Chiral palladium(II) and platinum(II) complexes of diaminocyclohexane: X-ray structures of (1 R,2 R)-(−)-1,2-diaminocyclohexane dihydrochloride and its corresponding oxalato platinum(II) complex

Abstract

The nucleophilic substitution reaction of the enantiomerically pure ligand, (1 R,2 R)-(−)-1,2-diaminocyclohexane [DACH] ( 1) with cis-bis(benzonitrile)palladium(II) dichloride [(PhCN) 2PdCl 2] leads to the formation of the complex [(DACH)PdCl 2] ( 2) in a high yield. The reaction of the corresponding platinum(II) complex [(PhCN) 2PtCl 2] with DACH, under the same reaction conditions, surprisingly, took a different course, in which nucleophilic addition to the benzonitrile ligand occurred forming an enantiomerically pure amidine complex [(PhCNHNH(C 6H 10)NH 2)Pt(NCPh)Cl]Cl ( 3), where the nitrogen ligand form a seven-membered chelate around the central atom. The aqua and oxalato derivatives of complex 2, [(DACH)Pd(H 2O) 2](NO 3) 2 ( 4) and [(DACH)Pd(C 2O 4)] ( 5) have also been prepared and characterized. The platinum analogue complex to 5, [(DACH)Pt(C 2O 4)] ( 6), was prepared starting from the enantiomerically pure isomer ( 1) and the platinum salt K 2PtX 4 (X=Cl, I). According to X-ray structural analysis carried out on the complex, the product does not consist of just the desired isomer, but a mixture of both the trans- l ( trans-(−)-1 R,2 R) and trans- d ( trans-(+)-1 S,2 S) isomers. No retention of optical isomerism was observed. The single crystal structural analysis was also carried out on the ligand N, N′-(1 R,2 R)-(−)-diaminocyclohexane dihydrochloride (DACH·2HCl)] ( 1a). The result indicates, however, that only the R, R-isomer exists in the free ligand.