HYDRIDE COMPLEXES OF PLATINUM(II) CONTAINING UNSYMMETRICAL DI(PHOSPHINE) LIGANDS - SYNTHESIS, CHARACTERIZATION AND EVIDENCE FOR PAIRWISE ADDITION OF HYDROGEN BASED ON PARAHYDROGEN INDUCED POLARIZATION

Unsymmetrical di(phosphine) ligands (dpp)(2)Rop (1a, b = bis(diphenylp hosphino)-2-alkyl-3-oxapropane (alkyl = methyl and ethyl)) and (dpp)(2 )oCy (1c=trans-2-diphenylphosphinocyclohexyl diphenylphosphinite) and their Pt(II) dichloride complexes, PtCl2((dpp)(2)mop) (2a), PtCl2((dpp )(2)eop) (2b) and PtCl2((dpp)(2)oCy) (2c), have been synthesized and c haracterized by NMR spectroscopy. The crystal structures of 2b and 2c show that the geometry about the platinum centers is square planar. In 2b, the metal and di(phosphine) ligand chelate ring are in a chair co nformation, whereas in 2c, the chelate ring conformation is a skewed b oat. Initial reaction of sodium borohydride with 2a, b, c yields the m onohydride monochloride complexes PtHCl((dpp)(2)mop) (5a), PtHCl((dpp) (2)eop) (5b) and PtHCl((dpp)(2)oCy) (5c). At longer reaction times, fl uxional dimeric species are obtained, [PtH((dpp)(2)mop)](2) (4a), [PtH ((dpp)(2)eop)](2) (4b) and [PtH((dpp)(2)oCy)](2) (4c), and in the case of 4c two different isomers exist. The dihydride complexes PtH2((dpp) (2)mop) (3a), PtH2((dpp)(2)eop) (3b) and PtH2((dpp)(2)oCy) (3c), are p repared by further reaction of NaBH4 and 2. Hydrogen cycling is facile in the dihydride complexes 3a, b, c, and oxidative addition of H-2 pr oceeds in a pairwise manner as determined by the observation of parahy drogen induced polarization (PHIP) in the H-1 NMR spectra. The reducti ve elimination of H-2 is also shown to be concerted by reaction of dih ydride complexes with D-2. Crystal data: 2b (C30H32Cl6OP2Pt), monoclin ic, space group P2(1)/c (No. 14), a=13.7040(1), b=11.3430(7), c=21.388 0(9) Angstrom, beta=97.923(9)degrees, V=3292.9(2) Angstrom(3) and Z=4; 2c (C30H30Cl2OP2Pt), monoclinic, space group P2(1)(No. 4), a=11.7360( 2), b=8.4311(2), c=14.2789(2) Angstrom, beta=101.290(1)degrees, V=1385 .52(4) Angstrom(3) and Z=2. (C) 1998 Elsevier Science S.A.