Protonolysis reactions

As described in the preceding sections, many domino reactions start with the formation of vinyl palladium species, these being formed by an oxidative addition of vinylic halides or triflates to Pd°. On the other hand, such an intermediate can also be obtained from the addition of a nucleophile to a divalent palladium-coordinated allene. Usually, some oxidant must be added to regenerate Pd11 from Pd° in order to achieve a catalytic cycle. Lu and coworkers [182] have used a protonolysis reaction of the formed carbon-palladium bond in the presence of excess halide ions to regenerate Pd2+ species. Thus, reaction of 6/1-386 and acrolein in the presence of Pd2+ and LiBr gave mainly 6/1-388. In some reactions 6/1-389 was formed as a side product (Scheme 6/1.98). 

The observation of stable Pt(IV) alkyl hydrides upon protonation of Pt(II) alkyls has provided support for the idea that the methane which had been observed in earlier studies (89-92) of protonation of Pt(II) methyls could be produced via a reductive elimination reaction from Pt(IV). An extensive study of protonation of Pt(II) methyl complexes was carried out in 1996 (56) and an excellent summary of these results appeared in a recent review article (14). Strong evidence was presented to support the involvement of both Pt(IV) methyl hydrides and Pt(II) cr-methane complexes as intermediates in the rapid protonolysis reactions of Pt(II) methyls to generate methane. The principle of microscopic... 

A number of systems have been studied where a formal ligand displacement reaction is followed by an isomerization process. One recently described example involves the cleavage of a Pt-C(alkyl) cr-bond in complexes of the type cis-[Pt(R)(R )(PEt3)2] to produce cis-[Pt(R)(PEt3)2(MeOH)]+ and R H, which subsequently isomerizes to nms-[Pt(R)(PEt3)2(MeOH)]+ (90). The first protonolysis reaction is characterized by significantly negative volumes of activation between... 

A straightforward protonolysis reaction of Me2Mg(TMEDA) with the carbon-acids cyclopentadiene, indene and fluorene affords the corresponding heteroleptic organomagnesium TMEDA complexes Me(Cp)Mg(TMEDA) (133), Me(indenyl)Mg(TMEDA) (134) and Me(fluorenyl)Mg(TMEDA) (135), respectively, in quantitative yield. The structnres in the solid state of these complexes have been determined by X-ray crystallography . In... 

The role of metallacycles, as intermediates in chromium-catalysed ethylene trim-erisation, is highlighted in this article. It is also shown that when 37 is treated with ethene in a protonolysis reaction, hexane and butane are liberated (1 3 ratio hexane butane). This observation gives strength to the argument that metallacycles are intermediates in chromium-catalysed ethylene trimerisation. Scheme 13 provides a simplified representation for chromium-based ethylene trimerisation. 

The overall high enantioselectivities are increased at lower temperature and can attain up to 74% ee. Epimerization is observed during the initiating rapid protonolysis reaction, but the optical purity of the precatalyst does not influence the configuration and optical purity of the product. 

Combination of reactions seen in Sections B4.1 and B4.2 with hydroboration/protonolysis reactions provides syntheses of stereodefined dienes. 

Structural evidence of the formation of alkylated siloxide complexes was obtained from the reaction of homoleptic tetramethylaluminates Ln(AlMe4)3 with one equivalent of tris(ferf.butoxy)silanol HOSi(Of-Bu)3. This fast protonolysis reaction results in heterobimetallic Ln/Al complexes Ln[OSi(Of-Bu)3](AlMe4)2(AlMe3) (Ln = Y, Ce, Pr, Nd, La) via quantitative... 

Other protonolysis reactions include reactions with carboxylic acids to give metal carboxylates (see Section 6) and with /3-diketones to give the metal /3-diketonates (see Section 4), as shown in equations (9) and (10), respectively. 

Protonolysis reactions of alkoxides and aryloxides are common one example is hydrolysis of the metal alkoxide, giving metal oxide with elimination of the alcohol. Although the aim is often to avoid such a reaction, it is of great interest in the deposition of high-purity metal oxides, which are used in areas such as optoelectronics, high f superconductors, and advanced ceramics. ... 

Tris(cyclopentadienyl) lanthanide complexes can be used as precursors for the synthesis of lanthanide derivatives via a protonolysis reaction (Figure 8.7) [15,16]. The biggest advantage of this method is that it excludes the formation of lanthanide -ate compounds [17],... 

Intramolecular hydroamination/cyclization, the addition of an N-H bond across an intramolecular carbon-carbon unsaturated bond, offers an efficient, atom economical route to nitrogen-containing heterocyclic molecules (Equation 8.37). Numerous organolanthanide complexes were found to be efficient catalysts for this transformation [124, 125]. The real active intermediates are organolanthanide amides, which are formed by the rapid protonolysis reactions of precatalysts with amine substrates. The proposed catalytic cycle of hydroamination/cyclization of aminoalkenes is presented in Figure 8.37 [124]. 

Mesitylboronic acid was used in reactions with group 13 metal alkyls. The expected B-O-M species was obtained only for M = Ga, according to the reaction in Equation 3. This is possibly due to the properties of Me3Ga, in which only one methyl group is used in the protonolysis reaction. 

The protonolysis reaction tolerates functionalities such as halide or ether groups in the alkylborane. However, p-dialkylaminoalkylboron compounds undergo elimination to give alkenes under these conditions (see Section 3.10.1.2). ° " Also, systems which are intrinsically labile to either acid or heat, such as some terpenoids, may give problems. For example, enantiomerically pure limonene produces 1 -men-thene which is substantially racemized on hydroboration-protonolysis (Scheme 15). 

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