Flexible Steric Bulk of Sugar Wingtip Substituents on Bis(n-Heterocyclic Carbene) Ligands of Diplatinum Complexes Via Chair-Twist-boat Conformational Changes.

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.