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(TrenTIPS)}2(μ-η2:η2-Sb2)] (3a, TrenTIPS = {N(CH2CH2NSiPri3)3}3–):[{Th(TrenTIPS)}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(TrenTIPS)}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(TrenTIPS)(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 Sb22– dianion form.