Generation of Metallacyclic Structures from the Reactions of Vinyl Ethers with a Tp^Me2Ir^III Compound

Abstract

The vinyl ethers CH 2 dCHOEt and CH 2 dCHOPr n react with the Ir III fragment [Tp Me2 Ir(C 6 H 5 ) 2 ] [1; Tp Me2 ) hydrotris(3,5-dimethylpyrazolyl)borate] with the formation of unusual metallacyclic structures. Each of the ethers gives rise to three different metallacyclic units in complexes 2-4. Compounds 2 are iridacyclopentenes that contain a chelating organic ligand with alkyl and carbene termini, {Ir[dC(OR)CH 2 CH(OR)CH 2 ]} (R ) Et, Pr n ), resulting from the C-C coupling of two molecules of the ether, following prior vinylic C-H activation in one of them. They readily eliminate a molecule of the respective alcohol, ROH, in an acid-catalyzed process that leads to metallacyclopenta-1,3-diene units in 4 {Ir[dC(OR)CHdCHCH 2 ]}. Complexes 3 have a more complex metallacyclic structure resulting from tridentate coordination of a formally dianionic ligand that possesses alkyl, alkoxide, and carbene functionalities. Generation of this ligand involves the participation of two molecules of the vinyl ether, with one of them undergoing C vinyl -O bond cleavage. The metallacyclic units that define the molecular structures of 2-4 have been unequivocally characterized by X-ray crystallography.

Synthetic, Mechanistic, and Theoretical Studies on the Generation of Iridium Hydride Alkylidene and Iridium Hydride Alkene Isomers

“…The existence in 7 of a chelating aryloxide alkyl ligand reveals unmistakably that the reaction of 1·N 2 and 2,6-Me 2 C 6 H 3 OMe proceeds with rupture of the ArO À Me bond of the ether, followed by C À C coupling of the resulting one-carbon unit with one of the aryl orthomethyl substituents, which prior to the latter event has suffered a CÀH bond-activation reaction. The IrÀCH 2 bond (Ir1 À C23 in Figure 1) has a length of 2.04(1) , comparable to values found for related Ir III À C sigma bonds, [10,12] and its higher trans influence, in comparison with the aryl oxide and NCMe groups, causes the Ir1 À N1 bond trans to the Scheme 4. The activation of 2,6-dimethyl-substituted anisoles by 1.…”

“…The rearrangement of the 2,6‐dimethyl‐substituted anisoles presented in Scheme is a very unusual reaction. CO bond cleavage in allylic and vinylic systems is a known reaction that is usually facilitated by coordination of the CC bond 12b. 15 However, alkyl and aryl ethers are less reactive and in the absence of organometal reagents, cleavage of their CO bonds requires heating with concentrated HBr or HI 16.…”

Cyclometalated Iridium Complexes from Intramolecular C–H Activation of [IrCp*Cl{═C(OMe)CH═C(CH3)R}L] (R = CH3, Ph; L = PPh2Me, PMe3)

“…In the case of Ir–C single-bond lengths these values vary from 2.117(7) to 2.130(6) Å. All of these values are slightly longer than those found for the iridacyclopenta-1,3-dienes obtained by Paneque et al , …”

“…The product of this reaction, “a metallacycle”, can also be obtained by other routes. In particular, some metallacyclic compounds have been formed with pincer ligands, by activation of the vinyl ethers, and with free pyridyl-functionalized carbenes …”

Successive Activation of C–H and C–O Bonds of Vinyl Ethers by a Diphosphine and Hydrido-Bridged Diiridium Complex

“…To obtain insight into the reaction mechanism and reactivity to develop better catalytic reactions, it must be important to reveal the fundamental aspects of the activation of vinyl ethers by transition metal complexes. However, although there are many studies on C-H [31][32][33][34][35] and C-O [36][37][38][39][40][41] bond activation reactions by transition metal complexes, fundamental studies on the C-H and C-O bond activation of vinyl ethers by transition metal complexes are relatively unexplored [42][43][44][45][46][47][48][49][50][51][52][53].…”