Organoaluminium compounds addition with

The participation of a monomeric form of the organoaluminium compound in the olefin addition may result in a preliminary interaction between the olefin and vacant p-orbitals of the aluminium ion with the formation of a 7t-coraplex before insertion of the olefin into the At—C bond. The first-order kinetics of this process with respect to monomer implies that the concentration of the n-complexes with respect to the monomer OAC form is low at elevated reaction temperatures these complexes were not identified by physical methods. 

The interaction of ethylene with triethylaluminium has been studied in the gas phase under conditions under which the formation of 1 -butene is predominant The resulting kinetic parameters of this reaction are given in Table 8. It should be taken into account that in this case for the calculation of the rate constants of the addition reaction several additional assumptions are introduced concerning the concentrations of various OAC forms and the ratio of the rate constants of various reactions. Apparently not all the assumptions are fulfilled and the activation energies of the ethylene addition listed in Table 8 are overestimated. Ziegler et al. have found the following order of reactivity of olefin addition to organoaluminium compounds ... 

The kinetic parameters of the propagation of olefin polymerization on different active centers are compiled in Table 10. Apparently, for both the transition and non-transition metal compounds the insertion of the olefin into Mt—C bonds proceeds with the participation of coordinatively unsaturated metalalkyl compounds via intermediate n-complexes. The higher reactivity of transition metal compounds compared with organoaluminium compounds is primarily due to the lower activation energy of the propagation step when Mt is a transition metal. Many facts indicate that polarization of the Mt—C bond does not determine the reactivity of metalalkyl compounds in olefin addition, e.g. due to the decrease of reactivity in the order... 

Organoaluminium compounds can also be used to transfer the organic groups. With tin halogen bridged complexes such as R SnCl. AlCl R SnCl.AlCl are formed which hinder further alkylation. This can be prevented by addition of donors such as NaCl or an amine which complex with the aluminium halide as it is formed. 

Several papers report the interaction of organoaluminium compounds with ketones. The addition of dimethyl(alkynyl)-aluminium compounds to acetone and acetophenone leads to the products of alkynylation, but methylated products are also formed, eg ... 

Synthesis of p-Branched Carboxylic Acids by Additions with Organoaluminium Compounds ... 

Several recent reports deal with the regio- and stereo-selective ring-opening of epoxy-alcohols. The addition of organoaluminium compounds such as MesAl leads to 1,2-diol derivatives from a-alkoxy-epoxides [equation (12)] and... 

In addition, Wipf and co-workers104 have used silver(i)-catalyzed addition of zirconocenes to 3,4,6-tri-O-benzyl-D-glucal epoxide 93 for the stereoselective synthesis of a-C-glucosyl compounds 95 and 96 following a similar mechanism as in the reaction with organoaluminium and organoboron reagents (Scheme 32). 

Chiral -substituted carbonyl compounds have been prepared in high optical purity (64-98%) by the use of organoaluminium chemistry. Thus treatment of an acetal derived from an a, 6-unsaturated aldehyde and R,R- tartaric acid diamide with a trialkylalane gives largely the 1,4- addition product from which the desired ketone is derived by ozonolysis (Scheme 12). 1... 

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