Crystal structures of trans-[Ru(dppe) 2(CO)(Cl)](BF 4)·2(toluene) and trans-[Ru(dppm) 2(CO)(Cl)](BF 4)·CH 2Cl 2: a study of the steric and electronic ligand effects of trans-positioned diphosphine ligands

Abstract

Single-crystal X-ray diffraction studies were carried out on the complexes trans-[Ru(dppe) 2(CO)(Cl)](BF 4) ·2(toluene) ( 1) (where dppe = 1,2-bis(diphenylphosphino)ethane) and trans-[Ru(dppm) 2(CO)(Cl)](BF 4) ·CH 2Cl 2 ( 2) (where dppm = bis(diphenylphosphino)methane). Complex 1 crystallizes in the orthorhombic space group P2 12 12 with a = 14.366(3), b = 17.075(3), c = 12.433(2) A ̊ , V = 3049.8(10) A ̊ 3 and Z = 2 . The structure was refined to R = 3.02% for 3233 reflections above 6σ ( R = 4.46% for all 3991 point-group independent data); the Ru-cation lies on a site of C 2 symmetry, leading to disorder of the Cl and CO ligands. Complex 2 crystallizes in the orthorhombic space group Pna2 1, with a = 22.425(7), b = 11.515(4), c = 19.511(10) A ̊ , V = 5038(3) A ̊ 3 and Z = 4 . The structure was refined to R = 4.43% for 4770 reflections above 6σ ( R = 7.09% for all 6631 point-group independent data). The crystal structure data suggest increased intramolecular interligand interactions with the trans-bis(dppe) complexes relative to the trans-bis(dppm) complexes. In order to furth assess the steric ligand effects of dppm and dppe on the redox chemistry of ruthenium complexes, the electrochemical data for complexes 1 and 2 as well as for trans-Ru(dppe) 2(Cl) 2 and trans-Ru(dppm) 2(Cl) 2 were analyzed. The E pa value for the oxidation of complex 1 was more positive than the E pa value for the oxidation of complex 2; similarly, the E 1 2 value for the oxidation of trans-Ru(dppe) 2(Cl) 2 was more positive than the E 1 2 value for the oxidation of trans-Ru(dppm) 2(Cl) 2. The increase in the redox potentials for the oxidation of the dope complexes may be due to the enhanced intramolecular interligand interactions of the dppe ligands, which is in agreement with the crystal structure data.