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†
The tris(mercaptoimidazolyl)hydroborato complexes, [κ3-S2H-TmBut]Na(THF)3 and [κ3-S2H-TmAd]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 = But, 1-Ad). X-ray diffraction studies indicate that the compounds are monomeric and that the [TmR] 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 κx-Sx and κx+1-SxH coordination modes to be identified. Furthermore, the various κx-Sx and κx+1-SxH coordination modes have also been analyzed with respect to the conformations of the [TmR] ligands, which differ by rotation of the imidazolethione moieties about the B–N bond.