Preparation and characterization of mixed-ligand cobalt(iii) complexes containing (3-aminopropyl)dimethylphosphine (pdmp). Conformation of the six-membered pdmp chelate ring

Abstract

Several new cobalt(III) complexes containing (3-aminopropyl)dimethylphosphine (pdmp) have been prepared, and their molecular structures have been determined. A dichloro complex of trans(Cl,Cl)-cis(P,P)-[CoCl₂(pdmp)₂]PF₆ (1) was prepared from trans-[CoCl₂(py)₄]Cl·6H₂O and pdmp. X-Ray crystallography confirmed the (C₂)-chair₂ conformation of two six-membered pdmp chelate rings in 1, while the analogous 1,3-bis(dimethylphosphino)propane (dmpp) complex trans-[CoCl₂(dmpp)₂]ClO₄ (3) exhibited the (D_2d)-twist₂ conformation. Substitution reactions of 1 for ethane-1,2-diamine (en), pentane-2,4-dionate (acac), and N,N-dimethyldithiocarbamate (dtc) gave the mixed-ligand tris(chelate)-type complexes of [Co(en)₂(pdmp)]Cl₂(PF₆) (5), [Co(acac)(pdmp)₂](PF₆)₂ (7), and [Co(dtc)_3–n(pdmp)_n](PF₆)_n [n = 1 (9) or 2 (10)], respectively. The conformer of the complex cation in 5 was assigned as lel·ob·chair by X-ray analysis. In the case of the acac complex 7, both trans(P,N) (7a) and trans(N,N) (7b) isomers were isolated, and the complex cations were characterized as syn-chair₂ and anti-chair₂ conformers, respectively, with respect to the six-membered pdmp chelate rings. These conformers coincide with the most stable ones anticipated by the DFT optimum geometry calculations. In the crystal structure of trans(P,N)-[Co(dtc)(pdmp)₂](BPh₄)₂ (10′) one of the pdmp chelate rings adopted a skew-boat (twist) conformation, which reduced the intramolecular steric ring–ring interaction effectively. The DFT optimized geometries for several isomers and/or conformers of [CoCl₂(pdmp)₂]⁺ were compared.