Indian Journal of Chemistry Vol. 33A, April 1994, pp. 354-356 Reactions of [RuH(CO)Cl(PPh 3 )3] with imidazole, 2-methylimidazole, 2-ethylimidazole and pyrazole D S Pandey", K B Pandeya & I P Tripathi Department of Chemistry, APS University, Rewa 486 003, MP and U C Agarwala Department of Chemistry, lIT, Kanpur 208 016 Received 20 July 1993; revised 15 November 1993. , accepted 27 December 1993 Reactions of [RuH(CO)CI(PPh 3zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA h) have been carried out with imidazole, 2-methylimidazole, 2-ethyl- imidazole and pyrazole in the presence of suitable anions [BF4- ,BPh 4 -, CI0 4 -, & PF 6 -). The reaction products are found to be cationic and have been characterized by elemental analyses, fR, Uv/vis and NMR spectral studies. The complex [RuH(CO)CI(PPh 3 h] (I) and its related species have been a subject of continuing attention during the past several years!" 5. Usually the complex (I) undergoes three types of reactions. (A) Substi- tution of a PPh 3 molecule by a neutral ligand yielding [RuH(CO)CI(PPh3)2L] (where L = CO, RNC, etc.) where L in most cases goes trans to hydride ion; (8) substitution reactions involv- ing chloride abstraction leading to the formation of cationic or neutral complexes" - 8 of the type [RuH(CO)(PPh3h-nLI+ nJh [where x = 1, L = P (OR),xwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA n = I' x = I L = PPh 2 (OR) n = 3' x = 0 -~ " '" I = S2CY-, Y = NR 2 , n = 1,2]; and (C) insertion of arenediazonium salts, 2-vinylpyridine, methyl sor- bate, dimethyl furnerate, acryonitrile, carbon- disulphide, dialkyl and diaryl carbodiimides, 1,3 diaryl triazines and acetylenes in Ru-H bond to yield the corresponding inserted complexes? -15. In a few cases both CI ion and a PPh 3 molecule are substituted resulting in the formation of cationic com- plexes '> "!". Our interest in such reaction mecha- nisms prompted us to investigate the substitution reactions of complex (1) with relatively less studied pyrazoles and imidazoles. In this note, we report the results of the reactions of pyrazole, imidazole and their derivatives with [RuH(CO)Cl(PPh,),]. Experimental All the chemicals used were of AR grade. The solvents were purified and dried using the literature procedures. The reactions were carried out under dry nitrogen atmosphere. The complex [RuH(CO)CI(PPh 3 h] was prepared as described elsewhere-? and the ligands were used as such without further purification. The melting points of the complexes were determined on a Fischer John's melting point apparatus. The IR spectra of the complexes in K8r discs were recorded on a Perkin- Elmer-580 spectrophotometer and I H, 31 P NMR and electronic spectra on a Jeol FX-90 Q and Shimadzu UV -160 spectrophotometer respectively. The complexes were analyzed for C, H, N by the Micro analytical laboratory of the CDRI, Lucknow. Procedure In a typical reaction, a mixture of [RuH(CO)CI(PPh3 )3] ('" 1.0 mmol) and the ligand (2.0 mmol) in 30 ml of benzene was refluxed for >- 5 h. In the case of methyl imidazole or ethyl imidazole refluxing was carried out for 8-9 h. After cooling the resulting solution at room temperature, the insoluble impurity present in the solution was removed by filtration and a solution of a suitable anion (8F 4 -, BPh4 , CIOi, PF (;) in 25 rnl of methanol was added to the filtrate. The solution thus obtained was left for slow crystallization. After 12-14 h shiny, micro- crystalline complexes were formed in the solution, which were separated by filtration, washed twice with methanol and finally twice with diethyl ether. The crystals were dried in vacuo. Results and discussion The analytical data of the reaction products. alongwith the observed 1Hand 31 PMR signals and UV absorption bands are given in Table I. The analytical data suggest that reactions of the ligands (pyrazole and imidazole) with [RuH(CO)CI(PPh 3 h] yield stable cationic complexes according to the following equation, Reflux [RuH(CO)CI(PPh,hl + 2L ----+. [RuH(CO)(PPh,hL 2 l + Benzene (where L = pyrazole or imidazole). Evidently, the substitution reactions take place only when unsubstituted pyrazoles and imidazoles are used. Although the electron donating CH 1 or C2HS group should make the ligands more basic, their non-reactivity reflects perhaps steric crowding in the complex [RuH(CO)Cl(PPh3 hL I j .r x (where x = 0.1, L = CH 3 , or C 2 Hs).