m, 417&W7;; N, 57673-31-1; IV', 66973-03-3; v, 76721-83-0; V-d2, 91897-7&0; V-d3, 91880-34-1; [ (CsHs)4As]+[Ru3(CO),(r3-C2-t-Bu)]-, 76741-75-8; CF,COOD, 599-00-8.Complexes tr~ns-Pt(PMe~)~ClR, where R = (1-methylcyclobuty1)methyl (mcbm, l), (adamanty1)methyl (adm, 81, 4-methylpentyl-l,l-d2 (9), and 4-methyl-4-pentenyl (lo), and also PtCl(dmpe)(mcbm) [dmpe = 1,2-bis(dimethylphosphino)ethane] (2) have been prepared. Pyrolysis of 1 or 2 at 140 "C yields 2-methyl-1,Cpentadiene (12) as the only organic product, and tran~-HPt(PMe~)~Cl (13) is isolated in high yield in the case of 1. Added PMe3 retards the pyrolysis of 1, leading to formation of [HPt(PMe3)3!C1 (14) and exhibiting kinetics consistent with initial PMe3 dissociation. Decomposition of 8 requires heating at 240 "C for hours. Pyrolysis of 9 at 140 "C forms 13 and 4-methyl-1-pentene-l,l-d2 with very little rearrangement of the deuterium label. Treatment of 1 with Ag+ in acetone at -80 "C forms [trans-Pt-(PMed2(mcbm)(acetone)]+ (15) that rearranges above -40 "C to (C~~-P~(PM~~)~[~,~,~-~-(CH~)~C(M~)= (16) and above -10 "C to a mixture of [Pt(PMe3)2(2-4-q-2-methylpentenyl)]+ (17a) and [Pt(PMe3)2(1-3-q-2-methylpentenyl)]+ (17b), which is isolated as the PF, salt. Reaction of 1 with Ag+ in CD2C12 at -80 "C leads within 30 min to direct formation of 16, representing an extremely mild C-C activation step. Reaction of 10 with Ag+ at -80 "C followed by warming to -20 "C also generates 16. In contrast, 8 and Ag+ from [Pt(PMe3)2(adm)(acetone)]+ which is isolable at ambient temperature. Mechanistic implications of these reactions are discussed.