Co(II) Amide, Pyrrolate, and Aminopyridinate Complexes: Assessment of their Manifold Structural Chemistry and Thermal Properties

A series of cobalt(II) (silyl)amides, pyrrolates and aminopyridinates were synthesized. Inspired by the dimeric bis(trimethylsilylamido)cobalt(II) complex ([Co(TMSA)2]2), facile salt metathesis employing the ligand 2,2,5,5-tetramethyl-1,2,5-azadisilolidinyl (TMADS) yielded its congener [Co(TMADS)2]2. Novel, heteroleptic Lewis adducts of the former resulted in unusual three- to four-fold coordination geometry around the metal center. Similarily, the salt [Co(TMADS)3Li(DAD)2] was isolated which demonstrates an ion separated Co(II) anion with silylamide ligation and Li+ counter cation. Transpyrrolylation using [Co(TMSA)2]2 was established for the synthesis of bis[N,N’-2-(dimethylaminomethyl)pyrrolyl]cobalt(II), and bis(N-2-(tert-butyliminomethyl)pyrrolyl)cobalt(II). Treatment of CoCl2 with two equivalents of lithiated N,N-dimethyl(N’-tert-butyl)ethane-1-amino-2-amide and N,N-dimethyl(N’-trimethylsilyl)ethane-1-amino-2-amide resulted in the respective Co(II) amido-amines. Reaction of CoCl2 with lithium 4-methyl-N-(trimethylsilyl)pyridine-2-amide yielded the first binuclear, homoleptic Co(II) aminopyridinate complex with a distorted trigonal bipyramidal coordination environment (τ5 = 0.533) for one central Co(II) ion and a weakly distorted tetrahedral coordination geometry (τ4 = 0.845) for the other. All of the new compounds were thoroughly characterized in terms of composition and structure. Finally, the key thermal characteristics of volatility and thermal stability were assessed using a combination of thermogravimetric analysis and complementary bulk sublimation experiments.