Search

The synthesis of a series of palladium(II) complexes of unsymmetrical, hybrid selenoether and telluroether ligands is reported. While the reaction of Pd(II) precursors with symmetrical telluroether ligands containing two coordinating groups results in cleavage of Te–C bond, no such labilisation is observed using unsymmetrical ligands containing one coordinating group. Two novel unsymmetrical selenoether ligands namely, N,N -dimethyl-2-(o -tolylselanyl)aniline (10) and 2-((2,6-dimethylphenyl)selanyl)- N,N -dimethylaniline (11) were synthesized from N,N -dimethylbenzylamine via the ortho -lithiation route. When ligands 10 and 11 were treated with Pd(COD)Cl 2 (COD = 1,5-cyclooctadiene), the reaction afforded novel Pd(II) complexes of the form Pd(2-NMe 2 CH 2 C 6 H 4)(R)SeCl 2 , where R = 2-MeC 6 H 4 (16) and 2,6-MeC 6 H 3 (17) respectively. Similarly, when unsymmetrical telluroether ligands, N,N -dimethyl-2-(phenyltellanyl)aniline (12) , N,N -dimethyl-2-(o-tolyltellanyl)aniline (13), 2-((2,6-dimethylphenyl)tellanyl)- N,N -dimethylaniline (14) and 2-((2,6-diisopropylphenyl)tellanyl)- N,N -dimethylaniline (15), which contain one coordinating group with an sp 3 N-donor atom, were treated with Pd(COD)Cl 2 , the palladium telluroether complexes of the form Pd(2-NMe 2 CH 2 C 6 H 4)(R)TeCl 2 , where R = C 6 H 5 (18), 2-MeC 6 H 4 (19), 2,6-MeC 6 H 3 (20) and 2,6- i PrC 6 H 3 (21) respectively were obtained. The selenoether complexes 16 and 17 and telluroether complexes 18 , 20 and 21 were characterized by single crystal X-ray diffraction studies. In the asymmetric unit of complex 18 , two molecules are present and due to the presence of weak, intermolecular Te⋯Cl interactions, the two molecules exist as symmetrically related dimer. The N-donor substituents, which were involved in intramolecular chalcogen bonding (IChB) with the chalcogen atoms in the free ligand, made six-membered chelating rings in the complexes. Again, when bis(2-phenylazophenyl- C,N ′)selenide 22 was treated with Pd(COD)Cl 2 , it afforded ortho C–H bond activated cyclopalladated complex 24. However, when bis(2-phenylazophenyl- C,N ′)telluride 23 was treated with Pd(COD)Cl 2 , due to strong IChB from two N-donor substituents, the reaction afforded cleaved product, [2-(phenylazo)phenyl-C,N′]tellurenyl chloride, 25. All the metal complexes exhibited significant downfield chemical shifts in 77Se/125Te NMR spectra as compared to the corresponding free ligands. The downfield shifts in the 77Se/125Te NMR signal in the complexes might be attributed to the coordination of the chalcogen atoms to the electropositive Pd(II) center. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • New NNN- and CNC type N-hetrocyclic nitrenium ions (NHN) within tridentate pincer scaffold are reported. • The Natural Bond Order (NBO) calculations and Atoms in Molecules (AIM) analyses on the metal complexes adequately substantiate the presence of interaction between triazolium N with metal centre. • Synthesis of two new selone based OSeO type pincer ligands is reported. Abstract The synthesis of three new NNN- and CNC type N-heterocyclic nitrenium (NHN) ion based pincer ligands is reported from 1,3-di-(2′-bromoethyl)-triazolium bromide (5). The reaction of 5 with ammonium hexafluorophosphate followed by two equivalent of pyrrolidine/diethylamine afforded NHN ions (10a and 10b). The reaction of 5 with N-butylbenzimidazole (6) afforded nitrenium ion 7 , where the chelating arms have benzimidazole based carbene carbons. In an attempt to synthesize hybrid NHN ligand containing soft tellurium donor in the chelating arm, 1-(2′-bromoethyl)-benzotriazole was first reacted with in situ generated NaTePh to afford tellurated benzotriazol (13). However, when compound 13 was treated with methyl iodide, an unexpected methylation underwent at tellurium center to afford compound 14. Reaction of 7 with Hg(OAc) 2 and 10a with CuI afforded complexes 8 and 11 respectively. Both these complexes are characterized by NMR (1H, 13C), HRMS and CHN analysis. The Natural Bond Order (NBO) calculations and Atoms in Molecules (AIM) analyses sufficiently substantiate the presence of interaction between triazolium N atom with metal centre. The reaction of N,N′-disubstituted benzimidazoles, 17a – 17b with in situ generated Na 2 Se 2 in the presence of potassium tert -butoxide at room temperature afforded two novel benzimidazoline-2-chalcogenones (18a and 18b). Nitrenium ion (10a – 10b), tellurated benzotriazole (13 and 14) and selone 18a are authenticated by single crystal X-ray diffraction studies. [ABSTRACT FROM AUTHOR]

