Synthesis, characterization and reactivity of carbohydrate platinum(iv) complexes with thioglycoside ligands

摘要

Reactions of fac-[PtMe_3(4,4′-R_2bpy)(Me _2CO)][BF_4] (R = H, 1a; ~tBu, 1b) and fac-[PtMe_3(OAc-κ~2O,O′)(Me_2CO)] (2), respectively, with thioglycosides containing thioethyl (ch-SEt) and thioimidate (ch-STaz, Taz = thiazoline-2-yl) anomeric groups led to the formation of the carbohydrate platinum(iv) complexes fac-[PtMe_3(4,4′-R _2bpy)(ch*)][BF_4] (ch* = ch-SEt, 8-14; ch-STaz, 15-23) and fac-[PtMe_3(OAc-κ~2O,O′)(ch*)] (ch* = ch-SEt, 24-28; ch-STaz = 29-35), respectively. NMR (~1H, ~(13)C, ~(195)Pt) spectroscopic investigations and a single-crystal X-ray diffraction analysis of 19 (ch-STaz = 2-thiazolinyl 2,3,4,6-tetra-O-benzoyl-1-thio-β-d-galactopyranose) revealed the S coordination of the ch-SEt glycosides and the N coordination of the ch-STaz glycosides. Furthermore, X-ray structure analyses of the two decomposition products fac-[PtMe_3(bpy)(STazH-κS)][BF_4] (21a) and 1,6-anhydro-2,3,4-tri-O-benzoyl-β-d-glucopyranose (23a), where a cleavage of the anomeric C-S bond had occurred in both cases, gave rise to the assumption that this decomposition was mediated due to coordination of the thioglycosides to the high electrophilic platinum(iv) atom, in non-strictly dried solutions. Reactions of fac-[PtMe_3(Me_2CO)_3][BF _4] (3) with ch-SEt as well as with ch-SPT and ch-Sbpy thioglycosides (PT = 4-(pyridine-2-yl)-thiazole-2-yl; bpy = 2,2′-bipyridine-6-yl), having N,S and N,N heteroaryl anomeric groups, respectively, led to the formation of platinum(iv) complexes of the type fac-[PtMe_3(ch*)][BF _4] (ch* = ch-SEt, 36-40, ch-SPT 42-44, ch-Sbpy 45, 46). The thioglycosides were found to be coordinated in a tridentate κS, κ~2O,O′, κS,κN,κO and κS,κ~2N,N′ coordination mode, respectively. Analogous reactions with ch-STaz ligands succeeded for 2-thiazolinyl 2,3,4-tri-O-benzyl-6-O-(2,2′-bipyridine-6-yl)-1-thio-β-d- glucopyranoside (5h) resulting in fac-[PtMe_3(ch-STaz)][BF _4] (41, ch-STaz = 5h), having a κ~3N,N′, N′′coordinated thioglycoside ligand.