Insertion into phenoxides

Mg11 insertion into labile hydroporphyrins is effected by the use of IMg(2,6-di-f-butyl-4-methyl-phenoxide)-Li(2,2,6,6-tetramethylpiperidide).169... 

Various 2-substituted benzofurans 165 are obtained by the interaction of iodo-nium salts 164 with sodium phenoxide in methanol (Scheme 63) [126, 127]. This reaction proceeds via the intramolecular alkylidene carbene insertion into the ortho-CH bond of the phenoxy ring. Furopyridine derivatives 167 can be prepared similarly by the intramolecular aromatic C-H insertion of the alkylidenecarbenes generated by the reaction of alkynyliodonium tosylates 166 with potassium salts of 4- or 3-hydroxypyridines [128]. 

A transition metal catalyzed synthesis of ethers by carbene insertion into the O—bond has been reported. Not only saturated but also unsaturated alcohols can be utilized in this catalytic process. ° Intermolecular and intramolecular oxirane ring opening reactions by alkoxides and phenoxides also provide efficient and stereospecific preparations of acyclic and cyclic ethers. The procedures have been surveyed in detail. ... 

Mc3Si)3SiO as opposed to MesSiO". This in turn might facilitate nucleophilic attack of CO2 by the siloxide ligand (see section 5.3). It should be noted that CO2 readily inserts into rare earth phenoxides to generate stable carbonate complexes. These species could be involved as the actual catalysts in the copolymerization of CO2 with epoxides. ... 

In contrast to the well-known alkylation paths, namely, S l and Sn2, the fluoroalkylation reaction was rationalized by an unusual ionic chain mechanism [26]. As shown in Scheme 14.3, the reaction was initiated with the direct attack of electron-positive bromine (5+) on the BrCF2CF2Br by phenoxide. Tetrafluoroethy-lene (CF2=CF2) was generated in situ after loss of bromide anions. The phenoxides added to the CF2=CF2 to give the reactive fluorocarbanions, which were quickly terminated by bromide to form 2-bromo-tetrafluoroethyl aryl ethers. In the elimination step, zinc inserted into the C—Br bond of 2-bromo-tetrafluorethyl aryl ethers in a similar way to the preparation of Grignard reagents. Finally, the aryl trifluorovinyl ethers were obtained by the elimination of ZnBrF salt at elevated temperature. 

The reactivities of hydrido(phenoxo) complexes of trons-[MH(OPh)L2] (6 M = Ni 7 M = Pt) (L = phosphine) were examined (Eqs. 6.29, 6.30 Scheme 6-16), and a high nucleophiUdty for the metal-bound phenoxide was suggested [9, 10]. Reaction with methyl iodide produced anisole and trans-[MH(I)L2] for both Ni and Pt complexes. Phenyl isocyanate also provided the insertion products into the metal-phenoxo... 

Attempts to induce the insertion of CO into the W-OPh bond of (CO)sWOPh" have failed at CO pressures up to 500 psi. In situ high pressure FTIR measurements revealed only the presence of the starting phenoxide tungsten complex. 

Phenoxide ion, unlike alkoxides, interacts favorably with alkynyliodonium species. Reaction of two equivalents of lithium phenoxide with the [bis(phenyliodonium)ethyne, 30, results in diphenoxyacetylene, 79 [24] [Eq. (36)]. Benzofurans, 81, are obtained in the reaction of 23 with PhONa in methanol [Eq. (37)] [64]. As indicated, these products arise via insertion of the intermediate carbene, 80, into the ortho-C-H bond. 

One can also envision that the quinone could trap the hydridopalladium species resulting from the B-hydrogen elimination that releases the oxidized organic product (Equation 16.129). Insertion of quinone into the palladium hydride would form an enolate that would tautomerize to the phenoxide complex. Protonation with the reagent containing an 0-H or N-H bond would generate the free hydroquinone and Pd(II). As noted in Chapter 17 on carbonylation, quinone has been used as an additive with this mechanism in mind to prevent tire Pd(II) hydroesterification catalysts from undergoing reduction to palladium(O). ... 

The insertion chemistry of alkyl and hydrido, aryloxy derivatives of the group 10 metals has been studied. Although the phenoxide trani-[Pt(H)(OPh)(PEt3)2] undergoes only 10% insertion of CO2 (1 atm) into the Pt-OPh bond, reaction with PhNCO cleanly produces the corresponding A-phenylcarbamato complex. " Similarly the nickel compounds fran -[Ni(H)(OPh)(L)2] react with PhNCO but in this case there is evidence that the reaction is reversible. " ... 

Treatment of the bis(alkyne) compounds [Re(0)(l)(RC R)2] with HOPh leads to the corresponding phenoxide. The structure of the 2-butyne, phenoxide showed a pseudo-tetrahedral coordination sphere. The orientation of the phenoxide ligand was interpreted in terms of minimizing jr-antibonding interactions. Unlike corresponding alkoxides, the phenoxide complex did not participate in any insertion chemistry. The tris(alkyne) [Re(l)(RC=CR)3] is converted into the corresponding phenoxide by simply treating with phenol. ... 

The reaction of the carbonato complex with C02 has allowed the demonstration of a facile insertion-deinsertion equilibrium. The study of the deinsertion reaction has allowed estimation of the activation parameters as being = 130 4.0 kJ mor and AS = 121.6 11.9 J moP K . From the above values the authors have calculated an approximate value of the equiUbrium cmistant for the carboxylation reaction equal to 3 x 10 M at 195 K (or a AG value for the same reaction of < 50 kJ moP ), showing that the insertion of CO2 into the M-O-alkyl bond is both kineticaUy and thermodynamically very favored. This trend has also been confirmed for the insertion of CO2 into the Nb-OR bond in [Nb(OR)5]2 (R = methyl, ethyl, aUyl) (see Sect. 6.2.2.1), a catalyst for the synthesis of dialkyl carbonates [67]. Very recently, the facile insertion of CO2 into metal-phenoxide bonds has been reported [68] for cobalt and zinc complexes (Fig. 4.2). It should be noted that such metal systems are used as catalysts in the copolymerization of CO2 with epoxides. 

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