Olefination with transition metal derivatives

Chemical Properties. Higher a-olefins are exceedingly reactive because their double bond provides the reactive site for catalytic activation as well as numerous radical and ionic reactions. These olefins also participate in additional reactions, such as oxidations, hydrogenation, double-bond isomerization, complex formation with transition-metal derivatives, polymerization, and copolymerization with other olefins in the presence of Ziegler-Natta, metallocene, and cationic catalysts. All olefins readily form peroxides by exposure to air. 

Organometallic tr complexes having hydrogen ona. p carbon commonly react with triphenylmethyl (or trityl) cation. While main-group alkyls fragment to alkene, metal cation and triphenylmethane, comparable transition-metal derivatives produce rearranged cationic olefin n complexes and triphenylmethane ... 

Another possibility for the formation of free radical species from hypochlorite is through its reactions with transition metal ions. Thus, Guilmet and Meunier (1980) reported a manganese-promoted epoxidation of olefins such as styrene (Equation 5.13) and cyclohexene in a two-phase dichloromethane-water solvent mixture. The epoxide oxygen was derived from HOCl, not from air, but no mechanistic details were speculated upon. Further evidence needs to be obtained on the possibility of free-radical reactions in water and wastewater chlorination. 

The preparation and reactions of transition-metal derivatives of members of this group of compounds are described in Chapter 5. Their use as starting materials for other compounds is frequently referred to elsewhere in this Volume, and interested readers are recommended to browse widely. The toxicity of fluoro-olefins has been reviewed and correlated with their nucleophilicity. ... 

Pitcher, Buckingham, and Stone 285) have discussed the anomalous chemical shift of fluorine atoms bonded to the a-carbon atom of perfluoro-alkyl-transition metal derivatives in terms of mixing of nonbonding electrons of the halogen with orbitals of the metal. Bennett, Pratt, and Wilkinson (27) have discussed the shielding of protons of olefins in the complexes of these ligands with transition metals. 

A combination of PQQ derivatives with transition metals leads to form the efficient redox systems. Dropwise addition of terminal olefin to the solution of PdCl2 (0.1 molar equiv.), trimethyl ester of PQQ, (PQQTME, 0.1 molar equiv.) and H2O in DMF under molecular oxygen results in the formation of 2-alkanone (Scheme 3.2). It should be noted that PQQTME constitutes a catalytic redox cycle. The orthoqui-none function appears to reoxidize the reduced palladium species generated in situ. Use of 1,7- or 1,10-phenanthrolinequinone gives a poor result maybe due to the coordination of paUadium(II) species towards the pyridine moiety opposite to the quinone group [5]. Mediation ofp-benzoquinone in the palladium-catalyzed oxidation reactions has been reported to require electrochemical or cobalt porphyrin catalyzed oxidation of the quinol [6-8]. The above-mentioned results provide an example for efficient redox systems of coenzyme derivatives with transition metals, which is demonstrated to be synthetically useful. 

With discoveries of boron-based cocatalysts such as triphenyl-boron, ammonium tetraphenylborate salts, and finally pentafiuorophenyl derivatives of borate [B(C6H5)4] , olefin polymerization catalysis was developed without a reliance on alkylaluminum species. Although the activity with nonfiuori-nated boron-based cocatalysts was invariably low, the fiuorinated analogs exhibited olefin polymerization behavior similar to that of metallocene/MAO catalyst systems. The boron and borate compoimds are typically used in a 1 1 molar ratio with transition metal (stoichiometric or near stoichiometric). Because these activators do not alkylate the transition metal, the metallocene precatalyst employed must already bear alkyl groups. Thus, zirconocene dimethyl species combine with boron or borate activators to nerate active cationic polymerization catalysts. Figure 8 shows typical activation reactions with borate (a, b) and boron (c) activators. 

With transition metal carbonyl hydrides, the M—H system may add to the olefin. Tetrafluoroethylene gives the derivatives M—CF2CF2H, chlorofluoro-olefins react similarly [227, 229, 230, 231, 232, 233]. 

Garbonylation of Olefins. The carbonylation of olefins is a process of immense industrial importance. The process includes hydroformylation and hydrosdylation of an olefin. The hydroformylation reaction, or oxo process (qv), leads to the formation of aldehydes (qv) from olefins, carbon monoxide, hydrogen, and a transition-metal carbonyl. The hydro sdylation reaction involves addition of a sdane to an olefin (126,127). One of the most important processes in the carbonylation of olefins uses Co2(CO)g or its derivatives with phosphoms ligands as a catalyst. Propionaldehyde (128) and butyraldehyde (qv) (129) are synthesized industrially according to the following equation ... 

Professor Stone s paper points out that the reactivity of [ (ti-C5H5) (OC) 2WsCR] towards transition metal complexes is similar to that of an alkyne. It would be of interest to examine this compound and several of its derivatives which contain OW double bonds with respect to their reactivity patterns towards the BH3 group to determine if reactions analogous to the hydroboration reaction of alkynes and olefins would occur (1) or reactions similar to the attempted hydroboration described below would take place. 

There have also been several papers [61-63] on the importance of carefully establishing the reaction mechanism when attempting the copolymerization of olefins with polar monomers since many transition metal complexes can spawn active free radical species, especially in the presence of traces of moisture. The minimum controls that need to be carried out are to run the copolymerization in the presence of various radical traps (but this is not always sufficient) to attempt to exclude free radical pathways, and secondly to apply solvent extraction techniques to the polymer formed to determine if it is truly a copolymer or a blend of different polymers and copolymers. Indeed, even in the Drent paper [48], buried in the supplementary material, is described how the true transition metal-catalyzed random copolymer had to be freed of acrylate homopolymer (free radical-derived) by solvent extraction prior to analysis. 

These reactions are covered in other chapters of Volume 11 (Chapters 11.06 and 11.07). This part deals only with examples which are in connection with other sections of this chapter. Additions of metallocarbenoids to unsaturated partners have been extensively studied. Most of the initial studies have involved the transition metal-catalyzed decomposition of cr-carbonyl diazo compounds.163,164 Three main reaction modes of metallocarbenoids derived from a-carbonyl diazo precursor are (i) addition to an unsaturated C-C bond (olefin or alkyne), (ii) C-H insertion, and (iii) formation of an ylid (carbonyl or onium).1 5 These reactions have been applied to the total synthesis of natural... 

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