The synthesis of a novel telluroxane cluster, [(R 2 TeO)(μ -TeO 2)(OTeR 2)][TeO(OH) 2 ] (R=C 6 H 5 NNC 6 H 4) is achieved by the oxidation of bis[2-(phenylazo)-phenyl- C,N ́] telluride with NaIO 4. The X-ray crystallographic diffraction studies in corroboration with Density Functional Theory calculation reveal that the cluster is stabilized by intramolecular Te···N and intra- and intermolecular O∙∙∙Te secondary bonding interactions. [Display omitted] The oxidation reaction of diorganotelluride R 2 Te, 1 (where R = C 6 H 5 NNC 6 H 4) with NaIO 4 resulted in the isolation of a telluroxane cluster, namely [(R 2 TeO)(μ -TeO 2)(OTeR 2)][TeO(OH) 2 ], 2. The formation of 2 was confirmed by multinuclear (1H, 13C and 125Te) NMR and FT-IR spectroscopy, and elemental analysis. The structure of compound 2 was further corroborated by X-ray crystallographic studies. It is observed that telluroxane cluster 2 was stabilized by intramolecular Te···N and intra- and intermolecular O∙∙∙Te secondary bonding interactions. The detailed electronic structural properties of the cluster were thoroughly investigated by Density Functional Theory (DFT) calculations. In particular, the hybridization of the Te atoms were calculated by Natural Bonding Orbital (NBO) analysis. The natural charges accumulated on the Te and the O atoms in compound 2 were calculated by Natural Population Analysis (NPA). In addition, the HOMO-LUMO energy gap in 2 was calculated. [ABSTRACT FROM AUTHOR]

• A series of novel Ru and Os complexes of the bidentate ligand, N,N′-bis(2-pyridyl)benzene-1,2-diamine is reported. • The electronic structures of the complexes and their accessible oxidized and reduced forms were experimentally studied. • The experimental observations are validated by DFT and TD-DFT calculations. The synthesis of Ru and Os complexes of the ligand, N,N′-bis(2-pyridyl)benzene-1,2-diamine namely, [RuIII(acac) 2 (Py-bqdi)], (9), [RuII(Ph-trpy)(Py-bqdi)Cl], (10) and [OsII(bpy) 2 (Py-bqdi)](ClO 4), (11 ClO 4) [where Py-bqdi = N,N′-dipyridyl- o -benzoquinonediimine, acac = 2,4-pentanedionate, Ph-trpy = 4′-phenyl-2,2′:6′,2″-terpyridine, bpy = 2,2′-bipyridine] is reported. The molecular structures of complexes 9 - 11 ClO 4 are authenticated by single crystal X-ray diffraction studies. The electronic structural properties of the complexes, in particular, the accessible oxidized/reduced forms of the complexes, are examined by using an array of analytical techniques (magnetic resonance, UV–Vis-NIR spectroscopy and electrochemistry). Comprehensive Density Functional Theory (DFT) calculations have also been carried out to provide additional support to the experimental work. [ABSTRACT FROM AUTHOR]