The underappreciated influence of ancillary halide on metal–ligand proton tautomerism

Jain, Anant Kumar; Gau, Michael R.; Carroll, Patrick J.; Goldberg, Karen I.

doi:10.1039/d2sc00279e

Cited by 8 publications

(24 citation statements)

References 62 publications

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“…The solution-phase 31 P{ 1 H} NMR spectra of [ LH Rh][X] complexes display features that contrast dramatically with each other as well as with those of their Ir analogues. For reference, the 31 P{ 1 H} NMR spectrum for each of the [ LH Ir][X] complexes displayed two sets of doublets, consistent with the two phosphines in magnetically inequivalent environments . Accordingly, the presence of an NMR-active 103 Rh nucleus (natural abundance 100%) should result in two sets of doublets of doublets for the [ LH Rh][X] complexes.…”

Section: Resultsmentioning

confidence: 87%

“…The syntheses of the [ LH Rh][X] complexes were carried out following procedures similar to those for their Ir counterparts . Addition of 2 molar equiv of the LH ligand (2-(di- tert -butylphosphaneyl)-1 H -imidazole) to [Rh(coe) 2 (acetone) 2 ][PF 6 ] (coe = cyclooctene) in acetone resulted in an instantaneous formation of Rh-1 ( J Rh–P = 152 Hz), where both phosphine ligands are bound in a κ 2 fashion (Figure ).…”

Section: Resultsmentioning

confidence: 99%

“…14 Addition of 2 molar equiv of the LH ligand (2-(di-tertbutylphosphaneyl)-1H-imidazole) 27 to [Rh(coe) 2 (acetone) 2 ]-[PF 6 ] (coe = cyclooctene) 28 in acetone resulted in an instantaneous formation of Rh-1 (J Rh−P = 152 Hz), where both phosphine ligands are bound in a κ 2 fashion (Figure 1). The analogous reaction of 2 molar equiv LH with [Ir-(coe) 2 (acetone) 2 ][PF 6 ] starting material to generate Ir-1 required heating at 60 °C for 1 h. 14 The faster rate of the substitution reaction for Rh is consistent with the increased lability of the (coe/acetone) ligands on the second-row metal center relative to that of third-row Ir. Exposing the acetone solution of Rh-1 to an atmosphere of carbon monoxide (CO) gas resulted in the formation of the square-planar [ LH Rh][PF 6 ] complex, where one of the phosphine ligands is bound in a κ 1 fashion, while the other is bound in a κ 2 fashion (Figure 1).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…In a previous study, we described the synthesis of Ir(I) carbonyl complexes bearing two protic imidazolyl phosphine ligands . The protonated imidazolyl Ir cations were found to equilibrate with their neutral Ir hydride counterparts in solution (Scheme ).…”

Section: Introductionmentioning

confidence: 99%

“…13 In a previous study, we described the synthesis of Ir(I) carbonyl complexes bearing two protic imidazolyl phosphine ligands. 14 The protonated imidazolyl Ir cations were found to equilibrate with their neutral Ir hydride counterparts in solution (Scheme 1). The sterics and electronics of different halides provided insight into these competing effects on the metal−ligand proton tautomeric (MLPT) equilibria.…”

Section: ■ Introductionmentioning

confidence: 99%

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Comparing Square-Planar Rh^I and Ir^I: Metal–Ligand Proton Tautomerism, Fluxionality, and Reactivity

et al. 2022

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A series of low-valent square-planar Rh complexes [ LH Rh][X] (X = PF6, Br, Cl, I) bearing two protic imidazolyl phosphines (one κ2) and a CO ligand were synthesized and fully characterized. A comparison of the CO stretching frequencies with those of the previously reported [ LH Ir][X] complexes indicates a much lower electron density at the Rh centers. This lower electron density at Rh results in a lower propensity to undergo ligand to metal proton transfer, and in contrast to observations with Ir, the [ LH Rh][X] complexes (X = Cl, Br, I) do not equilibrate with their metal-protonated congeners. Furthermore, the weaker bond strengths of Rh complexes compared to Ir lead to an increased degree of fluxionality in the former, along with a difference in reactivity with hydrogen (H2) and iodine (I2).

