Facile C–N coupling of coordinated ammonia and labile carbonyl or acetonitrile promoted by a thiolate-bridged dicobalt reaction scaffold

Abstract

At low temperature, interaction of the thiolate-bridged dicobalt carbonyl complex [Cp*Co(I)(μ-SEt)₂(CO)CoCp*][I] (Cp* = η⁵-C₅Me₅) (1) with NH₃ resulted in the C–N coupling of the coordinated CO and amido group that originate from ammonia activation to afford a dicobalt formylamino complex [Cp*Co(μ-SEt)₂(μ-η¹:η¹-OCNH₂)CoCp*][I] (2). Interestingly, at relatively high temperatures, the labile CO ligand was replaced by NH₃ to give a thiolate-bridged dicobalt ammonia complex [Cp*Co(I)(μ-SEt)₂(NH₃)CoCp*][I] (3). Subsequently, in the presence of the dehalogenation reagent AgPF₆, the Co₂S₂ scaffold can simultaneously activate NH₃ and MeCN to produce the complex [Cp*Co(MeCN)(μ-SEt)₂(NH₃)CoCp*][PF₆]₂ (4). Furthermore, in the presence of NaOEt, the facile occurrence of the intramolecular cyclization led to the formation of acetamidino-bridged dicobalt complex [Cp*Co(μ-SEt)₂(μ-η¹:η¹-NH(CCH₃)NH)CoCp*][PF₆] (5), which may proceed through the nucleophilic attack of amido from NH₃ to coordinated MeCN followed by the hydrogen atom transfer process. In the presence of MeCN, treatment of 5 with HBF₄ released the corresponding [MeC(NH₂)NH₂]BF₄; meanwhile, the [Co₂S₂] core structural scaffold remained. In this Co₂S₂ reaction system, the cooperative activation effect between the two cobalt centers plays an important role for NH₃ activation and functionalization.