Synthesis, Reactivity Studies, Structural Aspects, and Solution Behavior of Half Sandwich Ruthenium(II)N,N′,N″-Triarylguanidinate Complexes

Abstract

[(η(6)-C(10)H(14))RuCl(μ-Cl)](2) (η(6)-C(10)H(14) = η(6)-p-cymene) was subjected to a bridge-splitting reaction with N,N',N''-triarylguanidines, (ArNH)(2)C═NAr, in toluene at ambient temperature to afford [(η(6)-C(10)H(14))RuCl{κ(2)(N,N')((ArN)(2)C-N(H)Ar)}] (Ar = C(6)H(4)Me-4 (1), C(6)H(4)(OMe)-2 (2), C(6)H(4)Me-2 (3), and C(6)H(3)Me(2)-2,4 (4)) in high yield with a view aimed at understanding the influence of substituent(s) on the aryl rings of the guanidine upon the solid-state structure, solution behavior, and reactivity pattern of the products. Complexes 1-3 upon reaction with NaN(3) in ethanol at ambient temperature afforded [(η(6)-C(10)H(14))RuN(3){κ(2)(N,N')((ArN)(2)C-N(H)Ar)}] (Ar = C(6)H(4)Me-4 (5), C(6)H(4)(OMe)-2 (6), and C(6)H(4)Me-2 (7)) in high yield. [3 + 2] cycloaddition reaction of 5-7 with RO(O)C-C≡C-C(O)OR (R = Et (DEAD) and Me (DMAD)) (diethylacetylenedicarboxylate, DEAD; dimethylacetylenedicarboxylate, DMAD) in CH(2)Cl(2) at ambient temperature afforded [(η(6)-C(10)H(14))Ru{N(3)C(2)(C(O)OR)(2)}{κ(2)(N,N')((ArN)(2)C-N(H)Ar)}]·xH(2)O (x = 1, R = Et, Ar = C(6)H(4)Me-4 (8·H(2)O); x = 0, R = Me, Ar = C(6)H(4)(OMe)-2 (9), and C(6)H(4)Me-2 (10)) in moderate yield. The molecular structures of 1-6, 8·H(2)O, and 10 were determined by single crystal X-ray diffraction data. The ruthenium atom in the aforementioned complexes revealed pseudo octahedral "three legged piano stool" geometry. The guanidinate ligand in 2, 3, and 6 revealed syn-syn conformation and that in 4, and 10 revealed syn-anti conformation, and the conformational difference was rationalized on the basis of subtle differences in the stereochemistry of the coordinated nitrogen atoms caused by the aryl moiety in 3 and 4 or steric overload caused by the substituents around the ruthenium atom in 10. The bonding pattern of the CN(3) unit of the guanidinate ligand in the new complexes was explained by invoking n-π conjugation involving the interaction of the NHAr/N(coord)Ar lone pair with C═Nπ* orbital of the imine unit. Complexes 1, 2, 5, 6, 8·H(2)O, and 9 were shown to exist as a single isomer in solution as revealed by NMR data, and this was ascribed to a fast C-N(H)Ar bond rotation caused by a less bulky aryl moiety in these complexes. In contrast, 3 and 10 were shown to exist as a mixture of three and five isomers in about 1:1:1 and 1·0:1·2:2·7:3·5:6·9 ratios, respectively in solution as revealed by a VT (1)H NMR, (1)H-(1)H COSY in conjunction with DEPT-90 (13)C NMR data measured at 233 K in the case of 3. The multiple number of isomers in solution was ascribed to the restricted C-N(H)(o-tolyl) bond rotation caused by the bulky o-tolyl substituent in 3 or the aforementioned restricted C-NH(o-tolyl) bond rotation as well as the restricted ruthenium-arene(centroid) bond rotation caused by the substituents around the ruthenium atom in 10.

Ruthenium Complexes with an Anthyridine‐based Ligand. Synthesis, Characterization and Catalytic Activity

“…This observation is in agreement with other related h 6 -p-cymene ruthenium complexes, which is due to the different conformers obtained by the rotation of the p-cymene ring about the rutheniumarene (centroid) bond axis. 7 In addition to the spectroscopic analysis, the detailed coordination configurations of complexes 5 and 6×(CH 2 Cl 2 ) 2 were confirmed by X-ray diffraction analysis on their single crystals. Crystallography Both complexes 5 and 6×(CH 2 Cl 2 ) 2 were obtained in single crystalline form by re-crystallization from dichloromethane/hexane solutions.…”

“…Both ruthenium atoms in 6 are surrounded by the h 6 -bonded p-cymene ring, a chelating bipyridine fragment, and the chloride and attains a pseudo octahedral "three legged piano stool" geometry. 7 A notable feature of the structure 6 is that two cymene rings are opposite along the anthyridine rings presumably due to the steric interaction. All Ru-N bond lengths are quite similar, at 2.06~2.12 Å, which are in agreement with those of other reported ruthenium p-cymene complexes.…”

“…All Ru-N bond lengths are quite similar, at 2.06~2.12 Å, which are in agreement with those of other reported ruthenium p-cymene complexes. 7 Both bite angles N(1)-Ru (1) (2) is 5.443 Å, indicating that two metal centers are far away from each other. Catalysis According to the above investigation on Ru(II) complexes, it would be interesting to test the catalytic activity of these species particularly the di-ruthenium complex 6.…”

Half Sandwich Electron Deficient N,N′,N′′‐Triarylguanidinatoruthenium(II) Complexes: Syntheses, Reactivity Studies, and Structural Aspects

“…Numerous guanidinatoruthenium(II) complexes of symmetrical N , N′ , N′′ ‐triphenylguanidine, [(PhNH) 2 C=NPh] have been prepared and stucturually characterized . Subsequently, half sandwich guanidinatoruthenium(II)‐, rhodium(III)‐ and iridium(III) complexes of symmetrical N , N′ , N′′ ‐triarylguanidines, [(ArNH) 2 C=NAr] were prepared by us and others with the objectives aimed at understanding their structures in solid state and in solution and to further understand their utility as catalysts in base free and base assisted transfer hydrogenation reactions …”

“…Such reactions involving metal azide/alkyne known as early as 1974, metal alkyne/organic azide, metal azide/metal alkyne, popularly known as inorganic click (iclick) reaction, are the emerging reactions for metal triazolate complexes that could contain either a metal‐nitrogen bond or a metal‐carbon bond depending upon the reaction partners . Continuing our interests in understanding the reactions of guanidinatometal azido complexes with alkynes and factors that dictate the stereochemistry of o ‐substituted N , N′ , N′′ ‐triarylguanidinato ligand in the resulting triazolate complexes,, we report herein the reactions of 5 with diethylacetylenedicarboxylate (DEAD) and bis(diphenylphosphanyl)acetylene (DPPA) which afforded two distinct products, namely 9 and 10 respectively. The utility of 3 as catalyst in click reaction involving phenyl acetylene and 4‐tolyl azide was also explored.…”