Sodium borohydride palladium complexes

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

Methods (i) and (ii) require palladium(II) salts as reactants. Either palladium acetate, palladium chloride or lithium tetrachloropalladate(II) usually are used. These salts may also be used as catalysts in method (iii) but need to be reduced in situ to become active. The reduction usually occurs spontaneously in reactions carried out at 100 °C but may be slow or inefficient at lower temperatures. In these cases, zero valent complexes such as bis(dibenzylideneacetone)palladium(0) or tetrakis(triphenylphos-phine)palladium(O) may be used, or a reducing agent such as sodium borohydride, formic acid or hydrazine may be added to reaction mixtures containing palladium(II) salts to initiate the reactions. Triarylphosphines are usually added to the palladium catalysts in method (iii), but not in methods (i) or (ii). Normally, 2 equiv. of triphenylphosphine, or better, tri-o-tolylphosphine, are added per mol of the palladium compound. Larger amounts may be necessary in reactions where palladium metal tends to precipitate prematurely from the reaction mixtures. Large concentrations of phosphines are to be avoided, however, since they usually inhibit the reactions. 

Several examples of the cyclization of indole derivatives with alkenic side chains in the 3-position have been reported.6 In these examples, palladium chloride in combination with silver tetrafluoroborate is the cyclizing agent. The palladium tetrafluoroborate, presumably formed, should be a very reactive palladating species and probably is the reason why these reactions proceed at room temperature, although the mechanism is not yet completely clear. These reactions were worked up reductively (by addition of sodium borohydride) in order to reduce the expected alkenic product or any relatively stable organopalladium complexes that may have been formed (equation 4).6... 

The extremely broad functional group tolerance of the Pd-catalysed N-de protection of Aloe groups was a crucial design feature in a synthesis of the epoxy-quinol core of the Manumycin family of antitumour antibiotics [Scheme 8,80].195 Note the convenient generation of the Pd(0) catalyst in situ from reaction of dichlorobis(triphenylphosphine)palladium(II) with tributylstannane. The use of sodium borohydride and borane dime thy lamine complex is illustrated in Schemes 8.81193 and 8.82194 respectively. 

Vinyl halides add to allylic amines in the presence of Ni(cod)2 where cod=l, 5-cyclooctodine, followed by reduction with sodium borohydride. Aryl iodides add to alkynes using a platinum complex in conjunction with a palladium catalyst. A palladium catalyst has been used alone for the same purpose, and the intramolecular addition of a arene to an aUcene was accomplished with a palladium or a GaCl3 catalyst, " AUcyl iodides add intramolecularly to aUcenes with a titanium catalyst, or to alkynes using indium metal and additives. The latter cyclization of aryl iodides to alkenes was accomplished with indium and iodine or with Sml2. " ... 

Partial reduction of dichloro(norbomadiene)palladium with sodium borohydride at — 40 C gave an intermediate 25 which could not be isolated but was assumed to be a homoallyl complex which upon reductive cleavage gave norbornene, norbomane and nortricyclene in a ratio of 9 7 1, while oxidative decomplexation gave norbornenone and nortricyclenone in a 1 1 ratio. ... 

The most widely used methods of preparation of palladium(O) phosphine complexes are the reduction of palladium(II) salts in the presence of tertiary phosphine ligands (eq (48)-(50)) [65-67]. Palladium(II) dichloride and bis(2,4-pentanedionalo)palladi-um(II) (Pd(acac)2) are the typical starting materials. A variety of reducing agents including hydrazine [65], sodium borohydride [68], sodium alkoxide [69], and triethyl-alminum [66] were employed. 

The pale yellow [Ni(PEt3)4] is also tetrahedral but with some distortion. In sharp contrast to nickel, palladium forms no simple carbonyl, Pt(CO)4 is prepared only by matrix isolation at very low temperatures and reports of K4[M(CN)4] (M = Pd, Pt) may well refer to hydrido complexes in any event they are very unstable. The chemistry of these two metals in the zero oxidation state is in fact essentially that of their phosphine and arsine complexes and was initiated by L. Malatesta and his school in the 1950s. Compounds of the type [M(PR3)4], of which [Pt(PPh3)4] has been most thoroughly studied, are in general yellow, air-stable solids or liquids obtained by reducing complexes in H2O or H20/EtOH solutions with hydrazine or sodium borohydride. They are tetrahedral molecules whose most important property is their readiness to dissociate in solution to form... 

