observed in the resulting product mixture were [PtC12(dmpe)], cis-[PtC12(PPh3)2], and [Pt(dmpe)2]C12. No evidence for the cationic complex [PtCl(PPh,)(dmpe)]+ was obtained.Reaction of [PH)12(dmpe)l with PMePb2. (a) [PtCMdmpe)] (0.037 g, 0.088 mmol) was mixed with CDCI, in a 5-mm NMR tube. After the tube had been flushed with argon, PMePh, (16.3 pL, 0.088 mmol) was added. 3'P(1HJ NMR analysis of the resulting mixture indicated that the predominant platinum-containing species was [PtC1(PMePhz)(dmpe)]C1.(b) When [PtCl,(dmpe)] (0.032 g, 0.077 mmol) was reacted with PMePh, (28.8 pL, 0.16 mmol) in CDC13 in the same way as above, the 31P(1HJ NMR spectrum indicated that the predominant platinum-con-
Inorg. Chem. 1987, 26, 1524-1528 taining species in solution was [PtCI(PMePh,),]Cl. Dimethyl sulfoxide, Me2S0, is commonly used to dissolve cis-and trans-diamminedichloroplatinum(II), cis-and trans-DDP, prior to use in experiments comparing their biological activities. The solvolysis reactions of cis-and trans-DDP in Me2S0 have been investigated in this study. Me2S0 substitutes for a single chloride ligand in both cases to form c~s-[P~(NH,)~(MQSO)CI]CI (1-Cl) and tr~ns-[Pt(NH~)~(Me~S0)Cl]Cl (2-Cl). The half-lives of the cis and trans isomers in Me2S0 at 37 OC are 60 and 8 min, respectively, as determined by both optical and Is5Pt NMR spectroscopy. Kinetic studies gave activation parameters for cis-DDP solvolysis of AH* = 18.9 (1) kcal mol-' and AS* = -14.5 (2) eu (optical spectroscopy) and AH' = 19.8 (3) kcal mol-' and AS* = -1 1.6 (3) eu (IssPt NMR spectroscopy). Activation parameters for solvolysis of trans-DDP were AH' = 15.5 (1) kcal mol-' and AS* = -21.4 (2) eu (optical spectroscopy) and @ = 16.9 (3) kcal mol-' and AS* = -17.7 (4) eu (Is5Pt NMR spectroscopy). The mixed perchlorate/chloride salt of 2, trans-[Pt(NH3)2(Me2SO)Cl](C104)o,8Clo,z, has been crystallized and its structure determined by single-crystal X-ray diffraction methods. The compound crystallizes in the orthorhombic space group Pnma with a = 10.554 (3) A, b = 7.446 (1) A, c = 14.161 (2) A, V = 11 11.79 A), and Z = 4. The final RI value was 0.0395 for 799 observed reflections. The geometry of platinum is square planar, with Pt-S, Pt-N, and Pt-Cl distances of 2.204 (4), 2.1 1 (2) and 2.03
