The preparation, structure and fluxional behaviour of isonitrile derivatives of Cp 2Fe 2(CO) 4- x(CS) x ( x = 1, 2)

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The complexes Cp 2Fe 2(CO) 2(CS)(CNR) (R = Me, Et, Pr i, Bu t; Cp = η 5-C 5H 5) exist in solution as interconverting Cp(CO)Fe(μ-CO)(μ-CS)Fe(CNR)Cp ∡ Cp(CO)Fe(μ-CS)(μ-CNR)Fe(CO)Cp isomers, with the proportion of the bridged isonitrile isomer increasing in the order Bu t < Pr i < Et < Me. A single crystal X-ray determination of the CNPr i derivative shows it to have a cis-Cp(CO)Fe(μ-CO)(μ-CS)Fe(CNPr i)Cp geometry in the solid state. Cp 2Fe 2(CO)(CS)(CNMe) 2 and Cp 2Fe 2(CO)(CS) 2(CNMe) exist respectively as the single isomers Cp(CO)Fe(μ-CS)(μ-CNMe)Fe(CNMe)Cp and Cp(CO)Fe(μ-CS) 2Fe(CNMe)Cp in solution. Interconversions of isomers are discussed in terms of the Adams-Cotton mechanism.