Unique Fluxional Behavior. Synthesis, Structure, and Properties of Novel (Diamine)platinum(II) Complexes of 9-Fluorenylidene- and Benzhydrylidenemalonate Ligands

Abstract

New (diamine)platinum(II) complexes A₂PtX₂ (A₂ = trans-(±)-1,2-diaminocyclohexane (DACH), tetrahydro-4H-pyran-4,4-diylbis(methylamine)(THPDMA); X₂ = 9-fluorenylidenemalonate(FM), benzhydrylidenemalonate(BHM)) have been synthesized and characterized by means of multinuclear NMR spectroscopy and X-ray analysis. (DACH)Pt(FM) crystallizes in space group P2₁/c with eight formula units in a cell of dimensions a = 20.071(7) Å, b = 12.717(3) Å, c = 24.512(6) Å, β = 103.25(2)°, and V = 6090(3) Å.³ (DACH)Pt(BHM) crystallizes in space group P1̄ with four molecular units in a cell of dimensions a = 11.048(3) Å, b = 13.639(3) Å, c = 14.043(6) Å, α = 90.17(3)°, β = 91.31(4)°, γ = 89.98(3)°, and V = 2116(1) ų. The platinum atom in both complexes adopts a typical square planar arrangement with two nitrogen atoms in cis position. The 9-fluorenylidene and benzhydrylidene groups of the amine ligands chelated to platinum are strikingly bent up by 88.8(3) and 80.8(2)°, respectively, from the platinum square plane in the solid state. Variable temperature ¹H NMR spectra of the title complexes in dimethyl sulfoxide solution reveals that the amine proton resonances are sensitive to the fluxional motion of the remote arylidene groups, and suggests that interconversion occurs between two “bent-up” and “bent-down” forms. The prominent difference between the FM and BHM complexes is observed in solution, due to the presence or absence of the angle constraint of the anionic coligands.