The chain gang: Crude glycerol, a by‐product in the production of biodiesel, can be telomerized with 1,3‐butadiene to form C8‐chain ethers. The development of suitable catalyst systems for the direct telomerization of crude glycerol at the biodiesel plant provides a route to useful building blocks from cheap starting materials for commercially valuable products such as detergents and surfactants.

Glycerol is considered a potential renewable building block for the synthesis of existing as well as new chemicals. A promising route is the telomerization of 1,3-butadiene with glycerol leading to C8 chain ethers of glycerol with applications in, for example, surfactant chemistry. Recently, we reported a new set of palladium-based homogeneous catalytic systems for the telomerization of 1,3-butadiene with glycerol and found that palladium complexes bearing methoxy-functionalized triphenylphosphine ligands are highly active catalysts capable of converting crude glycerol without any significant loss of activity. Herein, we present a detailed account of these investigations by reporting on the influence of the butadiene/glycerol ratio, temperature, and reaction time on product selectivity and activity allowing further optimization of catalyst performance. Maximum activity and yield were reached for high 1,3-butadiene/glycerol ratios at a temperature of 90 degrees C, whereas the selectivity for mono- and diethers of glycerol could be optimized by combining high reaction temperatures and short reaction times with low butadiene/glycerol ratios. Variation of the PdII metal precursors and the metal/ligand ratio showed that palladium precursors with halogen ligands gave unsatisfying results, in contrast to precursors with weakly coordinated ligands such as [Pd(OAc)2] and [Pd(acac)2]. [Pd(dba)2], the only Pd0 precursor tested, gave the best results in terms of activity, which illustrates the importance of the ability to form a Pd0 species in the catalytic cycle. Finally, base addition resulted in a shortening of the reaction time and most likely facilitates the formation of a Pd0 species. Based on these results, we were able to realize the first attempts towards a rational ligand design aimed at a high selectivity for mono- and diether formation.

The rhodium-catalyzed asymmetric hydrogenation of various β-dehydroamino acid derivatives to give optically active β-amino acids has been examined. Chiral monodentate 4,5-dihydro-3Hdinaphthophosphepines, which are easily tuned and accessible in a multi-10-g scale, have been used as ligands. The enantioselectivity is largely dependent on the nature of the substituent at the phosphorous atom and on the structure of the substrate. Applying optimized conditions up to 94% ee was achieved.

Dedicated to Professor Giambattista Consiglio, a good friend and excellent chemist, for his remarkable contributions to the advancement of stereoselective catalysis A range of a,b-unsaturated acids and esters have been selectively reduced to the corresponding saturated acid derivatives by hydrogen transfer. As the reducing agent, formic acid was used in the presence of Rh I complexes formed with the powerful chiral ligand Ph-binepine (1), an axially chiral binaphthalenetype monodentate P-donor ligand. Very high stereoselectivities (up to 97% ee) were obtained in the case of itaconic acid (2a).Introduction. -The reduction of unsaturated functional groups by means of transition-metal-mediated hydrogen transfer from a suitable hydrogen donor such as i-PrOH or HCOOH has experienced increasing success over the last years [1]. This mild methodology represents a viable alternative to catalytic hydrogenation by molecular H 2 due to its operational simplicity and reduction of the risks associated with the use of an easily inflammable gas of high diffusibility. Significant advances in this area have been achieved in the asymmetric reduction of ketones and imines with catalysts of excellent activity/selectivity based on Ru and Rh complexes with monotosyl-substituted diamines or amino alcohols as chiral modifiers [1a].Less efforts have been devoted to the transfer hydrogenation of C=C bonds. Although this process is thermodynamically favored, even when alcohols are used as H-donors, only the reduction of conjugated C=C bonds is of practical significance, while simple alkenes and dienes are poorly reactive. A perusal of the literature shows that transfer hydrogenation of conjugated acid derivatives such as itaconic acid and a-(acetamido)cinnamic acid selectively takes place at the C=C bond, and stereoselectivities higher than 90% can be sometimes attained in this reaction when performed in the presence of Ru [2] or Rh complexes [3] with chiral bidentate diphosphines such as binap [2], bppm [3a -f], or deguphos [3g]. No example of the application of monodentate phosphines as chiral inducers in this reaction has been reported thus far, in spite of the excellent performances displayed by binaphthalene-templated monoA C H T U N G T R E N N U N G dentate P-ligands [4], such as phosphonites [5], phosphites [6], and phosphoramidites [7], in the Rh-catalyzed hydrogenation of a wide variety of substrates.