Aqua and Diethyl Ether PNNP Complexes of Ruthenium(II): Structure and Solution Behavior

Addition of water to CD2Cl2 solutions of the five-coordinate complex [RuCl(PNNP)]PF6 (2) (formed by treating [RuCl2(PNNP)] (1) with TlPF6 (1 equiv) in dichloromethane) yields the aqua complexes cis-β-[RuCl(OH2)(PNNP)]PF6 (3) and trans-[RuCl(OH2)(PNNP)]PF6 (4) in a 6:1 ratio (PNNP is the chiral ligand (1S,2S)-N,N′-bis[o-(diphenylphosphino)benzylidene]cyclohexane-1,2-diamine). An excess of H2O (10 equiv) is needed for quantitative conversion of 2. The cis-β isomer 3 is more labile than the trans analogue 4 and is in slow-regime chemical exchange with five-coordinate 2 in CD2Cl2. The trans aqua complex 4 does not dissociate in CDCl3 over 6 h, but undergoes rapid equilibration with 2 and 3 upon dissolution in CD2Cl2. The X-ray structure of (Λ)-cis-β-3 shows an intramolecular hydrogen bond between the aqua and the chloro ligands. The elusive Et2O adduct [RuCl(OEt2)(PNNP)]PF6 (5), obtained by treating 1 with (Et3O)PF6 (1 equiv) in dichloromethane, is formed as the cis isomer only. At room temperature, 5 exists in equilibrium with five-coordinate 2 and free Et2O. The equilibrium is fast on the NMR time scale and is shifted toward 5 at low temperature.