First enantiopure imine CN-palladacycle of non-metallocenic planar chirality with the [2.2]paracyclophane backbone

Herein the preparation of a planar chiral imine CN-palladacycle free of redox activity is reported. The direct cyclopalladation of a [2.2]paracyclophane-derived imine (HL) afforded the racemic dimer {Pd(η2-L)(-Cl)}21; its ortho-palladated structure was confirmed by spectroscopic (1H and 31P NMR) data for mononuclear derivatives and the X-ray study of the phosphane adduct (η2-L)PdCl(PPh3) 4. Both the (Spl,Spl)- and (Rpl,Rpl)-enantiomers of dimer 1 were isolated by the diastereoselective decoordination of the (RC)-valinate auxiliary ligand (Val) from the adduct (η2-L)Pd(κ2-Val) 5 using column chromatography on silica gel. The absolute configuration of these new CN-palladacycles was established by the independent synthesis of the (Rpl,Rpl)-enantiomer of dimer 1 from the pre-resolved (Spl)-4-formyl[2.2]paracyclophane.

Figure optionsDownload as PowerPoint slide

(Rpl,Rpl)-Di-μ-chlorobis{4-(N-2,6-dimethylphenyl)iminomethyl[2.2]paracyclophan-5-yl-C,N}dipalladium(II)C50H48Cl2N2Pd2Ee = >98%[α]D24=+559 (c 0.247, CH2Cl2)Source of chirality: resolution of starting carbaldehydeAbsolute configuration: (Rpl)

(Rpl,Rpl)-Di-μ-chlorobis{4-(N-2,6-dimethylphenyl)iminomethyl[2.2]paracyclophan-5-yl-C,N}dipalladium(II)C50H48Cl2N2Pd2Ee = >98%[α]D22=+551 (c 0.247, CH2Cl2)Source of chirality: diastereoselective decoordination of auxiliary ligand from (RC)-valinate derivative on silica gelAbsolute configuration: (Rpl)

(Spl,Spl)-Di-μ-chlorobis{4-(N-2,6-dimethylphenyl)iminomethyl[2.2]paracyclophan-5-yl-C,N}dipalladium(II)C50H48Cl2N2Pd2Ee = >98%[α]D22=-549 (c 0.253, CH2Cl2)Source of chirality: diastereoselective decoordination of auxiliary ligand from (RC)-valinate derivative on silica gelAbsolute configuration: (Spl)

(Spl,RC)-{4-(N-2,6-Dimethylphenyl)iminomethyl[2.2]paracyclophan-5-yl-C,N}(valinato-N,O)-palladium(II)C30H34N2O2PdEe = >98%[α]D24=-589 (c 0.367, CH2Cl2)Source of chirality: diastereoselective decoordination of auxiliary ligand from (RC)-valinate derivative on silica gelAbsolute configuration: (Spl,RC)