Metallacycloheptatrienes of Iridium(III):  Synthesis and Reactivity

Abstract

The Ir(I)−butadiene complex TpMe2Ir(η4-CH2C(Me)C(Me)CH2) (1) (TpMe2 = hydrotris(3,5-dimethylpyrazolyl)borate) reacts with ≥3 equiv of DMAD (RC⋮CR, R = CO2Me) in CH2Cl2 at 60 °C, in the presence of adventitious water, with formation of the iridacycloheptatriene (2), by the oxidative coupling of three molecules of DMAD in the metal coordination sphere. In a related process, TpMe2IrPh2(N2) (4) gives two benzoannelated iridacycloheptatrienes, the symmetrical species (5) and the unsymmetrical one (6). The water ligand in these complexes is labile, and derivatives substituted with CO, PMe3, and NCMe have been obtained. 2, 5, and 6 react, at 25 °C, with oxo-transfer oxidizing reagents such as tBuOOH with formation of the keto-metallabicyclic products 7−9, which result from the selective oxo attack to the γ,δ-CC double bond, irrespective of this being of the benzo or the (R)CC(R) type. In the latter case, further oxidation takes place with tBuOOH, at ambient temperature, with formation of an iridabenzene (11) and an iridanaphthalene (12) (with five and three electron-withdrawing CO2Me substituents, respectively) in which the carboxylate MeO2CCO2 - ligand completes the metal coordination sphere. Interestingly, substitution of this group by OH- or MeO- allows the formation of Jackson−Meisenheimer complexes, reflecting the inherent aromaticity of these electron-deficient metalloaromatics. Finally, the hydrogenation of the iridacycloheptatrienes has been studied. All new compounds have been fully characterized by microanalysis, IR and NMR spectroscopies, and, in some cases, single-crystal X-ray diffraction studies.

Coupling of Aromatic Aldehydes with CO2Me-Substituted TpMe2Ir(III) Metallacyclopentadienes

“…As can be observed, the metallacycle features a boat structure with the central C=C bond pointing towards the metal centre as previously observed in related species 22,23 The aldehyde ligand is coordinated to the iridium atom by the 17 oxygen atom and the Ir-O(1) bond distance is a normal one of 2.090(2) Å. Also, the two Ir-C(sp 2 )…”

“…The reaction of the iridacycle 1 13 with benzaldehyde (1.5 equiv., C 6 H 6 , 120 ºC) leads to the bicyclic compound 2a in almost quantitative spectroscopic (NMR) yield (eq 2).…”

“…Species 2a has been completely characterized by spectroscopy 5 methods including single crystal X-ray diffraction studies. Inspection of both the 1 H and 13 C NMR spectra immediately reveals the lack of the 2:1 symmetry exhibited by the starting material 1 and thus independent resonances are observed for the nuclei of each of the pyrazolyl arms of the Tp Me2 ligand. In the 1 H NMR spectrum, the most characteristic resonance is a singlet at 5.24 ppm that corresponds to the Ir-CH(E)-proton that derives from the aldehydic H atom.…”

“…In the 1 H NMR spectrum, the most characteristic resonance is a singlet at 5.24 ppm that corresponds to the Ir-CH(E)-proton that derives from the aldehydic H atom. In the 13 …”

Nucleophilic Aromatic Addition Reactions of the Metallabenzenes and Metallapyridinium: Attacking Aromatic Metallacycles with Bis(diphenylphosphino)methane to Form Metallacyclohexadienes and Cyclic η2‐Allene‐Coordinated Complexes

“…In contrast, well-characterized metallabenzenes bearing electron-withdrawing groups have rarely been isolated. [6,[8][9][10] The iridabenzenes and related iridanaphthalene reported by Paneque et al represent the first examples of metallabenzenes with electron-withdrawing groups, namely CO 2 Me. [8] We prepared a series of phosphoniumsubstituted metallabenzenes, including osmabenzenes and ruthenabenzenes.…”