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Palladium‐Based Telomerization of 1,3‐Butadiene with Glycerol Using Methoxy‐Functionalized Triphenylphosphine Ligands
Author(s) -
Palkovits Regina,
Nieddu Ilenia,
Kruithof Cornelis A.,
Klein Gebbink Robertus J. M.,
Weckhuysen Bert M.
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200800792
Subject(s) - telomerization , glycerol , palladium , catalysis , chemistry , triphenylphosphine , selectivity , glyceraldehyde , 1,3 butadiene , ligand (biochemistry) , catalytic cycle , metal , organic chemistry , combinatorial chemistry , polymer chemistry , biochemistry , receptor , dehydrogenase , enzyme
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 C 8 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 °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 Pd II 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 Pd 0 precursor tested, gave the best results in terms of activity, which illustrates the importance of the ability to form a Pd 0 species in the catalytic cycle. Finally, base addition resulted in a shortening of the reaction time and most likely facilitates the formation of a Pd 0 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.