{MI(CO)X(CNArDArF2)4} (DArF = 3,5-(CF3)2C6H3; M = Re and Tc; X = Br and Cl) Complexes: Convenient Platforms for the Synthesis of Low-Valent Rhenium and Technetium Compounds

[Re­(CO)­Br­(CNArDArF2)4] and [Tc­(CO)­Cl­(CNArDArF2)4] (ArDArF = 2,6-(3,5-(CF3)2C6H3)2-4-F-C6H2) were prepared by reactions of [Re­(CO)5Br] or (NBu4)­[Tc2(CO)6(μ-Cl)3] with the sterically encumbered isocyanide CNArDArF2. These two compounds proved to be excellent starting materials for the synthesis of unprecedented low-valent rhenium and technetium complexes. The reduction of [Re­(CO)­Br­(CNArDArF2)4] with Na/Hg produces an equimolar mixture of [Re­(CO)­(CNArDArF2)4] and Na­[Re­(CO)­(CNArDArF2)4] containing the transition metal in the formal oxidation states “0” and “–1”, respectively. The reduction of [Tc­(CO)­Cl­(CNArDArF2)4] with Na/Hg produces Na­[Tc­(CO)­(CNArDArF2)4], which was characterized by 19F and 99Tc NMR spectroscopy. The reactivity of Na­[Re­(CO)­(CNArDArF2)4] resembles that of [Re­(CO)5]−, proved by reactions with a number of electrophiles such as MeI, HCl, or F6C5C­(O)­Cl.