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

Abstract The complex Cp*Fe(dippe)Fe(CCCC)Fe(CO) 2 Cp* ( 3b , dippe=1,2-bis(diisopropylphosphino)ethane, Cp*=pentamethylcyclopentadienyl) was prepared by activation of the terminal butadiyne Cp*(CO) 2 FeC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) 2 Cp* ( 3a , P 2 =dppe, dppe=1,2-bis(diphenylphosphinoethane); 3b , P 2 =dippe) with HBF 4  · Et 2 O produced the secondary iron butatrienylidene complexes [Cp*(P 2 )Fe{CCCC(H)Fe(CO) 2 Cp*}][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) 2 Cp*}][OSO 2 CF 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 Mossbauer spectroscopies, mass spectrometry and cyclic voltammetry. Their electronic structures are discussed in connection with the spectroscopic data.