4-Chloro-5-methyl-3-diphenylphosphino-1-phenyl-1,2,3,6- tetrahydrophosphinine as a bidentate P-ligand in a cis chelate Pt(II) complex Gyo ¨ rgy Keglevich a, * , Melinda Sipos a , De ´nes Szieberth b , Gyo ¨rgy Pet } ocz c , La ´szlo ´ Kolla ´r c a Department of Organic Chemical Technology, Budapest University of Technology and Economics, 1521 Budapest, Hungary b Department of Inorganic Chemistry, Budapest University of Technology and Economics, 1521 Budapest, Hungary c Department of Inorganic Chemistry, University of Pe ´cs and Research Group for Chemical Sensors of the Hungarian Academy of Sciences, 7624 Pe ´ cs, Hungary Received 17 March 2004; accepted 23 June 2004 Available online 20 August 2004 Abstract Double deoxygenation of a 3-phosphinoxido-1,2,3,6-tetrahydrophosphine oxide (2) led to bisphosphine 3–2 with an inverted ring P atom. The reaction of bidentate P-ligand 3–2 with dichlorodibenzonitrilo platinum(II) yielded the mixture of a novel cis chelate complex (7 = PtCl 2 (3–2)) and a cis bis(3-diphenylphosphino-1,2,3,6-tetrahydrophosphininyl) complex (8 = PtCl 2 (g 1 -5) 2 ) containing two units of monodentate P-ligand 5. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Phosphorus heterocycles; Phosphines; Theoretical studies; Platinum complexes; Chelation 1. Introduction The phosphines are important ligands in transition metal complexes that can be catalysts in a great variety of homogeneous catalytic reactions among them hydro- genation and hydroformylation [1]. Especially the chiral homo- and heterobidentate P-ligands, such as BINAP, DIOP, DIPAMP and BINAPHOS are of practical inter- est [2]. In this paper, the preparation and the coordina- tion properties of a novel bidentate P-ligand containing one of the phosphine moieties in an unsaturated six- membered hetero ring, while the other one as an exocy- clic diphenylphosphino substituent in position 3 is described. The parent bis(phosphine oxide), 3-diphenylphos- phinoxide-1-phenyl-1,2,3,6-tetrahydrophosphinine oxide (2) was obtained by the diastereoselective Michael addi- tion of diphenylphosphine oxide at the a,b-double bond of 1,2-dihydrophosphinine oxide (1) [3], as it was described (Scheme 1) [4]. The preferred conformer, a twist-boat containing the Ph 2 P(O) moiety and the oxygen atom of the ring P‚O in the trans disposition (2*) was established by DFT cal- culations. A novel intramolecular H-bonding between the oxygen atom of the Ph 2 P(O) moiety and the suitable hydrogen atom of the C(6)H 2 unit was found to stabilise the twist-boat form [5]. The bis(phosphine oxide) (2) was deoxygenated by a standard procedure applying trichlorosilane–pyridine in boiling benzene [6] to give a diphosphine (3). Accord- ing to DFT ab initio calculations [7], the isomer with in- verted P 1 -atom (3–2) containing the Ph 2 P group and the 0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2004.06.062 * Corresponding author. Tel.: +36 1 463 1111/58 53; fax: +36 1 463 3648. E-mail address: keglevich@oct.bme.hu (G. Keglevich). Journal of Organometallic Chemistry 689 (2004) 3158–3162 www.elsevier.com/locate/jorganchem