Reaction of KPPh2 and Br(CH2)(5)CH=CH2 gives the phosphine PPh2(CH2)(5)CH=CH2 (89%), which is treated with the platinum tetrahydrothiophene complex [Pt(mu-Cl)(C6F5)(S(CH2CH2-)(2))](2) to yield trans-(Cl)(C6F5)Pt(PPh2 (CH2)(5) CH=CH2)(2) (4b, 80%). Ring-closing alkene metathesis (Grubbs' catalyst) gives trans-(Cl)(C6F5)Pt(PPh2)(CH2)(5)PPh2) (5b, 84%), which features a trans-spanning diphosphine ligand. The Z/E C=C mixture is hydrogenated (1 atm, 10% Pd/C) to give trans-(Cl)(C6F5)Pt(PPh2(CH2)(12)pph(2)) (6b, 99%). The crystal structures of 4b and (Z)-5b are determined. In the former, both (CH2)(5)CH=CH2 moieties are directed on the same side of the platinum square plane. Low temperature C-13 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 Delta H-double dagger and Delta S-double dagger values of 6.0 +/- 0.4 kcal mol(-1) and -13.9 +/- 2.6 eu. The (31)p, C-13, and H-2 CP/MAS NMR spectra of polycrystalline 6b and 6b-d(2) are studied, and indicate appreciable conformational mobility of the methylene chain in the solid state. (c) 2006 Elsevier B.V. All rights reserved.