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Steric Effects Dictate the Formation of Terminal Arylborylene Complexes of Ruthenium from Dihydroboranes.

ABSTRACT: The steric and electronic properties of aryl substituents in monoaryl borohydrides (Li[ArBH₃ ]) and dihydroboranes were systematically varied and their reactions with [Ru(PCy₃ )₂ HCl(H₂ )] (Cy: cyclohexyl) were studied, resulting in bis(?)-borane or terminal borylene complexes of ruthenium. These variations allowed for the investigation of the factors involved in the activation of dihydroboranes in the synthesis of terminal borylene complexes. The complexes were studied by multinuclear NMR spectroscopy, mass spectrometry, X-ray diffraction analysis, and density functional theory (DFT) calculations. The experimental and computational results suggest that the ortho-substitution of the aryl groups is necessary for the formation of terminal borylene complexes.

SUBMITTER: Lenczyk C

PROVIDER: S-EPMC7079023 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Steric Effects Dictate the Formation of Terminal Arylborylene Complexes of Ruthenium from Dihydroboranes.

Lenczyk Carsten C Roy Dipak Kumar DK Nitsch Jörn J Radacki Krzysztof K Rauch Florian F Dewhurst Rian D RD Bickelhaupt F Matthias FM Marder Todd B TB Braunschweig Holger H

Chemistry (Weinheim an der Bergstrasse, Germany) 20190917 59

The steric and electronic properties of aryl substituents in monoaryl borohydrides (Li[ArBH3 ]) and dihydroboranes were systematically varied and their reactions with [Ru(PCy3 )2 HCl(H2 )] (Cy: cyclohexyl) were studied, resulting in bis(σ)-borane or terminal borylene complexes of ruthenium. These variations allowed for the investigation of the factors involved in the activation of dihydroboranes in the synthesis of terminal borylene complexes. The comp ...[more]

PMID: 31433081

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Project description:Ruthenium polypyridyl complexes are good candidates for photoactivated chemotherapy (PACT) provided that they are stable in the dark but efficiently photosubstitute one of their ligands. Here the use of the natural amino acid l-proline as a protecting ligand for ruthenium-based PACT compounds is investigated in the series of complexes Λ-[Ru(bpy)2(l-prol)]PF6 ([1a]PF6; bpy = 2,2'-bipyridine and l-prol = l-proline), Λ-[Ru(bpy)(dmbpy)(l-prol)]PF6 ([2a]PF6 and [2b]PF6; dmbpy = 6,6'-dimethyl-2,2'-bipyridine), and Λ-[Ru(dmbpy)2(l-prol)]PF6 ([3a]PF6). The synthesis of the tris-heteroleptic complex bearing the dissymmetric proline ligand yielded only two of the four possible regioisomers, called [2a]PF6 and [2b]PF6. Both isomers were isolated and characterized by a combination of spectroscopy and density functional theory calculations. The photoreactivity of all four complexes [1a]PF6, [2a]PF6, [2b]PF6, and [3a]PF6 was studied in water (H2O) and acetonitrile (MeCN) using UV-vis spectroscopy, circular dichroism spectroscopy, mass spectrometry, and 1H NMR spectroscopy. In H2O, upon visible-light irradiation in the presence of oxygen, no photosubstitution took place, but the amine of complex [1a]PF6 was photooxidized to an imine. Contrary to expectations, enhancing the steric strain by the addition of two ([2b]PF6) or four ([3a]PF6) methyl substituents did not lead, in phosphate-buffered saline (PBS), to ligand photosubstitution. However, it prevented photoxidation, probably as a consequence of the electron-donating effect of the methyl substituents. In addition, whereas [2b]PF6 was photostable in PBS, [2a]PF6 quantitatively isomerized to [2b]PF6 upon light irradiation. In pure MeCN, [2a]PF6 and [3a]PF6 showed non-selective photosubstitution of both the l-proline and dmbpy ligands, whereas the non-strained complex [1a]PF6 was photostable. Finally, in H2O-MeCN mixtures, [3a]PF6 showed selective photosubstitution of l-proline, thus demonstrating the active role played by the solvent on the photoreactivity of this series of complexes. The role of the solvent polarity and coordination properties on the photochemical properties of polypyridyl complexes is discussed.

Dataset Information

Steric Effects Dictate the Formation of Terminal Arylborylene Complexes of Ruthenium from Dihydroboranes.

Publications

Steric Effects Dictate the Formation of Terminal Arylborylene Complexes of Ruthenium from Dihydroboranes.

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