Synthetic and Structural Studies of Binuclear Organopalladium(II) Complexes Including a Bis(pyridin-2-yl)phenylmethyl Complex With Four- and Eight-Membered Palladocycle Rings, trans(N,N)-(Pd(μ-Py₂PhC-N,N',C')Cl)₂.½CH₂Cl₂.½Me₂CO

Abstract

The byridin-2-yl) phenylchloromethanes PyPh₂CCl and Py₂PhCCl undergo oxidative addition reactions with bis ( dibenzylideneacetone )palladium(0) to form {Pd(PyPh₂C) Cl }₂ (1) and {Pd(Py₂PhC)C}₂.½2CH₂Cl₂.½Me₂CO (2), respectively. n.m.r , studies of (1) in CDCl₃ indicate presence of an equilibrium between two isomers, involving the ligand (pyridin-2-yl ) diphenylmethyl in η³-coordination, {Pd(η³-PyPh₂C)(μ- Cl )}₂. Complex (2) has two bis (pyridin-2-yl) phenylmethyl groups present as bridging N,C′- ligands , with the groups also N,C- bidentate to each palladium, to form a binuclear compex containing four- and eight- membered palladocycles:

PdC(CN)CNPdC(CN)CN

Both palladium(II) centres in (2) have square-planar 'trans-PdCN₂Cl' coordination, so that (2) may be represented as trans(N,N)-{Pd(μ- Py₂PhC-N,N′, C′) Cl }₂.½CH₂Cl₂.½Me₂CO. A complex similar to (2), trans(N,N)-{Pd(μ- PyPhCH -N,C?)( γmpy ) Cl }₂.CH₂Cl₂ (3), forms on reaction of the lithium derivative of 2-benzylpyridine, Li( PyPhCH ), with dichlorobis (4-methylpyridine)palladium(II); (3) reacts with excess 2-benzylpyridine with displacement of γmpy to form trans(N,N)-{Pd(μ- PyPhCH -N,C?)(PyPhCH₂) Cl }₂ (4). In developing an alternative isolation procedure for (3), involving column chromatography with 4% ethyl acetate in chloroform, the coordination complex trans- bis{1-phenyl-1-(pyridin-2-yl)prop-1-en-2-olato-O,N}palladium(II), Pd{( PyPhC )C(Me)O}₂ (5), was isolated in low yield. X-Ray structural studies of (2)-(5) have been completed, with all four complexes crystallizing in the monoclinic system; (2): space group P2₁/c, a 9.649(6), b 21.116(9), c 18.627(7)Ǻ,β 111.42(4)°, Z 4; (3): P2₁/c, a 13.967(2), b 13.996(3), c 18.886(2)Ǻ, β 98.74(1)°, Z 4; (4): P2₁/n, a 14.274(9), b 14.584(14), c 20.97(2)Ǻ, β 109.18(5)°, Z 4; (5): P21/c, a 15.184(3), b 7.887(6), c 19.240(2)Ǻ, β 97.51(1)°, Z 4.