Formates as Reducing Agents

First applied by Whitesides and Shaked in the 1980s [29], the FDH from Candida hoidinii has ever since been receiving great interest as an NADH regeneration system (Table 8.4). Variants with improved stability [30] or an enlarged cofactor spectrum (accepting also NADP ) [31] have been reported. Due to its popularity, FDH is commercially available from various suppliers [lb]. Also, sources for novel FDHs are constantly being explored [32]. 

The very successful FDH regeneration system is also frequently evaluated to promote enoate reductase (ER)-catalyzed reductions of conjugated C=C double bonds [42]. With commercially available FDHs, however, a problem of overreduction is frequently encountered contaminating ADHs from the FDH-over-expressing strain also catalyze the NAD(P)H-dependent carbonyl reduction of the starting material and the product, which can lead to complex product mixtures. 

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Sodium azide, reaction with l butyl chloroacetate, 46, 47 reaction with diazomum salt from o amino-f> -ni trobiphcny L, 46, 86 Sodium chlorodifluoroacetate, 47, SO reaction with tnphenylphosphme and benzaldehyde, 47, SO Sodium ethoxide, 46, 2S reaction with diethyl succinate, 46,2S Sodium formate as reducing agent in preparation of palladium catalyst, 46, 90... 

Sodium formate as reducing agent in preparation of palladium catalyst, 46,90... 

Thus, the Heck reaction between iodobenzene and ethyl acrylate proceeds efficiently using PdCfi dissolved in 28b, cholinium acetate as the base and ammonium formate as reducing agent. Trans-Q y cinnamate is produced in 60% after heating at SO C for 1 h. 

Solutions of anhydrous stannous chloride are strongly reducing and thus are widely used as reducing agents. Dilute aqueous solutions tend to hydrolyze and oxidize in air, but addition of dilute hydrochloric acid prevents this hydrolysis concentrated solutions resist both hydrolysis and oxidation. Neutralization of tin(II) chloride solutions with caustic causes the precipitation of stannous oxide or its metastable hydrate. Excess addition of caustic causes the formation of stannites. Numerous complex salts of stannous chloride, known as chlorostannites, have been reported (3). They are generally prepared by the evaporation of a solution containing the complexing salts. 

Sodium borohydride reductions of gold(I) complexes give Au clusters at RT if sodium borohydride in ethanol is dropped slowly into a suspension of the Au(I) complex in the same solvent. The immediate coloring of the reaction mixture (mostly red), even after only a few drops of the borohydride have been added, indicates fast formation of Au clusters. In view of the complicated composition of these compounds the fast formation is surprising. The use of H2 and CO with HjO as reducing agents in the synthesis of gold clusters has been described (see Table 1, Method A, 8.2.2.2). 

Another way to work in transient conditions is to stop suddenly (or conversely to instantaneously introduce) one of the reactants, in order to destabilize the system and to enhance the concentration of labile species. With this method, for example, Poignant et al. studied the DeNO. reaction mechanism on a H—Cu-ZSM-5 catalyst, using propane or propene as reducing agents. The introduction of 2000 ppm of hydrocarbon in a flow of NO (2000 ppm) + 5% 02 allowed to evidence the formation of acrylonitrile, which behaved as an intermediate. Its reactivity with NO+ species constituted a fundamental point to describe a detailed SCR mechanism for NO removal on zeolitic compounds [137],... 

There has been an increasing number of reports of the utilization of zinc hydride complexes as precursors in organic transformations and as reducing agents. Zinc hydrides have been less well investigated than the other group 13 hydrides due to the formation of polymeric and oligomeric species that are difficult to characterize. 

In contrast to the allyl system, where the reduction of an isolated double bond is investigated, the reduction of extensively delocalized aromatic systems has been in the focus of interest for some time. Reduction of the systems with alkali metals in aprotic solvents under addition of effective cation-solvation agents affords initially radical anions that have found extensive use as reducing agents in synthetic chemistry. Further reduction is possible under formation of dianions, etc. Like many of the compounds mentioned in this article, the anions are extremely reactive, and their intensive studies were made possible by the advancement of low temperature X-ray crystallographic methods (including crystal mounting techniques) and advanced synthetic capabilities. 

Polysilanes as reducing agents. In a paper on the formation of conductive circuits by UV patterning of polysilane films, the inherent reducing ability of polysilanes to effect the reduction of a silver salt to silver metal was described.307 PMPS, PPHS [(PhSiH) ], and PDFIS were separately spin-coated on glass or silicon wafer substrates, and after drying... 

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