New diphosphine ligands based on heterocyclic aromatics inducing very high regioselectivity in rhodium-catalyzed hydroformylation: effect of the bite angle Kranenburg, M.; van der Burgt, Y.E.M.; Kamer, P.C.J.; van Leeuwen, P.W.N.M.; Goubitz, K.; Fraanje, J. Published in: Organometallics DOI:10.1021/om00006a057Link to publication Citation for published version (APA):Kranenburg, M., van der Burgt, Y. E. M., Kamer, P. C. J., van Leeuwen, P. W. N. M., Goubitz, K., & Fraanje, J. (1995). New diphosphine ligands based on heterocyclic aromatics inducing very high regioselectivity in rhodiumcatalyzed hydroformylation: effect of the bite angle. Organometallics, 14, 3081-3089. DOI: 10.1021/om00006a057 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. The effect of the bite angle on regioselectivity in the rhodium-catalyzed hydroformylation reaction was studied with a series of bidentate diphosphines based on xanthene-like backbones as ligands. The bite angles of these ligands are fine-tuned by subtle alterations of the backbone of the ligands. When the bridge (X) in the 10-position of xanthene is varied, the bite angle as calculated from molecular mechanics increases stepwise from 102 to 131", whereas the changes in steric bulk and electronic effects are virtually absent for the following ligands: bis(2-(diphenylphosphino)phenyl) ether (DPEphos, 11, X = H, H; 4,6-bis(dipheny1phosphino)-10,lO-dimethylphenoxasilin (Sixantphos, 2), X = Si(CH&; 2,8-dimethyl-4,6-bis(dipheny1phosphino)phenoxathiin (Thixantphos, 3), X = S; 9,9-dimethyl-4,6-bis(dipheny1phosphino)xanthene (Xantphos, 4), X = C(CH&; 4,6-bis(diphenylphosphino)dibenzofuran (DBFphos, 51, X = bond. In the hydroformylation of l-octene the regioselectivity increased regularly with increasing bite angle: a t 40 "C up to 98.3% n-aldehyde was obtained with Xantphos, without isomerization or hydrogenation of l-octene. DBFphos does not form chelates, and consequently no increased selectivity was observed. The selectivity of the catalyst was almost unaffected by raising of the temperature to 80 "C, resulting in a higher turnover frequency (to0 with a constant selectivity: 97.7% n-aldehyde, 0.5% isomerization, and a tof value of 800 mol (mol of Rh)-l h-l. Xantphos induces the highest selectivity for the formation of the linear alde...

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The design of artificial catalysts able to compete with the catalytic proficiency of enzymes is an intense subject of research. Non-covalent interactions are thought to be involved in several properties of enzymatic catalysis, notably (i) the confinement of the substrates and the active site within a catalytic pocket, (ii) the creation of a hydrophobic pocket in water, (iii) self-replication properties and (iv) allosteric properties. The origins of the enhanced rates and high catalytic selectivities associated with these properties are still a matter of debate. Stabilisation of the transition state and favourable conformations of the active site and the product(s) are probably part of the answer. We present here artificial catalysts and biomacromolecule hybrid catalysts which constitute good models towards the development of truly competitive artificial enzymes.

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