Acyclic unsaturated ligands metal complexes

The usefulness of such a series is twofold (I) If two different unsaturated ligands are found in the same complex, one can predict which ligand will react, and (2) it is possible to eslimaie how activating a metal fragment must be in order to cause a reaction to occur. Notice that hydrocarbons of even hapticity are more reactive than those with odd hapticity. In addition, acyclic ligands are more reactive than cyclic ones. 

Figure 4.9. Frontier orbitals available for metal-carbon bonding in complexes of acyclic unsaturated systems C I I 2- (a) Allyl ligand H2CCHCH2 (b) buta-l,3-diene H2C=CHCH=CH2 (c) trimethylenemethane 6(012)3.

Davies et al. have developed a succinct set of guidelines to predict the most favorable position of nucleophilic attack on electronically saturated cationic metal complexes beating more than one unsaturated hydrocarbon ligand. In essence, the so-called DGM rules state that (i) polyenes (L -type ligands) are more reactive than polyenyls (L, -type ligands see also Scheme 11) (ii) open or acyclic ligands react before closed or cyclic ligands and (iii) addition to... 

The invention of Ru-binap dicarboxylate complexes extends the scope of asymmetric hydrogenations . Simple acyclic acids are hydrogenated with enantioselectivities from 80 to 100%. The procedure is applicable to /3,y-unsaturated carboxylic acids with about 80% e.e. . Deuterium incorporation indicates that a mechanism involving a metal monohydride complex operates. An amino group on the chiral phosphine ligand enhances the efficacy of ferrocenylphosphine-Rh complexes toward trisubstituted acyclic acids . 

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