In a more detailed study, the structure of the catalyst precursor was determined and found to be Pd(Diop),32. Other L2Pd and L2Ni complexes [L = Diop, BPPM, BINAP, etc.] were prepared [e.g., by in situ reduction of Pd(Il)Cl,L with sodium borohydride or as isolated palladium(O) complexes] and used as catalysts for the asymmetric addition of hydrogen cyanide to norbornene. norbornadiene, benzonorbornadiene, and cyclopentadiene dimer. In the presence of excess ( + )-Diop and L,Pd, norbornene gives 91 -95% of exo-2-cyanonorbornane with 24% cc of the ( + )-(15.25,4/ )-isomer. Similarly, use of the ( —)-Diop complex leads to the (-)-(l/ ,2f ,4S)-isomer with 24% ee (95% yield). Lower reaction temperatures, instead of the 120 "C used above, give better ee values (80 =C 32% ee with 94% yield 35 °C 35 % ee with 6% yield)32. 

Preparation of the jcy/o-configurated deoxyimino sugars 805 and 807 from 802 or 806 illustrates the value of tartaric acid in enantiospecific syntheses of valuable target molecules. Ozonolysis of 802 followed by reduction with sodium borohydride in methanol provides 803. Subsequent borane-dimethylsulfide—THF complex reduction, OTBS deprotection with 60% aqueous acetic acid, and purification with Amberite IRA400(OH) resin provides, after acidification, 804 in 75% yield. Catalytic debenzylation in the presence of palladium hydroxide occurs quantitatively to afford (27, 3/ ,4R)-2-(2-hydroxyethyl)-3,4-dihydroxypyrrolidine hydrochloride (805) in an overall yield of 53% (Scheme 176). 

Carbopalladation. Allylic amines and sulfides form palladium complexes in high yield with dilithium tetrachloropalladate (THF, 20°, 6-8 hours). These complexes react with certain carbanions at the jS-position, a site that is not susceptible to nucleophilic displacement in allylic amines and sulfides. The complexes need not be isolated these reactions are conducted in THF at room temperature by reaction of the allylic amine or sulfide with the carbanion in the presence of 1 equiv. of LizPdCU (equations I and II). The products are the palladium complexes 1 and 3. These are reduced by sodium borohydride or sodium cyanoborohydride... 

In a new kind of process, iV-allylskatole reacts with a nitrile and a palladium acetonitrile complex to give a palladium complex of proposed structure (51), presumably via intramolecular acylation of the nitrilium cation (50). The complex (51) can be converted into the pyrazinoindole (52) by reaction with benzylamine or the tetrahydro analog (53) with sodium borohydride (Scheme 14) <86JA6224>. Acylation has been effected at C-7 in some 4,6-dimethoxyindoles <94ti(M97>. 

Recently, Wang [64] prepared by radieal copolymerization a cinchona alkaloid copolymer the methyl acrylate-co-quinine (PMA-QN (71)) (Scheme 34). Complexed with palladium(II), its catalytic activity in the heterogeneous catalytic reduction of aromatic ketones by sodium borohydride was studied. High yields in their corresponding alcohols are obtained but it is found that the efficiency of the catalyst depended on the nature of the solvent and the ketone which related to the accessibility of the catalytic active site. The optical yields in methanol and ethanol 95% were lower than in ethanol. This ability was attributed to a bad coordination between PMA-QN-PdCl2 and sodium borohydride and a reaction rate which was very rapid. The stability of the chiral copolymer catalyst was studied... 

The ff,7t-complex XXIII, obtained by treatment of XXII with bis(benzo-nitrile)palladium dichloride, is reductively cleaved by sodium borohydride under gentle conditions to give 4-chlorocyclooctene (XXIV) in 67% yield (Albelo et aU 1975). 

The C-3 functionalization of 30 was achieved in two steps, that is, first, treatment with l-dimethylamino-2-nitroethylene to the unsaturated nitroacetate 31 and then reduction of the double bond with sodium borohydride in tetiahydrofuran-methanol to furnish the desired nitroacetate 31 in 30% overall yield from the aldehyde 29. Asymmetric formation of the C-5, C-10 bond of the nitroacetate 31 was achieved by using the palladium (0) complex catalyst. The best results of this key cyclization were obtained using Pd(dba)2 and (5,5)-... 

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