Alkanes Palladium catalysts

Haloalkynes (R—C=C—X) react with ArSnBu3 and Cul to give R—C= C—Ar. Acetylene reacts with two equivalents of iodobenzene, in the presence of a palladium catalyst and Cul, to give 1,2-diphenylethyne. 1-Trialkylsilyl alkynes react with 1-haloalkynes, in the presence of a CuCl catalyst, to give diynes and with aryl triflates to give 1-aryl alkynes. Alkynes couple with alkyl halides in the presence of Sml2/Sm. Alkynes react with hypervalent iodine compounds " and with reactive alkanes such as adamantane in the presence of AIBN. ... 

Alkynes may also be hydrogenated, initially to alkenes, and then further to alkanes. By suitable modification of the catalyst, it has proved possible to stop the reaction at the intermediate alkene. Typically, platinum or palladium catalysts partially deactivated (poisoned) with lead salts are fonnd to be suitable for reduction of alkynes to alkenes. Again, syn addition is observed. 

Hydrogen undergoes catalytic hydrogenation adding to unsaturated hydrocarbons, such as alkenes and alkynes forming alkanes. The reaction is catalyzed by nickel, platinum or palladium catalysts at ambient temperature. Hydrogenation of benzene over platinum catalyst yields cyclohexane, C6H12. 

Palladium catalysts, 230 of alkyl silyl ethers to alkanes Nickel boride, 197 of alkyl sulfonates to alkanes Lithium triethylborohydride, 153 of alkynes to cis-alkenes... 

Addition of Hydrogen Alkenes react with hydrogen gas in the presence of a platinum or palladium catalyst to yield the corresponding alkane product. For example,... 

Conversion of an alkene (or an alkyne) into an alkane is readily achieved by shaking it under hydrogen at room temperature and at atmospheric pressure in the presence of a platinium or palladium catalyst. With a Raney nickel catalyst somewhat higher temperatures and pressures are employed (see Section 2.17.1, P- 88). 

The card can actually be studied in two ways. You may ask yourself What reagents will convert alkenes into alkanes Or, using the back of the card What chemical reaction is carried out with hydrogen and a platinum or palladium catalyst This is by no means the only way to use the cards— be creative Just making up the cards will help you to study. 

Supported noble metals and in particular, palladium, are being widely used for the complete combustion of methane and other alkanes to form CO2 and H2O, environmentally acceptable emission products and extremely low NOx levels [ 1-3], A considerable amount of research effort has been devoted to the process, however, there does not appear to be a consensus with regard to either the mechanism of the reaction or the chemical identity of the active catalytic species [4-8]. This state of affairs is further complicated by the fact that the chemical state of the catalyst is extremely sensitive to the reaction conditions, including time-on-stream and reaction temperature [9-12]. It has also been demonstrated that the nature and form of the support plays a key role in modifying both the activation and deactivation steps encountered with palladium catalyst particles [13-16]. 

Compound A reacts with NaBH4 to give compound D. Compound B reacts with hydrogen gas over a palladium catalyst to give the same compound D. Compound C reacts with neither reagent. Suggest a structure for compound D from the data given and explain the reactions. (Note, H2 reduces alkenes to alkanes in the presence of a palladium catalyst.)... 

X You will meet Lindlar s catalyst in Chapter 31 but we will mention it now because of its special chemoselectivity. Unlike the other hydrogenations we have described, the Lindlar catalyst will hydrogenate alkynes to alkenes, rather than alkenes to alkanes. This requires rather subtle chemoselectivity alkenes are usually hydrogenated at least as easily as alkynes, so we need to be sure the reaction stops once the alkene has been formed. The Lindlar catalyst is a palladium catalyst (Pd/CaC03) deliberately poisoned with lead. The lead lessens the activity of the catalyst and makes further reduction of the alkene product slow most palladium catalysts would reduce... 

In principle, two regioisomers are produced by the reaction of terminal alkenes and hydrosilanes one where the terminal carbon forms a bond to the silyl group (normal product) and the other which has the silyl group at the inner carbon (branched product). Platinum and rhodium catalysts yield in general the normal products, whereas palladium catalysts sometimes prefer the reaction pathway leading to the branched products. Ruthenium and rhodium afford additional by-products such as alkenylsilanes and alkanes. A typical example is the hydrosilylation of 1-octene (equation 30). ... 

