Novel platinum group metal complexes bearing bidentate chelating pyrimidyl-NHC and pyrimidyl imidazolyl-thione ligands: Syntheses, spectral and structural characterization Venkateswara Rao Anna a , Raghavaiah Pallepogu b , Zhong-Yuan Zhou c , Mohan Rao Kollipara a,⇑ a Department of Chemistry, North-Eastern Hill University, Shillong 793022, India b School of Chemistry, University of Hyderabad, Hyderabad, India c Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, Hong Kong, PR China article info Article history: Received 9 November 2011 Received in revised form 22 December 2011 Accepted 23 December 2011 Available online 29 December 2011 Keywords: NHC Ruthenium Rhodium Iridium 1-Pyrimidyl-3-methylimidazolyl bromide abstract A family of novel platinum group metal complexes containing bidentate chelating 1-pyrimidyl-3-meth- ylimidazolyl bromide (HL1ÁBr) and 1-pyrimidyl-3-methylimidazolyl-2-thione (L2) ligands has been syn- thesized. The synthetic protocol for the formation of these complexes differs from one ligand to the other. Treatment of ligand (HL1ÁBr) with the metal precursors led to the formation of complexes via in situ car- bene transfer reactions. The silver–NHC complex (1) was formed by the reaction of HL1ÁBr with silver oxide under light-free conditions. Subsequent addition of appropriate metal precursors to the silver– NHC complex yielded [(g 6 -arene)Ru(L1)Cl]PF 6 complexes {arene = C 6 H 6 (2), p- i PrC 6 H 4 Me (3), C 6 Me 6 (4)} on stirring at room temperature, whereas the complexes [CpRu(L1)(PPh 3 )]PF 6 {Cp = C 5 H 5 (5), C 9 H 7 (6)} were obtained under reflux conditions. In the case of ligand L2, stirring of equimolar quantities of metal precursors and the ligand at room temperature yielded [(g 6 -arene)Ru(L2)Cl]PF 6 {arene = C 6 H 6 (7), p- i PrC 6 H 4 Me (8), C 6 Me 6 (9)}, and [Cp / M(L2)Cl]PF 6 {Cp / =C 5 Me 5 , M = Rh (10), Ir (11)}. All these com- plexes were characterized by CHN analysis, IR, NMR and mass spectrometry besides confirmation by sin- gle crystal X-ray diffraction studies for some representative complexes as their hexafluorophosphate salts [3]PF 6 ,[5]PF 6 ,[8]PF 6 and [10]PF 6 . Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Platinum group metal complexes of stable N-heterocyclic carb- enes (NHCs) are currently receiving much attention for their wide range of applications in the field of catalysis [1–7]. N-heterocyclic carbene ligands can form stable bonds with main group metals as well as with transition metals in various oxidation states due to their strong r-donating and weak p-accepting character [8]. Some investigations have focused on carbene ligands containing additional functional groups based on donors such as phosphorus, nitrogen, and oxygen. N-heterocyclic carbenes having an additional donor group are an important class of ligands for catalysis. The pyr- idine–NHC ligand combination has received much attention for its utility in transition metal chemistry catalysis and biological appli- cations [9–19]. Many transition metal complexes containing func- tionalized N-heterocyclic carbenes as ligands, display a wide range of applications in organic transformations [20–23]. During recent years, ruthenium–NHC complexes have shown a great potential for the design of new metal-based drugs and biomedical applica- tions [24–26]. Investigations using metal–NHC complexes as cata- lytic reagents and luminescent emitters [27,28] are becoming prominent currently. Williams first reported the synthesis of bidentate bis-thione ligands (SS R ) by reaction of their correspond- ing imidazolium salts with elemental sulfur in the presence of a base [29,30]. A nickel complex, with a new hard-soft nitrogen-sul- fur pyridine–NHC thione ligand, has been shown to assist olefin polymerization [31]. Herein, we report the syntheses and characterization of novel ruthenium-pyrimidine–NHC complexes as well as the syntheses of ruthenium, rhodium and iridium complexes containing the hard-soft nitrogen-sulfur ligand 1-pyrimidyl-3-methylimidazolyl- 2-thione (L2). The following ligands are used in this study (Chart 1). 2. Results and discussion 2.1. Ligand synthesis and characterization The ligand 1-pyrimidyl-3-methylimidazolyl bromide (HL1ÁBr) [32,33] was synthesized by refluxing a mixture of 2-bromopyrim- idine with a stoichiometric amount of N-methylimidazole in tolu- ene to yield a white solid. The new hard–soft nitrogen–sulfur 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.12.048 ⇑ Corresponding author. Tel.: +91 364 272 2620; fax: +91 364 255 0076. E-mail address: mohanrao59@gmail.com (M.R. Kollipara). Inorganica Chimica Acta 387 (2012) 37–44 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica