Carbon bonds, transition metal

Examples of linear addition reactions that form C-O, C-S, C-N, C-P, C-C, and C-Si bonds are reviewed. Only a few of the growing number of linear additions that form a carbon-transition metal bond are included... 

Organometallic Complexes with Silicon-Transition Metal or Silicon-Carbon-Transition Metal Bonds... 

ORGANOMETALLIC COMPLEXES WITH SILICON-CARBON-TRANSITION METAL BONDS... 

Olefinic compounds will often insert into carbon-transition metal bonds as CO does, and this reaction is an important step in many catalytic syntheses. When this step is combined with an oxidative addition of an organic halide to a palladium(O) complex in the presence of a base, a very useful, catalytic olefinic substitution reaction results (26-29). The oxidative addition produces an organopalladium(II) halide, which then adds 1,2 to the olefinic reactant (insertion reaction). The adduct is unstable if there are hydrogens beta to the palladium group and elimination of a hydridopalladium salt occurs, forming a substituted olefinic product. The hydridopalladium salt then reforms the... 

Heck explained the formation of ketones under Oxo conditions by the second mechanism, but the first mechanism seems equally likely. The second mechanism alone seems capable of explaining unsaturated products and is important in providing an example of an olefin insertion into a carbon-transition metal bond. 

Insertion reactions with carbon monoxide or sulfur dioxide are well known for compounds with carbon-transition-metal bonds, e.g.,... 

Although the tin hydride + alkyl halide method is probably the most important way of making alkyl radicals, we should mention some other methods that are useful. We said at the beginning of the chapter that carbon-metal bonds, particularly carbon-transition metal bonds, are weak and can homolyse to form radicals. Alkyl mercuries are useful sources of alkyl radicals for this reason. They can be made by a number of routes, for example, from Grignard reagents by transmetailation. 

Carbon-transition metal bonds can also be formed by cocondensing transition-metal atoms with isonitriles. Thus, using Ni and Fe with t-butyl isocyanide, methyl isocyanide, cyclohexyl isocyanide and vinyl isocyanide the NiL4 and FeL, complexes are formed. Palladium cocondensed with isonitriles yields PdLj polymeric structures with terminal and bridged isonitrile ligands ... 

It is worth noting that no overbinding seems to occur in the local density description of alkali chemisorption on nickel clusters, in contrast to findings for carbon transition metal bonds (23,27,28). At present, it would be premature to correlate this difference with the character of the various bonds (covalent vs. ionic). Clearly, density gradient corrections to the energy functional (31) would be highly useful in deciding this question. 

The mechanism of hydrosilylation on a transition metal catalyst involves an intermediate with a carbon-transition metal bond. Carbon monoxide, if present, inserts into the carbon-metal bond to give an... 

In conclusion, electronic density of the transition metal may be influenced, case by case, by the effect of the reaction with aluminum alkyl and, as a result, the carbon-transition metal bond stability, olefin coordination and insertion capacity, stereochemical control of active centre and chain transfer and propagation processes, hence polymer MWD, may also be affected. This is particulary true for soluble catalytic systems for which the existence of active centres as bimetallic complexes is likely. 

The termination reactions appear to be quantitative and specific for the reaction of saturated polymer molecules attached to aluminium and titanium [116], but applied to diene polymerizations the method is less satisfactory mainly because of the greater stability of allylic carbon-transition metal bonds. Polybutadiene has been labelled by terminating with tritiated methanol with the Cr(acac)3/AlEt3 catalyst [55], and similarly polyisoprene prepared with VCl3/AlEt3 [107]. Polybutadiene prepared with Til4/Al(i-Bu)3 has been labelled using C02 [115]. 

Otganometal complexes with silicon-transition metal or silicon-carbon-transition metal bonds... 

As a facile method of carbon-carbon bond formation, the insertion of carbon-carbon multiple bonds into carbon-transition-metal bonds is a very important fundamental reaction in organotransition-metal chemistry. However, in contrast to the tremendous number of reports about the insertion of carbon-carbon multiple bonds into carbon-transition-metal bonds, direct insertion of carbon-heteroatom multiple bonds, such as carbonyl and nitrile groups, without using stoichiometric organometallic reagents, has received scant attention.111 A palladium(II)-catalysed cycliza-tion reaction of alkynes with carbon-heteroatom multiple bonds under mild conditions has been developed, using insertion of carbon-heteroatom multiple bonds into the carbon-palladium bond as the key step.[2]... 

Secondly, in contrast to alkali metals, transition metals can complex with both electron donor and electron acceptor ligands. Complexation with the former leads to increasing elytron (tensity on the transition metal, to the resulting decrease in electron ativity and, correspondingly, to an increase in the ionic character (asynunetry) of the carbon-transition metal bond. This should inevitably affect the microstructure of the resulting polydiene. The expected tendoicy of the change in this structure is as follows from the 1,4-cts to... 

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