First synthesis and spectroscopic characterization of isolated butatrienylidene complexes of transition metals

Abstract

The complex Cp*Fe(dippe)Fe(CCCC)Fe(CO) 2Cp* ( 3b, dippe=1,2-bis(diisopropylphosphino)ethane, Cp*=pentamethylcyclopentadienyl) was prepared by activation of the terminal butadiyne Cp*(CO) 2FeCCCCH ( 2) with the chloro iron complex Cp*(dippe)FeCl ( 1b) in the presence of KPF 6 and KOBu t . Treatment of Cp*(P 2)Fe((CCCC)Fe(CO) 2Cp* ( 3a, P 2=dppe, dppe=1,2-bis(diphenylphosphinoethane); 3b, P 2=dippe) with HBF 4 · Et 2O produced the secondary iron butatrienylidene complexes [Cp*(P 2)Fe{CCCC(H)Fe(CO) 2Cp*}][BF 4] ( 4a, P 2=dppe, 75%; 4b, P 2=dippe, 93%). The slightly more stable tertiary butatrienylidene iron derivatives [Cp*(P 2)Fe{CCCC(CH 3)Fe(CO) 2Cp*}][OSO 2CF 3] ( 5a, P 2=dppe, 22%; 5b, P 2=dippe, 75%) were made by reacting the precursor complexes 3a– b with methyl triflate under similar conditions. All the compounds 4a– b and 5a– b are almost stable in solution at 20°C. They are light and air sensitive, even in solid state. The solid samples can be stored under argon for few days in the dark at 5°C. The complexes 4a– b and 5a– b were characterized by multinuclear NMR, IR, UV–vis, and Mössbauer spectroscopies, mass spectrometry and cyclic voltammetry. Their electronic structures are discussed in connection with the spectroscopic data.