Penta- and Tetracyanoferrates

Kinetic parameters for formation of [Fe(CN)5L] from [Fe(CN)5(OH2)] have been reported for a variety of incoming ligands L. One study has dealt with 

8 Inert-Metal Complexes Other Inert Centers 

4 -bipyridyl and the ethane- and ethene-bipyridyls (25) and (26). The particular interest here was to compare reactivities for each of these three ligands as such, in their mono-protonated or mono-JV-methylated forms, and in their derivatives with [Fe(CN)5] or [Co(NH3)5] coordinated to one of the nitrogens. The kinetic consequences of coordinating [Co(NH3)5] to one end of the entering ligand have also been probed for pyrazine and the alkyne-bipyridyl derivatives (27) and (28). Dissociation rate constants have been reported for many of the products of these reactions. These kinetic studies can be put into context with 

Kinetic parameters have been established for solvolysis of the pentacyanofer-rate(III) derivative [Fe(CN)5(N02)] . For aquation, which is acid-catalyzed at pH 5, A//= = 43kJmol-, =-80 J K mol , and A =+2 cm mol . Intrinsic and solvational contributions are presumably closely balanced in the case of A Rate constants for solvolysis of [Fe(CN)5(N02)] in water, methanol, dimethyl sulfoxide, and dimethylformamide correspond with the electron-donating abilities of the respective solvents. Activation volumes for the nonaqueous solvents, between +20 and +27 cm mor reflect the dissociative nature of these solvoly-ses. Rate constants for dissociation of the [Fe(CN)5(2,6-Me2pyrazine)] anion in binary aqueous solvents containing methanol, acetone, or acetonitrile correlate well with acceptor numbers for the respective media, though with a very different 

Activation parameters for 5 A interconversion of the 1,2-diamine rings in complexes [Fe (CN)4(diamine)] , containing, e.g., ci5-l,2-diaminocyclohexane or me o-butanediamine, have been determined by NMR spectroscopy. Activation enthalpies are in the range 25 to 40 kJ moP activation entropies between 0 and -8 J mol These iron(III) complexes disproportionate according to third-order kinetics, with rate constants which reflect the steric strains in the respective diamine chelate rings.  

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