Insertion into OH bond

Insertion into OH bond. For instance, ethyl diazoacetate inserts into RO-H compounds to give XLI (R=Et, Pr, Bu, acetyl) compounds with catalytic amounts (substrate/catalyst=600) of rhodium(II) acetate [79, 80]. 

Exclusive formation of furans clearly indicates that the intramolecular 1,5-insertion into the C—H bonds of methylene groups cannot compete with that into OH bonds of enols. However, the stereochemistry of enolized carbene intermediates plays an important role in this reaction as acetylace-tone affords a mixture of furan 37 and cyclopentene 38 in a 64 36 ratio in 61% yield (Scheme 14). 

In the course of studies of the insertion of carbenes, generated in the photolysis of spirocyclic diazarines, 528, into OH bonds (equation 314) it has been observed641 that formation of ethers from carbene 527 and ROH(D) is associated with partial rearrangement (equation 315). 

Copper salt catalyzed G-insertion of isonitriles, CO, or diazo compounds into NH-bonds of amines gives good yields of form-amidines, formamides, or N-alkylated products respectively Recently, the analogous C-insertion of isonitriles into OH-bonds of alcohols has been reported . A variety of compounds, otherwise difficult to obtain, such as certain carbodiimides, acylamidines, or isonitriles, can be prepared by H2S-elimination with acylchloro-formamidines . 

The chemistry of alkenyl- and alkyl-substituted cyclopropylidenes has been explored. They were generated from a. gm-dihalide by lithium-halogen exchange, and were shown to give both allenes and 1,5-CH bond insertion reactions. A new mechanism for the insertion of carbenes into OH bonds was proposed on the basis of a computational study. A cyclic five-membered transition state, composed of the car-bene and two hydroxyl-containing molecules, was shown to be lower in energy than proton transfer or direct insertion into an OH bond. ... 

Considerably less is known about the chemistry of palladium and platinum 1,1-dithio complexes. Of late, there has been only one report that dealt with the synthesis of a large number of palladium dithiocar-bamates 392). Twenty-five yellow palladium dithiocarbamate complexes were obtained by reaction of PdCla with NaR2dtc in methanol solution. Several other reports have appeared in which a few dithiocarbamate complexes of palladium were synthesized. Thus, the novel [Pd (OH)2dtc 2], which is soluble in water, was isolated 393). The synthesis of optically active palladium(II) complexes of AT-alkyl-a-phen-ethyldithiocarbamates, similar to (XXIV), via the reaction between the optically active amine, CS2, and PdCl2, has been described. From ORD and CD spectra, it has been established that the vicinal contribution of a remote, asymmetric carbon center could give rise to optical activity of the d—d transitions of palladium 394). Carbon disulfide has been shown to insert into the Pt-F bond of [PtF(PPh3)3]HF2, and X-ray studies indicated the structure (XXIX). 

The mechanism involves a metal atom insertion into the O—H bond, thus resulting in the formation of an adsorbed metal—OH species (at the same or similar binding site) and a new metal—H bond. This is a classic bond activation process, which involves a significant stretch of the O—H bond in order to lower the antibonding ooh orbital to enable it to accept electron density from the metal. The reaction has been calculated by DFT to be endothermic by +90 kJ/mol over Pt(lll) surfaces with an activation barrier of +130 kJ/mol [Desai et al., 2003b]. 

Pyrolysis or photolysis of methanesulfonyl azide in 2-methyl butane (RH) produces formal C H insertion adducts attributed to reactions of the thermally generated nitrene. The selectivity of this nitrene for 3°/2°/l° C—H bonds was 6/2.3/1.0 Sulfonyinitrenes, like acylnitrenes, insert into the OH bonds of alcohols. 

Fig. 13.59). Srivastava et al. carried out similar experiments and demonstrated that the singlet was formed initially upon photolysis. This species either inserts into the OH bond of water or it suffers intersystem crossing to the lower energy triplet. As in the former study, the only reaction found for the triplet was hydrogen atom transfer. 

The key intermediate in the reduction of metal ions by carbon monoxide and water is the hydroxycarbonyl (18). Initially (18) was proposed to form by a migratory insertion of CO into a M—OH bond, but more recent studies have favored a direct attack of water or hydroxide on a coordinated carbonyl (4,62). This latter view is in accord with the expected reactivity of coordinated CO toward nucleophiles. Intermediate (18) may then decarboxylate to give C02 and either a reduced metal ion or a metal hydride, as in (29) and (30), respectively. 

In recent years there has been a growing interest in the chemistry of carbon dioxide, stimulated by current anxieties about alternative petrochemical feedstocks. One aspect under active exploration involves carbon dioxide activation via coordination to a transition metal, and indeed transition metal ions do form C02 complexes.177 The number of simple and reasonably stable complexes is still relatively small and usually limited to low oxidation state metal ions. There are many systems where C02 is used as a reagent giving rise to systems which, while not true C02 complexes, may simplistically be viewed as the products of insertion into metal-ligand bonds, e.g. reaction (9), where if L = H, formates are produced if L = OH, carbonates or bicarbonates result L = NR2 yields dialkylcarbamates and if L = R, carboxylate products result. Much of this area has recently been reviewed and will not be considered further.149... 

The relative rates of insertion into the OH bond of methanol and addition to 2-methylbut-2-ene indicate that the jS-thiophosphinoylcarbene (59) has enhanced nucleophilicity.66 This was interpreted as being due to hyperconjugative electron... 

Larger rings such as (36) were made by insertion of a rhodium carbenoid into phenolic OH bonds.37 Triarylamines have been isolated from a rhodium-catalysed reaction of diarylamines with 2-diazocyclohexane-l,3-dione 38... 

Only An(III) and An(IV) ions have been inserted into macrocyclic crown-ethers, e.g., in [UCl3(18-crown-6)]2[U02Cl3(OH)H20]. Hydrogen bond interactions between etheric oxygen and coordinated water molecules were only observed in the corresponding U02+ complexes [282]. The infrared spectrum and isotope effect of uranium-crown-ether complexes were reported [435], as well as the crystal structures... 

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