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Iridium complexes of an ortho-trifluoromethylphenyl substituted PONOP pincer ligand.

ABSTRACT: The synthesis and iridium coordination chemistry of a new pyridine-based phosphinito pincer ligand 2,6-(Ar^F₂PO)₂C₅H₃N (PONOP-Ar^F; Ar^F = 2-(CF₃)C₆H₄) are described, where the P-donors have ortho-trifluoromethylphenyl substituents. The iridium(III) 2,2'-biphenyl (biph) derivative [Ir(PONOP-Ar^F)(biph)Cl] was obtained by reaction with [Ir(biph)(COD)Cl]₂ (COD = 1,5-cyclooctadiene) and subsequent halide ion abstraction enabled isolation of [Ir(PONOP-Ar^F)(biph)]⁺ which features an Ir ← F-C bonding interaction in the solid state. Hydrogenolysis of the biphenyl ligand and formation of [Ir(PONOP-Ar^F)(H)₂]⁺ was achieved by prolonged reaction of [Ir(PONOP-Ar^F)(biph)]⁺ with dihydrogen. This transformation paved the way for isolation and crystallographic characterisation of low valent iridium derivatives through treatment of the dihydride with tert-butylethylene (TBE). The iridium(I) π-complex [Ir(PONOP-Ar^F)(TBE)]⁺ is thermally stable but substitution of TBE can be achieved by reaction with carbon monoxide. The solid-state structure of the mono-carbonyl product [Ir(PONOP-Ar^F)(CO)]⁺ is notable for an intermolecular anagostic interaction between the metal centre and a pentane molecule which co-crystallises within a cleft defined by two aryl phosphine substituents.

SUBMITTER: Poole EW

PROVIDER: S-EPMC9872493 | biostudies-literature | 2023 Jan

REPOSITORIES: biostudies-literature

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Iridium complexes of an ortho-trifluoromethylphenyl substituted PONOP pincer ligand.

Poole Ethan W EW Bustos Itxaso I Hood Thomas M TM Smart Jennifer E JE Chaplin Adrian B AB

Dalton transactions (Cambridge, England : 2003) 20230124 4

The synthesis and iridium coordination chemistry of a new pyridine-based phosphinito pincer ligand 2,6-(ArF2PO)2C5H3N (PONOP-ArF; ArF = 2-(CF3)C6H4) are described, where the P-donors have ortho-trifluoromethylphenyl substituents. The iridium(III) 2,2'-biphenyl (biph) derivative [Ir(PONOP-ArF)(biph)Cl] was obtained by reaction with [Ir(biph)(COD)Cl]2 (COD = 1, ...[more]