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Section: Resultsmentioning

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Comparing Square-Planar Rh^I and Ir^I: Metal–Ligand Proton Tautomerism, Fluxionality, and Reactivity

et al. 2022

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The Role of Anionic Ligands on Photoreactivity in Mo(VI) Dioxo Complexes of the Form MoO₂X₂(NN)**

Fosshat

Fronczek

Chambers

2023

Chemistry A European J

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The photoreactivity of d 0 metal dioxo complexes in activating CÀ H bonds has been recently studied. [1][2][3] We have previously reported that MoO 2 Cl 2 (bpy-t Bu) is an effective platform for light initiated CÀ H activation with unique product selectivity for the overall functionalization. [1] Herein we expand on these studies and report the synthesis and photoreactivity of several new Mo(VI) dioxo complexes with the general formula MoO 2 (X) 2 (NN); where X=F À , Cl À , Br À , CH 3 À , PhO À , t BuO À and NN = 2,2'-bipyridine (bpy) or 4,4'-tert-butyl-2,2'bipyridine (bpy-t Bu). Among these compounds, MoO 2 Cl 2 (bpy-t Bu) and MoO 2 Br 2 (bpy-t Bu) are able to participate in bimolecular photoreactivity with several substrates containing CÀ H bonds of various types such as allyls, benzyls, aldehydes (RCHO) and alkanes. MoO 2 (CH 3 ) 2 bpy and MoO 2 (PhO) 2 bpy do not participate in bimolecular photoreactions and instead they undergo photodecompositions. Computational studies indicate that the nature of the HOMO and LUMO is critical in supporting photoreactivity, with access to an LMCT (bpy!Mo) being necessary for tractable hydrocarbon functionalization.

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Bifunctional Ligands: Evaluating the Role of Acidic Protons in the Secondary Coordination Sphere

Jain,

Malakar,

Cannon

et al. 2024

Chemistry A European J

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To evaluate bifunctional ligand reactivity involving NH acidic sites in the secondary coordination sphere of metal complexes, complexes where the proton has been substituted with a methyl group (NMe) are often investigated. An alternative strategy would involve substitution of the NH group for an O. This contribution considers and compares the merits of these approaches; the synthesis and characterization of cationic square planar Rh carbonyl complexes bearing diprotic bispyrazole pyridine ligand L1, and the bis‐methylated pyrazole pyridine ligand L1Me are described. The syntheses and characterization of the novel monoprotic pyrazole isoxazole pyridine ligand L2 and aprotic bisisoxazole pyridine ligand L3, and their corresponding Rh carbonyl complexes are also described. The different CO stretching frequencies of all four Rh‐complexes suggest that substitutions of NH with NMe, as well as O, lead to significant electronic differences, and these differences are further demonstrated to lead to different ligand addition/substitution reactivities of the four isoelectronic Rh‐complexes. Overall, the results suggest that the electronic differences arising due to NH substitutions can be significant and must be accounted for prior to invoking the participation of the proton.

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The underappreciated influence of ancillary halide on metal–ligand proton tautomerism

Abstract: Ligand protonated IrI bisphosphine carbonyl complexes isolated as halide salts equilibrate with their neutral IrIII–H congeners in solution. The equilibrium constant and energy barrier to interconversion are dependent on the identity of the halide.

Cited by 8 publications

References 62 publications

Comparing Square-Planar Rh^I and Ir^I: Metal–Ligand Proton Tautomerism, Fluxionality, and Reactivity

Comparing Square-Planar Rh^I and Ir^I: Metal–Ligand Proton Tautomerism, Fluxionality, and Reactivity

The Role of Anionic Ligands on Photoreactivity in Mo(VI) Dioxo Complexes of the Form MoO₂X₂(NN)**

Bifunctional Ligands: Evaluating the Role of Acidic Protons in the Secondary Coordination Sphere

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The underappreciated influence of ancillary halide on metal–ligand proton tautomerism

Abstract: Ligand protonated IrI bisphosphine carbonyl complexes isolated as halide salts equilibrate with their neutral IrIII–H congeners in solution. The equilibrium constant and energy barrier to interconversion are dependent on the identity of the halide.

Cited by 8 publications

References 62 publications

Comparing Square-Planar RhI and IrI: Metal–Ligand Proton Tautomerism, Fluxionality, and Reactivity

Comparing Square-Planar RhI and IrI: Metal–Ligand Proton Tautomerism, Fluxionality, and Reactivity

The Role of Anionic Ligands on Photoreactivity in Mo(VI) Dioxo Complexes of the Form MoO2X2(NN)**

Bifunctional Ligands: Evaluating the Role of Acidic Protons in the Secondary Coordination Sphere

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Product

Resources

About

Comparing Square-Planar Rh^I and Ir^I: Metal–Ligand Proton Tautomerism, Fluxionality, and Reactivity

Comparing Square-Planar Rh^I and Ir^I: Metal–Ligand Proton Tautomerism, Fluxionality, and Reactivity

The Role of Anionic Ligands on Photoreactivity in Mo(VI) Dioxo Complexes of the Form MoO₂X₂(NN)**