On the ROMP of 2-norbornene with an in situ ruthenium carbene complex: ESI-MS, NMR and DFT analyses André L. Bogado a, * , Marília I.F. Barbosa b , Gezimar D. de Souza b , Marília A. Trappi b , Edson R. Filho b , Leonardo T. Ueno a , Antonio E.H. Machado c , Alzir A. Batista b, 1 a Faculdade de Ciências Integradas do Pontal, Universidade Federal de Uberlândia, Av. José João Dib, 2545, Ituiutaba, CEP 38302-000, MG, Brazil b Departamento de Química, Universidade Federal de São Carlos, CP 676 Rod. Washington Luís Km 235, São Carlos CEP 13565-905, SP, Brazil c Instituto de Química, Laboratório de Fotoquímica (LAFOT), Universidade Federal de Uberlândia, Av. João Naves de Ávila, 2121, Bloco 5K, Uberlândia, CEP 38408-100, MG, Brazil article info Article history: Received 19 June 2009 Received in revised form 8 April 2010 Accepted 9 April 2010 Available online 21 April 2010 Keywords: Ruthenium diphosphino ROMP reaction DFT-calculation ESI-MS complex analysis abstract During the reaction between [{RuCl(dppb)} 2 -(m-Cl) 2 ] and ethyldiazoacetate (EDA) a neutral carbene complex was observed in situ in a methylene chloride solution, with vigorous N 2 evolution. This reaction was investigated by ESI-MS analysis, which suggests the formation of a mononuclear carbene containing ruthenium complex as product, [RuCl 2 (dppb)(]CHC(O)OCH 2 CH 3 ]. The carbene complex was also detected by proton NMR with d 22.8 ppm for the heteronuclear coupling, 3 J HP ¼ 7 Hz, and 31 P{ 1 H} NMR with a singlet signal at d 30 ppm. The DFT calculation suggests a square pyramidal ruthenium structure for [RuCl 2 (dppb)(]CHC(O)OCH 2 CH 3 ] with 16 valence electrons and the carbene moiety trans to a vacant site. The carbene complex, generated in situ, was applied to the polymerization of 2-norbornene, achieving a wide range of turnover numbers and PDI values. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Transition metal complexes that catalyze CeC bond formation via olefin metathesis are of considerable interest and synthetic utility, for instance in ring-opening metathesis polymerization (ROMP). The discovery, by Grubbs [1], that ruthenium carbene complexes of the general type [RuCl 2 (P) 2 (]CHR)] (where P ¼ electron-rich monophosphine and R ¼ phenyl, CH]CH 2 Ph 2 , etc) are highly active single component (pre)catalysts for all types of alkene metathesis reactions denoted a real breakthrough, which has triggered an avalanche of interest in such transformations [1]. In view of this, many ruthenium carbene complexes have been synthesized and successfully applied to metathesis reactions. The generally accepted mechanism of metathesis reactions (Chauvin mechanism) consists of a sequence of formal [2 þ 2] cycloadditions/cycloreversions, involving alkenes, metal carbenes, and metallacyclobutane intermediates [2]. Among the metal complexes used as catalysts or precatalysts (that convert into metal alkylidenes in situ), tungsten or molybdenum alkylidene complexes, developed by Schrock and co-workers [3e5], and ruthenium car- bene complexes, introduced by Grubbs and co-workers [6e10], are undoubtedly the most popular and versatile. Ruthenium complexes containing one chelating bis (tertiary phosphine) ligand per metal atom are key species for catalysis and are also precursors in the synthesis of new complex derivatives. Unsaturated complexes with 16 or 14 valence electrons with the general formula [{RuCl(PeP)} 2 -(m-Cl) 2 ] {PeP ¼ chiral or achiral chelating diphosphines}, have been used to provide “Ru II (PeP)” moieties as the active component of catalysts [11] and synthetic precursors [12,13]. The complex [{RuCl(dppb)} 2 -(m-Cl) 2 ] {dppb ¼ 1,4-bis(diphe- nylphosphine)butane} can be achieved by H 2 reduction of mixed valence dinuclear complex (Ru II /Ru III ) [{RuCl(dppb)} 2 -(m-Cl) 3 ] [12,14], or more appropriately by H 2 reduction of the aqua complex mer -[RuCl 3 (dppb)(H 2 O)] [15] (Ru III ), as depicted in Scheme 1 . During the reaction between [{RuCl(dppb)} 2 -(m-Cl) 2 ] and ethyl- diazoacetate (EDA), a neutral carbene complex was observed in situ in a methylene chloride solution, with vigorous N 2 evolution (see Scheme 2). It is interesting to mention that a similar carbene complex was described by Fogg and cvo-workers, [16, 17] with [RuCl 2 (PeP) (PPh 3 )] as precursor {where PeP ¼ aromatic and non-aromatic diphosphino ligand}, which was obtained in situ after reaction with phenyldiazomethane (PDM). The structure suggests was similar to the carbene complex described here, but the catalytic activity in the * Corresponding author. Tel.: þ55 34 3269 2195; fax: þ55 34 3269 2389. 1 Tel.: þ55 16 33518285; fax: þ55 16 3351 8350. E-mail addresses: albogado@pontal.ufu.br (A.L. Bogado), daab@power.ufscar.br (A.A. Batista). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem 0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2010.04.001 Journal of Organometallic Chemistry 695 (2010) 1708e1714