Easy Access to Bio-Inspired Osmium(II) Complexes through Electrophilic Intramolecular C(sp²)-H Bond Cyclometalation

Abstract

Mild electrophilic C(sp2)-H cyclometalation of 2-phenylpyridine and N,N-dimethylbenzylamine by the chloro-bridged osmium(II) dimer [OsCl(micro-Cl)(eta6-C6H6)]2 in acetonitrile affords cyclometalated pseudotetrahedral OsII complexes [Os(C approximately N)(eta6-C6H6)(NCMe)]PF6 (C approximately N=o-C6H4py-kappa C,N (2) and o-C6H4CH2NMe2-kappa C,N (5), respectively) in good to excellent yields. The cyclometalation reactions are super sensitive to the nature of an external base. Sodium hydroxide is essential for cyclometalation of 2-phenylpyridine, but NaOH retards metalation of N,N-dimethylbenzylamine, the tertiary amine being self-sufficient as a base. Further reactions of compounds 2 and 5 with 1,10-phenanthroline or 2,2'-bipyridine (N approximately N) lead to the substitution of the eta6-bound benzene to produce octahedral species [Os(C approximately N)(N approximately N)(NCMe)2]PF6 or [Os(C approximately N)(N approximately N)2]PF6 in MeCN or MeOH as solvent, respectively. The cis configuration of the MeCN ligands in [Os(C approximately N)(phen)(NCMe)2]PF6 has been confirmed by an X-ray crystallographic study. Electrochemical investigation of the octahedral osma(II)cycles by cyclic voltammetry showed a pseudoreversible MIII/II redox feature at (-50)-(+109) and 190-300 mV versus Ag/AgCl in water and MeCN, respectively. As a possible application of the compounds, a rapid electron exchange between the reduced active site of glucose oxidase enzyme from Aspergillus niger and the electrochemically generated OsIII species has been demonstrated. The corresponding second-order rate constants cover the range (0.7-4.8)x10(6) M(-1) s(-1) at 25 degrees C and pH 7.

CCC–Pincer–NHC Osmium Complexes: New Types of Blue-Green Emissive Neutral Compounds for Organic Light-Emitting Devices (OLEDs)

“…The perpendicular plane is formed by the aryl C(1) and carbene C(7) atoms of the generated chelate ligand, which acts with a bite angle of 76.4(2)°, the hydride trans to the carbene unit (C(7)–Os–H(01) = 162(3)°), and the carbonyl ligand disposed trans to the aryl group (C(1)–Os–C(41) = 177.8(3)°). The Os–C(1) bond length of 2.141(5) Å compares well with the Os–aryl distances found in other five-membered osmacycles resulting from ortho-metalation reactions, whereas the Os–C(7) bond length of 2.075(5) Å agrees well with those reported for Os NHC compounds with normal coordination of the NHC unit. , In addition, we should mention the separations between the hydrogen atom H(15) of the benzimidazolium moiety and the fluorine atoms F(1A) and F(4A) of the tetrafluoroborate anion, 2.60(6) and 2.59(6) Å, which are slightly shorter than the sum of the van der Waals radii of the hydrogen and fluorine ( r vdW (H) = 1.20, r vdW (F) = 1.47 Å), suggesting ion pairing.…”

Halide Control of N,N-Coordination versus N,C-Cyclometalation and Stereospecific Phenyl Ring Deuteration of Osmium(II) p-Cymene Phenylazobenzothiazole Complexes

“…In the reaction between [Os(η 6 - p -cym)X 2 ] 2 and L , the direction may be guided via initial coordination to the azo bond nitrogen, and C–H activation occurs spontaneously and remarkably in the absence of an additional base. Cerón-Camacho et al have reported the successful electrophilic cyclo-osmation of the bidentate ligands 2-PhPy and N,N -dimethylbenzylamine, 33 the latter of which was also achieved in the absence of a base. The ligand is believed to act as both a substrate and a base for its own C–H bond cleavage.…”

Introducing the 4-Phenyl-1,2,3-Triazole Moiety as a Versatile Scaffold for the Development of Cytotoxic Ruthenium(II) and Osmium(II) Arene Cyclometalates

“…Ruthena­(II)­cycles may be prepared by transmetalation from toxic organomercurated precursors, or more conveniently by carboxylate-assisted C–H activation. , While numerous examples of cytotoxic cyclometalated ruthenium­(II) arene compounds can be found in the literature, osma­(II)­cycles seem to have been largely neglected. Ryabov and co-workers have reported and characterized osma­(II)­cycles of the form [Os­( p -cym)­(2-PhPy C∧N )­L] (L = Cl, MeCN; 2-PhPy = 2-phenylpyridine) as intermediates in the synthesis of [Os­(II)­(chel) 3 ] metalacycles as electron carriers for active sites of oxidoreductases, − and N -pyridyl 1,2,3-triazolylidene ligand-bearing Os­(II) metalacycles were explored for their applicability in transfer hydrogenation catalysis . However, the biological properties and particularly the cytotoxicity of osma­(II)­cycles of the form [Os­(arene)­L C∧N Cl] remain nearly unexplored and were only touched upon by Pfeffer and co-workers, who reported the promising cytotoxicity of [Os­( p -cym)­(2-PhPy C∧N )­Cl] in the low micromolar range …”