Cyano and isonitrile complexes

Hexakis(alkylisonitrile) and hexakis(arylisonitrile) complexes of Tc(I), Tc(CNR)(,J, were prepared by reduction of TCO4 in aqueous solution with Na2S204 in the presence of the isonitrilc ligands. White, crystalline hexakis(terf-butylisonitrile)technetium(l) hexa-fluorophosphate was obtained by refluxing a mixture of water and ethanol of pH 12 con- 

Hcxakis(alkylisonitrile) complexes of Tc(I) arc an important class of potential radiopharmaceuticals. Some Tc NMR chemical shifts cf selected [Tc(CNR)e,] compounds are compiled in Table 12.20.A. 

The hexacoordinate complexes [Tc lCNRlsjpFsj readily undergo oxidative addition with Xt (X = Cl. Br) to provide the seven-coordinate, light-yellow complex salts [Tc (CNR)6X][PF6 2 [394]. 

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Cyclopentadienyl and Arene Complexes Cyano and Isonitrile Complexes... 

Although carbonyl and cyclopentadienyl complexes are well known for Tc(I) and Tc(III), none appear to have been reported for Tc(II). This may be ascribed to the tendency to follow the 18-electron rule, which, due to the odd number of electrons, would require dimer formation for compliance. Similarly, no Tc(II) cyano or isonitrile complexes appear to have been isolated. 

These complexes have been used as starting materials in the preparation of other alkoxy and phenoxy complexes, phenylimido complexes, analogous amine complexes, dioxotetrapyridinerhenium(V) salts and dioxobis(ethylene-diamine) rhenium (V) salts, cyano complexes of rhenium-(V), acetylacetone complexes, hydrides, carbonyls, and isonitrile complexes. The products of reactions using the materials described here as sources are normally easier to purify than those obtained by other methods. 

The syntheses of iron isonitrile complexes and the reactions of these complexes are reviewed. Nucleophilic reagents polymerize iron isonitrile complexes, displace the isonitrile ligand from the complex, or are alkylated by the complexes. Nitration, sulfonation, alkylation, and bromina-tion of the aromatic rings in a benzyl isonitrile complex are very rapid and the substituent is introduced mainly in the para position. The cyano group in cyanopentakis(benzyl isonitrile)-iron(ll) bromide exhibits a weak "trans" effect-With formaldehyde in sulfuric acid, benzyl isonitrile complexes yield polymeric compositions. One such composition contains an ethane linkage, suggesting dimerization of the transitory benzyl radicals. Measurements of the conductivities of benzyl isonitrile iron complexes indicate a wide range of A f (1.26 e.v.) and o-o (1023 ohm-1 cm.—1) but no definite relationship between the reactivities of these complexes and their conductivities. 

Cyanopentakis(benzyl isonitrile)iron(II) bromide, which represents a new class of iron isonitrile complexes, was investigated in some detail. This complex is diamagnetic and dissociates in nitrobenzene into two univalent-univalent ions as indicated by cryoscopic and conductivity measurements. It exhibits two peaks in the triple bond region of the infrared spectrum one at 2200 cm.—1 assigned to the isonitrile groups and another at 2092 cm.-1 assigned to the cyano group. The structure proof of cyanopentakis (benzyl isonitrile) iron (II) bromide is ... 

Alkylation of cyano groups to form isonitrile complexes was achieved with alkyl bromides and iodides for the complexes [Tr-C5H5Fe(CO)(CN)2] [Eqs. (8) and (9)], [7t-C5H5M CO)3CN] (M = Mo, W), and [tt-CjHsMo... 

Cyclopentadienyl Complexes Cyano, Isonitrile, and Thiocyanate Complexes Aqua, Halide, and Related Dimeric Complexes Carboxylato and /3-Diketonato Complexes... 

Reactions between 5-cyanotetrazole and transition metals, when performed in boiling acetone, lead to hydrolysis of the cyano group and formation of 5-carbamyl tetrazolate complexes (68). Complexes containing 1- or 5-substituted tetrazolate anions can also be obtained by 1,3-dipolar cycloaddition of organic isonitriles (RNC) (15) or nitriles (RCN) (61), respectively, to coordinated azide ligands [Eqs. (3) and (4)]. 

The acid cleavage of simple [RCo(CN)5] derivatives is complex because cyano ligands on a metal ion are also susceptible to protonation. The protonated CN becomes an isonitrile-type ligand and undergoes an insertion reaction with the alkyl ligand to give, ultimately, a nitrile or a carboxylic acid 114,116). 

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