In another nonelectrolytic process, aryl acetic acids are converted to vic-diaryl com-ponnds 2ArCR2COOH ArCRaCRaAr by treatment with sodinm persulfate Na2S20g and a catalytic amormt of AgN03-" Photolysis of carboxylic acids in the presence of Hg2p2 leads to the dimeric alkane via decarboxylation. Both of these reactions involve dimerization of free radicals. In still another process, electron-deficient aromatic acyl chlorides are dimerized to biaryls (2 ArCOCl Ar—Ar) by treatment with a disUane R3SiSiR3 and a palladium catalyst. ... 

In the second step, the triple bond in 63 is selectively reduced to the cz -alkene using the Lindlar catalyst to form 64. In this case, the Lindlar catalyst is a poisoned heterogeneous palladium catalyst on barium sulfate. The deactivation of the catalyst with quinoline is responsible for the selective hydrogenation to the alkene and not through to the alkane. The reason for the highly stereoselective reduction with syn-addition to the cw-alkene is that one face of the triple bond is shielded by the catalyst surface. 

Optically active alcohols, amines, and alkanes can be prepared by the metal catalyzed asymmetric hydrosilylation of ketones, imines, and olefins [77,94,95]. Several catalytic systems have been successfully demonstrated, such as the asymmetric silylation of aryl ketones with rhodium and Pybox ligands however, there are no industrial processes that use asymmetric hydrosilylation. The asymmetric hydrosilyation of olefins to alkylsilanes (and the corresponding alcohol) can be accomplished with palladium catalysts that contain chiral monophosphines with high enantioselectivities (up to 96% ee) and reasonably good turnovers (S/C = 1000) [96]. Unfortunately, high enantioselectivities are only limited to the asymmetric hydrosilylation of styrene derivatives [97]. Hydrosilylation of simple terminal olefins with palladium catalysts that contain the monophosphine, MeO-MOP (67), can be obtained with enantioselectivities in the range of 94-97% ee and regioselectivities of the branched to normal of the products of 66/43 to 94/ 6 (Scheme 26) [98.99]. 

The Lindlar catalyst [Pd/CaC03/PbO] is a poisoned palladium catalyst, which ensures that the reduction stops at the alkene (and does not go on to give an alkane). Reduction to the alkane requires a Pd/C catalyst (see Section 6.2.2.10). 

Significantly, unactivated sp3 C—H bond oxidation has been achieved using oxime or pyridine as a directing group and PhI(OAc)2 as a stoichiometric oxidant in the presence of a palladium catalyst (Equation 11.28) [66], y-C- H bonds are selectively oxygenated. The selectivity is dramatically influenced by the steric and electronic properties of the alkane substrates. 

Figure 13.3. Compensation plot of Arrhenius parameters for alkane hydrogenolysis (mainly C2 to C4) on various platinum and palladium catalysts. 1 = Pt 2 = Pd.

Very little has been published on hydrogenolysis of the lower alkanes using either nickel or palladium ° catalysts, perhaps because both are liable to suffer rapid deactivation by carbon deposits, or to show unstable behaviour. With -butane, both gave predominantly terminal C—C bond fission at low conversion, but there are no detailed kinetic studies to report. 

The L -iodane PhI(OAc)2 has been used extensively, most notably by Sanford, to oxygenate the C-H bonds of arenes and even alkanes in the presence of palladium catalysts." Interestingly, this reaction was likely mediated by a binuclear complex featuring two Pd(III) atoms joined by a palladium-palladium (Pd-Pd) bond however, this complex can disproportionate into a Pd(IV)-Pd(II) complex without a formal Pd-Pd bond, and this intricate interplay is often controlled by the presence and nature of hypervalent iodine oxidants." We discovered that this reaction manifold could be extended to include the amination of arene substrates heating 2-phenylindole 51 in the presence of the -iodane 49 and palladium acetate provided the ortho-aminated product 52 in a 19% yield however, switching the metal from palladium acetate... 

Indirect electrochemical oxidative carbonylation with a palladium catalyst converts alkynes, carbon monoxide and methanol to substituted dimethyl maleate esters (81). Indirect electrochemical oxidation of dienes can be accomplished with the palladium-hydroquinone system (82). Olefins, ketones and alkylaromatics have been oxidized electrochemically using a Ru(IV) oxidant (83, 84). Indirect electrooxidation of alkylbenzenes can be carried out with cobalt, iron, cerium or manganese ions as the mediator (85). Metalloporphyrins and metal salen complexes have been used as mediators for the oxidation of alkanes and alkenes by oxygen (86-90). Reduction of oxygen and the metalloporphyrin generates an oxoporphyrin that converts an alkene into an epoxide. 

Hydrogenation reduction of acid chloride to aldehyde using BaS04-poisoned palladium catalyst. Without this poisoning, the resulting aldehyde may be further reduced to the corresponding alcohol. The possible by-products are alcohol, ester and alkane. 

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