New phosphino-oxazoline and related phosphino-iminolate palladium complexes; structure of an unusual zwitterionic dinuclear Pd(II) complex

Abstract

Reaction of the phosphino-oxazoline chiral ligand (4-(R)-phenyl-2-oxazoline-2-ylmethyl)diphenylphosphine) (abbreviated (R)-PCH₂ox^Ph) with [Pd(dmba-C,N)(μ-Cl)]₂ or [PdCl₂(cod)] (cod = 1,5-cyclooctadiene) led to the formation of [Pd(dmba-C,N){(R)-PCH₂ox^Ph-κ²P,N}]Cl 1 and [PdCl₂{(R)-PCH₂ox^Ph-κ²P,N}] 5, respectively. Deprotonation of the palladium phosphino-oxazoline complex 1 occurred at the PCH₂ group and resulted in the formation of an anionic P,N chelate with a prochiral carbon atom in [Pd(dmba-C,N){(R)-PCHox^Ph-κ²P,N}] 2. Reaction of 2 with [Pd(dmba-C,N)(μ-Cl)]₂ led to the unexpected and diastereoselective formation of the dinuclear complex [{Pd(dmba-C,N)Cl}-(R)-{CHPPh₂-(R)-ox^Ph}Pd(dmba-C,N)] 4 in which a Pd(dmba-C,N)Cl moiety is directly bonded to the carbon α to the P atom of the anionic P,N chelate of 2. This results in an unsual zwitterionic structure. In the course of this work, crystals of [(dmba-C,N)Pd(μ-OH)(μ-Cl)Pd(dmba-C,N)]·1/2[Pd(dmba-C,N)(μ-Cl)]₂7 were obtained and the single crystal X-ray analyses of complexes 2, 4·2THF, 5·CH₂Cl₂, [PdCl(Me){(R)-PCH₂ox^Ph-κ²P,N}] 6 and 7 are presented.