Cobalt complexes isocyanide

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... 

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). 

Trigonal-bipyramidal Complexes. Cobalt carbonyl reacts with isocyanides, disproportionating to Co1 and Co-1 ... 

Isocyanide complexes have found numerous applications in organic synthesis and catalysis. Isocyanides undergo polymerization in the presence of many transition metal complexes, for instance, metal carbonyls, metallocenes, cyclopentadienyl carbonyls, nickel(II), palladium(II), and cobalt(II) complexes. Exceptionally high activity is exhibited by nickel and cobalt carbonyls. The resulting polymers are Schiff bases ... 

The catalyst CoCl2 2H20 (0.033 g 0.2 mmol), metal hexacarbonyl (3.0 mmol M = Cr, 0.660 g M = Mo, 0.792 g M = W, 1.056 g) and toluene (10 mL) are added to the reaction flask. The stirred mixture is heated to reflux and the appropriate amount of tert-butylisocyanide required to achieve monosubstitution (3.6 mmol, 0.403 mL), disubstitution (6.6 mmol, 0.704 mL), or trisubstitution (9.6 mmol, 1.076 mL) is added by microsyringe to the hot reactants. This gives an immediate blue coloration due to the formation of a cobalt chloride-isocyanide complex. 

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). 

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). 

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). ... 

NOCgHj, Benzoyl isocyanide, chromium complex, 26 32,34,35 N0C,3H,3, Formanide, N-(l-(l-naphthal-enyl)ethyll-, rhenium complex, 29 217 NOPCjsHjj, Benzamide. 2-(diphenylphos-phino)-N-phenyl-, 27 324 NOPCjjHjj, Benzamide, Af-[2-(diphenyl-phosphino)phenyl]-, 27 323 NO2CH3, Methane, nitro-, antimony complex, 29 113 cobalt complex, 29 114 NOjCjHj, 4-Pyridinecarboxylic acid, rhodium complex, 27 292 NO2P2C3JH33, Phosphorus(l-t-), p-nitrido-bis(triphenyl-, acetate, 27 296 NO2SC3H7, L-Cysteine, molybdenum complex, 29 255,258... 

Rearrangements are less common, since the complexes are usually stable. However, if a cobalt-acetylene complex is reacted with an isocyanide, a metallacycle (145) is formed. ... 

---