Polyhedron Vol. 1 I, No. 2, pp. 243-250, 1992 Printed in Great Britain 0277-5387/92 SS.oO+ .OO 0 1992 Pergamon Press plc zyxwvutsr PALLADIUM(H) COMPLEXES OF 2-(2,5- DIMETHOXYPHENYL)~l,lO-PHENANTHROLINE (phenhqM%) AND 2-(2,5-HYDROQUINONYL)-l,lO- PHENANTHROLINE (phenhqH,).* THE X-RAY CRYSTAL STRUCTURE OF [PdCl(phenhqH)] l Hz0 - (CH,),SO ROBERT A. BERTHON, STEPHEN B. COLBRANf and DONALD C. CRAIG Department of Inorganic and Nuclear Chemistry, University of New South Wales, P.O. Box 1, Kensington, Australia 2033 (Received 26 April 1991; accepted 23 August 1991) Abstract-The reactions of pdCl,]- or [PdCl,(PhCN)J with 2-(2,5_dimethoxyphenyl)- l,lO-phenanthroline (phenhqMe,) are solvent dependent: in dichloromethane the complex [PdC12(phenhqMe2)] (1) was obtained whereas further reaction occurred in methanol pro- ducing [PdCl(phenhqMe2)] (2) in which the cyclometallated ligand acts as a C,N,N-donor. Reaction of [PdCl,(MeCN),] with phenhqMe2 in acetonitrile at reflux followed a different course and yielded [PdCl(phenhqMe)] (3), in which the cyclometallated ligand acts as a O,N,N-donor. The O,N,N-chelated hydroquinonyl complex [PdBr(phenhqH)] (4) was for- med from 1 by treatment with BBr3. Higher yields of [PdCl(phenhqH)] (5), the chloro analogue of 4, were obtained in direct preparations starting with the free ligand 2,5- hydroquinonyl-l,lO-phenanthroline (phenhqH,). An equilibrium is established between 5 and the C,N,N-cyclometallated product [PdCl(phenhqH2)] (6) in dimethylformamide heated at reflux. The X-ray crystal structure of 5 - Hz0 * (CH3)2SO, which exhibits cen- trosymmetric twin-stranded chains of n-stacked dimers of 5 held together by hydrogen bonding to bridging water molecules, is described. Parabenzoquinones, and their parasemiquinone and parahydroquinone redox derivatives, are important in chemical and biochemical redox reac- tions. ’ There is an extensive coordination chemistry characterized for orthoquinones that largely arises from the chelating ability of the orthoquinonyl ligand in all three available oxidation states (i.e. as the quinone, semiquinone or catecholate).2,3 In contrast the information available for transition metal complexes of a-parabenzoquinones is rela- tively sparse.4 The reason may be directly correlated to the absence of chelate coordination sites and the low basicity of benzoquinones.5 In order to * Symbols: phen = 1,lO-phenanthrolinyl; hq = para- hydroquinonyl; q = parabenzoquinonyl [e.g. hqH, = 2,5-hydroquinonyl and hqMe, = 2,5-hydroquinonyldi- methylether (i.e. 2,5-dimethoxyphenyl)]. t Author to whom correspondence should be addressed. overcome these difficulties, we have prepared chel- ating-parabenzoquinonyl ligands, or their para- semiquinone and parahydroquinone redox equi- valents, by ortho-functionalization of parabenzo- quinone with more usual ligand groups such as phosphines,6 cyclopentadienyls7 and phenanthro- lines. ’ In this paper we report the preparation of palladium(I1) complexes derived from the pre- cursor ligands to 2-(2,5-benzoquinone)- 1,l O-phen- anthroline (phenq), namely the ligands 2-(2,5-dime- thoxyphenyl)- zyxwvutsrqponmlkjihgfedcbaZYXWVU 1, zyxwvutsrqponmlkjihgfedcbaZYXW 1 0-phenanthroline (phenhqMe2) and 2-(2,5-hydroquinonyl)-l,lO-phenanthroline (phenhqH,) and demonstrate that cyclometallation reactions of the complexes of both ligands lead to C,N,N- as well as O,N,N-cyclometallated products. We have previously reported the preparation of all three ligands along with examples of their ruthen- ium(I1) complexes. ’ 243