39 research outputs found
Rotaxane synthesis exploiting the M(i)/M(III) redox couple
No full textIn the context of advancing the use of metal-based building blocks for the construction of mechanically interlocked molecules, we herein describe the preparation of late transition metal containing [2]rotaxanes (1). Capture and subsequent retention of the interlocked assemblies are achieved by the formation of robust and bulky complexes of rhodium(iii) and iridium(iii) through hydrogenation of readily accessible rhodium(i) and iridium(i) complexes [M(COD)(PPh3)2][BArF4] (M = Rh, 2a; Ir, 2b) and reaction with a bipyridyl terminated [2]pseudorotaxane (3·db24c8). This work was underpinned by detailed mechanistic studies examining the hydrogenation of 1p;:p;1 mixtures of 2 and bipy in CH2Cl2, which proceeds with disparate rates to afford [M(bipy)H2(PPh3)2][BArF4] (M = Rh, 4a[BArF4], t = 18 h @ 50 °C; Ir, 4b[BArF4], t < 5 min @ RT) in CH2Cl2 (1 atm H2). These rates are reconciled by (a) the inherently slower reaction of 2a with H2 compared to that of the third row congener 2b, and (b) the competing and irreversible reaction of 2a with bipy, leading to a very slow hydrogenation pathway, involving rate-limiting substitution of COD by PPh3. On the basis of this information, operationally convenient and mild conditions (CH2Cl2, RT, 1 atm H2, t ≤ 2 h) were developed for the preparation of 1, involving in the case of rhodium-based 1a pre-hydrogenation of 2a to form [Rh(PPh3)2]2[BArF4]2 (8) before reaction with 3·db24c8. In addition to comprehensive spectroscopic characterisation of 1, the structure of iridium-based 1b was elucidated in the solid-state using X-ray diffraction
Single-crystal to single-crystal addition of H<sub>2</sub>to [Ir(<sup>i</sup>Pr-PONOP)(propene)][BAr<sup>F</sup><sub>4</sub>] and comparison between solid-state and solution reactivity
No full textThe reactivity of the Ir(I) PONOP pincer complex [Ir(iPr-PONOP)(η2-propene)][BArF4], 6, [iPr-PONOP = 2,6-(iPr2PO)2C6H3N, ArF = 3,5-(CF3)2C6H3] was studied in solution and the solid state, both experimentally, using molecular density functional theory (DFT) and periodic-DFT computational methods, as well as in situ single-crystal to single-crystal (SC-SC) techniques. Complex 6 is synthesized in solution from sequential addition of H2 and propene, and then the application of vacuum, to [Ir(iPr-PONOP)(η2-COD)][BArF4], 1, a reaction manifold that proceeds via the Ir(III) dihydrogen/dihydride complex [Ir(iPr-PONOP)(H2)H2][BArF4], 2, and the Ir(III) dihydride propene complex [Ir(iPr-PONOP)(η2-propene)H2][BArF4], 7, respectively. In solution (CD2Cl2) 6 undergoes rapid reaction with H2 to form dihydride 7 and then a slow (3 d) onward reaction to give dihydrogen/dihydride 2 and propane. DFT calculations on the molecular cation in solution support this slow, but productive, reaction, with a calculated barrier to rate-limiting propene migratory insertion of 24.8 kcal/mol. In the solid state single-crystals of 6 also form complex 7 on addition of H2 in an SC-SC reaction, but unlike in solution the onward reaction (i.e., insertion) does not occur, as confirmed by labeling studies using D2. The solid-state structure of 7 reveals that, on addition of H2 to 6, the PONOP ligand moves by 90° within a cavity of [BArF4]- anions rather than the alkene moving. Periodic DFT calculations support the higher barrier to insertion in the solid state (ΔG‡ = 26.0 kcal/mol), demonstrating that the single-crystal environment gates onward reactivity compared to solution. H2 addition to 6 to form 7 is reversible in both solution and the solid state, but in the latter crystallinity is lost. A rare example of a sigma amine-borane pincer complex, [Ir(iPr-PONOP)H2(η1-H3B·NMe3)][BArF4], 5, is also reported as part of these studies.</p
