Self-assembly of bidentate ligands for combinatorial homogeneous catalysis based on an A-T base pair model*
Bernhard Breit and Wolfgang Seiche
Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany
Abstract: A new concept for generation of chelating ligand libraries for homogeneous metal complex catalysis based on self-assembly is presented. Thus, self-assembly of structurally simple monodentate ligands in order to give structurally more complex bidentate ligands is achieved employing hydrogen bonding. Based on this concept and on the 2-pyridone/hydroxypyridine tautomeric system, a new rhodium catalyst was identified which operated with excellent activity and regioselectivity upon hydroformylation of terminal alkenes. In order to generate defined unsymmetrical heterodimeric ligands, an A-T base pair analog-the aminopyridine/isoquinolone system-was developed which allows for complementary hydrogen bonding. Based on this platform, a 4 x 4 phosphine ligand library was screened in the course of the rhodium-catalyzed hydroformylation of 1-octene. A catalyst operating with outstanding activity and regioselectivity in favor of the linear aldehyde was discovered.
Keywords: bidentate ligands; homogeneous catalysis; combinatorial; BINAP; XANTPHOS; 2-pyridone; 2-hydroxypyridine; 6-DPPon; rhodium catalyzed; hydroformylation.
*Pure Appl. Chem. 78, 197-523. An issue of reviews and research papers based on lectures presented at the 13th IUPAC International Symposium on Organometallic Chemistry Directed Towards Organic Synthesis (OMCOS-13), Geneva, Switzerland, 17-21 July 2005.