Cyanopyridine complexes

The pressure dependence for the substitution of pyridine and substituted pyridine is reported in Figure 23, from which it follows that the larger effects observed for the 4-acetyl- and 4-cyanopyridine complexes are consistent with the volume difference expected between the LF and MLCT excited states. The positive volumes of activation support the operation of a dissociative D substitution mechanism as a result of LF excitation [101], The photosubstitution reactions of complexes of the type M(CO)4phen (M = Cr, Mo, W) have received attention from various groups, mainly because of possible roles played by both LF and MLCT excited states in such processes (Fig. 24). For the overall reaction given in Eq. (30),... 

Limiting rate constants for loss of pyrazine or of piperidine from their respective pentacyanoferrate(II) derivatives are affected to only a very small extent by the acetone content of binary aqueous mixtures.Probably here, as in the earlier case of the 4-cyanopyridine complex in aqueous alcohols, " this minor effect on rate constants conceals large but almost equal effects on the initial and transition states. This proved impossible to assess, due to the authors failure to find salts of appropriate solubility for the requisite measurements and transfer chemical potential derivations. It may be that the recently characterized transition metal(II) salts could lead to an answer. 

The dependence of rate constant on incoming nucleophile concentration has been established, at 298 K in 40% methanol, for reaction of the 4-cyanopyridine complex [Fe(CN)5(4-CNpy)] "with an extensive range of nucleophiles. The range... 

Chromium(ii) reduction of the three isomeric nitrile-bonded cyanopyridine complexes proceeds with efficient transfer of the ligand from chromium to cobalt. The protonated forms of the complexes are relatively unreactive. Reduction of the 2-isomer leads to the unexpected product (16), consistent with the sequence of reactions (61). The other two isomers lead to the complexes [Cr(H20)s(NC5H4CN)] +,... 

A convenient and easily accessible way to quantify hydrophobicity is the determination of the octanolAvater partition coefficient (log P) and we have determined the hydrophobicity of 13 selected ruthenium-arene complexes (71). As expected, hydrophobicity increases with an increase of the size of the coordinated arene ring, but decreases significantly when the chloride is replaced by neutral ligands such as pyridine and 4-cyanopyridine. The latter observation is somewhat counter intuitive at first inspection, but correlates with replacement of anionic chloride to yield a dicationic complex. The hydrophobicity... 

Pyridine and 4-cyanopyridine react with [Cr2(02CCF2H)4(Et20)2] to give the mixed oxidation state, oxo-centred complexes [Cr11Cr2II0(02CCF2H)6(py)3(Et2O)] and... 

Table 15 Some IR Spectral Data (cm ) for Silver(I) Complexes of Cyanopyridines...

Metal complexes of several zinc, cadmium and mercury salts with 2-, 3- and 4-cyanopyridine have been reported.495 In none of the complexes was cyanide coordination observed. Zinc halides react with 3- and 4-cyanopyridine, but not with 2-cyanopyridine, to give 1 2 complexes which are assigned a monomeric tetrahedral structure on the basis of IR evidence. The cadmium halides also form 1 2 complexes with all the cyanopyridines, except cadmium chloride, which reacts with 2-cyanopyridine to give a 1 1 complex. The former contain... 

Several other complexes with N-donor ligands have been prepared.1065 The complexes CoM(NCS)4(L)6 (M = Zn or Cd L = 2-, 3- or 4-cyanopyridine, nicotinamide, ethyl nicotinate or isonicotinic acid hydrazide) are best formulated as CoL6M(SCN)4. The complexes CoHg(SCN)4L2 (L = 2-, 3- or 4-aminopyridine, 3-cyanopyridine or ethyl nicotinate) possess only bridging SCN ligands, and have the polymeric structure (139). On the other hand, the complexes CoZn(NCS)4L2 (L = 2-, 3- and 4-aminopyridine) contain both bridging and terminal SCN groups, and are postulated to have the dimeric structure (140). 

In recent years there has been considerable interest in the reactions of nitriles in the coordination sphere of metal ions. Breslow et al.312 first reported that the hydrolysis of 2-cyano-l,10-phenanthro-line to the corresponding carboxamide is strongly promoted by metal ions such as copper(II), nickel(II) and zinc(II). Base hydrolysis of the 1 1 nickel complex is 107 times faster than that of the uncomplexed substrate. The entire rate acceleration arises from a more positive value of AS. Somewhat similar effects have been observed for base hydrolysis of 2-cyanopyridine to the corresponding carboxamide. In this case rate accelerations of 109 occurred with the nickel(II) complex.313... 

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