Dehydrogenation of Alcohols by Bis(phosphinite) Benzene Based and Bis(phosphine) Ruthenocene Based Iridium Pincer Complexes

Abstract

Dehydrogenation of alcohols by three iridium pincer complexes, IrH(Cl)[2,6-( t Bu 2 PO) 2 C 6 H 3 ] (1), {IrH-(acetone)[2,6-( t Bu 2 PO) 2 C 6 H 3 ]}{BF 4 } (2), and IrH(Cl)[{2,5-( t Bu 2 PCH 2 ) 2 C 5 H 2 }Ru(C 5 H 5 )] ( 3), is reported, in both the presence and the absence of a sacrificial hydrogen acceptor. Dehydrogenation of secondary alcohols proceeds in a catalytic mode with turnover numbers up to 3420 (85% conversion) for acceptorless dehydrogenation of 1-phenylethanol. Primary alcohols are readily decarbonylated even at room temperature to give catalytically inactive 16e Ir−CO adducts. The mechanism of this transformation was studied in detail, especially for EtOH; new intermediates were isolated and characterized.

Formation of a C–C double bond from two aliphatic carbons. Multiple C–H activations in an iridium pincer complex

“…Large two-bond 1 H– 13 C couplings of 42.9 Hz and 42.5 Hz for 3- syn and 3- anti , correspondingly, indicate a mutual trans arrangement of the hydride and CO ligands. 9 Therefore, the phenyl group occupies the position opposite to the pincer ligand. A three-bond 1 H– 13 C coupling of 3.3 Hz is consistent with an anti mutual orientation of C(α)–H and Ir–CO in 3- syn , and the smaller coupling of 1.1 Hz implies a syn arrangement for 3- anti , according to the well-known dependence of couplings on the dihedral angle.…”

Pincer‐Type Complexes for Catalytic (De)Hydrogenation and Transfer (De)Hydrogenation Reactions: Recent Progress

“…Alcohol dehydrogenation : In the area of alcohol dehydrogenation, extensive studies have been performed by the groups of Baratta,91 Gelman,92 Milstein,9, 93 Szymczak,11 Koridze,94 Hanson,76 and Jones and Schneider 60. To be more precise, in 2011 Baratta et al.…”

“…In 2013, Koridze and co‐workers tested the iridium POCOP pincer complexes 64 , 76 , and 77 for the dehydrogenation of secondary alcohols (Table 15),94 attaining a TON of up to 3560 at 89 % conversion.…”

Synthesis of Bicyclic Proline Derivatives by the Aza‐Cope–Mannich Reaction: Formal Synthesis of (±)‐Acetylaranotin

“…The formation of 25′ is also thermodynamically favourable, as are the methane decoordination and phosphine recoordination steps. Species related to 25′ , 26 a′ and 27 have recently been characterised in a mechanistic study of alcohol decarbonylation at an iridium pincer complex 25. Importantly, the rate‐limiting step is the H 2 dissociation from 13 H′ , as in the case of methanol, although the subsequent rearrangement of the β‐agostic intermediate via TS′ 23‐24 has a similar, only slightly lower barrier (see the two entries for pathway F with EtOH in Table 3).…”