Iridium Bis(phosphinite) p-XPCP Pincer Complexes:  Highly Active Catalysts for the Transfer Dehydrogenation of Alkanes

Abstract

A series of new bis(phosphinite) p-XPCPIrHCl pincer complexes ([PCP = eta(3)-5-X-C(6)H(2)[OP(tBu)(2)](2)-1,3], X = MeO (4a), Me (4b), H (4c), F (4d), C(6)F(5) (4e), and Ar(F) [=3,5-bis(trifluoromethyl)phenyl] (4f)) have been synthesized. Treatment of compounds 4a-f with NatOBu in cyclooctane (COA)/tert-butylethylene (TBE) mixtures generates species with unprecedented catalytic activity for the catalyzed transfer dehydrogenation of COA with TBE as acceptor to form cyclooctene (COE) and tert-butylethane (TBA). With substrate:precatalyst ratios of 3030COA:3030TBE:1p-XPCPIrHCl (4):1.1NaOtBu, turnover numbers (TONs) between 1400 and 2200 (up to 72% conversion in TBE) and initial turnover frequencies (TOFs) between 1.6 and 2.4 s(-1) have been observed at 200 degrees C.

Phosphido pincer complexes of platinum: synthesis, structure and reactivity

“…The methyl ligand in [ i Pr-PPP]Pt(CH 3 ) is unambiguously observed in the 13 C NMR spectrum as a doublet of triplets flanked by satellites at -12.0 ppm with a 2 J P-C of 37.7 Hz relative to the phosphido donor and a 2 J P-C of 7.5 Hz relative to the neutral phosphine donors.…”

Highly Active and Recyclable Heterogeneous Iridium Pincer Catalysts for Transfer Dehydrogenation of Alkanes

“…[16] Metalation of the free ligand could only be achieved under an H 2 atmosphere; the resulting iridium hydrido chloride was reduced to the iridium dihydride (1d) and tetrahydride in analogy with the synthesis of 1a and the corresponding tetrahydride. Although we were not successful in obtaining crystals of either (Me 2 N-PCP)IrH 2 or (Me 2 N-PCP)IrH 4 , the reaction of this mixture with CO, in analogy with the reaction of the unsubstituted PCP hydrides, gave clean conversion to (Me 2 N-PCP)Ir(CO) which was crystallographically characterized. [17] For catalytic runs, 1d was generally used as a mixture of (Me 2 N-PCP)IrH 2 and (Me 2 N-PCP)IrH 4 (the iridium PCP and POCOP tetrahydrides readily convert to the dihydrides under catalytic conditions).…”

“…The iridium bis(phosphine) ( t-Bu PCP) complex, 1a, [3] has been investigated by Jensen, Kaska and Goldman, [3] while the bis(phosphinite) ( t-Bu POCOP) complexes, 2a-e, have been studied by Brookhart. [4,5] Other related iridium pincer systems have also shown good activity in alkane dehydrogenation.…”

Reactions of Anilines and Benzamides with a 14-Electron Iridium(I) Bis(phosphinite) Complex: N−H Oxidative Addition versus Lewis Base Coordination

“…Detailed mechanistic studies of this system have complemented the studies of Goldman on 1 and provided interesting contrasts suggesting the phosphinite POCOP system prefers the Ir(I) oxidation state relative to the PCP systems. [29][30][31] In this manuscript we report the reaction of a series of substituted anilines and benzamides with the phosphinite pincer complex 10. In the case of the anilines, either the Ir(III) oxidative addition adduct, the Ir(I) σ-complex, or a mix of these products is formed depending on the nature of the para-substituent.…”