Platinum(II) complexes of some unsymmetrical diphosphenes

Abstract

Reaction of the unsymmetrical diphosphene Ar*P=PArF1 (Ar* = 2,4,6-tBu3C6H2, ArF = 2,4,6-(CF3)3C6H2) with the dimeric platinum(II) species trans-[Pt(PEt3)Cl(μ-Cl]2 led initially to the formation of two different monomeric Pt(II) complexes trans-[Pt(PEt3)Cl2(Ar*P=PArF)] 2 and trans-[Pt(PEt3)Cl2(ArFP=PAr*)] 3, where the underlined phosphorus atom coordinates to Pt. These were readily identifiable by 31P NMR solution-state spectroscopy, but attempts to separate them by column chromatography were unsuccessful. When the reaction was repeated on a larger scale, a third complex cis-[Pt(PEt3)Cl2(ArFP=PAr*)] 4 was detected in solution, with P-ArF bound to Pt. Calculations of energies and 31P NMR chemical shifts confirm that this species is expected to be the thermodynamically most stable monomeric reaction product. For comparison, we have also prepared the analogous Pt(II) complex trans-[Pt(PEt3)Cl2(Ar*P=PAr*)] 6 of the symmetrical diphosphene Ar*P=PAr* 5, and obtained its 31P NMR parameters in solution. The mixed diphosphene Ar′P=PArF7 (Ar′ = 2,6-(CF3)2C6H3) reacts with the same platinum(II) dimer to yield a single cis-complex 8. Calculations have enabled us to assign the 31P chemical shifts of this unsymmetrical diphosphene 7, and to show that the Ar′ group is coordinated to Pt in the unique product cis-[Pt(PEt3)Cl2(Ar′P=PArF)] 8.