Synthesis of chiral bidentate aminophosphine palladium (II) complexes and their use in asymmetric cycloaddition reactions.

Abstract

The chiral (P,N)-ligated dichloropalladium (II) complexes, cis-dichloro[(+) O-diphenylphosphino-N-methylephedrine] palladium dichloride (2.15a), cis-dichloro[(S)-Prophos] palladium dichloride (2.15b), and cis-dichloro[(S)-1-methyl-2-(diphenylphosphinomethyl)pyrrolidine] palladium dichloride (2.15c) complexes, have been synthesized and completely characterized in the solid state. The synthetic procedure involves a simple one pot reaction of equivalent amounts of (CH3CN) 2PdCl2 and the corresponding ligand. These complexes are active precatalysts for the cycloaddition reactions of aziridines and heterocumulenes, yielding imidazolidinimines (2.34, X=NAr) for the case of carbodiimides. The cycloaddition reactions of aziridines and isocyanates are dependent on the catalyst used. When 2.15b is the catalyst, one product (imidazolidinones 2.34, X=O) is formed. However, when either 2.15(a,c) are used, two products (imidazolidinones 2.34, X=O and oxazolidinimines 2.35, X=O) are formed. Catalysts 2.15(a--c) failed to provide stereoselectivity. The one pot reaction of (CH3CN) 2PdCl2 and two equivalents of the chiral aminophosphinite ligand L*, [L* = (+)O-diphenylphosphino-N-methylephedrine (2.2), (S)-1-methyl-2-(diphenylphosphinomethyl) pyrrolidine (2.8)] resulted in the formation of [Ph2P(O)PdL*Cl] 2.18(a,c). A mechanism was proposed explaining the formation of the phosphine oxide moiety [Ph2P(O)] in these complexes. The structure of 2.18a was confirmed by an X-Ray crystal structure determination. The geometry of the compound is square planar with a slight distortion caused by the "trans-influence" of the phosphorus groups, causing them to be cis to each other.* *Please refer to dissertation for diagrams.