Reactions of pentaammineruthenium complexes with 1,2- and 1,4-dicyanobenzene and cyanobenzamides: evidences of neighboring group participation q Elia Tfouni a, * , Anto ˆnio Marcos de Souza Mace ˆdo a , Luciana nunes Cardoso b , Kleber Queiroz Ferreira b ,E ´ rica Cristina de Oliveira b , Ze ˆnis Novais da Rocha b a Departamento de Quı ´mica da Faculdade de Filosofia, Cie ˆncias e Letras de Ribeira ˜ o Preto, Universidade de Sa ˜ o Paulo, Av.Bandeirantes, 3900, 14040901 Ribeirao Preto, Brazil b Instituto de Quı ´mica da, Universidade Federal da Bahia, Brazil Received 30 July 2004; accepted 7 September 2004 Dedicated to the memory of Professor Rex. E. Shepherd Abstract The spectral (UV–Vis and IR) and electrochemical behavior of the nitrile bonded complexes [Ru(NH 3 ) 5 L] 2+ (L = 1,4-dicyano- benzene (1,4-dcb), 1,2-dicyanobenzene (1,2-dcb)), [Ru(NH 3 ) 5 (NHC(OH)-bz-4-CN)] 3+ , [Ru(NH 3 ) 5 (NHC(O)-bz-2-CN)] 2+ and [Ru(NH 3 ) 5 (NH(C)NHC(O)bz)] 3+ (NH(C)NHC(O)-bz = 3-imino-1-oxo-isoindoline) are described. Oxidation of [Ru(NH 3 ) 5 L] 2+ , at 0 6 pH P 6, is followed by hydrolysis of the coordinated nitrile to give amide complexes in which the amide is through the nitro- gen, with pH-dependent rate constants. The estimated values of the rate constant of hydrolysis (k obs ) at 25 °C are 2.9 · 10 3 s 1 for [Ru(NH 3 ) 5 (1,4-dcb)] 3+ and 5.6 · 10 3 s 1 for [Ru(NH 3 ) 5 (1,2-dcb)] 3+ at pH 4.65. Reduction of [Ru(NH 3 ) 5 (NHC(O)-bz-4-CN)] 2+ and [Ru(NH 3 ) 5 (NHC(O)-bz-2-CN)] 2+ is followed by two reactions, one is an aquation forming [Ru(NH 3 ) 5 (OH 2 )] 2+ and free ligand, and the other an intramolecular linkage isomerization forming [Ru(NH 3 ) 5 (NC-bz-4-NH 2 C(O))] 2+ and [Ru(NH 3 ) 5 (NC-bz-2-NH 2 C(O))] 2+ . The oxidized1,2-cyanobenzamide complex [Ru(NH 3 ) 5 (NHC(OH)-bz-2-CN)] 3+ undergoes an amide to nitrile intramolecular linkage isomerization, followed by a cyclization reaction resulting in [Ru(NH 3 ) 5 (NH-(C)(HN-C(O)-2-bz))] 3+ ((NH-(C)(HN-C(O)-2-bz)) = 3-imino-1-oxo-isoindoline bonded through the exocyclic nitrogen) (pK a = 4.3). The rates of these reactions, which occur with neigh- boring group participation, increase with acidity. The reduced form, [Ru(NH 3 ) 5 (NH-(C)(HN-C(O)-2-bz))] 2+ , is relatively substitution inert. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Ruthenium; dicyanobenzene; Cyanobenzamide; Neighboring group participation; Nitrile hydrolysis 1. Introduction A general feature, the hydrolysis of nitriles in aqueous solutions, is greatly enhanced by coordination of RCN in a metal complex as demonstrated by 10 6 –10 8 -fold in- crease in the rates of hydrolysis compared to the uncoor- dinated ligand [1–9]. These rates can be lower, though, in cases where the metal ion is capable of p back-bonding, such as with ruthenium(II) ammines. This reaction is 0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2004.09.008 q Taken in part from: E.C. Oliveira, M.Sc. Dissertation, Univer- sidade de Sa ˜o Paulo, Ribeira ˜o Preto, Brazil, 1998. A.M.S. Mace ˆdo, M.Sc. Dissertation, Universidade Federal da Bahia, Salvador, Brazil, 2002. * Corresponding author. Tel.: +55166023748; fax: +55166331851. E-mail address: eltfouni@usp.br (E. Tfouni). www.elsevier.com/locate/ica Inorganica Chimica Acta 358 (2005) 2909–2920