Radical-Type Reactivity of Metalla[1.1.1]propellanes of Group 14: Syntheses, Structures, and Reduction Chemistry of Transition Metal-Terminated Bicyclo[1.1.1]pentastannanes

Abstract

Two selected metalla[1.1.1]propellanes of group 14, Sn5Dep6 (1) and Ge5Mes6 (2) (Dep = 2,6-Et2C6H3, Mes = 2,4,6-Me3C6H2), were reacted with [FeCp(CO)2]2 and [RuCp(CO)2]2. While 2 did not show any reaction with [FeCp(CO)2]2 or did not lead to any isolable product in the case of [RuCp(CO)2]2, the tin propellane 1 quantitatively (monitored by 1H NMR) afforded the first transition metal-terminated bicyclo[1.1.1]pentastannanes, [{MCp(CO)2}2{μ-Sn5Dep6}] (M = Fe (3), Ru = (4)), in 68% (3) and 66% (4) isolated yield. This behavior confirms the radical-type reactivity of metalla[1.1.1]propellanes, in this case 1. The title compounds 3 and 4 have been characterized in detail using various methods. X-ray structure analyses corroborated that the two ligand-free bridgehead tin atoms within the Sn5 scaffold are bonded to the transition metal fragments. Electrochemical studies revealed the reduction chemistry of 3 and 4 in THF solutions to be very interesting. A detailed preparative and electrochemical study, including the isolation and characterization of the monosubstituted cobaltocenium salt [CoCp*2]+[{FeCp(CO)2}{Sn5Dep6}]− (5), elucidated a complex redox cycle consisting of a cascade of bond-breaking and bond-making processes