Isomeric [RuCl2(dmso)2(indazole)2] complexes: ruthenium(ii)-mediated coupling reaction of acetonitrile with 1H-indazole

Abstract

Reaction of the antitumor complex trans-[Ru(III)Cl4(Hind)2]- (Hind = indazole) with an excess of dimethyl sulfoxide (dmso) in acetone afforded the complex trans,trans,trans-[Ru(II)Cl2(dmso)2(Hind)2] (1). Two other isomeric compounds trans,cis,cis-[Ru(II)Cl2(dmso)2(Hind)2] (2) and cis,cis,cis-[Ru(II)Cl2(dmso)2(Hind)2] (3) have been obtained on refluxing cis-[Ru(II)Cl(2)(dmso)(4)] with 2 equiv. of indazole in ethanol and methanol, respectively. Isomers 1 and 2 react with acetonitrile yielding the complexes trans-[Ru(II)Cl2(dmso)(Hind){HN=C(Me)ind}].CH3CN (4.CH3CN) and trans,cis-[Ru(II)Cl2(dmso)2{HN=C(Me)ind}].H2O (5.H2O), respectively, containing a cyclic amidine ligand resulting from insertion of the acetonitrile C triple bond N group in the N1-H bond of the N2-coordinated indazole ligand in the nomenclature used for 1H-indazole. These are the first examples of the metal-assisted iminoacylation of indazole. The products isolated have been characterized by elemental analysis, IR spectroscopy, UV-vis spectroscopy, electrospray mass-spectrometry, thermogravimetry, differential scanning calorimetry, 1H NMR spectroscopy, and solid-state 13C CP MAS NMR spectroscopy. The isomeric structures of 1-3 and the presence of a chelating amidine ligand in 4 and 5 have been confirmed by X-ray crystallography. The electrochemical behavior of 1-5 and the formation of 5 have been studied by cyclic voltammetry.

The Complexes [OsCl2(azole)2(dmso)2] and [OsCl2(azole)(dmso)3]: Synthesis, Structure, Spectroscopic Properties and Catalytic Hydration of Chloronitriles

“…It should also be noted that cis,fac-[RuCl 2 (Hind)(dmso) 3 ] has been shown to undergo replacement of indazole by acetonitrile at room temperature with formation of cis,fac-[RuCl 2 (MeCN)-(dmso) 3 ]. [17] This suggests another possible catalytic pathway for chloronitrile hydration, but does not explain the different efficiency of catalysts 5-8. The catalytic nitrile hydration mechanism proposed by Chottard et al [41] for cobalt(III) complexes with sulfenato-S ligands under mildly acidic conditions exploits the nucleophilic properties of coordinated sulfenates.…”

“…[17] We (1) and complexes 2, 5 and 6 in acetonitrile. No amidine formation was observed in an acetonitrile solution of 1 at room temperature after five days.…”

“…[8][9][10] In addition, Ru II -dmso complexes have been successfully employed as precursors for the synthesis of a large variety of compounds, and, in particular, of [Ru II Cl 2 (azole) 2 (dmso) 2 ] geometric isomers, [11][12][13][14][15][16] 2 ] species are able to mediate the insertion of the CϵN group of acetonitrile in the N1-H bond of the N2-coordinated indazole, these being the first examples of the metal-assisted iminoacylation of indazole. [17] Comparison of the chemistry of ruthenium(II) dmso complexes with that of osmium(II) dmso species has permitted us to unravel expected similarities between these two types of complexes, but also remarkable, although less pro-the hydration of trichloroacetonitrile to trichloroacetamide and dichloroacetonitrile to dichloroacetamide with high selectivity. The catalyst efficiency depends strongly on the nature of the complex and the azole ligand present.…”

“…Scheme 1. We anticipated (i) the isolation of "pure" isomers of composition [OsCl 2 (azole) 2 (dmso) 2 ], due to the distinct kinetic inertness of Os II complexes over Ru II species, without any competing isomerisation reactions interfering, (ii) the isolation of other species, the formation of which under similar reaction conditions does not occur in the case of ruthenium analogues, and (iii) the elucidation of previously unknown facets of the reactivity profile of the compounds prepared. In particular, in order to establish the scope of the recently discovered metal-assisted iminoacylation of indazole, [17] we checked the reactivity of the isolated trans,cis,cis- [ 3 ] by treatment with a stoichiometric amount of the corresponding azole ligand. [12,15a,16b] If, however, the azole ligand is added in excess and the reaction is carried out at elevated temperatures, isomers of the composition [RuCl 2 (azole) 2 (dmso) 2 ] are produced.…”

“…One oxidative response is found for all complexes. Taking into account the similar responses in the analogous ruthenium complexes, [17] these electron-transfer processes are assigned to Os II -Os III oxidation. The oxidation potentials for 1-4 (0.94-0.71 V) are markedly lower than those for 5-8 (1.66-1.40 V), which is in agreement with the stronger net electron-acceptor character of the S-coordinated dmso as compared with the azole li-gands, which are more effective σ-donors.…”