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Synthesis and characterization of pyrrole-based group 4 PNP pincer complexes.

Authors :: Tomsu G
Stöger B
Kirchner K
Source :: Monatshefte fur chemie [Monatsh Chem] 2024; Vol. 155 (2), pp. 173-181. Date of Electronic Publication: 2024 Feb 09.
Publication Year :: 2024
Abstract: The synthesis, characterization, and reactivity of several group 4 metal complexes featuring a central anionic pyrrole moiety connected via CH <subscript>2</subscript> linkers to two phosphine donors is described. Treatment of [P(NH)P- i Pr] with [MCl <subscript>4</subscript> (THF) <subscript>2</subscript> ] (M = Zr, Hf) in the presence of base yields the dimeric complexes [M(PNP <superscript> i Pr</superscript> )(μ-Cl)(Cl) <subscript>2</subscript> ] <subscript>2</subscript> featuring two bridging chloride ligands. These complexes react with sodium cyclopentadienyl and SiMe <subscript>3</subscript> I to give the mononuclear complexes [M(PNP <superscript> i Pr</superscript> )(η <superscript>5</superscript> -Cp)(Cl) <subscript>2</subscript> ] and [M(PNP <superscript> i Pr</superscript> )(I) <subscript>3</subscript> ], respectively. The latter react with MeMgBr to form the trialkyl complexes [M(PNP <superscript> i Pr</superscript> )(Me) <subscript>3</subscript> ]. Upon treatment of [Ti(NMe <subscript>2</subscript> ) <subscript>4</subscript> ] with [P(NH)P- i Pr] a complex with the general formula [Ti(PNP <superscript> i Pr</superscript> )(NMe <subscript>2</subscript> ) <subscript>3</subscript> ] is obtained. DFT calculations revealed that the most stable species is [Ti(κ <superscript>1</superscript> N - PNP <superscript> i Pr</superscript> )(NMe <subscript>2</subscript> ) <subscript>3</subscript> ] featuring a κ <superscript>1</superscript> N -bound PNP ligand. When [P(NH)P- i Pr] is reacted with [Ti(NMe <subscript>2</subscript> ) <subscript>4</subscript> ] in CH <subscript>2</subscript> Cl <subscript>2</subscript> complex [Ti(PNP <superscript> i Pr</superscript> )(Cl) <subscript>2</subscript> (NMe <subscript>2</subscript> )] is formed. Treatment of a solution of [P(NH)P- i Pr] and [Zr(NMe <subscript>2</subscript> ) <subscript>4</subscript> ] with SiMe <subscript>3</subscript> Br affords the anionic seven-coordinate tetrabromo complex [Zr(PNP <superscript> i Pr</superscript> )(Br) <subscript>4</subscript> ][H <subscript>2</subscript> NMe <subscript>2</subscript> ]. The corresponding hafnium complex [Hf(PNP <superscript> i Pr</superscript> )(Br) <subscript>4</subscript> ][H <subscript>2</subscript> NEt <subscript>2</subscript> ] is obtained in similar fashion by utilizing [Hf(NEt <subscript>2</subscript> ) <subscript>4</subscript> ] as metal precursor. All complexes are characterized by means of NMR spectroscopy. Representative complexes were also characterized by X-ray crystallography.<br />Supplementary Information: The online version contains supplementary material available at 10.1007/s00706-024-03171-x.<br /> (© The Author(s) 2024.)