Construction of alkyl-substituted pentaphosphido ligands in the coordination sphere of cobalt.

Rare mono- and diorganopentaphosphido cobalt complexes are accessible by P-P condensation using the unprecedented, reactive cobalt-gallium tetraphosphido complex [K(dme){(BIAN)Co(μ-η:η-P)Ga(nacnac)}] (). Compound was prepared in good yield by reaction of [K(EtO){(BIAN)Co(η-1,5-cod)}] [, BIAN = bis(mesitylimino)acenaphthene diimine, cod = 1,5-cyclooctadiene] with [Ga(nacnac)(η-P)] (nacnac = CH[CMeN(2,6-iPrCH)]). Reactions with RPCl (R = iPr, Bu, and Cy) selectively afford [(BIAN)Co(-PR)] (), which feature η-coordinated 1,1-diorganopentaphosphido ligands. The mechanism of formation of these species has been studied by P{H} NMR spectroscopy and DFT calculations. In the case of (R = iPr), it was possible to identify the intermediate [(BIAN)Co(μ-η:η-PiPr)Ga(nacnac)] () by single-crystal X-ray diffraction. A related, monosubstituted organopentaphosphido cobalt complex [(BIAN)Co(μ-η:η-P Bu)GaCl(nacnac)] () was isolated by reacting dichloroalkylphosphane BuPCl with . Heterobimetallic complexes such as thus may enable the targeted construction of a range of new metal-coordinated polyphosphorus frameworks by P-P condensation.