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...

Fundamental research into the Li-O2 battery system has gone into high gear, gaining momentum because of its very high theoretical specific energy. Much progress has been made toward understanding the discharge mechanism, but the mechanism of the oxygen evolution reaction (OER) on charge (i.e., oxidation) remains less understood. Here, using operando X-ray diffraction, we show that oxidation of electrochemically generated Li2O2 occurs in two stages, but in one step for bulk crystalline (commercial) Li2O2, revealing a fundamental difference in the OER process depending on the nature of the peroxide. For electrochemically generated Li2O2, oxidation proceeds first through a noncrystalline lithium peroxide component, followed at higher potential by the crystalline peroxide via a Li deficient solid solution (Li(2-x)O2) phase. Anisotropic broadening of the X-ray Li2O2 reflections confirms a platelet crystallite shape. On the basis of the evolution of the broadening during charge, we speculate that the toroid particles are deconstructed one platelet at a time, starting with the smallest sizes that expose more peroxide surface. In the case of in situ charged bulk crystalline Li2O2, the Li vacancies preferentially form on the interlayer position (Li1), which is supported by first-principle calculations and consistent with their lower energy compared to those located next to oxygen (Li2). The small actively oxidizing fraction results in a gradual reduction of the Li2O2 crystallites. The fundamental insight gained in the OER charge mechanism and its relation to the nature of the Li2O2 particles is essential for the design of future electrodes with lower overpotentials, one of the key challenges for high performance Li-air batteries.

The electronic effect in the rhodium diphosphine catalyzed hydroformylation was investigated. A series of electronically modified thixantphos ligands was synthesized, and their effects on coordination chemistry and catalytic performance were studied. Phosphine basicity was varied by using p-(CH3)2N, p-CH3O, p-H, p-F, p-Cl, or p-CF3 substituents on the diphenylphosphine moieties. X-ray crystal structure determinations of the complexes (thixantphos)Rh(CO)H(PPh3) and (p-CH3O-thixantphos)Rh(CO)H(PPh3) were obtained. The solutions structures of the (diphosphine)Rh(CO)H(PPh3) and (diphosphine)Rh(CO)2H complexes were studied by IR and NMR spectroscopy. IR and 1H NMR spectroscopy showed that the (diphosphine)Rh(CO)2H complexes consist of dynamic equilibria of diequatorial (ee) and equatorial−apical (ea) isomers. The equilibrium compositions proved to be dependent on phosphine basicity; the ee:ea isomer ratio shifts gradually from almost one for the p-(CH3)2N-substituted ligand to more than nine for the p-CF3-substituted ligand. Assignments of bands to ee and ea isomers and the shifts in wavenumbers in the IR spectra were supported by calculations on (PH3)2Rh(CO)2H, (PH3)2Rh(CO)2D, and (PF3)2Rh(CO)2H complexes using density functional theory. In the hydroformylation of 1-octene and styrene an increase in l:b ratio and activity was observed with decreasing phosphine basicity. Most remarkably for 1-octene the selectivity for linear aldehyde formation was between 92 and 93% for all ligands. These results indicate that the chelation mode in the (diphosphine)Rh(CO)2H complexes per se is not the key parameter controlling the regioselectivity. Mechanistic explanations of the effect of the natural bite angle on regioselectivity are reconsidered.

The mechanism and kinetics of the solvolysis of complexes of the type [(L-L)Pd(C(O)CH(3))(S)](+)[CF(3)SO(3)](-) (L-L = diphosphine ligand, S = solvent, CO, or donor atom in the ligand backbone) was studied by NMR and UV-vis spectroscopy with the use of the ligands a-j: SPANphos (a), dtbpf (b), Xantphos (c), dippf (d), DPEphos (e), dtbpx (f), dppf (g), dppp (h), calix-6-diphosphite (j). Acetyl palladium complexes containing trans-coordinating ligands that resist cis coordination (SPANphos, dtbpf) showed no methanolysis. Trans complexes that can undergo isomerization to the cis analogue (Xantphos, dippf, DPEphos) showed methanolyis of the acyl group at a moderate rate. The reaction of [trans-(DPEphos)Pd(C(O)CH(3))](+)[CF(3)SO(3)](-) (2e) with methanol shows a large negative entropy of activation. Cis complexes underwent competing decarbonylation and methanolysis with the exception of 2j, [cis-(calix-diphosphite)Pd(C(O)CH(3))(CD(3)OD)](+)[CF(3)SO(3)](-). The calix-6-diphosphite complex showed a large positive entropy of activation. It is concluded that ester elimination from acylpalladium complexes with alcohols requires cis geometry of the acyl group and coordinating alcohol. The reductive elimination of methyl acetate is described as a migratory elimination or a 1,2-shift of the alkoxy group from palladium to the acyl carbon atom. Cis complexes with bulky ligands such as dtbpx undergo an extremely fast methanolysis. An increasing steric bulk of the ligand favors the formation of methyl propanoate relative to the insertion of ethene leading to formation of oligomers or polymers in the catalytic reaction of ethene, carbon monoxide, and methanol.