Abstract
AbstractA 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 [Li(DAD)2][Co(TMADS)3] 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.
Highlights
Ever since Alfred Werner coined the term coordination complex in 1893,[1] and was able to exemplify his far-reaching theory using the example of hexol in 1911,[2] the coordination chemistry of the later transition metal cobalt (Co) expanded vastly and has been subject of extensive research
With our long-term research focusing on the synthesis of inorganic complexes and their evaluation as precursors for the application in chemical gas phase deposition processes such as metal organic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD),[3,4] and our recent interest in the chemistry of the later transition metal Co,[5] we identified prior mentioned classes as promising model systems for our studies
Beginning with [Co(TMSA)2]2, Power and coworkers hereby focused on the synthesis and bonding characterization of low-coordinate Co(II) silylamides of the type [Co(TMSA)2L],[11] and [Co(N(SiMe3)Dipp)L],[15] with Dipp being 2,6diisopropylphenyl and L being a series of Lewis bases ranging from THF and pyridine to several phosphines derivates
Summary
Ever since Alfred Werner coined the term coordination complex in 1893,[1] and was able to exemplify his far-reaching theory using the example of hexol in 1911,[2] the coordination chemistry of the later transition metal cobalt (Co) expanded vastly and has been subject of extensive research. While the likely best known Co(II) silylamide [Co(N(SiMe3)2)2]2 in the following referred to as [Co(TMSA)2]2 has not found application in this field yet, the recent usage of its Lewis base coordinated congener [Co(TMSA)2(THF)] in ALD[10] raises the question if all-nitrogen Lewis adducts of the type [Co(TMSA)2L] could be viable precursor candidates. In this regard, it is noteworthy, that a number of Co(II) silylamides and Lewis adducts adapted from them have already been studied in recent years in terms of their structural, electronic and magnetic properties.[11–17]. This is likewise applicable to Co(II) pyrrolate and aminopyridinate complexes of which a few examples have been reported but never been compared in terms of structure and thermal properties.[18–22]
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