FULL PAPER DOI: 10.1002/ejic.201200117 Formation of Cyclometallated N-Heterocyclic Carbene (NHC) Complexes from L n RuCl 2 (L = Cyclooctadiene, PPh 3 , DMSO) Precursors Nicola Bramananthan, [a] Elena Mas-Marzá, [a] Francys E. Fernandéz, [a] Charles E. Ellul, [a] Mary F. Mahon, [a] and Michael K. Whittlesey* [a] Keywords: Carbene ligands / Ruthenium / C-H activation Both [Ru(cod)Cl 2 ] n and [Ru(PPh 3 ) 3 Cl 2 ] react with the N-iPr substituted N-heterocyclic carbene IiPr 2 Me 2 [1,3-diiso- propyl-4,5-dimethylimidazol-2-ylidene] at elevated tempera- ture to give the cyclometallated triscarbene product [Ru- (IiPr 2 Me 2 )'(IiPr 2 Me 2 ) 2 Cl] (1), which also contains an agosti- cally bound NHC ligand. Although [Ru(cod)Cl 2 ] n fails to re- act with the bulkier tert-butyl carbene ItBu 2 [1,3-di-tert-but- ylimidazol-2-ylidene], [Ru(PPh 3 ) 3 Cl 2 ] affords the cyclometall- ated monocarbene complex [Ru(ItBu 2 )'(PPh 3 ) 2 Cl] (2). Cyclo- Introduction Substitutionally labile ruthenium halide complexes such as [(arene)RuCl 2 ] 2 and [Ru(cod)Cl 2 ] n have proven to be valuable precursors for the synthesis of ruthenium N-het- erocyclic carbene (NHC) complexes and in many cases lead to well-defined products. Thus, the arene dimers provide an entry point into [(arene)Ru(NHC)Cl 2 ] species, which have been found to display good catalytic activity for a range of reactions including radical polymerizations and oxi- dations. [1] Wolf has reported that the cyclooctadiene precur- sor provides access to the N-methyl-substituted tetrakiscar- bene complex trans-[Ru(IMe 4 ) 4 Cl 2 ], [2] which has also been prepared by Radius (along with analogues containing propyl and mixed methyl/isopropyl-substituted NHCs) using [Ru(PPh 3 ) 3 Cl 2 ]. [3] Wolf has also shownthat when [Ru- (cod)Cl 2 ] n and the isopropyl-substituted NHC IiPr 2 Me 2 re- acted in the presence of a tertiary phosphane (PPh 3 , PCy 3 ) and a strong base (KOtBu), products containing cyclo- metallated IiPr 2 Me 2 ligands were formed. [4] In spite of this combination of reagents being identical to that used to pro- duce an in situ ruthenium complex to catalyze the conver- sion of alcohols and amines to amides, [5] none of the iso- lated metallated products showed any catalytic activity. We have described the synthesis of a number of cyclo- metallated Ru-NHC products containing both N-alkyl- and N-aryl-substituted NHCs using ruthenium dihydrido and [a] Department of Chemistry, University of Bath, Bath BA2 7AY, UK Fax: +44-1225-386231 E-mail: m.k.whittlesey@bath.ac.uk Eur. J. Inorg. Chem. 2012, 2213–2219 © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2213 metallation of the N-ethyl derivative IEt 2 Me 2 [1,3-diethyl- 4,5-dimethylimidazol-2-ylidene] takes place upon heating with [Ru(DMSO) 4 Cl 2 ] to give the tris-DMSO product, [Ru- (IEt 2 Me 2 )'(DMSO) 3 Cl] (3), which undergoes substitution of the S-bound DMSO ligands in the presence of CO and PPh 3 to yield [Ru(IEt 2 Me 2 )'(CO) 3 Cl] (4) and [Ru(IEt 2 Me 2 )'(PPh 3 ) 2 - Cl] (6). In contrast, IEt 2 Me 2 reacts with [Ru(PPh 3 ) 3 Cl 2 ] to give [Ru(IEt 2 Me 2 ) 4 Cl 2 ] (7). The molecular structures of com- pounds 1–4, 6 and 7 have been determined. hydrido halido precursors. [6] For the RuHX species (X = F, Cl), the NHC acts not only as a ligand, but also as a base to facilitate the elimination of HX. [7] In light of the research by Wolf, Radius and others, we turned our attention to ru- thenium dichlorido starting materials and now report the use of [Ru(cod)Cl 2 ] n , [Ru(PPh 3 ) 3 Cl 2 ] as well as [Ru(DMSO) 4 - Cl 2 ] to afford a range of new cyclometallated Ru N-alkyl NHC complexes. Results and Discussion Cyclometallated IiPr 2 Me 2 and ItBu 2 Complexes from [Ru(cod)Cl 2 ] n and [Ru(PPh 3 ) 3 Cl 2 ] By employing the same approach used by Wolf and co- workers, [2] reactions of [Ru(cod)Cl 2 ] n with an excess (4 equiv.) of ItBu 2 [1,3-di-tert-butylimidazol-2-ylidene], IEt 2 Me 2 [1,3-diethyl-4,5-dimethylimidazol-2-ylidene] and IiPr 2 Me 2 [1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene] were attempted in toluene solution at 100 °C for 4 h. No clean Ru-NHC products could be isolated from the reaction involving the tert-butyl carbene, most likely because of its very bulky nature. [8] The reaction with the N-ethyl-substi- tuted carbene gave one major product, which was identified as the previously reported purple cationic tetrakiscarbene hydrido complex [Ru(IEt 2 Me 2 ) 4 H] + on the grounds of a very low frequency hydride resonance at δ = –41 ppm in the 1 H NMR spectrum. [9] In the case of IiPr 2 Me 2 , a homogen- eous red–orange solution was formed from which a mixture of purple and orange microcrystalline solids were isolated. The former was characterized as [Ru(IiPr 2 Me 2 ) 4 H] + , [9] while the latter was identified as the new cyclometallated