Amide Formation from Aldimine and Water Promoted by Coordinated Metal Redox. Chemistry of a Family of Isomeric Ru(II)(diimine)2Cl2, Ru(III)(diimine)2Cl2(1+), and Ru(III)(diimine)(amide-imine)Cl2 Complexes

Article abstract of DOI:10.1021/ic00116a025

The relevant N,N-coordinating ligands are RN=C(H)-C(H)=NR (general abbreviation D, specific abbreviations D(1) and D(2) for R = cyclohexyl and p-tolyl, respectively) and [RN=C(H)-C(=O)-NR](1-) (abbreviations A, A(1), A(2)). Oxidation of cis- and trans-Ru(II)D2Cl2 by aqueous cerium(IV) (H2O2 can also be used for trans-RuD2Cl2) affords in excellent yield the amide complexes cis- and trans-Ru(III)DACl2 with retention of parental isomeric structure. Spectral and magnetic characterization data of the complexes are reported along with the X-ray structures of cis-RuD(1)2Cl2.PhMe and cis-RuD(1)A(1)Cl2.CH2Cl2. The ruthenium(III)-ruthenium(II) couples of the complexes follow E(1/2) systematics (other things remaining the same in each case): geometry, cis > trans; ligand, D > A; substituent,p-tolyl > cyclohexyl. The Ru(III)D2Cl2(1+) moiety has been electrogenerated in solution, and cis-[Ru(III)D(1)2Cl2]ClO4 has been isolated and characterized in the pure state. The conversion RuD2Cl2 RuDACl2 actually occurs via RuD2Cl2(1+), which reacts with water, affording the amide complex. The reaction is first order with respect to both RuD2Cl2(1+) and H2O, and the activation parameters are ΔH(#) = 12.5 kcal mol**-1 and ΔS(#) = -29.8 eu in the case of trans-RuD(2)2Cl2. It is proposed that the water molecule adds to the azomethine function and theα-hydroxy amine function of the adduct is rapidly oxidized via aninduced electron transfer pathway. The net reactions are as follows: RuD2Cl2 RuD2Cl2(1+) + e; RuD2Cl2(1+) + H2O RuDACl2 + 2e + 3H(1+). A crucial reaction condition appears to be the easy accessibility of two oxidation states of the metal ion related by facile transfer of one electron, the higher oxidation state being sufficiently polarizing to induce water binding at the aldimine site. Crystal data for the complexes are as follows: cis-RuD(1)2Cl2.PhME, crystal system monoclinic, space group P21/c, a = 14.808(6) ?, b = 19.442(7) ?, c = 13.989(6) ?, β = 117.18(3)°, V = 3583(2) ?**3, Z = 4, R = 3.70%, Rw =4.31%; cis-RuD(1)A(1)Cl2.CH2Cl2, crystal system monoclinic, space group P21/c, a = 11.295(4) ?, b = 27.064(14) ?, c = 12.064(4)?, β = 107.52(2)°, V = 3517(2) ?**3, Z = 4, R = 6.53%, Rw = 6.95%.