Cobalt complexes hydrocarbons

Hydridotris(pyrazolyl)borates, as cobalt complex ligands, 44 274-278 Hydroboration, 16 230-234 chain lenghtening, 16 231-232 role in sythesis, 16 231, 232 Hydrocarbons clusters, 18 57-59... 

Careful studies by Doyle et al. (163) have also shown that soluble ruthenium species are inactive for hydrocarbon formation. A soluble system could be maintained in heptane solvent at 250°C under 100 atm of 1 1 H2/CO for many hours by taking precautions to avoid the possible introduction of impurities into the system and by slowly raising the temperature. No hydrocarbon formation was observed in this reaction. Only upon heating to about 260°C was the disappearance of soluble ruthenium complexes noted, along with the formation of linear alkanes. These results may suggest that metastable homogeneous ruthenium solutions can be formed, as has been reported for cobalt complexes (56) precipitation of the metal may be an autocatalytic process. 

Cobalt vapor interacts with norbornene to produce Co(C7H10)3, a 15-electron complex, apparently isostructural with Ni(C7H10)3. The cobalt complex is soluble in hydrocarbon solvents to afford deep blue solutions decomposing rapidly and autocatalytically at -15° (5a, 134). It has not yet been possible to isolate this complex in a pure state but some of the reactions have been examined by trapping experiments ... 

The trimeric lithium-cobalt complex [LiCo(C2H4)(PMe3)3]3 (69) 94), the first lithium carrier in hydrocarbon solvents, clearly involves interactions of the lithium atom with the hydrocarbon ligands as well as the cobalt atoms, but further ligation with solvent donor atoms is not required. 

Another cobalt complex having only hydrocarbon ligands, (1,3-butadiene)cyclopentadienylcobalt, has been obtained as a volatile red solid melting at 103°-105°C by reaction of the diene with dicyclopenta-dienylcobalt or (1-benzoyl-1,3-cyclopentadiene)cyclopentadienylcobalt (489). The compound decomposes slowly in air. 

It has been reported that other hydrocarbons, e. g., naphthenic naphthas, may also be suitable for the production of acetic acid [58]. This was studied on a pilot scale but never, apparently, commercialized. A large number of metal ions, both varivalent and non-varivalent, were studied. Feeds ranged from pure to very complex hydrocarbon mixtures. While it is difficult to draw any firm conclusions, it was possible to make significant yields of acetic acid. Manganese-ion catalysts were quite effective they produced higher formic acid/acetic acid ratios than cobalt-ion catalysts, as one would expect. 

Carbon-Carbon Bond-forming Reactions via Organometal1ic Electrophilies. - Functionalization of unsaturated hydrocarbons by nucleophilic attack on their metal complexes continues to receive attention. Sequential double nucleophilic addition to a cationic cobalt complex of butadiene... 

The sodium salt of IBA proved to be quite stable, selective, and sensitive, unfortunately the reaction was not reversible, and the sensitivity decreased with each sample injection. However, a cobalt complex of IBA was made, and found to remedy the situation. Further improvement of the coating could be obtained by the addition of small amount of pesticide to the methylene chloride solution of the cobalt-lBA complex. A modified coating with paraoxon was found to be more sensitive to parathion than DDVP and DIMP. No serious interference was observed from SO2, CO2, CO, NO2, NH3, and chlorinated hydrocarbon pesticides except if combined by solvent. 

Reductive Dehalogenations Microemulsions are usually more useful than micelles for electrochemical synthetic applications because larger amounts of polar and nonpolar reactants can be solubilized. Electrochemical catalysis has been used in microemulsions for the electrolytic conversion of organohalide pollutants to hydrocarbons [53] using mediators such as metal phthalocyanines and cobalt complexes. Microemulsions were used for the complete electrochemical catalytic... 

Cobalt.—Aromatic hydrocarbon hydrogenations with a discrete metal complex have now been achieved for the first time. Thus hydrogenation of benzene to cyclohexane proceeds slowly at 25 °C and < 760 mmHg pressure in the presence of [Co( y -C3HB)- P(OMe)3)3]. Alkylbenzenes are converted into alkylcyclohexanes, anisole into methoxycyclohexane, and ethylbenzoate into ethyl cyclohexenylcarboxylate. The suggested mechanism of reaction is summarized in Scheme 14. ... 

A preliminary report is published of work which, though incomplete mechanistically, is of sufficient interest in connection with the Co-C bond to justify inclusion here/ Hydrocarbons R , RH, and R2, are formed from the alkyl-mer- AT-(2-aminoethyl)-7-methylsalicylideneminato (ethyl-enediamine)cobalt ion, [RCo(7-Mesalen)(en)], in aqueous perchloric acid. Use of DCIO4 in D2O shows that RH is formed from the cobalt complex although RN(0)(t-Bu) radicals could be trapped on addition of t-BuNO. There is an induction period this is decreased and the steady-state concentration of RN(0)(t-Bu) is increased as acidity rises. Two diol-dehydrase reactions catalyzed by B12 coenzyme can also be made to occur using this system. 

Treatment of dicobalt octarbonyl with a 2 1 mixture of t-butylacety-lene and acetylene forms a remarkable cobalt complex of stoicheimometry Co2(CO)4(C2HBu )2(C2H2). The structure of this compound, 9.7, provides a fascinating insight into a mechanism of polymerization of acetylenes. The bonding of the hydrocarbon residue in complex, 9.7, may be described in terms of a fly-over , bis-enyl system. The distance Co—C3 (fl enyl) is 2-04 A. 

It is very well established that 16-electron species such as [CsRsML] (M = Rh, Ir) generated in situ undergo facile oxidative addition of CH bonds of saturated hydrocarbons or arenes (see COMC (1995) and COMC (1982)). This situation is likely to be due to the fact that iridium and rhodium complexes are kinetically far more stable than cobalt. However, during the last decade, some CH activations were found to take place on some typical cobalt complexes. 

Two known cobalt complexes of cyclooctatetraene are of the type CgHg(CoC5H5) , with = 1 or 2. In the mononuclear complex COT acts as a 1,5-diene with the eight-membered hydrocarbon in the tub configuration 153,154), while the binuclear complex probably has a central CgHg ligand with a plane tetragonal structure 147,154). 

Some electron exchanges of cobalt complexes involve changes in spin configuration, from low-spin to high-spin such that S S V2, and this can lead to another source of non-adiabaticity. The spin forbidden factor, Xs> is entirely empirical within the present formalism, as well as within the TM formalism. For the complexes Co(phen)3 + + experimental evidence, also supplemented by quantum mechanical calculations, suggest that Xs 10. and as a rule of thumb we will employ this value for spin-forbidden electron transfers in transition-metal complexes. Where no heavy metals or paramagnetic species are involved, we expect to have Xs 10 , as shown in Chapter 15 for aromatic hydrocarbons. 

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