyridyl ligands have been
demonstrated to catalyze olefin hydroarylation. Herein, studies on
the influence of dipyridyl motif variation are reported. Increasing
the chelate ring size of dipyridyl-ligated PtII complexes
from five- to six-membered rings by replacing 4,4′-di-tert-butyl-2,2′-bipyridine with 2,2′-dipyridylmethane
has been shown to increase catalytic activity and longevity for catalytic
ethylene hydrophenylation. For 2,2′-dipyridyl ligands, the
presence of methyl groups in the 6/6′-positions of the pyridyl
rings reduces the extent of dialkylation to produce diethylbenzenes
but also increases the rate of catalyst decomposition. Substituting
the methylene spacer between the pyridyl rings of 2,2′-dipyridylmethane
with more electron-withdrawing groups also reduces catalytic efficiency.
The steric profile of PtII complexes with increased chelate
ring size or substituents in the 6/6′-positions of the pyridyl
rings provides a marked change in regioselectivity for ethylene hydroarylation
using ethylbenzene as well as the linear to branched selectivity for
the hydrophenylation of propylene.