A convenient method for the generation of {Rh(PNP)}+ and {Rh(PONOP)}+ fragments : reversible formation of vinylidene derivatives
No full textThe substitution reactions of [Rh(COD)2][BArF4] with PNP and PONOP pincer ligands 2,6-bis(di-tert-butylphosphinomethyl)pyridine and 2,6-bis(di-tert-butylphosphinito)pyridine in the weakly coordinating solvent 1,2-F2C6H4 are shown to be an operationally simple method for the generation of reactive formally 14 VE rhodium(I) adducts in solution. Application of this methodology enables synthesis of known adducts of CO, N2, H2, previously unknown water complexes, and novel vinylidene derivatives [Rh(pincer)(CCHR)][BArF4] (R = tBu, 3,5-tBu2C6H3), through reversible reactions with terminal alkynes
A flexible, extremely sterically demanding triazenide ligand : synthesis and coordination chemistry
No full textRhodium(I) pincer complexes of nitrous oxide
No full textThe synthesis of two well‐defined rhodium(I) complexes of nitrous oxide (N2O) is reported. These normally elusive adducts are stable in the solid state and persist in solution at ambient temperature, enabling comprehensive structural interrogation by 15N NMR and IR spectroscopy, and single‐crystal X‐ray diffraction. These methods evidence coordination of N2O through the terminal nitrogen atom in a linear fashion and are supplemented by a computational energy decomposition analysis, which provides further insights into the nature of the Rh–N2O interaction.
The synthetic exploitation of nitrous oxide (N2O) is an enduring challenge that draws topical interest as a means to remediate the detrimental impact emission of this kinetically stable gas on the environment.1 Whilst the application of homogenous transition‐metal complexes is an attractive prospect, the underpinning inorganic chemistry is conspicuously under‐developed.2 Indeed, the number of discrete transition‐metal complexes of N2O is currently limited to a handful of examples (A–D), of which only two have been structurally characterised in the solid state using X‐ray diffraction (Figure 1).3, 4-7 This paucity is attributed to the extremely poor ligand properties of N2O, conferred by a low dipole moment, weak σ‐donor and π‐acceptor characteristics, and the propensity of these adducts for subsequent N−N or N−O bond cleavage.
Oxidative addition of a mechanically entrapped C(sp)–C(sp) bond to a rhodium(I) pincer complex
No full textBy use of a macrocyclic phosphinite pincer ligand and bulky substrate substituents, we demonstrate how the mechanical bond can be leveraged to promote the oxidative addition of an interlocked 1,3‐diyne to a rhodium(I) center. The resulting rhodium(III) bis(alkynyl) product can be trapped out by reaction with carbon monoxide or intercepted through irreversible reaction with dihydrogen, resulting in selective hydrogenolysis of the C–C σ‐bond
DATASET A Gold(I)–Acetylene Complex Synthesised using Single-Crystal Reactivity
No full textAs a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.Using single-crystal to single-crystal solid/gas reactivity the gold(I) acetylene complex [Au(L1)(eta 2-HC equivalent to CH)][BArF4] is cleanly synthesized by addition of acetylene gas to single crystals of [Au(L1)(CO)][BArF4] [L1=tris-2-(4,4 '-di-tert-butylbiphenyl)phosphine, ArF=3,5-(CF3)2C6H3]. This simplest gold-alkyne complex has been characterized by single crystal X-ray diffraction, solution and solid-state NMR spectroscopy and periodic DFT. Bonding of HC equivalent to CH with [Au(L1)]+ comprises both sigma-donation and pi-backdonation with additional dispersion interactions within the cavity-shaped phosphine.
