Experimental, structural, and theoretical studies of diplatinum complexes containing bridging phenylethenylidene ligands including the excited-state chemistry and photophysics of photochemically generated species

Article abstract of DOI:10.1021/om00112a025

The results of a comprehensive investigation of the chemistry of the diplatinum compound [Pt₂(μ-C=CHPh)(C≡CPh)(PEt₃)₄]BF ₄ (1) and related derivatives are presented. Complex 1 reacts with halides, NCS^-, and various RS^- nucleophiles to give the neutral compounds [Pt₂(μ-C=CHPh) (C≡CPh) (PEt₃)₃X] with loss of one PEt₃ ligand. These Pt₂X complexes react with acid and X^- nucleophile to give the neutral compounds [Pt₂(μ-C=CHPh) (PEt₃)₃X₂] upon loss of phenylacetylene. The X-ray structures of the Pt₂Cl, Pt₂I, and Pt₂Br₂ complexes have been determined. [Pt₂(μ-C=CHPh)(C≡CPh)(PEt₃)₃Cl]: monoclinic; P2₁/c; Z = 4; a = 11.685 (1) A?, b = 20.810 (7) A?, c = 19.172 (4) A? β = 123.96 (1)°. [Pt₂(μ-C=CHPh)-(C≡CPh)(PEt₃)₃I]: orthorhombic; Pbca; Z = 8; a = 18.004 (3) A?, b = 22.805 (4) A?, c = 19.328 (4) A?. [Pt₂(μ-C=CHPh)(PEt₃)₃Br₂]: monoclinic; Cc; Z = 8; a = 10.359 (1) A?, b = 33.054 (9) A?, c = 19.855 (5) A? β= 93.40 (2)°. SC-MEH-MO calculations of the electronic structure of compound 1 indicate a large negative charge on each of the Pt atoms which is reminiscent of the results reported earlier from similar calculations on the anion Pt₂(P₂O₅H₂)₄ ^4-. Similarities between the photochemistry of the complexes reported herein and that known for Pt₂(P₂O₅H₂)₄^4- are presented. Complex 1 reacts with MeI under photolysis to give Pt₂I and Pt₂I₂, and it reacts as a catalyst under photolysis to produce acetone and molecular hydrogen from 2-propanol. The complex Pt₂Cl emits a red-orange luminescence at 696 nm in a 4:1 ethanol/methanol matrix at 77 K upon excitation at 410 nm. This luminescent state has an average lifetime of 1.7 μs and is attained with an "optical" quantum yield of 0.010 (2).