The X-ray structural characterization and solution dynamics of bis[(μ-2,6-dimethylphenylisocyanide)- (cyclopentadienyl)(2,6-dimethylphenylisocyanide)iron(I)

Abstract

The X-ray structure of trans-[{Fe(η 5-C 5H 5)(CNC 6H 3Me 2-2,6) 2} 2] ( 1a) and the solution dynamics of both cis- and trans-[{Fe(η 5-C 5H 5)(CNC 6H 3Me 2-2,6) 2} 2] have been studied. The trans-isomer of 1a crystallizes in the space group P2 1/ n with a 14.588(4), b 8.811(2) and c 14.847(4) Å, β 92.08(2)°. The molecule lies across a crystallographic centre of inversion with a trans arrangement of cyclopentadienyl ligands and a strictly planar bridging Fe 2C 2 ring. The FeFe bond lenght is 2.518(1) Å and the bridging isocyanide ligands are symmetrically bonded to iron with a mean FeC(bridging) bond lenght of 1.928(3) Å. Solution 1H NMR spectra of 1a show the presence of both cis- and trans-isomers, and a 500 MHz 1H NMR study at low temperature reveals two distinct exchange processes; the lower energy one results in the coalescence of the signals for the inequivalent methyl groups on the bridging isocyanide ligands of the cis-isomer, whereas the higher energy process brings about coalescence of the methyl signals for the bridging and terminal isocyanide ligands of the trans-isomer. At elevated temperatures all the methyl signals coalesce.