Hydrometallation of Unsaturated Compounds

Abstract

18 IntroductionTo the number of signifi cant hydrometallating reagents that have been introduced into organic synthesis should be added the stable hydrides of transition metals (Zr) and nontransition metals (B, Al, Mg).Today, hydrides of the these metals and their derivatives are widely used in the reduction of alkenes, dienes, alkynes, allenes, heteroolefi ns and carbonyl compounds as well as for the production of the corresponding organometallic compounds and selective alkene functionalization via the synthesis of compounds containing polar metal -carbon (M − C) bonds. These may be involved in reactions with electrophilic or nucleophilic reagents affording functional derivatives.Generally, the thermal additions of the above hydrides to alkenes proceed via the four -center transition state (1) , with subsequent cleavage of the M − H bond and metal addition. In this case the corresponding organometallic compounds are formed according to Scheme 18.1 .The use of metal complex catalysts in organic and metalloorganic chemistry allows the chemo -, regio -and stereoselective hydroalumination of unsaturated compounds under mild conditions with high yields.The role of a transition metal catalyst in these reactions is determined by its ability to activate the starting substrate by coordination to the metal center forming the intermediate hydride complex (2) . The latter, being a more active hydrometallating reagent, attacks alkenes under mild conditions with subsequent transmetallation of the starting hydride affording the target organic compound (3) according to Scheme 18.2 .To date, a large number of reports have appeared in the literature on the application of hydride reagents in both thermal and catalytic hydrometallation of unsaturated compounds. Hydroboration, hydroalumination, hydrozirconation and hydromagnesiation of unsaturated compounds such as alkenes, dienes or alkynes are considered the most effective reactions for producing the related metalloorganic compounds. It is not possible to consider all these reactions within the

Bimetallic Zr,Zr-Hydride Complexes in Zirconocene Catalyzed Alkene Dimerization

“…Hydride metal complexes attract significant attention in the field of organometallic chemistry due to their ability to function as highly active reagents or catalytically active centers for various reactions. According to numerous studies, Ti subgroup complexes that contain M-H bond supposedly act as active species, for example, in di-, oligo-, and polymerization of alkenes [1][2][3][4][5], as well as in the reduction of unsaturated compounds [6][7][8]. With respect to the alkene di-, oligo-, and polymerization reactions catalyzed by both Ti subgroup metallocenes and methylaluminoxane (MAO), this assumption had been repeatedly proposed (Scheme 1); however, these studies lack direct evidence of the metal hydride complex action.…”

“…The goal of this research was to find the conditions for selective alkene dimerization in two catalytic systems: Cp 2 ZrCl 2 -(AlR 3 or HAlBu i 2 (R = Me, Et, Bu i ))-MMAO-12, and [Cp 2 ZrH 2 ] 2 -ClAlR 2 (R = Me, Et, Bu i )-MMAO-12, and to reveal the structure of the zirconium hydride intermediates that initiate the alkene transformations. On the first step of the catalytic experiments, we studied the effect of MMAO-12 on the activity and chemoselectivity of systems Cp 2 ZrCl 2 -XAlBu i 2 (X = H, Bu i ) that hydroaluminate the terminal alkenes in the absence of the activator [7]. As shown elsewhere, the catalytic system based on HAlBu i 2 and zirconocene dichloride demonstrates low activity in the alkene hydroalumination (hydroalumination product (2)); this experiment was taken as a reference point (Scheme 2, Table 1 (entry 1)) [30][31][32].…”

Alkene and Olefin Functionalization by Organoaluminum Compounds, Catalyzed with Zirconocenes: Mechanisms and Prospects

“…The catalytic alkene hydroalumination has found wide application as an eicient regio-and stereoselective method for the double and triple bond reduction providing important synthons for organic and organometallic chemistry [4,[13][14][15]. Various transition metal complexes can be used as the catalysts of the reaction, however, the compounds based on the metals with no vacant d orbital show much less activity in the reaction (e.g., Cu, Zn vs. Ti, Zr, Co, Ni) [16][17][18][19][20][21].…”

“…Catalytic alkene and acetylene carbo-and cycloalumination are convenient one-pot synthetic routes to the acyclic and cyclic OACs that could be converted into alcohols, halides, heterocycles, carbocycles and others [2][3][4][5][6][7][8][9][10][11]. The using of enantiomerically pure complexes as the catalysts afords the asymmetric induction in the reactions.…”

A Tribute to Prof. Usein M. Dzhemilev

“…These findings stimulated further development of the fundamental catalytic 1,2-ethylmagnesiation, 1,2-carboalumination and β-ethylation reactions of non-activated olefins (Scheme 14). [17][18][19][20][21][22][23][24][25][26][27] Probably, the most notable discovery of a chemist is that of a reaction that bears his name. The 1,2-ethylmagnesiation reaction is known throughout the world synthetic practice as the Dzhemilev reaction.…”