Isocyanides substitution reactions

The reactions of nucleophilic reagents with cationic and uncharged metal carbonyl complexes have received much attention in the past, and it is not surprising that these studies have now been extended to isocyanide metal complexes. Different products in these reactions can arise by three general routes these include ligand substitution, reactions involving attack at a ligand, and reduction of the metal complex. All have been observed in reactions with metal isocyanide complexes. 

Most of the substitution reactions with the homoleptic Tc(I) isocyanide complexes presented in the preceding section had to be performed at elevated temperatures and were often characterized by low yield. The reason for this behaviour is the exceptionally high kinetic and thermodynamic stability of this class of compounds. From this point of view, 4a are not very convenient or flexible starting materials, although they are prepared directly from 3a in quantitative yield. The exceptionally high kinetic and thermodynamic stability is mirrored by the fact that it was not possible to substitute more than two isocyanides under any conditions. On the other hand, oxidation to seven-coordinated Tc(III) complexes occurs very readily. Technetium compounds of this type, which are not expected to be very inert, could open up a wide variety of new compounds, but this particular field has not been investigated very thoroughly. A more convenient pathway to mixed isocyanide complexes that starts with carbonyl complexes of technetium will be described in Sects. 2.3 and 3.2. 

Substitution reactions on cationic gold(I) derivatives afford the corresponding complexes containing two isocyanides (Figures 7.30 and 7.31) [29]. A structure—... 

The complex Mn2(/x-H)(/x-PPh2)(CO)8 undergoes carbonyl substitution reactions with phosphite, phosphine, or isocyanide ligands, either thermally or... 

In contrast, stepwise substitution reactions on M(CO)6 (M = Cr, Mo, W) have been achieved with a series of heterogeneous catalysts including co-balt(ll) chloride (27), activated charcoal (159), and platinum metals dispersed on oxide or carbon supports (31), to give mono-, di-, tri-, and complete substitution (124) in yields > 90%. Representative reaction times are given in Table II (159). The efficiency of the method was further demonstrated by the stepwise synthesis of the mixed isocyanide complexes m-Mo(CO)4(CNMe)(CNBu ) and /ac-Mo(CO)3(CNMeXCNBu )2 from Mo(CO)6 in <25 min in 85 and 95% yields, respectively (159). 

Fe(CO)s is fairly inert to substitution reactions, usually requiring Carius tube reactions or high boiling solvents, both with extended reaction times, to reach, in the case of isocyanides (765), disubstitution. As a testimony to the unreactivity of Fe(CO)5 only three publications have appeared on isocyanide reactions with complexes related to this molecule since 1974. Thus, photolysis of Fe(CO)3 P(OAryl)3 2 in the presence of CNMe gave Fe(CO)2 P(OAryl)3 2(CNMe) (766), substitution reactions on Fe(CO)4MA with CNCH2Ph produced Fe(CO)4 x(CNCH2Ph)JtMA (x = 1 -3)(767), and the reaction of Fe3(CO)l2 with CN(CH2) NC (n = 2,6) produced exclusively the dimer [Fe(CO)4]2CN(CH2) NC (168). 

The catalytic substitution reactions of metal carbonyl clusters, including [M3(CO)i2] (M = Fe, Ru, or Os), [Ru4H4(CO)i2], [Rh6(CO)i6], and [Co3(CO)9(/it-CCl)], with isocyanides or Group V-donor ligands may be induced by either electrochemical or chemical (benzophenone ketyl) reduction. The most favorable conditions for efficient substitution include (1) the formation of a radical anion with a significant lifetime and (2) the use of a ligand which is not reduced by [Ph2CO], and which is less of a tt acid than CO (166). 

First, we will discuss reactions in which hydrogen or a metallic ion (or in one case phosphorus or sulfur) adds to the heteroatom and second reactions in which carbon adds to the heteroatom. Within each group, the reactions are classified by the nature of the nucleophile. Additions to isocyanides, which are different in character, follow. Acyl substitution reactions that proceed by the tetrahedral mechanism, which mostly involve derivatives of carboxylic acids, are treated at the end. 

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