Isolation of enantiomerically pure organometallic palladium compounds: synthesis of the triangles prepared from enantiopure [cis-Pd2(C6H4PPh2)2(NCCH3)4]2+

Abstract

Reaction of the racemic [Pd(C₆H₄PPh₂)Br]₄ (1) with the silver salt of 1R-(1α,2β,3α)]-3-methyl-2-(nitromethyl)-5-oxocyclopentaneacetate, (R)-AgO₂CR*, results in the formation of a mixture of diastereoisomers (RRR)-2 and (SRR)-2 of the formula Pd₂(C₆H₄PPh₂)₂(O₂CR*)₂ that were separated by standard chromatographic methods. Each diastereoisomer was readily converted into the tetrametallic stereoisomers (SS)-1 and (RR)-1, of the formula [Pd(C₆H₄PPh₂)Br]₄ that were isolated and characterized by X-ray crystallography. The R enantiomer of the solvated cationic species [cis-Pd₂(C₆H₄PPh₂)₂(NCCH₃)₄]²⁺, obtained from (RR)-1, was reacted with ammonium terephthalate yielding RRR-[Pd₂(C₆H₄PPh₂)₂]₃(O₂CC₆H₄CO₂)₃, (RRR)-5. The reaction of ammonium diphenyldicarboxylate with the S enantiomer of the solvated species, gave SSS-[Pd₂(C₆H₄PPh₂)₂]₃(O₂CC₆H₄C₆H₄CO₂)₃, (SSS)-6. Compounds 5 and 6 have been crystallographically characterized. Reactions performed with racemic [Pd₂(C₆H₄PPh₂)₂(CH₃CN)₄]²⁺, have also been studied and the relative chiralities of the triangles have been determined by ³¹P NMR spectroscopy.