The reaction of [Fe-2(eta-C5H5)(2)(CO)(CNMe)(mu-CO)(mu-CNMe2)](+) and related salts with trifluoromethanesulphonic acid, HOSO2CF3: structure of cis-[Fe-2(eta-C5H5)(2)(CO)(2)(mu-CNMe) (mu-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), cistrans 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.