Flexible steric bulk of sugar wingtip substituents on bis(N-heterocyclic carbene) ligands of diplatinum complexes via chair–twist-boat conformational changes

Abstract

In the p-toluenethiolate-bridged diplatinum complex bearing ethylene-bridged bis(N-heterocyclic carbene) ligands, all four acetyl-protected glucopyranosyl wingtip substituents adopt the chair conformation, giving rise to an open structure around the Pt₂S₂ core that allows the complex to react with a Grignard reagent. In contrast, in the corresponding diplatinum complex with o-xylene-bridged bis(N-heterocyclic carbene) ligands, two of the four acetyl-protected glucopyranosyl groups adopt the twist-boat conformation to relieve the steric repulsion among the wingtip N-substituents, resulting in a covered structure around the Pt₂S₂ core that inhibits reaction with a Grignard reagent.