Multiple C−H Activations of Methyl tert-Butyl Ether at Pincer Iridium Complexes: Synthesis and Thermolysis of Ir(I) Fischer Carbenes¹

Abstract

The C-H activation of methyl tert-butyl ether (MTBE) mediated by pincer iridium complexes derived from PNP and PCP frameworks has been studied. Double C-H activation of MTBE by these complexes leads to formation of Ir(I) Fischer carbenes of the type (pincer)IrdC(H)O t Bu via elimination of H 2 . In one case, the structure of the Fischer carbene has been confirmed by single-crystal X-ray analysis. For both systems, the carbenes are obtained as kinetic products, and prolonged thermolysis leads to the formation of thermodynamically stable trans-(pincer)Ir(H) 2 (CO) complexes. A mechanism for this transformation is presented along with reactivity studies supporting the proposal.

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

“…As mentioned above, Whited and Grubbs showed that an iridium(I) carbene system that exhibited FLP reactivity could be generated by multiple C–H cleavage events at tert -butyl methyl ether (MTBE) (Scheme 14) [71,87]. For the (PNP)Ir system developed by Ozerov, it was found that an initial C–H activation of the most accessible methyl C–H bond in MTBE was followed by slow α-hydrogen elimination and reductive elimination of H 2 to afford the Ir(I) alkoxycarbene.…”

Carbene–Transition Metal Complexes Formed by Double CH Bond Activation

“…Although an analogue of the iridium oxocarbene 63 with the PCP pincer ligand first prepared by Grubbs et al is as yet unknown, the counterpart of 64 with this chelating ligand was generated by heating a mixture of the chloro hydrido compound [(PCP)Ir(H)Cl] and NaOtBu in MeOtBu at 70 8C. [51] Apart from the conversion of 63 into 64, the most striking reactions of the iridium oxocarbene 63 are those with CO 2 and their analogues COS, PhNCO, CS 2 , and PhNCS, which is a form of atom or group transfer without predecent. [48,52,53] Whited and Grubbs first found that exposure of a solution of 63 in C 6 D 6 to an atmosphere of CO 2 resulted in the quantitative formation of the iridium(I) carbonyl 65 (Scheme 21).…”

Carben‐Übergangsmetallkomplexe durch zweifache C‐H‐Bindungsaktivierung

“…Während ein Analogon des Iridiumoxocarbenkomplexes 63 mit einem PCP‐Pinzettenliganden, der erstmals von Grubbs et al. hergestellt wurde, bisher nicht bekannt ist, wurde das Gegenstück von 64 mit diesem PCP‐Chelatligand beim Erwärmen eines Gemischs der Chloro(hydrido)‐Verbindung [(PCP)Ir(H)Cl] und NaO t Bu in MeO t Bu bei 70 °C erhalten 51…”