Selective dehydrogenation of alcohols and diols catalyzed by a dihydrido iridium PCP pincer complex

Morales‐Morales, David; Redón, Rocı́o; Wang, Zhaohui; Lee, Do W.; Yung, Cathleen; Magnuson, Kevin; Jensen, Craig M.

doi:10.1139/cjc-79-5-6-823

Cited by 11 publications

(13 citation statements)

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“…The C-O stretching frequency of ( tBu PPP)Ir(CO) in benzene observed in the IR spectrum is 1922 cm -1 . This value is very similar to that reported for ( tBu PCP)Ir(CO) 65 (in n-hexane), 1914 cm -1 , 60 indicating that the iridium centers of these complexes have similar electronic properties. Crystallization of ( tBu PPP)Ir(CO) was successful, and XRD analysis yielded a structure (Figure 3) with a unit cell containing two molecules.…”

Section: Scheme 2 Metalation Of (supporting

confidence: 87%

Reactivity of Iridium Complexes of a Triphosphorus-Pincer Ligand Based on a Secondary Phosphine. Catalytic Alkane Dehydrogenation and the Origin of Extremely High Activity

Gordon

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Emge

et al. 2021

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The selective functionalization of alkanes and alkyl groups is a major goal of chemical catalysis. Toward this end, a bulky triphosphine with a central secondary phosphino group, bis(2 di-t-butyl-phosphinophenyl)phosphine (tBuPHPP), has been synthesized. When complexed to iridium it adopts a meridional (“pincer”) configuration. The secondary phosphino H atom can undergo migration to iridium to give an anionic phosphido-based-pincer (tBuPPP) complex. We describe novel metal-ligand cooperativity of the iridium-phosphido unit. Stoichiometric reactions of the (tBuPPP)Ir complexes reflect a distribution of steric bulk around the iridium center in which the coordination site trans to the phosphido group is quite crowded, one coordination site cis to the phosphido is even more crowded, while the remaining site is particularly open. The (tBuPPP)Ir precursors are the most active catalysts reported to date for dehydrogenation of n-alkanes, by about two orders of magnitude. The electronic properties of the iridium center are very similar to that of well-known analogous (RPCP)Ir catalysts. Accordingly, DFT calculations predict that (tBuPPP)Ir and (tBuPCP)Ir are, intrinsically, comparably active for alkane dehydrogenation. While dehydrogenation by (RPCP)Ir proceeds through an intermediate trans-(PCP)IrH2(alkene), (tBuPPP)Ir follows a pathway proceeding via cis-(PPP)IrH2(alkene), thereby circumventing unfavorable placement of the alkene at the bulky site trans to phosphorus. (tBuPPP)Ir and (tBuPCP)Ir, however, have analogous resting states: square planar (pincer)Ir(alkene). Alkene coordination at the crowded trans site is therefore unavoidable in the resting states. Thus the resting state of the (tBuPPP)Ir catalyst is destabilized by the unusual architecture of the ligand, and this is largely responsible for its unusually high catalytic activity.

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Section: Scheme 2 Metalation Of (supporting

confidence: 87%

Reactivity of Iridium Complexes of a Triphosphorus-Pincer Ligand Based on a Secondary Phosphine. Catalytic Alkane Dehydrogenation and the Origin of Extremely High Activity

Gordon

Lease

Emge

et al. 2021

Preprint

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“…However, the correlation of ν CO and Ir−CO distances is not so straightforward when we compare the data for benzene-based bis(phosphine) pincer complex Ir(CO)[2,6-( t Bu 2 PCH 2 ) 2 C 6 H 3 ] ( 29 ). According to the X-ray diffraction study, for two crystallographic isomers, the Ir−CO distances are 1.873(10) and 1.852(12) Å. Noteably, the values of the P(1)−Ir−P(2) angle for these isomers in 29 (164.510(8)° and 163.080(9)°) are markedly larger than those in complexes 21 (157.91(3)°) and 30 (157.55(3)°).…”

Section: Resultsmentioning

confidence: 95%

“…The X-ray crystal structures of the ferrocene-based complex Ir(CO)[ t - Bu P,C,P Fe ] ( 21 ) and benzene-based bis(phosphinite) complex Ir(CO)[2,6-( t Bu 2 PO) 2 C 6 H 3 ] 4e ( 30 ) were determined in the present study. The complex Ir(CO)[2,6-( t Bu 2 PCH 2 ) 2 C 6 H 3 ] ( 29 ) was characterized earlier by X-ray crystallography …”

