Note Synthesis, structure and some reactions of (C 5 Me 4 hex) 2 Ru 2 (CO) 4 Siyabonga Ngubane a , Mikael Hakansson b , Susan Jagner b, * , John R. Moss a, * , Akella Sivaramakrishna a a Department of Chemistry, University of Cape Town, Rondebosch 7701, South Africa b Department of Inorganic Chemistry, Chalmers University of Technology, SE-412 96, Goteborg, Sweden Received 16 August 2007; received in revised form 2 October 2007; accepted 8 October 2007 Available online 25 October 2007 Abstract The synthesis of the new cyclopentadiene, C 5 Me 4 (hex)H is described and its reaction with Ru 3 (CO) 12 to yield (C 5 Me 4 hex) 2 Ru 2 (CO) 4 (hex = n-hexyl) is reported. The X-ray crystal structure of the dimer confirms the structure with bridging and terminal CO groups. Reac- tions of the dimer to yield (C 5 Me 4 hex)Ru(CO) 2 X (X = Cl, Br, I) are reported. IR, NMR and mass spectra are reported for all new com- pounds. The solubility of the dimer is found to be 10 times greater than that for (C 5 Me 5 ) 2 Ru 2 (CO) 4 . Ó 2007 Elsevier B.V. All rights reserved. Keywords: Ruthenium; Carbonyl; Dimer; Structure; Cyclopentadienyl 1. Introduction Our initial reason to synthesise the compound (C 5 Me 4 hex) 2 Ru 2 (CO) 4 ,(2) was to try and solubilise this type of dimeric complex in saturated hydrocarbon solvents for further study [1]. Since there have been many structural studies already carried out on complexes of the type Cp x 2 Ru 2 (CO) 4 (where Cp x = substituted cyclopentadienyl ligand) [2], this was an ideal opportunity to investigate how changing the substituents on the cyclopentadienyl ligand might affect the overall structure of the dimers. This sort of study is particularly pertinent in light of the remark- able change in chemistry in going from (C 5 Me 5 ) 2 ZrCl 2 to (C 5 Me 4 H) 2 ZrCl 2 . Thus, the pentamethylcyclopentadienyl compound is reduced under N 2 to give an end-on dinitro- gen bridged dimer (C 5 Me 5 ) 4 Zr(l-N 2 )(N 2 ) 2 whereas the tet- ramethyl cyclopentadienyl compound gives a side-on dinitrogen bridged dimer (C 5 Me 4 H) 4 Zr 2 (l-N 2 ) and it is the latter dimer that reacts further with hydrogen to yield ammonia [3,4]. Thus, small changes in the ligands can have a big influ- ence on the chemistry of their complexes. 2. Results and discussion 2.1. Preparation of C 5 Me 4 (hex)H (1) Synthesis of the new ligand 1 is an adaptation of the method used by Schumann et al. [5] for a similar pent-4- enyl derivative. Nucleophilic attack of hexyllithium on 2,3,4,5-tetramethylcyclopent-2-enone ligand gave the crude compound 1 as a dark yellow oil. Purification of the ligand was accomplished by column chromatography. Further purification was achieved by vacuum distillation in which two fractions were obtained. The first fraction was col- lected at 72 °C (0.7 mmHg) and the second fraction was collected in the range of 98–100 °C (0.6 mmHg). The frac- tion (b.p. 72 °C at 0.7 mmHg) was identified by NMR spec- troscopy as the pure product. Adding 1.5 molar excess of the hexyllithium reagent and increasing the reaction time by stirring overnight instead of 2 h as reported for the pent-4-enyl derivative gives much better yields and no starting ketone and/or intermediate alcohol is identified in the final product. In this case, no fraction distillation 0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2007.10.031 * Corresponding authors. E-mail address: John.Moss@uct.ac.za (J.R. Moss). www.elsevier.com/locate/jorganchem Available online at www.sciencedirect.com Journal of Organometallic Chemistry 693 (2008) 343–348