Optical Resolution and the Study of Ligand Effects on the Ortho-Metalation Reaction of Resolved (±)-Diphenyl[1-(1-naphthyl)ethyl]phosphine and Its Arsenic Analogue

Abstract

Two highly air-sensitive asymmetric ligands (± )-diphenyl[1-(1-naphthyl)ethyl]phosphine and its arsenic analogue [(±)-L] have been prepared and resolved by the fractionalization of a pair of diastereomeric palladium complexes containing the appropriate ligand and ortho-metalated (R)-(1-(dimethylamino)ethyl)naphthylene. X-ray structural analysis revealed that the less soluble isomers in each resolution contained the resolving ligand of the S absolute configuration. The resolved ligands coordinated as monodentates with only the phosphorus or arsenic donor coordinated to the resolving organopalladium unit. Due to the steric congestions between the phenyl and the naphthyl rings, the Ph2E-C distances in both monodentate ligands are unusually long [1.885(2) Å for E = P and 2.035(7) Å for E = As]. The (R)-naphthylamine auxiliary could be removed chemoselectively from the resolved complexes by treatment with concentrated hydrochloric acid to give the corresponding bis(μ-chloro) complexes (-)-[(S)-LPdCl2]2. Treatments of these dimeric complexes with sodium acetate in ethanol gave the novel ortho-metalated complex bis(μ-chloro)-bis[(S)-1-[1-(diphenylphospha)ethyl]naphthylenyl-C 2,PJdipalladium(II), with [α]D +559° (CH 2Cl2), and the analogous ortho-metalated (S)-arsa complex, with [α]D +349° (CH2Cl2). The Ph2E-C distances recorded for the ortho-metalated phosphine complex are 1.841 (6) and 1.846(5) Å, and those recorded for the organometallic arsa rings are 1.938(9) and 1.945(9) Å. These Ph2E-C distances are noticeably shorter than those recorded for their analogous monodentate complexes. The intrachelate E-Pd-C angles of the analogous amino, phospha, and arsa complexes involved in the current study are similar [within the range of 80.5(2)-82.1(3)°] although it is noticeable that As > P > N.