DIIRON AMINOALKYLIDENE COMPLEXES

The reactions of the sulfonium salts [Fe-2(CO)(2)(cp)(2)(mu-CO){mu-C(X)SMe(2)}]SO3CF3 [X = CN (1a), H (1b)] with a variety of amines are presented. 1a yields ammonium cations [Fe-2(CO)(2)(cp)(2)(mu-CO){mu-C(CN)NR(3)}] [R = Me (2), Dabco (3) (Dabco = 1,4-diazabicyclo[2.2.2]octane)], aminoalkylidene [Fe-2(CO)(2)(cp)(2)(mu-CO){mu-C(CN)NR(2)}] (4), isocyanide [Fe-2(CO)(2)(cp)(2)(mu-CO)(mu-CNR)] (7), or diaminoalkylidene [Fe-2{CN(H)(CH2)(2)N(H)}(CO)(cp)(2)(mu-CO)(2)] (11) complexes by reacting with tertiary amines, secondary amines, primary amines, or ethylenediamine, respectively. 1b and secondary amines yield [Fe-2(CO){C(H)NR(2)}(cp)(2)(mu-CO)(2)] (6). The formation of type 4 bridging and 6 terminal aminoalkylidene derivatives also via mu-C addition of CN- or H- to aminoalkylidyne [Fe-2(CO)(2)(cp)(2)(mu-CO)(mu-CNR(2))](+), respectively, as well as the preparation of the terminal [Fe-2{C(CN)NPr2i}(CO)(cp)(2)(mu-CO)(2)] (5) from 1a and NHPr2i, allows to clarify the role of electronic and steric effects in determining the position of the aminoalkylidene ligands. The X-ray structure of 5 has been determined. The crystal contains two independent molecules of the trans-isomer. The terminally bonded aminoalkylidene ligand exhibits weaker Fe-C(carbene) (Fe-C 1.915(3) Angstrom) and stronger C(carbene)-N(amine) pi bonds (C-N 1.320(4) Angstrom) with respect to the bridging coordination. Electrochemistry shows that 5 undergoes a chemically reversible one electron oxidation to the corresponding monocation [5](+), which has been characterized by X-band EPR spectroscopy. All the complexes have been spectroscopically characterized, and a variable-temperature NMR on [Fe-2(Co){C(H)NMe(2)}(cp)(2)(mu-CO)(2)] (6a) indicates exchange of the aminoalkylidene ligand between the two Fe atoms.