Hydroformylation phosphine-directing group

Functional group-directed hydroformylation. Phosphine and phosphite moieties in olefinic substrates exert strong directing effects on the regioselectivity of hydroformylation. For example, hydroformylation of 4-(diphenylphosphino)-l-butene (32) catalyzed by Rh2(OAc)4/4PPh3 gives branched aldehyde 33, which subsequently is reduced to provide the corresponding alcohol 34 as the sole product (Eq. 16)." Under the same conditions, 1-hexene affords the linear alde-... 

Apart from this special behavior, a reliable protection of the phosphine group during synthesis and storage can be achieved by adduct formation with BH3. Several methods are described in the literature to remove the BHj group before the catalytic reaction by the reaction of amines or acids [162]. Moreover, under hydroformylation conditions, CO can successfully compete with the phosphine for BH3 and thus initiate the breakage of the P-B bond [163]. Phosphine hgands generated in this manner from phosphine borane adducts did not differ in the catalytic properties observed with phosphines directly submitted to the catalyst formation. 

A phosphine ligand, such as PhjPOMe, capable of bonding covalently to an alkene substrate (e.g. to OH or HNTs groups) (57) (58), has been employed to direct rhodium-catalysed hydroformylation to the formation of branched products, namely hemiacetals (59), with high regio- and enantio-selectivities. ... 

Seok and colleagues investigated the hydroformylation of allyl alcohol with paraformaldehyde in the presence of HRh(CO)(PPh3)3 (Scheme 3.4) [14]. Similar to that found in the reaction with syngas (see Section Allyl and homoallyl alcohols in Chapter 4), the functional group in the olefinic substrate directed the regiochemistry of the reaction and a cyclic transition state between catalyst and substrate was assumed. A maximum isomeric product ratio of lib = 21 was achieved. The addition of syngas to the reaction with paraformaldehyde or an excess of phosphine inhibited the formation of the linear aldehyde. 

Previously discussed ligands 1 (and 2) direct the incorporation of the formyl in a proximal distance to the phosphine group. In contrast, distal-selective hydroformylation can be achieved with phosphine auxiliaries of type 3, where the carbon atom involved in the transacetalization and the phosphine group, which binds temporarily on the rhodium center, are linked by a tether of five atoms. The principle is exemplarily shown in Scheme 4.124 [5]. 

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