Thionitrosyl Complexes of Technetium and Rhenium with Sterically Encumbered <i>m</i>-Terphenyl Isocyanides─Steric Bulk Matters

Low-valent thionitrosyl complexes of technetium and rhenium with the bulky isocyanides CNAr^Tripp2, CNAr^Dipp2, and CNAr^Mes2 (Tripp = 2,4,6-triisopropylphenyl, Dipp = 2,6-diisopropylphenyl, Mes = 2,4,6-trimethylphenyl) have been synthesized by reactions of the corresponding nitridotechnetium-(V) or rhenium-(V) compounds with disulfur dichloride. The structures of the products and the oxidation states of the resulting metal ions are mainly controlled by the steric bulk of the terphenyl isocyanide ligands. Bis-(isocyanide) Tc-(II) and Re-(II) were obtained exclusively with CNAr^Tripp2 or CNAr^Dipp2, which is in contrast with the more diverse reaction outcomes with the less bulky CNAr^Mes2, where the products also include metal-(I) and dimeric compounds. The obtained complexes [Re^VNCl₂(CNAr^Tripp2)₂(MeOH)], [Re^VNCl₂(CNAr^Dipp2)₂], [Re^VNCl₂(CNAr^Mes2)₃], [Tc^VNCl₂(CNAr^Tripp2)₂], [Re^II(NS)-Cl₃(CNAr^Tripp2)₂], [Re^II(NS)-Cl₃(CNAr^Dipp2)₂], [Re^I(NS)-Cl₂(CNAr^Mes2)₃], [Tc^II(NS)-Cl₃(CNAr^Tripp2)₂], [Tc^II(NS)-Cl₃(CNAr^Dipp2)₂], [Tc^II(NS)-Cl₂(CNAr^Mes2)₃]-Cl, and [{Tc-(NS)-Cl-(CNAr^Mes2)₂}₂Cl₂] were studied spectroscopically and partially by X-ray diffraction.