Section: Resultsmentioning

confidence: 99%

Highly Active Iridium Catalysts for Alkane Dehydrogenation. Synthesis and Properties of Iridium Bis(phosphine) Pincer Complexes Based on Ferrocene and Ruthenocene

et al. 2006

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Novel bis(phosphine) pincer complexes of iridium based on ferrocene and ruthenocene have been synthesized. The reaction of 1,3-bis((di-tert-butylphosphino)methyl)metallocenes [t-BuP,CH,PM] (M = Fe, 10; M = Ru, 13) with [Ir(COE)2Cl]2 in refluxing toluene leads to the corresponding chloro-hydrido pincer complexes as a mixture of H-endo- (M = Fe, 11; M = Ru, 14) and H-exo-IrH(Cl)[t-BuP,C,PM] (M = Fe, 12; M = Ru, 15) isomers. Treatment of compounds 11, 12 and 14, 15 with NaH in hot cyclooctane generates corresponding dihydrido complexes IrH2[t-BuP,C,PM] (M = Fe, 6; M = Ru, 7). Reactivity of the chelated iridium atom in hydrido-iridium pincer complexes and oxidation centered at the iron atom of ferrocene-based pincer complexes were studied. Complexes H-exo-IrH(Cl)(CO)[t-BuP,C,PFe] (20), Ir(CO)[t-BuP,C,PFe] (21), and Ir(CO)[2,6-(tBu2PO)2C6H3] (30) were characterized by X-ray crystallography. On the basis of νCO values for carbonyl iridium derivatives, electronic characteristics of the corresponding fragments {Ir[t-BuP,C,PM]} n (n = 0, +1) were elucidated. Complexes 6 and 7 reveal unprecedented catalytic activity in cyclooctane dehydrogenation in the presence of tert-butylethylene as a hydrogen acceptor: turnover numbers 3300, 2571, and 1843 were obtained for 6, 7, and the known complex IrH2[2,6-(tBu2PO)2C6H3] (4c), respectively, at 180 °C for 8 h. The high catalytic activity for 6 and 7 and the difference in the catalytic activity of these “isostructural” complexes are discussed in terms of steric and electronic effects.

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“…It appears likely, however, that surface hydroxyl groups, resembling chemisorbed water species, may hydrate olefins to alcohols. These alcohols would be readily dehydrogenated by the iridium catalyst, 34 yielding aldehydes and ketones containing a carbonyl functional group. Preliminary experiments showed that cofeeding propene and small quantities of water over supported pincer-iridium complexes formed acetone.…”

Section: Resultsmentioning

confidence: 99%

Continuous-Flow Alkane Dehydrogenation by Supported Pincer-Ligated Iridium Catalysts at Elevated Temperatures

et al. 2018

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Pincer-ligated iridium complexes of the form [Ir(R4PCP)L] (R4PCP = κ3-C6H3-2,6-(XPR2)2; X = CH2, O; R = tBu, iPr) are efficient homogeneous alkane dehydrogenation catalysts that have been reported to be highly active at temperatures of 240 °C or below. In this work, silica-supported [Ir(C2H4)(p- t Bu2PO- tBu4POCOP)] (1/SiO 2 ) was used to study a model continuous-flow gas-phase acceptorless alkane dehydrogenation system. This particular supported framework is thermally stable at temperatures up to 340 °C, 100 °C above the highest temperature at which analogous homogeneous complexes have been reported to show stable activity, with observed butane dehydrogenation rates of ca. 80 molbutenes molcat. –1 h–1. Solid-state 31P MAS NMR and ATR IR are used to demonstrate that the backbone pincer ligand remains intact and coordinated at 340 °C. The complex is fully converted to [Ir(CO)(p- t Bu2PO- tBu4POCOP)] (3/SiO 2 ) above 300 °C. 3/SiO 2 is observed to be catalytically active at the higher temperatures tested, and reaction rates are comparable to those of 1/SiO 2 . 3/SiO 2 and 1/SiO 2 act as resting states for the active 14-electron fragment, through dissociation of the CO or olefin ligand, respectively. Given that 3/SiO 2 is air resistant at ambient temperature and is structurally stable and catalytically active at elevated temperatures, it is a suitable candidate as a catalyst for the highly endothermic acceptorless dehydrogenation of alkanes.

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Selective dehydrogenation of alcohols and diols catalyzed by a dihydrido iridium PCP pincer complex

Cited by 11 publications

References 0 publications

Reactivity of Iridium Complexes of a Triphosphorus-Pincer Ligand Based on a Secondary Phosphine. Catalytic Alkane Dehydrogenation and the Origin of Extremely High Activity

Reactivity of Iridium Complexes of a Triphosphorus-Pincer Ligand Based on a Secondary Phosphine. Catalytic Alkane Dehydrogenation and the Origin of Extremely High Activity

Highly Active Iridium Catalysts for Alkane Dehydrogenation. Synthesis and Properties of Iridium Bis(phosphine) Pincer Complexes Based on Ferrocene and Ruthenocene

Continuous-Flow Alkane Dehydrogenation by Supported Pincer-Ligated Iridium Catalysts at Elevated Temperatures

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