Dipnictogen Radical Chemistry: A Dithorium-Supported Distibene Radical Trianion

Although two examples of σ-bonded trans-bent [RSbSbR]^•- (R = bulky organo- or Ga-groups) that formally contain the Sb₂^•3- radical trianion moiety are known in p-block chemistry, d- or f-element Sb₂^•3- radical trianion complexes, with or without R-substituents, have remained elusive. Here, we report that reduction of a 77:23 mix of [{Th(Tren^TIPS)}₂(μ-η²:η²-Sb₂)] (3a, Tren^TIPS = {N(CH₂CH₂NSiPrⁱ₃)₃}^3-):[{Th(Tren^TIPS)}₂(μ-SbH)] (3b) with 1.5 equiv of KC₈ in the presence of 1.1 equiv of 2.2.2-cryptand yields the emerald green Sb₂^•3- radical complex [K(2.2.2-cryptand)][{Th(Tren^TIPS)}₂(μ-η²:η²-Sb₂)] (4), providing an f-block Sb₂^•3- radical trianion complex, and the heaviest actinide-N₂ radical analogue. When the recrystallization conditions are modified, a small crop of red crystals determined to be [K(2.2.2-cryptand)]₃[{Th(Tren^TIPS)(μ-η³:η³-Sb₃)}₂(μ-K)] (5) were also isolated, highlighting the complexity of heavy group 15 homodiatomic reduction chemistry. SQUID magnetometry and EPR spectroscopy suggest that the Sb₂^•3- radical trianion in 4 is fairly well isolated, due to electrostatic binding to Th, with pseudoaxial g-values reflecting the distinctive Sb₂^•3- radical trianion side-on bridging π-bonded coordination mode. Spectroscopically validated computational analysis of 3a and 4 confirms the stronger donating capability, and weaker Sb-Sb bond, of Sb₂^•3- radical trianion compared to the Sb₂^2- dianion form.