A new synthetic method for the preparation of [(η 5-C 5H 5)Fe(CO)(L)(un)]BF 4 (L = CO, PPh 3; un = unsaturated hydrocarbon) complexes and reduction of the η 2-acetylene complexes

Abstract

The reaction of (η 5-C 5H 5)Fe(CO) 2I with AgBF 4 in CH 2Cl 2 generates the reactive intermediate [(η 5-C 5H 5)Fe(CO) 2] + in solution which, when mixed with 2 or 3 equivalents of an olefinic or acetylene ligand produces η 2-olefin and η 2-acetylene complexes in ca. 70% yield. The analogous reaction of (η 5-C 5H 5)Fe(CO)(PPh 3)I with AgBF 4 in CH 2Cl 2 produces [(η 5-C 5H 5)Fe(CO)(PPh 3)] + in solution which also reacts readily with olefins and acetylenes to yield new π-complexes. The dicarbonyl complexes are generally more stable than the phosphine-substituted complexes. The η 2-acetylene complexes in both systems can be reduced with hydride reagents to yield the corresponding neutral σ-vinyl compounds. Although unstable in the dicarbonyl system, these vinyl compounds in the phosphine system are quite stable and show no tendency to isomerize or thermally decompose to a metal hydride as previously established for the analogous alkyl derivatives. Attempts to prepare cyano-substituted olefin complexes lead instead to new complexes in which the iron bonds to these ligands through the nitrogen lone-pair.