Conjugate transition metal catalyst

Physical and Chemical Properties. The (F)- and (Z)-isomers of cinnamaldehyde are both known. (F)-Cinnamaldehyde [14371-10-9] is generally produced commercially and its properties are given in Table 2. Cinnamaldehyde undergoes reactions that are typical of an a,P-unsaturated aromatic aldehyde. Slow oxidation to cinnamic acid is observed upon exposure to air. This process can be accelerated in the presence of transition-metal catalysts such as cobalt acetate (28). Under more vigorous conditions with either nitric or chromic acid, cleavage at the double bond occurs to afford benzoic acid. Epoxidation of cinnamaldehyde via a conjugate addition mechanism is observed upon treatment with a salt of /-butyl hydroperoxide (29). 

The discovery by Ziegler that ethylene and propylene can be polymerized with transition-metal salts reduced with trialkyl aluminum gave impetus to investigations of the polymerization of conjugated dienes (7—9). In 1955, synthetic polyisoprene (90—97% tij -l,4) was prepared using two new catalysts. A transition-metal catalyst was developed at B. E. Goodrich (10) and an alkaU metal catalyst was developed at the Ekestone Tke Rubber Co. (11). Both catalysts were used to prepare tij -l,4-polyisoprene on a commercial scale (9—19). 

In the process of radical polymerization a monomolecular short stop of the kinetic chain arises from the delocalization of the unpaired electron along the conjugated chain and from the competition of the developing polyconjugated system with the monomer for the delivery of rr-electrons to the nf-orbitals of a transition metal catalyst in the ionic coordination process. Such a deactivation of the active center may also be due to an interaction with the conjugated bonds of systems which have already been formed. 

The addition of allcenes to alkenes can also be accomplished by bases as well as by the use of catalyst systems consisting of nickel complexes and alkylaluminum compounds (known as Ziegler catalysts), rhodium catalysts, and other transition metal catalysts, including iron. These and similar catalysts also catalyze the 1,4 addition of alkenes to conjugated dienes, for example. 

To date, the reductive cyclization of allenic alkenes remains undeveloped. However, the reductive cyclization of activated alkene partners in the form of 1,3-dienes and conjugated enones has been achieved using late transition metal catalysts. Indeed, the hydrosilylative dimerization of 1,3-dienes reported in 1969 appears to be the first reductive... 

The first application of NMR diffusion measurements to determine the aggregation state of a transition metal catalyst concerned the chiral, tetranuclear Cu(i) catalysts 130-132, used in the conjugate addition reactions of anions to a,p-unsatu-rated cyclic ketones. Compounds 130-132 react wdth isonitriles to form 133-135, and do not degrade to lower molecular weight species (see Eq. (20)) [109]. 

Mo catalysts are uniquely effective in the polymerization of S-containing disubstituted acetylenes. Though there is a possibility that S and O in the monomer deactivate group 5 and 6 transition metal catalysts, the basicity of S is weakened by the conjugation with the triple bond, resulting in the lower coordinating ability to the propagating... 

Organometallic reagents can be used direcdy or with a transition metal catalyst in tandem vicinal difunctionalization reactions. Relatively basic reagents find greater use with substrate molecules that are not enolizable so that competitive a-deprotonation is avoided and with substrates that have been activated towards conjugate addition by an electron-withdrawing a-substituent. 

A comprehensive review on the whole field of polymerization of conjugated dienes by transition-metal catalysts was compiled by Porri and Giar-russo in 1989 [50]. 

Iododi- -butyltin hydride-Lil system allows the conjugate hydrostannation of enals under mild and neutral conditions without the assistance of transition metal catalysts (Equation (28)).89 Bu2SnIH alone gives a mixture of hexanal and the allylic alcohol derived from both 1,4- and 1,2-reductions, respectively. The formation of an ate complex Li+[Bu2SnI2H] and its TBP structure are confirmed by 119Sn NMR spectra.89... 

Catalytic hydroboration is a new methodology of great synthetic potential. The reaction is usually carried out with catecholborane in the presence of rhodium, palladium, iridium and ruthenium compounds.2 In contrast to olefins, very little is known on catalytic hydroboration of conjugated dienes and enynes. Our earlier studies on the uncatalyzed monohydroboration of conjugated dienes,6 reports on the hydroboration of 1-decene with catecholborane catalyzed by lanthanide iodides,7 and monohydroboration of 1,3-enynes in the presence of palladium compounds,8 prompted us to search for other transition metal catalysts for monohydroboration of conjugated dienes and enynes 9 10... 

The C-H bond cleavage of active methylene compounds with a transition metal catalyst is another method for the functionalization of these C-H bonds. To date, several reactions have been developed. In particular, the asymmetric version of this type of catalytic reaction provides a new route to the enantioselective construction of quaternary carbon centers. One of the most attractive research subjects is the catalytic addition of active methylene C-H bonds to acetylenes, allenes, conjugate ene-ynes, and nitrile C-N triple bonds. The mthenium-catalyzed reaction active methylene compounds with carbonyl compounds involving aldehyde, ketones, and a,y3-unsatu-rated ketones and esters is described in this section. 

Like simple alkynes, conjugated diynes undergo cyclotrimerization in the presence of transition metal catalysts, but whereas simple alkynes give symmetrically substituted benzenes almost exclusively, diynes give symmetrical (256) and unsymmetrical... 

The original material (subsequently called URPAC) is accessible in various morphologies with a large number of Ziegler-Natta type and other transition metal catalysts. It has been studied in detail with spectroscopic and other physicochemical methods. Quantum theoretical model calculations have provided insights into the energetics of conjugated double bond systems. 

Additions to conjugated systems are further facilitated by some of the features discussed previously e.g., additions to dienes" " and enynes" in the presence of transition-metal catalysts and additions to enynes containing a suitably placed intramolecular function such as hydroxyl. Although uncatalyzed intermolecular additions to alkynylsilanes are not yet demonstrated, additions are seen in the presence of a transition-metal catalysts" and intramolecular additions to alkynylsilane functions by suitably placed internal organomagnesium-halide functions are facile. ... 

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