Oxygen- versus carbon-coordination of the alpha-stabilized phosphorus ylide Ph3P=C(H)R in palladacycles bearing secondary amines

Abstract

The ortho-metalated complex [Pd(x){j 2 (C,N)-[C 6 H 4 CH 2 NRR 0 (Y)}] (2a-4a and 2b-3b) was prepared by refluxing in benzene equimolecular amounts of Pd(OAc) 2 and secondary benzylamine [a, EtNHCH 2 Ph; b, t-BuN-HCH 2 Ph followed by addition of excess NaCl. The reaction of the complexes [Pd(x){j 2 (C,N)-[C 6 H 4 CH 2 NRR 0 (Y)}] (2a-4a and 2b-3b) with a stoichiometric amount of Ph 3 P=C(H)COC 6 H 4 -4-Z (Z = Br, Ph) (ZBPPY) (1:1 molar ratio), in THF at low temperature, gives the cationic derivatives [Pd(OC(Z-4-C 6 H 4 C=CHPPh 3 ){j 2 (C,N)-[C 6 H 4 -CH 2 NRR 0 (Y)}] (5a-9a, 4b-6b, and 4b 0 -6b 0 ), in which the ylide ligand is O-coordinated to the Pd(II) center and trans to the ortho-metalated C(6)H(4) group, in an ''end-on carbonyl''. Ortho-metallation, ylide O-coordination, and C-coordination in complexes (5a-9a, 4b-6b, and 4b 0 -6b 0 ) were characterized by elemental analysis as well as various spectroscopic techniques.

Activation of Chiral (Salen)AlCl Complex by Phosphorane for Highly Enantioselective Cyanosilylation of Ketones and Enones

“…However, subsequent studies revealed that the high efficiency of the cyanosilylation step was due to orthogonal activation of chiral complex 1 and TMSCN by phosphorane 2a and Ph 3 PO, respectively (Scheme B). This not only suggests the potential of phosphoranes as a type of ligand motif to develop chiral metal catalysts, an untrodden path in the chemistry of ylides, but paves the way to a powerful catalyst system consisting of (salen)­AlCl complex 1 , phosphorane 2e , and Ph 3 PO for asymmetric ketone cyanosilylation. It is worth mentioning that because of the importance of cyanohydrins as precursors of tetrasubstituted α-hydroxy carbonyl derivatives, much effort has been devoted to cyanation of ketones .…”