Asymmetric bis-PNP pincer complexes of zirconium and hafnium – a measure of hemilability

The ‘POCOP’ pincer ligand, [2,6-(R2PO)2C6H3], has been attached to titanium in both Ti(III) and Ti(IV) complexes for the first time. Using a lithium-halogen exchange route [2.6-(R2O)2C6H3]Li ([RPOCOP]Li) can be synthesised. Both the iso-propyl and tert-butyl derivatives can be made, but only the latter isolated. These can be reacted with the Ti(III) and Ti(IV) synthons to make [tBuPOCOP]TiCl2 (1), [tBuPOCOP]TiCl3 (2) and {[iPrPOCOP]TiCl2(µ-Cl)}2 (4). In the presence of Ti(IV), THF and [RPOCOP]Li an unprecedented ligand rearrangement occurs. 1 can be derivatised with alkylating agents to make bis-methyl, phenyl and neopentyl complexes. The last of these can activate H2 to make a rare example of a titanium hydride chloride, with the metal pincer fragment staying attached. This opens the door for this archetypical pincer ligand to be used with early transition metals.

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“…Accordingly, a large number of transition metal complexes has been prepared to date using this class of ligand. With respect to group 4 metals pyrrole-based PNP pincer complexes are rare [ 22 , 23 ]. We have recently described several Ti(IV) and Ti(III) PNP complexes [ 24 ] which were shown to undergo ketone insertion reactions into a Ti(IV)-P bond thereby forming new complexes with tridendate PNO-ligands.…”

Section: Introductionmentioning

confidence: 99%

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

Tomsu,

Stöger,

Kirchner

2024

Monatsh Chem

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The synthesis, characterization, and reactivity of several group 4 metal complexes featuring a central anionic pyrrole moiety connected via CH2 linkers to two phosphine donors is described. Treatment of [P(NH)P-iPr] with [MCl4(THF)2] (M = Zr, Hf) in the presence of base yields the dimeric complexes [M(PNPiPr)(μ-Cl)(Cl)2]2 featuring two bridging chloride ligands. These complexes react with sodium cyclopentadienyl and SiMe3I to give the mononuclear complexes [M(PNPiPr)(η5-Cp)(Cl)2] and [M(PNPiPr)(I)3], respectively. The latter react with MeMgBr to form the trialkyl complexes [M(PNPiPr)(Me)3]. Upon treatment of [Ti(NMe2)4] with [P(NH)P-iPr] a complex with the general formula [Ti(PNPiPr)(NMe2)3] is obtained. DFT calculations revealed that the most stable species is [Ti(κ1N- PNPiPr)(NMe2)3] featuring a κ1N-bound PNP ligand. When [P(NH)P-iPr] is reacted with [Ti(NMe2)4] in CH2Cl2 complex [Ti(PNPiPr)(Cl)2(NMe2)] is formed. Treatment of a solution of [P(NH)P-iPr] and [Zr(NMe2)4] with SiMe3Br affords the anionic seven-coordinate tetrabromo complex [Zr(PNPiPr)(Br)4][H2NMe2]. The corresponding hafnium complex [Hf(PNPiPr)(Br)4][H2NEt2] is obtained in similar fashion by utilizing [Hf(NEt2)4] as metal precursor. All complexes are characterized by means of NMR spectroscopy. Representative complexes were also characterized by X-ray crystallography. Graphical abstract

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Asymmetric bis-PNP pincer complexes of zirconium and hafnium – a measure of hemilability

Abstract: Asymmetrically-bound pyrrolide-based bis-PNP pincer complexes of zirconium and hafnium have been formed. Their fluxional behaviour has been investigated using variable temperature NMR and DFT calculations.

Cited by 5 publications

References 33 publications

Synthesis and reactivity of titanium ‘POCOP’ pincer complexes

Synthesis and reactivity of titanium ‘POCOP’ pincer complexes

Synthesis and Reactivity of titanium ‘POCOP’ pincer complexes

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

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