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 w ith 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)). Thi s 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 r eaction with RX (R = H or alkyl; X = I- or [SO3CF3](-)) to give [Fe-2(eta-C 5H5)(2)(CO)(2){mu-CN(R)Me}(mu-CNMe2)][SO3CF3](2) (reaction (iv)). In reacti ons closely related to (i) and (iii), [Fe-2(eta-C5H5)(2)(L)(CN)(mu-CO)(mu-C NMe2)] (L = CO or CNMe) is converted by HOSO2CF3 to [Fe-2(eta-C5H5)(2)(L)(C O)(mu-CNH2)(mu-CNMe2)][SO3CF3](2) (reaction (v)); this is reversed by depro tonation and no intermediates are observed (reaction (vi)). The scope and l imitations of these reactions have been investigated. Replacement of L by i socyanides 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 t he CNR ligands and not their basicity. Reaction (i) does not take place wit h cis constrained complexes where the two cyclopentadienyl ligands are link ed by a -CH2C(O)-group, in donor solvents such as acetonitrile, or with wea ker acids such as CF3CO2H or CH3CO2H. Reaction (iii) does not take place wh en 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 reactio ns (i), (iii), (v) and (vi), cis<-->trans isomerism may accompany ligand mi gration, 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-CN Xy')(mu-CNMe2)][SO3CF3] is very unusual as in solution its nu(mu-C-NXy') ab sorption band has a very high frequency, >1900 cm(-1), and is very broad, c a. 200 cm(-1). The structure of cis-[Fe-2(eta-C5H5)(2)(CO)(2)(mu-CNMe)(mu-C NMe2)][BPh4] has been determined by X-ray crystallography. (C) 1999 Elsevie r Science S.A. All rights reserved.