Synthesis and characterization of trimethylplatinum(IV) complexes with sugar alcohol and amino sugar alcohol ligands—platinum-assisted formation of O-isopropylidene protecting groups and Schiff bases

Abstract

[PtMe 3(Me 2CO) 3]BF 4 ( 1) reacts in acetone with d-mannitol ( L1) in a 2:1 stoichiometry yielding platinum(IV) complexes of the type [(PtMe 3) 2L](BF 4) 2 with d-mannitol ( 2, L= L1) and 3,4- O-isopropylidene- d-mannitol ( 3, L= L1′), respectively, as ligand. Reaction of 1 with 1-amino-1-deoxy- d-glucitol (glucamine) ( L2) in acetone affords platinum-assisted formation of a Schiff base forming complex [PtMe 3( L2′)]BF 4 ( 4, L2′= N-isopropylidene-glucamine). Dissolving of complex 4 in water results in hydrolysis of the Schiff base yielding [PtMe 3( L2)]BF 4 ( 5). Reversibility of this reaction was shown by redissolving complex 5 in acetone resulting in the formation of the N-isopropylidene-glucamine complex 4. 1-( N-Methylamino)-1-deoxy- d-glucitol ( N-methylglucamine) ( L3) was found to react with [PtMe 3(Me 2CO) 3]BF 4 ( 1) yielding complex [PtMe 3( L3)]BF 4 ( 6). Formation of O-isopropylidene group in complex 3 as well as Schiff base formation and cleavage in complexes 4 and 5 are platinum-assisted. All complexes were isolated as colorless powdery substances. Coordination modes of carbohydrate ligands were revealed by 1H, 13C, and 195Pt NMR spectroscopic investigations. In the dinuclear complexes 2 and 3, the two PtMe 3 units are bound equivalent to d-mannitol ( L1) and 3,4- O-isopropylidene- d-mannitol ( L1′), respectively. Quantum chemical calculations on DFT level of the theory indicate a facial tridentately bound mannitol ligand (coordination mode: μ-κ 3 O 1, O 2, O 4:κ 3 O 3, O 5, O 6) in complex 2 and a bidentately bound 3,4- O-isopropylidene- d-mannitol ligand (coordination mode: μ-κ 2 O 1, O 2:κ 2 O 5, O 6) in complex 3. In complexes 4– 6, N-functionalized ligands are coordinated to platinum through N and the neighbored hydroxyl group and, likely, also through hydroxyl group at C4.