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Unsymmetrical di(phosphine) ligands (dpp)2Rop (1a, b = bis(diphenylphosphino)-2-alkyl-3-oxapropane (alkyl = methyl and ethyl)) and (dpp)2oCy (1c = trans-2-diphenylphosphinocyclohexyl diphenylphosphinite) and their Pt(II) dichloride complexes, PtCl2((dpp)2mop) (2a), PtCl2((dpp)2eop) (2b) and PtCl2((dpp)2oCy) (2c), have been synthesized and characterized 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 conformation, whereas in 2c, the chelate ring conformation is a skewed boat. Initial reaction of sodium borohydride with 2a, b, c yields the monohydride monochloride complexes PtHCl((dpp)2mop) (5a), PtHCl((dpp)2eop) (5b) and PtHCl((dpp)2oCy) (5c). At longer reaction times, fluxional dimeric species are obtained, [PtH((dpp)2mop)]2 (4a), [PtH((dpp)2eop)]2 (4b) and [PtH((dpp)2oCy)]2 (4c),and in the case of 4c two different isomers exist. The dihydride complexes PtH2((dpp)2mop) (3a), PtH2((dpp)2eop) (3b) and PtH2((dpp)2oCy) (3c), are prepared by further reaction of NaBH4 and 2. Hydrogen cycling is facile in the dihydride complexes 3a, b, c, and oxidative addition of H2 proceeds in a pairwise manner as determined by the observation of parahydrogen induced polarization (PHIP) in the 1H NMR spectra. The reductive elimination of H2 is also shown to be concerted by reaction of dihydride complexes with D2. Crystal data: 2b (C30H32Cl6OP2Pt), monoclinic, space group P21/c (No. 14), a = 13.7040(1), b = 11.3430(7), c = 21.3880(9) A, β = 97.923(9)°, V = 3292.9(2) A3 and Z = 4; 2c (C30H30Cl2OP2Pt), monoclinic, space group P21 (No. 4), a = 11.7360(2), b = 8.4311(2), c = 14.2789(2) A, β = 101.290(1)°, V = 1385.52(4) A3 and Z = 2. |
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