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Unraveling the Effect of Aromatic Groups in Mn(I)NNN Pincer Complexes on Carbon Dioxide Activation Using Density Functional Study.

ABSTRACT: Carbon dioxide utilization is necessary to reduce carbon footprint and also to synthesize value-added chemicals. The transition metal pincer complexes are attractive catalysts for the hydrogenation of carbon dioxide to formic acid. There is a need to understand the factors affecting the catalytic performance of these pincer complexes through a structure-activity relationship study using computational methods. It is a well-established fact that aromatic functionalities offer stability and selectivity to transition metal catalysts. However, their impact on the performance of the catalysts is lesser known in the case of metal pincer complexes. Hence, it is necessary to investigate the catalytic performance of Mn(I)NNN pincer complexes with variably activated aromatic functionalities. In this context, 15 catalysts are designed by placing different types of aromatic rings at the pincer carbons and two terminal nitrogen of Mn(I)NNN pincer complexes. A benzene moiety, placed at C2-C3 carbons of Mn(I)NNN pincer complex with identical aromatic groups at the terminal nitrogen, is found to be most efficient toward CO₂ hydrogenation than the rest of the catalysts. On the other hand, when N,N-dimethyl aniline is placed at C2-C3 carbons of Mn(I)NNN pincer complexes, then the catalytic performance is significantly decreased. Thus, the present study unravels the impact of aromatic groups in Mn(I)NNN pincer complexes toward the catalytic hydrogenation of carbon dioxide.

SUBMITTER: Parmar SV

PROVIDER: S-EPMC8639700 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:This report describes a synthetic protocols and the crystal structures involving a novel pincer-type H3[NNN] ligand, namely di-μ-bromido-μ-{2-(2,2-di-methylpropanimido-yl)-N-[2-(2,2-di-methyl-propanimido-yl)-4-methyl-phen-yl]-4-methylaniline}-bis-[(diethyl ether)lithium], [Li2Br2(C24H33N3)(C4H10O)2] (1) and a dinuclear metal complex, namely di-μ-bromido-2:3κ4Br:Br-bis-{2-(2,2-di-methylpropanimido-yl)-N-[2-(2,2-di-methyl-propanimido-yl)-4-methyl-phen-yl]-4-methylaniline}-1κ3N,N',N'';4κ3N,N',N''-tetra-μ-iso-propano-lato-1:2κ4O:O;3:4κ4O:O-diiso-propano-lato-1κO,4κO-2,3-dilithium-1,4-dititanium, [Li2Ti2Br2(C24H32N3)2(C3H7O)6] or {[NHNNH]Ti(O i Pr)3(LiBr)2}2 (2). Complex 1, which sits on a twofold rotation axis, is a rare example of a pincer-type ligand which bears ketimine side arms. A unique feature of complex 1 is that the ketimine N atoms have an LiBr(Et2O) fragment bonded to them, with the Li atom adopting a distorted tetra-hedral geometry. This particular fragment creates an LiBr bridge between the two ketimine sidearms, which leads to a cage-type appearance of the ligand. Complex 2 consists of the previously described ligand and a TiIV metal atom in an octa-hedral environment, and is located on an inversion center. Complex 2 crystallizes as a dinuclear species with the metal atoms being bridged by an LiBr entity [the Br atoms are disordered and refined in two positions with their site occupation factors refining to 0.674 (12)/0.372 (12)], and the Li cation being bonded to the isopropoxide O atoms (Li having a tetra-hedral coordination as in 1). The organic ligand of compound 2 exhibits disorder in its periphery groups; isopropyl and tert-butyl groups (occupation factors fixed at 0.6/0.4). The novel [NNN]H3 pincer-type ligand was characterized by multinuclear and multidimensional NMR, HRMS and X-ray crystallography. The dinuclear metal complex 2 was characterized by X-ray crystallography. Although each structure exhibits donor N-H groups, no hydrogen bonding is found in either one, perhaps due to the bulky groups around them. One of the ethyl groups of the ether ligand of 1 is disordered and refined in two parts with site-occupation factors of 0.812 (8) and 0.188 (8). One and a half toluene solvent mol-ecules are also present in the asymmetric unit of 2. The toluene mol-ecules were significantly disordered and could not be modeled properly, thus SQUEEZE [Spek (2015 ▸). Acta Cryst. C71, 9-18] was used to remove their contributions to the overall intensity data.

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Unraveling the Effect of Aromatic Groups in Mn(I)NNN Pincer Complexes on Carbon Dioxide Activation Using Density Functional Study.

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