The reaction of [Fe2(η-C5H5)2(CO)(CNMe)(μ-CO)(μ-CNMe2)]+ and related salts with trifluoromethanesulphonic acid, HOSO2CF3:: structure of cis-[Fe2(η-C5H5)2(CO)2(μ-CNMe) (μ-CNMe2)] [BPh4]

[Fe-2(eta-C5H5)(2)(L)(CNMe)(mu-CO)(mu-CNMe2)][SO3CF3] where L = CO reacts with HOSO2CF2 in chloroform solution at room temperature (r.t.) to give [Fe-2(eta-C5H5)(2)(CO)(2){mu-CN(H)Me}(mu-CNMe2)][SO3CF3](2) (reaction (i)). This salt readily and reversibly loses a proton to form [Fe-2(eta-C5H5)(2)(CO)(2)(mu-CNMe)(mu-CNMe2)][SO3CF3] (reaction (ii)) which, in solution, slowly reverts to [Fe-2(eta-C5H5)(2)(CO)(CNMe)(mu-CO)(mu-CNMe2)][SO3CF3] under the influence of UV radiation (reaction (iii)) although it can be trapped by reaction with RX (R = H or alkyl; X = I- or [SO3CF3](-)) to give [Fe-2(eta-C5H5)(2)(CO)(2){mu-CN(R)Me}(mu-CNMe2)][SO3CF3](2) (reaction (iv)). In reactions closely related to (i) and (iii), [Fe-2(eta-C5H5)(2)(L)(CN)(mu-CO)(mu-CNMe2)] (L = CO or CNMe) is converted by HOSO2CF3 to [Fe-2(eta-C5H5)(2)(L)(CO)(mu-CNH2)(mu-CNMe2)][SO3CF3](2) (reaction (v)); this is reversed by deprotonation and no intermediates are observed (reaction (vi)). The scope and limitations of these reactions have been investigated. Replacement of L by isocyanides shows that the ease with which t-CNR is converted to mu-CN(E-I)R (reactions (i) and (v)) decreases along the series CNR = CN-/CNH >> CNXy'(Xy' = C6H3Et2-2,6) > CNMe > CNEt which reflects the mu-seeking ability of the CNR ligands and not their basicity. Reaction (i) does not take place with cis constrained complexes where the two cyclopentadienyl ligands are linked by a -CH2C(O)-group, in donor solvents such as acetonitrile, or with weaker acids such as CF3CO2H or CH3CO2H. Reaction (iii) does not take place when L = CNMe or CNEt, or when mu-CNMe is replaced by mu-CNXy' even when L = CO. Reaction (vi) always takes place; however, if L = CNMe either it or the t-CO may end-up in the mu-site but the latter is preferred. During reactions (i), (iii), (v) and (vi), cis<-->trans isomerism may accompany ligand migration, but the cis is always the predominant product. Spectroscopic data is presented, assigned and used to distinguish between these isomers. Most is straight-forward, but the IR spectrum of [Fe-2(eta-C5H5)(2)(CO)(2)(mu-CNXy')(mu-CNMe2)][SO3CF3] is very unusual as in solution its nu(mu-C-NXy') absorption band has a very high frequency, >1900 cm(-1), and is very broad, ca. 200 cm(-1). The structure of cis-[Fe-2(eta-C5H5)(2)(CO)(2)(mu-CNMe)(mu-CNMe2)][BPh4] has been determined by X-ray crystallography. (C) 1999 Elsevier Science S.A. All rights reserved.