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

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 center dot 6H(2)O and pdmp. X-Ray crystallography confirmed the (C-2)-chair(2) 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)-twist(2) 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)]Cl-2(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 center dot ob center dot 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-chair(2) and anti-chair(2) 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.