Metal Catalyst and Additives

Monomeric or polymer-bound C0CI2 is an active acetalization and transac-etalization catalyst [17]. Its efficiency can be improved by the addition of chlorotrimethylsilane [18]. Also, Co2(CO)g or heterogeneous Co catalysts convert olefins in the presence of alcohols into acetals [19, 20]. HCo(CO)4, a typical hydroformylation catalyst and strong acid, is able to reduce under hydroformylation conditions (CO/H2 = 2 l, about 165bar, 160-210°C) acetals of aromatic aldehydes into the corresponding ethers. Interestingly, acetals of aliphatic aldehydes did not react under these conditions. 

With increasing P/Rh ratio, the rate of conversion decreased. Monodentate phosphines, especially PCyg, favored hydrogenation of the olefinic substrate and the transient aldehyde to give alkane and alcohol, respectively. With bidentate phosphines, a natural bite angle of about 110°, as realized with Xantphos, was essential for the success of the tandem reaction. Variation of the composition of the syngas mixture (ratio of CO/H2) had only a marginal effect. Remarkably, in the absence of H2 and under 10 bar of CO pressure, acetalization with 

In the absence of H2, the Rh(I)-catalyzed reaction of olefins with CO and alcohols may lead to esters or ethers [32]. The hydroesterification tendency is enhanced by amine ligands [3]. Strong basic amines, such as 2,6-lutidine, give higher yields of esters than basic amines, such as 2-picoline [3b]. 

Venanzi and coworkers [36] discovered that [Pt(H20)2(dppe)](Cp3S03)2 catalyzes the reaction of numerous aldehydes with monohydric and dihydric alcohols to give acetals in 90% yield. The platinum complex was at least as effective as the corresponding Pd congener, while much lower rates were observed with a related rhodium complex. Also, hydroxy-complexes of the type [Pt(P—PJJp-OHJlj were 

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Additions to conjugated systems are further facilitated by some of the features discussed previously e.g., additions to dienes" " and enynes" in the presence of transition-metal catalysts and additions to enynes containing a suitably placed intramolecular function such as hydroxyl. Although uncatalyzed intermolecular additions to alkynylsilanes are not yet demonstrated, additions are seen in the presence of a transition-metal catalysts" and intramolecular additions to alkynylsilane functions by suitably placed internal organomagnesium-halide functions are facile. ... 

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