Divergent Chemistry of Ditetrelynes (E₂R₂, E = Si, Ge) with Late Transition Metals and Low-valent Silicon Precursors

Abstract

In modern inorganic chemistry, achieving “gram-scale syntheses” of compounds featuring elements in unusually low oxidation states with unconventional bonding modes continues to be a central goal. Successful isolation of such compounds requires novel synthetic approaches and well-designed sterically demanding substituents to provide kinetic protection. The heavy analogues of alkynes, the <em>“ditetrelynes”</em> stand out as notable examples in this category. They exhibit a trans-bent core with a small HOMO–LUMO gap (&sim;2 eV) and partial diradical character. This unusual bonding of ditetrelynes renders them intriguing in terms of reactivity, and they have proven effective in small molecule activation, C-C coupling reactions, and even in catalysis. Within this framework, efforts will concentrate on pioneering new synthetic methodologies for the formation of heavier tetrel-element multiple bonds via activation/cleavage of ditetrelynes (E₂R₂, E = Si, Ge). <br /> In this work the high synthetic potential of Ge₂Tbb₂ and Si₂Tbb₂ was tested towards metal-carbonyls to synthesize and characterize novel unsaturated metallacycles (1-Co, 1-Rh, 5-Co, 9-Rh, 10-Co, 16-Co, 21-Rh) containing low-valent Si and Ge, and exploring their further reactivity, giving the first examples of inverted-carbene complexes (26-Co and 26-Rh) and a disilacyclopropenone complex (27-Rh). Moving further with the ditetrelyne chemistry, unprecedented bis-tetrylidene (31-Ni), tetrylidene-tetrylidyne (29-Co, 32-Ni), and bis-tetrylidyne (30-Co, 33-Fe, 34-Fe) complexes were synthesized and characterized via “Ge≡Ge” triple bond cleavage of a digermyne at a single metal center (M = Fe, Co, Ni). Finally, using a transition metal free metathesis reaction of a “Ge≡Ge” triple bond, a caac^Me-supported germasilyne (35-Si) was synthesized and exploring its unique reactivity led to the isolation of novel compounds such as a cationic silagermavinylidene (39-Si) and a potassium silenide (40-Si). The chemistry of silagermavinylidene helped further to isolate the germasilyne (43-Si), which showed a unique isomerization reaction to its vinylidenic form (44-Si) via caac^Me and halide migration. This transformation can be considered as an inverse reminiscent of the FBW-rearrangement in context of heavier tetrel chemistry.