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

Reaction of the racemic [Pd(C6H4PPh2)Br](4) (1) with the silver salt of 1R-(1 alpha,2 beta,3 alpha)]-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 Pd-2(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-Pd-2(C6H4PPh2)(2)(NCCH3)(4)](2+), obtained from (RR)-1, was reacted with ammonium terephthalate yielding RRR-[Pd-2(C6H4PPh2)(2)](3)(O2CC6H4CO2)(3), (RRR)-5. The reaction of ammonium diphenyldicarboxylate with the S enantiomer of the solvated species, gave SSS-[Pd-2(C6H4PPh2)(2)](3) (O2CC6H4C6H4CO2)(3), (SSS)-6. Compounds 5 and 6 have been crystallographically characterized. Reactions performed with racemic [Pd-2(C6H4PPh2)(2)(CH3CN)(4)](2+), have also been studied and the relative chiralities of the triangles have been determined by P-31 NMR spectroscopy.