The existence of pi-acetylene gold(I) compounds as intermediates in catalysis has been postulated, but their isolation or spectroscopic detection has remained elusive. Herein, the combination of a bulky cavity-shaped phosphine along with single-crystal to single-crystal reactivity allowed for the isolation of the first gold(I)-acetylene complex, which was thoroughly characterized by X-ray diffraction, solution and solid-state NMR, periodic DFT, and electronic structure analyses. imageThis work was supported by the European Research Council (ERC Starting Grant, CoopCat, Project 756575) and the Spanish Ministry of Science and Innovation (PID2022-139782NB-I00). M. N. acknowledges the Spanish Ministry of Science and Innovation and Junta de Andalucía for postdoctoral programs (FJC2018-035514-I and DOC_00149). Leverhulme Trust (RPG-2020-184; MRG, CLJ) and the Wild Overseas Scholar's Fund (CLJ); the University of St. Andrews (DJS) and EPSRC (EP/W015498/1, MAS; UK Catalysis Hub, EP/R026815/1, MRG). Dr A. Whitwood (York) for helpul discussions and Dr V. Annis (York) for technical assistance with 13C-acetylene experiments.Peer reviewe
Synthesis and rhodium complexes of macrocyclic PNP and PONOP pincer ligands
No full textThe synthesis of macrocyclic variants of commonly employed phosphine-based pincer ligands derived from lutidine (PNP-14) and 2,6-dihydroxypyridine (PONOP-14) is described, where the P-donors are trans-substituted with a tetradecamethylene linker. This was accomplished using an eight-step procedure involving borane protection, ring-closing olefin metathesis, chromatographic separation from the cis-substituted diastereomers, and borane deprotection. The rhodium coordination chemistry of these ligands has been explored, aided by the facile synthesis of 2,2′-biphenyl (biph) adducts [Rh(PNP-14)(biph)][BArF4] and [Rh(PONOP-14)(biph)][BArF4] (ArF = 3,5-(CF3)2C6H3). Subsequent hydrogenolysis enabled generation of dihydrogen, ethylene and carbonyl derivatives; notably the ν(CO) bands of the carbonyl complexes provide a means to compare the donor properties of the new pincer ligands with established acyclic congeners
Rhodium(III) and iridium(III) complexes of a NHC-based macrocycle : persistent weak agostic interactions and reactions with dihydrogen
No full textThe synthesis and characterization of five-coordinate rhodium(III) and iridium(III) 2,2′-biphenyl complexes [M(CNC-12)(biph)][BArF4] (M = Rh (1a), Ir (1b)), featuring the macrocyclic lutidine- and NHC-based pincer ligand CNC-12 are reported. In the solid state these complexes are notable for the adoption of weak ε-agostic interactions that are characterized by M···H–C contacts of ca. 3.0 Å by X-ray crystallography and ν(CH) bands of reduced wavenumber by ATR IR spectroscopy. Remarkably, these interactions persist on dissolution and were observed at room temperature using NMR spectroscopy (CD2Cl2) and solution-phase IR spectroscopy (CCl4). The associated metrics point toward a stronger M···H–C interaction in the iridium congener, and this conclusion is borne out on interrogation of 1 in silico using DFT-based NBO and QTAIM analyses. Reaction of 1 with dihydrogen resulted in hydrogenolysis of the biaryl and formation of fluxional hydride complexes, whose ground state formulations as [Rh(CNC-12)H2][BArF4] (2a″) and [Ir(CNC-12)H2(H2)][BArF4] (2b‴) are proposed on the basis of inversion recovery and variable-temperature NMR experiments, alongside a computational analysis. Reactions of 1 and 2 with carbon monoxide help support their respective structural properties
Metal Complexes of an Ionic Liquid-Derived Carbene
No full text
A range of metal carbene complexes containing the ionic liquid-derived N-heterocyclic carbene (NHC) 1-nbutyl-3-methylimidazol-2-ylidene (IBuMe, 1) have been prepared by (i) direct ligand substitution using the free NHC ([Mo(CO)5(IBuMe)] 2), (ii) transmetallation using the silver salt [AgCl(IBuMe)] (3) ([RhCl(NBD)(IBuMe)] (4) and [IrCl(COD)(IBuMe)] (5), NBD = 2,5-norbornadiene, COD = 1,5-cyclooctadiene) and (iii) direct reaction of a metal acetate with the hydrochloride salt of 1 (trans-[PdCl2(IBuMe)] (6)). The dicarbonyl cis-[RhCl(CO)2(IBuMe)] (7) has been prepared by diene substitution under a carbon monoxide atmosphere. The molecular structures of 2, 4, 5 and 6 are reported and the sigma donation and steric properties of 1 are discussed relative to those of common imidazol-2-ylidene ligands.
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