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

The complex Cp*Fe(dippe)Fe(C=CC=C)Fe(CO)(2)Cp* (3b, dippe = 1,2-bis(diisopr opylphosphino)ethane, Cp* = pentamethylcyclopentadienyl) was prepared by ac tivation of the terminal butadiyne Cp*(CO)(2)FeC=CC=CH (2) with the chloro iron complex Cp*(dippe)FeCl (1b) in the presence of KPF6 and KOBut. Treatme nt of Cp*(P-2)Fe((C=CC=C)Fe(CO)(2)Cp* (3a, P-2 = dppe, dppe = 1,2-bis(diphe nylphosphinoethane); 3b, P-2 = dippe) with HBF4. Et2O produced the secondar y iron butatrienylidene complexes [Cp*(P-2)Fe{=C=C=C=C(H)Fe(CO)(2)Cp*}][BF4 ] (4a. P-2 = dppe, 75%; 4b, P-2 = dippe, 93%). The slightly more stable ter tiary butatrienylidene iron derivatives [Cp*(P-2)Fe{=C=C=C=C(CH3)Fe(CO)(2)C p*}][OSO2CF3] (5a, P-2 = dppe. 22%; 5b, P-2 = dippe, 75%) were made by reac ting the precursor complexes 3a-b with methyl triflate under similar condit ions. All the compounds 4a-b and 5a-b are almost stable in solution at 20 d egrees 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 degrees 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 spectros copic data. (C) 1999 Elsevier Science S.A. All rights reserved.