Heteroatom-containing substituent

In the absence of heteroatom containing substituents (e.g. halo-, cyano-), at or conjugated with the radical center, carbon-centered radicals have nucleophilic character. Thus, simple alkyl radicals generally show higher reactivity toward electron-deficient monomers (eg. acrylic monomers) than towards electron-rich monomers (e.g, VAc, S) - Table 3.6. 

It is rather surprising that only a few diorganomagnesium compounds have been reported in which intramolecular coordination of a heteroatom-containing substituent is present. The synthesis of (2-Me2NCH2C6H4)2Mg (67) was reported. It has been used in a study on the infiuence of the presence of potentially intramolecular coordinating substituents on Schlenk equilibria However, it has never been structurally characterized. 

A series of diaUcylzinc compounds, functionalized with a heteroatom-containing substituent (Scheme 8), has been prepared and was strnctnrally characterized by X-ray crystallographic studies (66" and 69" ) or gas-phase electron diffraction (66, 67", 68 ° and 70"°). The relevant structural data are summarized in Table 4 and, as a representative example, the molecular geometry of 66 is shown in Fignre 33. 

If trans-subsituted carbene complexes containing ligands which have a greater (T-donor/n-acceptor ratio than CO (e.g., PRj, AsRj, SbRj or a Jt-aromatic ) are reacted with electron-pair acceptor acids, these ligands remain in the product complex. Only the heteroatom-containing substituent is removed from the carbene carbon and cationic carbyne complexes are formed ... 

A few reports on the hydrogenation of polystyrenes with heteroatom-containing substituents have been made. The hydrogenation of poly(styrene-co-methyl acrylate) was performed using a silica/alumina-supported Ni catalyst... 

In this section, the reactivity of carbon- and heteroatom-containing substituents attached directly or indirectly to the heterocyclic ring of 1,3-dithiole derivatives is discussed. Here, chemical manipulations on these systems exclude ring carbon and sulfur atoms, which are the subject of Section 4.12.6. Special 1,3-dithioles called Jt-extended TTFs, containing two or more 1,3-dithiole moieties linked together via =C-(C=C) -C= or similar conjugated spacers, are discussed with typical TTFs in Section 4.12.11, although formally they constitute an example of functionalization of the 1,3-dithiole by 2rt-extended substituents, terminated by another 1,3-dithiole moiety. 

Compounds as a Result of the Enforced Coordination of a Heteroatom-Containing Substituent.261... 

Iron and cobalt carbene complexes are capable of much more selective furan synthesis. Reactions of cobalt methoxycarbenes with internal alkynes give good to excellent yields of 2-methoxyfurans and have been applied to a synthesis of a natural product, bovolide [75 b]. Both terminal and internal alkynes are viable substrates in the preparation of 2-aminofurans from iron (dimethylamino)carbenes [78], although the nature of the rearrangement of the heteroatom-containing substituent is also as yet unclear [Eq. (33)]. The inclusion of elevated carbon monoxide pressure can divert this reaction to the production of pyrones [75c, 79]. 

The Schrock type carbyne complexes Np3W=C Bu, ( BuO)3W=C Bu and Cl3(dme)WsC Bu are very active catalysts for the polymerization of alkylsubstituted 1-alkynes and also for 1-alkynes with heteroatom containing substituents. The polymerization of disubstituted alkynes was only achieved with Cl3(dme)W=C Bu as catalyst. 

The introduction of cyclopentadienyl ligands with a heteroatom-containing substituent capable of bonding with the metal is exemplified by complexes 11-17 (Figure 14.5). When activated with MAO, these complexes form catalyst species with rather low activities and decreased syndioselectivities compared to those without heteroatom substituents. The catalyst activities of complexes 11 and... 

FIGURE 14.5 Structures of mono-Cp titanium complexes 11-17 with a heteroatom-containing substituent on the Cp ring. 

Usually, the reactions are complete within hours and give good conversions (40% -90+%). In general, the larger the alkyl or other substituted alkyl group on the ester, the slower the reaction rate. Heteroatom containing substituents do not have a... 

A rationalization of the cisUrans ratios of olefins produced in carbenic decomposition of diazo-compounds R CN2CH2R is based on competing electrostatic and steric effects in the intermediate singlet carbene. Heteroatom-containing substituents in the 3-position of cyclohexene can direct the addition of electrophilic species from a cis direction and rates of addition are sometimes accelerated. The addition of dichlorocarbeneto (284), however,... 

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