Platinum thiosemicarbazide and thiourea complexes: the crystal structure of [PtCl(dppe){SC(NHMe)NHNMe2-S}](PF6) and the influence of intramolecular hydrogen bonding on ligand co-ordination mode

The reaction of [PtCl2(dppe)] [dppe=1,2-bis(diphenylphosphino)ethane] with two equivalents of the thioureas NHRC(S)NHR (R=H, Me, Et) in the presence o f NH4PF6 led to substitution of both chlorides and formation of the complex es [Pt(dppe){SC(NHR)(2)}(2)](PF6)(2) (1a, R=H; 1b, R=Me; 1c, R=Et). In cont rast, the reaction of [PtCl2(dppe)] with one equivalent of the potentially bidentate thiosemicarbazides NHRC(S)NHNR: (R=Me, R'=H; R=Et, R'=H; R=Ph, R' =H; R=Me, R'=Me) in the presence of NH,PF, led to substitution of only one chloride and formation of the complexes [PtCl(dppe){SC(NHR)NHNR2'-S}](PF6) (2a, R=Me, R'=H; 2b, R=Et, R'=H; 2c, R=Ph, R'=H; 2d, R=Me, R'=Me). An X-ray analysis of complex 2d revealed that an intramolecular N-H ... Cl hydrogen bond [N(2)... Cl(1)=3.29(2) Angstrom] helps to stabilise the monodentate c o-ordination mode. The chloride ligand can be abstracted from complex 2d by treatment with TlPF6, and this reaction led to formation of [Pt(dppe){SC(N HMe)NHNMe2-S,N}](PF6)(2) 3d. Reaction of [PtCl2(dppe)] with unsubstituted t hiosemicarbazide NH2CCS)NHNH2 in the presence of NH4PF6 resulted in a mixtu re of products containing mono- and bidentate co-ordinated ligands, [PtCl(d ppe){SC(NH2)NHNH2-S}](PF6) 2e and [Pt(dppe){SC(NH2)NHNH2- S,N}](PF6)(2) 3e. [PtCl2(dppe)] also reacts with two equivalents of NHMeC(S)NHNMe2 in the pr esence of NH4PF6 to yield [Pt(dppe){SC(NHMe)NHNMe2-S}(2)](PF6)(2) 1d, in wh ich the thiosemicarbazide is acting as an S-donor, directly analogous to th e thiourea ligands in complexes 1a-c. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.