Synthesis of phosphinogallyliron complexes and their photochemical conversion to a naked gallium-bridged diiron complex

Abstract

The dichlorogallyliron complexes Cp’(OC)2FeGaCl2 (Cp’ = Cp* (4a), Cp (4b), Cp*: η5-C5Me5, Cp: η5-C5H5), when treated with LiPPh2 and/or Me3SiPPh2 in Et2O, produce the four-membered Ga2P2 cyclic diiron complexes [Cp’(OC)2FeGa(Cl)PPh2]2 (Cp’ = Cp* (5a), Cp (5b)) in 64% and 47% yields, respectively. Crystal structure analysis using X-ray crystallography revealed that the four-membered Ga2P2 cyclic structure in cis-5a is slightly puckered. The four-membered Ga2P2 cyclic structure remains undisturbed in a solution of complex 5a in C6D6 and C7D8. 5a exists as a mixture of the cis/trans geometric isomers in these solutions. The photochemical reaction with complex 5b in C6D6 produces a complex mixture. However, the photochemical reaction with complex 5a in C6D6 afforded the six-membered Fe-Ga-Fe-P-Ga-P cyclic diiron complex [{Cp*(OC)Fe}2(μ-Ga)(μ-Ph2PGaCl2PPh2)] (6a) in 61% yield (NMR yield). Crystal structure analysis revealed that complex 6a contains the Ga atom-bridged Fe-Ga-Fe fragment with two Fe−Ga multiple bonds.