PMID: 36602231

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Project description:Compound [Ir(C8H12)(C51H45P4)]Cl2 or [Ir(cod)(CH(dppm)2-κ3P,C,P)]Cl2 (1a), was obtained from [IrCl(cod)]2 and the carbodi-phospho-rane (CDP) salt [CH(dppm)2]Cl [where cod = cyclo-octa-1,5-diene and dppm = bis-(di-phenyl-phosphino)methane]. Treatment of 1a with thallium(I) tri-fluoro-methane-sulfonate [Tl(OTf)] and subsequent crystallization gave complex [Ir(C8H12)(C51H45P4)](OTf)2·CH3CO2C2H5·CH2Cl2 or [Ir(cod)(CH(dppm)2-κ3P,C,P)](OTf)2·CH3CO2C2H5·CH2Cl2 (1b) [systematic name: (cyclo-octa-1,5-diene)(1,1,3,3,5,5,7,7-octa-phenyl-1,7-diphospha-3,5-di-phospho-niaheptan-4-yl)iridium(I) bis-(tri-fluoro-methane-sulfonate)-ethyl acetate-di-chloro-methane (1/1/1)]. This five-coordinate iridium(I) complex cation adopts a trigonal-bipyramidal geometry with the CDP carbon and one cod double bond in axial sites. Compound 1b represents the first example of a non-meridional coordination of the PCP pincer ligand [CH(dppm)2]+ with a P-Ir-P angle of 98.08 (2)°. Compound 2, [IrCl2H(C51H44P4)]·(CH3)2CO or [IrCl2H(C(dppm)2-κ3P,C,P)]·(CH3)2CO [systematic name: di-chlorido-hydrido(1,1,3,3,5,5,7,7-octa-phenyl-1,5λ5,7-triphospha-3-phospho-niahept-4-en-4-yl)iridium(III) acetone monosolvate], crystallizes as an acetone monosolvate. It is a six-coordinate IrIII coordination compound. Here, the PCP pincer ligand is coordinated in a meridional manner; one chlorido ligand is positioned trans to the carbon donor, the remaining two coordination sites being occupied by the second chlorido and a hydrido ligand trans to each other. Complex 3, [IrCl2H(C51H45P4)]Cl·5H2O or [IrCl2H(CH(dppm)2-κ3P,C,P)]Cl·5H2O [systematic name: di-chlorido-hydrido(1,1,3,3,5,5,7,7-octa-phenyl-1,7-diphospha-3,5-di-phospho-niaheptan-4-yl)iridium(III) chloride penta-hydrate], represents the conjugate CH acid of 2. The ligand [CH(dppm)2]+ is coordinated in a meridional manner. In the cationic six-coordinate IrIII complex 4, [IrClH(CO)(C51H44P4)]Cl·2CH3OH·H2O or [IrClH(CO)(C(dppm)2-κ3P,C,P)]Cl·2CH3OH·H2O [systematic name: carbonyl-chlorido-hydrido(1,1,3,3,5,5,7,7-octa-phenyl-1,5λ5,7-triphospha-3-phos-pho-niahept-4-en-4-yl)iridium(III) chloride-methanol-water (1/2/1)], the chlorido ligand is found in the plane defined by the Ir center and the meridional PCP ligand; the H and CO ligands are positioned axially to this plane and trans to each other.

Project description:The mechanism for the borylation of an aromatic substrate by a cobalt pincer complex was investigated by density functional theory calculations. Experimental observations identified trans-(iPrPNP)CoH2(BPin) as the resting state in the borylation of five-membered heteroarenes, and 4-BPin-(iPrPNP)Co(N2)BPin as the resting state in the catalytic borylation of arene substrates. The active species, 4-R-(iPrPNP)CoBPin (R=H, BPin), were generated by reductive elimination of H2 in the former, through Berry pseudorotation to the cis isomer, and N2 loss in the latter. The catalytic mechanism of the resulting Co(I) complex was computed to involve three main steps: C-H oxidative addition of the aromatic substrate (C6H6), reductive elimination of PhBPin, and regeneration of the active complex. The oxidative addition product formed through the most favorable pathway, where the breaking C-H bond of C6H6 is parallel to a line between the two phosphine atoms, leaves the complex with a distorted PNP ligand, which rearranges to a more stable complex via dissociation and re-association of HBPin. Alternative pathways, σ-bond metathesis and the oxidative addition in which the breaking C-H bond is parallel to the Co-B bond, are predicted to be unlikely for this Co(I) complex. The thermodynamically favorable formation of the product PhBPin via reductive elimination drives the reaction forward. The active species regenerates through the oxidative addition of B2Pin2 and reductive elimination of HBPin. In the overall reaction, the flipping (refolding) of the five-membered phosphine rings, which connects the species with two phosphine rings folded in the same direction and that with them folded in different directions, is found to play an important role in the catalytic process, as it relieves steric crowding within the PNP ligand and opens Co coordination space. Metal-ligand cooperation based on the ligand's aromatization/dearomatization, a common mechanism for heavy-metal pincer complexes, and the dissociation of one phosphine ligand, do not apply in this system. This study provides guidance for understanding important features of pincer ligands with first-transition-row metals that differ from those in heavier metal complexes.

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Iridium complexes of an ortho-trifluoromethylphenyl substituted PONOP pincer ligand.

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Iridium complexes of an <i>ortho</i>-trifluoromethylphenyl substituted PONOP pincer ligand.

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