ONIOM study of the active species in Pd-phosphine catalyzed coupling reactions Export

@article{citeulike:933900, abstract = {This research employs the ONIOM scheme for hybrid quantum mechanics/molecular mechanics calculations. Palladium-phosphine catalysts used in bond coupling reactions are investigated. These complexes are of the form Pd{PR2(biaryl)}n, where n=1 or 2, R=tert-butyl (tBu) or cyclohexyl (Cy). The tBu substituted phosphines prefer a 'down' geometry, i.e. that in which the biaryl pendant group is proximal to the phosphorus lone pair. However, the Cy-substituted phosphine is less sterically hindered, leading to a more stable 'up' (distal to the phosphorus lone pair) conformer. Mono-phosphine Pd complexes exclusively prefer the 'down' (proximal to Pd) conformers; electronic density maps show that Pd- interactions further stabilize the down conformation. Palladium bis-phosphines, do not show a uniform choice of stable conformer. The steric contribution is more important in bis-phosphines, and is counteracted by the electronic preference. No Pd- interaction is observed for Pd{PR2(biaryl)}2. The dissociation energy of Pd{PR2(biaryl)}n is calculated. Compared to the Pd(PtBu3)2 system, the bond dissociation energy of PdL2 does not change much, except for Pd(tBu3)2(terphenyl), which has a bond energy of 6kcal/mol, and is thus expected to exist predominantly in the more active mono-phosphine form in solution.}, author = {Cundari, T. R.}, citeulike-article-id = {933900}, citeulike-linkout-0 = {http://www.ingentaconnect.com/content/els/01661280/2003/00000632/00000001/art00293}, keywords = {mine}, month = {August}, pages = {121--129}, posted-at = {2006-11-06 23:25:17}, priority = {2}, title = {ONIOM study of the active species in Pd-phosphine catalyzed coupling reactions}, url = {http://www.ingentaconnect.com/content/els/01661280/2003/00000632/00000001/art00293} }

TY - JOUR ID - citeulike:933900 L3 - citeulike-article-id:933900 N2 - This research employs the ONIOM scheme for hybrid quantum mechanics/molecular mechanics calculations. Palladium-phosphine catalysts used in bond coupling reactions are investigated. These complexes are of the form Pd{PR2(biaryl)}n, where n=1 or 2, R=tert-butyl (tBu) or cyclohexyl (Cy). The tBu substituted phosphines prefer a 'down' geometry, i.e. that in which the biaryl pendant group is proximal to the phosphorus lone pair. However, the Cy-substituted phosphine is less sterically hindered, leading to a more stable 'up' (distal to the phosphorus lone pair) conformer. Mono-phosphine Pd complexes exclusively prefer the 'down' (proximal to Pd) conformers; electronic density maps show that Pd- interactions further stabilize the down conformation. Palladium bis-phosphines, do not show a uniform choice of stable conformer. The steric contribution is more important in bis-phosphines, and is counteracted by the electronic preference. No Pd- interaction is observed for Pd{PR2(biaryl)}2. The dissociation energy of Pd{PR2(biaryl)}n is calculated. Compared to the Pd(PtBu3)2 system, the bond dissociation energy of PdL2 does not change much, except for Pd(tBu3)2(terphenyl), which has a bond energy of 6kcal/mol, and is thus expected to exist predominantly in the more active mono-phosphine form in solution. EP - 129 TI - ONIOM study of the active species in Pd-phosphine catalyzed coupling reactions SP - 121 KW - mine AU - Cundari, TR UR - http://www.ingentaconnect.com/content/els/01661280/2003/00000632/00000001/art00293 ER -