Cobalt isocyanides

Cobalt, cyclopentadienyl(ij -tolane)-(triphenylphosphine)-reaction with phenyl isocyanide, 1, 666 Cobaltacycles selenophenes from, 4, 968 Cobaltacyclopentadienes reactions, I, 671 Cobester... 

Several ESR studies of various cobalt(II) isocyanide complexes have been carried out (77,81,88). A Raman and infrared spectral study on [Co(CNR)5]-... 

In this contribution we describe facile, high-yield syntheses of the series of zerovalent iron isocyanide complexes Fe(CO)5 (CNC6H3Me2-l,3)n ( n = 1-5). The starting material is iron pentacarbonyl, and cobalt(II) chloride is used as a catalyst to achieve the stepwise replacement of carbonyl groups by 2-isocyano-l,3-dimethylbenzene.4,9... 

Representative new types of bonding modes that have been observed are as follows with the isocyanide symmetrically bridging three cobalt atoms through the isocyanide carbon (1) (59) with the isocyanide bridging two... 

A number of publications have appeared on the synthesis of cationic cobalt(I) complexes by known routes. The cations are of the well-established type [Co(CNR)5]+ (R = aryl) (119-122). Reactions of aromatic isocyanides with Co2(CO)g in refluxing toluene have given the fully substituted cobalt(O) dimer Co CNR) (R = xylyl, C6H2Me3-2,4,6, C6H2Br-4-Me2-2,6) (25,123). 

The stereochemistry of the pentakisisocyanidecobalt(I) and (II) complexes is apparently a function of crystallization procedures. To date, four isomeric structures have been identified for isocyanide complexes of co-balt(l) (121) and three for those of cobalt(II) (284). Crystal structure determinations of [Co(CNPh)5]C104 CHCl3 (285) and [Co(CNPh)5]-(CI04)2 C1CH2CH2C1 (284) have shown the coordination around the cobalt to be square pyramidal, whereas with [Co(CNC6H4Me-p)5][Co(NM A)3] (NMA = nitromalonaldehyde) a trigonal bipyramidal structure was found for the cation (286). 

Reaction of FeCo2(CO)9S with a series of phosphines (31, 133) and isocyanides (126) yielded mono-, di-, and trisubstituted derivatives, Eqs. (77) and (78). 57Fe-Mossbauer spectra of the phosphine-substituted derivatives indicated that substitution at cobalt occurs prior to substitution at iron (31). Unfortunately, no crystallographic evidence has been obtained for any of these derivatives, and the precise stereochemistry has not been resolved, even with the aid of l3C-NMR spectra (9). The problem is compounded with the isocyanide ligands since several isomers of the trisubstituted derivatives are formed. 

There are marked differences between the carbonyl cations of cobalt and its congeners, rhodium and iridium. For instance, the heavier elements form square-planar carbonyl cations as well as higher coordinate complexes. This is paralleled by the isocyanide cations thus cobalt forms [Co(CNR)5]+ cations (191), whereas rhodium and iridium form [M(CNR)4]+ cations (191, 192, 194). 

Cocyclization of acetylene with isocyanides gives interesting new cyclic compounds 103, 116). The reaction patterns are generally similar to the cocyclization wdth carbon monoxide which is already known 103, 117). Low-valent nickel, palladium, or cobalt complexes are active in the following reactions 102, 103) for which intervention of acetylene complexes has been suggested ... 

Recently, Yamazaki et al. 103) carried out stoichiometric reactions of cobalt-acetylene complexes with isocyanides and isolated the expected intermediate metalocyclic complexes (Scheme 6). 

The nucleophilic nature of these radicals allows addition to carbon-nitrogen multiple bonds, and in selected cases this has been demonstrated. Suitable substrates for such additions include protonated pyridines, thiazoles and imidazoles (equation 183), and nitroalkyl anions359. Yamamoto and coworkers have also described cobalt-mediated multiple additions of carbon tetrahalides, benzyl bromides or a-bromo ketones to isocyanides, which are postulated to occur through the corresponding alkylcobalt(III) complexes360. 

There is an extensive Co1 chemisty of monocyclopentadienyl compounds, of which CpCo(CO)2 is one example. The CO may be replaced by phosphines, alkenes, isocyanides, and so on. The dicarbonyl itself can be reduced to a radical ion that contains cobalt in the formal oxidation state 0.5, and can be isolated as its (Ph P)2N+ salt ... 

Optically active organometallic complexes have been used to study stereochemical reactions. Substituted cobalt nitrosyl complexes are interesting chiral see Chiral) complexes because they exhibit tetrahedral structures, whereas most optically active organometallic complexes are half-sandwich structmes with octahedral geometries. Diastereomeric cobalt complexes of the type Co(CO)(NO)(L)( L) (L = phosphite or phosphane L = optically active phosphane or isocyanide) have been synthesized from (4) via substitution (Scheme 6). ... 

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