Alkyl Cyanoferrates, Cyanocobaltates, and Cyanonickelates as New Reagents for Cross-Coupling with Organic Halides

Cyano ate-complexes of unknown structure (the following formulae are based only on the stoichiometry of the educts) are produced in situ by the action of 1-4 equivalents of methyllithium on M(CN)₂ (where M=Fe, Co, Ni) at -78°C. Some of these new reagents are very favorable to cross-coupling with organic halides: coupling with 1-bromononane can be achieved by Me₃Ni(CN)₂Li₃, Me₄Ni(CH)₂Li₄, or Me₄Fe(CN)₂Li₄ in 83-90% yield, and with 1-chlorononane by Me₄Ni(CN)₂Li₄ in 80% yield (Table 1). Me₂Fe(CN)₂Li₂ and Me₃Fe(CN)₂Li₃ couple with α-bromostyrene with similar yields (89 and 84%, respectively) as the homoleptic complexes Me₄FeLi₂ and Me₄CoLi₂ (Table 2), whereas Me₂Co(CN)₂Li₂ and Me₃Co(CN)₂Li₃ are clearly superior to these complexes in their coupling with 1-bromonaphthalene (giving 89 and 95% yield, respectively). Me₃Co(CN)₂Li₃ and Me₄Co(CN)₂Li₄ gave coupling products with 1-chloro- and 1-fluoronaphthalene in 77 and 67% yield, respectively. MeCo(CN)₂Li is by far superior to other stoichiometric reagents (Table 4) in the coupling (81%) with 1-bromo-2-phenylethyne (postulated mechanism: Scheme 4). Butyl cyano ate-complexes cause the cross-coupling on 1-bromononane and 1-bromonaphthalene in unsatisfactory yields due to side reactions (Table 1 and 3).

transition metal reagents - cyano ate-complexes - cross-coupling - organic halides - transmetalation