The syntheses, molecular and electronic structures of two μ 4-vinylidene tetrairon clusters

Abstract

The syntheses, crystal structures and electronic structures of the new μ 4-vinylidene clusters, Fe 4(CO) 12(CC(OCH 3) 2) and Fe 4(CO) 12(CC(OCH 3)CH 3), are reported. Fe 4(CO) 12(CC(OCH 3) 2) was prepared by the methylation of [Fe 4(CO) 12(CCO 2CH 3)] − with trimethyloxonium fluoroborate in methylene chloride at 25°C. Fe 4(CO) 12(CC(OCH 3)CH 3) was prepared in an analogous manner from [Fe 4(CO) 12(CC(O)CH 3)] −. Fe 4(CO) 12(CC(OCH 3) 2) crystallizes in the monoclinic space group P2 1/ c (C 2 h 5 No. 14) with a = 13.900(2), b = 8.909(2), c = 17.116(4) Å, β = 94.59(2)°; p calc = 2.03 g cm −3 for mol. wt 645.6 and Z = 4. Fe 4(CO) 12(CC(OCH 3)CH 3) crystallizes in the monoclinic space group P2 1/ c ( C 2 h 5 No. 14) with a = 28.441(6), b = 9.204(2), c = 17.466(4) Å, β = 108.51(2)°; p calc = 1.93 g cm −3 for mol. wt = 629.6 and Z = 8. Both clusters have an open butterfly core of four iron atoms with the vinylidene ligand bound to all four metal atoms. Molecular orbital calculations using the Fenske—Hall method were carried out for the two clusters. The molecular and electronic structures of the molecules are compared with each other and with those of μ 4-methylidyne clusters. Although both of these clusters contain a formal CC double bond in the vinylidene ligand, the presence of oxygen atoms in these ligands leads to a delocalized π system and only partial double bond character in this CC bond. Changes in the structure of the cluster framework can be correlated with the oxygen content and thus double bond character in the vinylidene ligand.