Molecular structures of tris(2-mercapto-1-tert-butylimidazolyl)hydroborato and tris(2-mercapto-1-adamantylimidazolyl)hydroborato sodium complexes: analysis of [TmR] ligand coordination modes and conformations

Abstract

The tris(mercaptoimidazolyl)hydroborato complexes, [κ³-S₂H-Tm^But]Na(THF)₃ and [κ³-S₂H-Tm^Ad]Na(THF)₃, which feature t-butyl and adamantyl substituents, have been synthesized via the reactions of the respective 1-R-1,3-dihydro-2H-imidazole-2-thiones with NaBH₄ in THF (R = Bu^t, 1-Ad). X-ray diffraction studies indicate that the compounds are monomeric and that the [Tm^R] ligands coordinate to the metal in a κ³-S₂H manner via two of the sulfur donors and the hydrogen attached to boron, a combination that is unprecedented for sodium derivatives. Analysis of the tris(mercaptoimidazolyl)hydroborato compounds that are listed in the Cambridge Structural Database has allowed for the formulation of a set of criteria that enables κ^x-S_x and κ^x+1-S_xH coordination modes to be identified. Furthermore, the various κ^x-S_x and κ^x+1-S_xH coordination modes have also been analyzed with respect to the conformations of the [Tm^R] ligands, which differ by rotation of the imidazolethione moieties about the B–N bond.