Synthetic and Structural Studies of Binuclear Organopalladium(II) Complexes Including a Bis(pyridin-2-y1)phenylmethyl Complex with Four- and Eight-Membered Palladocycle Rings, trans(N,N)-{(Pd(mu-Py2PhC-N,N',C')Cl}2.1/2CH2Cl2.1/2Me2CO

Abstract

The (pyridin-2-y1)phenylchloromethanes PyPh2CCl and Py2PhCCl undergo oxidative addition reactions with bis(dibenzylideneacetone)palladium(0) to form {Pd(PyPh2C)C1}2 (1) and {Pd(Py2PhC)C1}2.1/2CH2C12.1/2Me2CO (2), respectively. N.m.r, studies of (1) in CDC13 indicate presence of an equilibrium between two isomers, involving the ligand (pyridin-2-y1)diphenylmethyl in eta3-coordination, {Pd(eta3-PyPh2C)(mu-Cl)}2. Complex (2) has two bis(pyridin-2-y1)phenylmethyl groups present as bridging N,C'-ligands, with the groups also N,C-bidentate to each palladium, to form a binuclear complex containing four- and eight-membered palladocycles. Both palladium(II) centres in (2) have square-planar 'trans-PdCN2C1' coordination, so that (2) may be represented as trans(N,N)-{Pd(mu-Py2PhC-N,N',C')Cl)}2.1/2CH2C12.1/2Me2C0. A complex similar to (2), trans(N,N)-{(Pd(mu-PyPhCH-N,C')(gamma-mpy)Cl}2.CH2C12 (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 gamma-mpy to form trans(N,N)-{Pd(mu-PyPhCH-N,C')(PyPhCH2)C1}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-y1)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.