Pyrazolyl-Bridged Iridium Dimers. 17.¹ Tetrakis(alkene)diiridium(I) Complexes:  [Ir(η²-C₂H₄)₂(μ-Cl)]₂ as a Precursor to [Ir(η²-C₂H₄)₂(μ-pz)]₂. Stereochemically Nonrigid Behavior of the Analogue [Ir(η²-C₂H₄)(η²-C₂F₄)(μ-Cl)]₂

Abstract

The known bis(ethene) dimer [Ir(η2-C2H4)2Cl]2, 1, reacts with pyrazole in the presence of NEt3 to form the deep purple pyrazolyl-bridged diiridium(I) analogue [Ir(η2-C2H4)2(μ-pz)]2 (2), which is however stable only in an atmosphere of ethylene gas. Reaction of 2 with MeI affords a pale orange product formulated as the d7 2 diiridium(II) adduct [Ir(Me)(η2-C2H4)2(μ-pz)2Ir(I)(η2-C2H4)2] (3) on the basis of its 1H NMR spectrum, which provides no evidence for dissociation of 3 in solution (contrasting with the behavior of the corresponding adduct formed by the bis(cycloocta-1,5-diene) analogue of 2); like 2, 3 is unstable in the absence of excess ethylene. No congener of 2 could be obtained by similar treatment of the perfluoroethylene analogue [Ir(η2-C2H4)(η2-C2F4)Cl]2 (4) of 1, although 4 was found to be less unstable than previously suggested and has been fully characterized in solution below −70 °C by 19F as well as 1H NMR measurements. Thus, in acetone (but not in toluene or methylene chloride), 4 exists in equilibrium with two species, 4A and 4B, formulated as isomeric, mononuclear, 16e solvento complexes [Ir(η2-C2H4)(η2-C2F4)Cl(S)], S = acetone; 4:4A:4B (−90 °C) ca. 67:13:20. The slow-limiting 19F NMR spectrum of 4, which has been assigned with the aid of 19F−19F COSY data, unambiguously identifies a folded binuclear geometry that undergoes facile ring inversion of the chloro-bridged core, with ΔG 200 ⧧ ca. 39 kJ mol-1 estimated from the temperature-dependent NMR behavior. Coalescence data for signals attributed to mononuclear 4A are consistent with “propeller rotation” of the C2F4 ligand at d8 Ir(I), ΔG200 ⧧ ca. 41 kJ mol-1. Mononuclear, 18e, substituted cyclopentadienyl complexes Ir(η5-C5H4R)(η2-C2H4)(η2-L) (5, R = COCO2Et, L = C2H4; 6, R = COOMe, L = C2F4) can also be synthesized by bridge-cleavage reactions of 1 and 4, respectively.

Preparation and Properties of RhI and IrI Ethylene Complexes Containing the ChiralP,N-Chelate Ligand (4S)-2-[2-(Diphenylphosphanyl)phenyl]-4-isopropyl-1,3-oxazoline

“…Synthesis of [IrCl(η 2 ‐C 2 H 4 )(PN)] (2): Under argon, a red suspension of the bis(ethylene)iridium(I) dimer [Ir(μ‐Cl)(η 2 ‐C 2 H 4 ) 2 ] 2 5b (75 mg, 0.132 mmol) in diethyl ether (15 mL) was cooled to −20 °C and PN was added (98 mg, 0.262 mmol). A deep red solution was immediately formed and after a short time a red powder precipitated.…”

Metal–Ligand Electron Transfer in 4d and 5d Group 9 Transition Metal Complexes with Pyridine, Diimine Ligands

“…They were synthesized by reaction of the respective ligand with the dimeric [M(C 2 H 4 ) 2 Cl] 2 (M = Rh, [38] Ir [39] ) complexes. [13][14]40] The previously unpublished complexes 4 d -Ir, 4 e -Ir, 4 f -Rh/Ir, and 4 g -Rh were characterized by standard spectroscopic methods and also X-ray structure analysis, when suitable crystals could be obtained.…”

Pseudo‐tetrahedral Rhodium and Iridium Complexes: Catalytic Synthesis of E‐Enynes

“…Organic solvents were dried by standard procedures and distilled under argon prior to use or obtained oxygen‐ and water‐free from a Solvent Purification System. Complexes [{Ir(coe) 2 (μ‐Cl)} 2 ], [{Ir(C 2 H 4 ) 2 (μ‐Cl)} 2 ], [Rh(PhBP 3 )(C 2 H 4 )(NCMe)] ⋅ 2MeCN ( 2 ), and [Li(tmen)][PhB(CH 2 PPh 2 ) 3 ] were prepared according to the literature methods. Phenylacetylene was distilled under vacuum.…”