Hydrides reactions with alkenes

Indeed, if the new bonds are much stronger than the old, one can find an inverse kie. An instructive example of this is the reaction of a manganese hydride (deuteride) with alkenes 20... 

In the absence of triphenylphosphine a tris-SPO platinum complex forms when SPO is reacted with Pt(cod)2, which is insoluble and for which the structure is not known it could be either a hydride (4) or an oligomeric or a dimeric S PO complex (5) lacking one molecule of hydrogen. The reaction with alkene, CO and H2 gives complex 6, which was identified as the acyl tris-SPO complex by NMR. It shows an... 

In addition to their reactions with alkenes and carbanions as nucleophiles benzhydryl cations react with hydride donors.282 284 These hydride transfer reactions show the same linear dependence of log k upon E as the reactions with alkenes and the same constant relative selectivity, that is with slopes of plots close to 1.0, for structures ranging from cycloheptatriene to the... 

Most of the reported reactions between tetranuclear clusters and alkynes involve mixed-metal cluster species. In these systems hydride and carbon monoxide substitution generally occurs [Eq. (11)] (194-200), although in some cases Me3NO has been used to activate the starting material (201, 202), and in still others cluster breakdown takes place even under mild reaction conditions (203). Rh4(CO)12 (204) and Ir4(CO)12 (205) retain their nuclearity in reactions with alkynes, but in the latter case the metal framework geometry is altered (Fig. 7). The use of [Ir4(CO)11Br] instead of Ir4(CO)12 in reactions with alkenes produces alkene-substituted tetranuclear complexes (189), as shown in Fig. 7. Few other homonuclear clusters have been found to react with alkynes (206-208). In the reaction between the tetranuclear cluster Cp2W2Ir2(CO) 0 and diphenylacetylene two independent processes... 

Group VB and VIB hydrides react with alkenes and alkynes, thermally or under radical, photolytic or base catalysis, in reactions used primarily for substituted element (P, As, Sb) compound synthesis, e.g. ... 

Hoffmann. 1 A typical reaction is that of cyclohexene and chloroform with potassium ferf-butoxide to give 337. In general, reaction with alkenes give dichlorocyclopropanes [dibromocyclopropanes with bromoform (CHBr3) and diiodocyclopropanes with iodoform (CHI3)]. Tri-n-butyltin hydride (Bu3SnH) can be used to reduce the product dihalide to a monohalide (sec. 4.9.H). 

Before we close the discussion of carbene reactions with alkenes we mention tetrahedral boron hydride-substituted diazomethanes (8.11-8.13) which were obtained by the group of Jones (Li and Jones, 1992 Li et al., 1993) by manipulating substituted o-carboranes, as shown in (8-19). Reaction of 8.13 with ( )-but-2-ene yielded the pure (jE )-derivative, i.e., the product of singlet addition. With (Z)-but-2-ene 3 % triplet reaction product was observed. The percentage of triplet products was higher with 8.13 (22 and 18 7o with (E)- and (Z)-but-2-ene, respectively) (Huang et al., 1992). 

Hydride complexes of platinum have received considerable study since the preparation of PtHCl(PEt3)2- Spectroscopic studies by NMR techniques have been widely used because of the structural information which can be obtained from coupling constant data to Pt and other nuclei. Platinum is widely used as a heterogeneous catalyst, and vibrational studies on platinum hydride complexes have been useful for comparison of a hydrogen atom bonded to a single platinum with that bonded to a surface. Complexes of platinum have been used to catalyze hydrogenation, hydrosilylation and isomerization reactions with alkenes and alkynes, as well as H/D exchange reactions on alkanes. Hydride complexes are frequently proposed as intermediates in these reactions, and the pathways related to the known chemistry of hydride complexes. 

A modified stepwise hydroboration avoiding the use of lithium aluminum hydride has also been developed (Schane 23.30). It was discovered that trialkylsilane reacts rapidly with boron trihalide to form unsolvated dihaloborane. Subsequent reaction with alkenes in the presence of sufficient boron trihalide occurs rapidly at -78°C to afford alkylboron dihalides without detectable contamination by dialkylboron halides. If additional equivalents of both trialkylsilane and alkene are added, dialkylboron halides are obtained. The methodology has been successfully applied to the synthesis of l,l,I-tris(dichloroboryl)alkanes, important precursors for dicarbapentaboranes. ... 

Potassium trisiamylborohydride can now be made in a convenient manner and the reaction of cyclic boronic esters possessing a wide variety of sterlc requirements with potassium hydride gives rise to the corresponding borohydrides. These represent a new class of reducing agents whose stability and reactivity have been explored. Copper(I) alkylborohydrldes are obtained from 1 1 mixtures of cuprous chloride and sodium borohydride on reaction with alkenes in THF. 

Alkenes in (alkene)dicarbonyl(T -cyclopentadienyl)iron(l+) cations react with carbon nucleophiles to form new C —C bonds (M. Rosenblum, 1974 A.J. Pearson, 1987). Tricarbon-yi(ri -cycIohexadienyI)iron(l-h) cations, prepared from the T] -l,3-cyclohexadiene complexes by hydride abstraction with tritylium cations, react similarly to give 5-substituted 1,3-cyclo-hexadienes, and neutral tricarbonyl(n -l,3-cyciohexadiene)iron complexes can be coupled with olefins by hydrogen transfer at > 140°C. These reactions proceed regio- and stereospecifically in the successive cyanide addition and spirocyclization at an optically pure N-allyl-N-phenyl-1,3-cyclohexadiene-l-carboxamide iron complex (A.J. Pearson, 1989). 

Another reaction in the last step is the syn elimination ofhydrogen with Pd as H—Pd—X, which takes place with alkyl Pd complexes, and the Pd hydride and an alkene are formed. The insertion of an alkene into Pd hydride and the elimination of, (3-hydrogen are reversible steps. The elimination of, 3-hydrogen generates the alkene, and both the hydrogen and the alkene coordinate to Pd, increasing the coordination number of Pd by one. Therefore, the / -elimination requires coordinative unsaturation on Pd complexes. The, 3-hydrogen eliminated should be syn to Pd. 

Oxidation of ethylene in alcohol with PdCl2 in the presence of a base gives an acetal and vinyl ether[106,107], The reaction of alkenes with alcohols mediated by PdCl2 affords acetals 64 as major products and vinyl ethers 65 as minor products. No deuterium incorporation was observed in the acetal formed from ethylene and MeOD, indicating that hydride shift takes place and the acetal is not formed by the addition of methanol to methyl vinyl etherjlOS], The reaction can be carried out catalytically using CuClj under oxygen[28]. 

RhCl(PPh3)3 is a very active homogenous hydrogenation catalyst, because of its readiness to engage in oxidative addition reactions with molecules like H2, forming Rh—H bonds of moderate strength that can subsequently be broken to allow hydride transfer to the alkene substrate. A further factor is the lability of the bulky triphenylphosphines that creates coordinative unsaturation necessary to bind the substrate molecules [44]. 

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