Generation of trans-spanning diphosphine ligands via alkene metathesis: Synthesis, structure, and dynamic behavior of a missing link in a series of square-planar platinum complexes
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Reaction of KPPh2 and Br(CH2)5CH{double bond, long}CH2 gives the phosphine PPh2(CH2)5CH{double bond, long}CH2 (89%), which is treated with the platinum tetrahydrothiophene complex [Pt(-Cl)(C6F5)(S(CH2CH2-)2)]2 to yield trans-(Cl)(C6F5)Pt(PPh2(CH2)5CH{double bond, long}CH2)2 (4b, 80%). Ring-closing alkene metathesis (Grubbs' catalyst) gives {A figure is presented} (5b, 84%), which features a trans-spanning diphosphine ligand. The Z/E C{double bond, long}C mixture is hydrogenated (1 atm, 10% Pd/C) to give {A figure is presented} (6b, 99%). The crystal structures of 4b and (Z)-5b are determined. In the former, both (CH2)5CH{double bond, long}CH2 moieties are directed on the same side of the platinum square plane. Low temperature 13C NMR spectra of 6b show two sets of signals for the diastereotopic PPh2 groups. These coalesce upon warming, which requires the passage of the chloride ligand through the macrocycle. Analysis by the complete bandwidth method gives H and S values of 6.0 0.4 kcal mol-1 and -13.9 2.6 eu. The 31P, 13C, and 2H CP/MAS NMR spectra of polycrystalline 6b and 6b-d2 are studied, and indicate appreciable conformational mobility of the methylene chain in the solid state. 2006 Elsevier B.V. All rights reserved.
