New insight into the reactions of organoplatinum(II) complexes with diorganotin dichloride and diisothiocyanate: Oxidative addition, reductive elimination and α-elimination

Abstract

The reaction of electron rich [PtMe2(NN)] with SnMe2Cl2 in a 1:3/Pt:Sn mole ratio resulted in formation of Pt(IV) complexes [PtMe2(SnMe2Cl)Cl(NN)] {NN = 4,4′-Me2bpy (4,4′-dimethyl-2,2′-bipyridine) (7); 5,5′-Me2bpy (5,5′-dimethyl-2,2′-bipyridine) (8); bphen (4,7-diphenyl-1,10-phenanthroline) (9)}. NMR data show that the resulting complexes exist as the sole product corresponding to that of trans oxidative addition of SnMe2Cl2. The yellow polymorph of complex [PtCl2(5,5′-Me2bpy)] (10) was characterized by X-ray crystallography from the reaction of [PtMe2(5,5′-Me2bpy)] and excess of SnMe2Cl2 due to the reductive elimination of 8. On the other hand, the reaction of [PtMe2(NN)] with SnEt2Cl2 in a 1:3/Pt:Sn mole ratio resulted in formation of new complexes [PtMe2(SnEt2Cl)Cl(4,4′-Me2bpy)] (11), [PtMe2(SnEt2Cl)Cl(5,5′-Me2bpy)].SnEt2Cl2 (12) and [PtMe2(SnEt2Cl)Cl(bu2bpy)].SnEt2Cl2 (bu2bpy = 4,4′-di-tert-butyl-2,2′-dipyridine) (13). NMR data indicate that the PtSnEt2Cl bond is weaker than the PtSnMe2Cl bond. The X-ray crystal structure of 13 reveals that organoplatinum(IV) complex acts as a donor to the SnEt2Cl2 to form an adduct in a distorted trigonal bipyramid with the axial Cl⋯SnCl and equatorial SnEt2Cl units. Moreover, the X-ray crystal structure of the new yellow form of [PtClMe(4,4′-Me2bpy)] (14), which has been formed by the crystallization of a mixture of [PtMe2(4,4′-Me2bpy)] and excess of SnEt2Cl2, is described. The reaction of dimethylplatinum(II) complexes with dimethyltin diisothiocanate are reported for the first time which occur via Sn-NCS bond cleavage to afford the organoplatinum(IV) complexes [PtMe2(SnMe2NCS)(SCN)(NN)] {NN = bpy (17); phen (18); 5,5′-Me2bpy (19); bu2bpy (20); bphen (21)}. The crystal structures of the novel thiocyanatoplatinum(IV) complexes [PtMe2(SCN)2(bpy)] (22) and [PtMe2(SCN)2(5,5′-Me2bpy)]. H2O (23) are discussed which have been obtained due to the α-elimination of SnMe2. The crystal structures of 22–23 show that platinum adopts a slightly distorted octahedral geometry with trans- Pt(SCN)2 configuration in which SCN is bonded through sulfur atom while the nitrogen atom is coordinated to tin. NMR data indicate that the products dissociate via α-elimination of SnMe2 or reductive elimination of organotin(IV) compound and the stability of the organoplatinum(IV) compounds varies according to the trends [PtMe2(SnMe2Cl)Cl(NN)]>[PtMe2(SnMe2NCS)(SCN)(NN)]>[PtMe2(SnEt2Cl)Cl(NN)].