22770-27-0Relevant articles and documents
η2-Alkene Complexes of [Rh(PONOP-iPr)(L)]+Cations (L = COD, NBD, Ethene). Intramolecular Alkene-Assisted Hydrogenation and Dihydrogen Complex [Rh(PONOP-iPr)(η-H2)]+
Johnson, Alice,Royle, Cameron G.,Brodie, Claire N.,Martínez-Martínez, Antonio J.,Duckett, Simon B.,Weller, Andrew S.
, p. 13903 - 13912 (2021)
Rhodium-alkene complexes of the pincer ligand κ3-C5H3N-2,6-(OPiPr2)2 (PONOP-iPr) have been prepared and structurally characterized: [Rh(PONOP-iPr)(η2-alkene)][BArF4] [alkene = cyclooctadiene (COD), norbornadiene (NBD), ethene; ArF = 3,5-(CF3)2C6H3]. Only one of these, alkene = COD, undergoes a reaction with H2 (1 bar), to form [Rh(PONOP-iPr)(η2-COE)][BArF4] (COE = cyclooctene), while the others show no significant reactivity. This COE complex does not undergo further hydrogenation. This difference in reactivity between COD and the other alkenes is proposed to be due to intramolecular alkene-assisted reductive elimination in the COD complex, in which the η2-bound diene can engage in bonding with its additional alkene unit. H/D exchange experiments on the ethene complex show that reductive elimination from a reversibly formed alkyl hydride intermediate is likely rate-limiting and with a high barrier. The proposed final product of alkene hydrogenation would be the dihydrogen complex [Rh(PONOP-iPr)(η2-H2)][BArF4], which has been independently synthesized and undergoes exchange with free H2 on the NMR time scale, as well as with D2 to form free HD. When the H2 addition to [Rh(PONOP-iPr)(η2-ethene)][BArF4] is interrogated using pH2 at higher pressure (3 bar), this produces the dihydrogen complex as a transient product, for which enhancements in the 1H NMR signal for the bound H2 ligand, as well as that for free H2, are observed. This is a unique example of the partially negative line-shape effect, with the enhanced signals that are observed for the dihydrogen complex being explained by the exchange processes already noted.
Iridium PC(sp3)P Pincer complexes with hemilabile pendant arms: Synthesis, characterization, and catalytic activity
De-Botton, Sophie,Cohen, Shirel,Gelman, Dmitri
, p. 1324 - 1330 (2018)
A series of new PC(sp3)P pincer ligands possessing hemilabile alkoxyl side arms as well as their iridium complexes are reported. All new organometallic compounds were structurally characterized including X-ray analysis. The hemilability of the side arms was probed by reactions with CO, revealing the reversible coordination. The catalytic activity of the new complexes was tested by iridium-catalyzed transfer dehydrogenation of alkanes under mild conditions.
Synthesis of Pincer Iridium Complexes Bearing a Boron Atom and iPr-Substituted Phosphorus Atoms: Application to Catalytic Transfer Dehydrogenation of Alkanes
Tanoue, Keita,Yamashita, Makoto
, p. 4011 - 4017 (2015)
An iPr-substituted PBP-pincer ligand was synthesized and introduced to iridium metal to give iPr-(PBP)Ir(H)Cl and iPr-(PBP)Ir(C2H4) complexes. Both of these complexes were found to be moderately active for the catalytic transfer dehydrogenation of cyclooctane. (Chemical Equation Presented).
Supramolecular photochirogenesis with novel cyclic tetrasaccharide: Enantiodifferentiating photoisomerization of (Z)-cyclooctene with cyclic nigerosylnigerose-based sensitizers
Yang, Cheng,Liang, Wenting,Nishijima, Masaki,Fukuhara, Gaku,Mori, Tadashi,Hiramatsu, Hiroyuki,Dan-Oh, Yasufumi,Tsujimoto, Kazuo,Inoue, Yoshihisa
, p. 921 - 927 (2012)
Isophthalic and terephthalic acid monoesters of cyclic nigerosyl-(1→6) -nigerose (CNN), a cyclic tetrasaccharide composed of four d-glucopyranosyl residues connected by alternating α-1,3- and α-1,6-linkages, were synthesized as novel chiral supramolecular sensitizers for enantiodifferentiating photoisomerization of (Z)-cyclooctene () to planar chiral (E)-isomer (1E). Despite the saucer-shaped shallow cavity of CNN that does not immediately guarantee strong ground-state interactions with, the sensitizer-appended CNNs afforded optically active 1E in such enantiomeric excesses that are much improved than those obtained with an α-cyclodextrin analog and comparable with those obtained with a β-cyclodextrin analog. Interestingly, the enantiomeric excess values obtained were a critical function of temperature and solvent to show an inversion of the product chirality by changing the environmental variants. Nevertheless, all of the differential activation parameters calculated from the temperature-dependent enantiomeric excesses gave an excellent compensatory enthalpy-entropy relationship, indicating an operation of a single enantiodifferentiating mechanism in the present chiral photosensitization with modified CNNs. Chirality 24:921-927, 2012. 2012 Wiley Periodicals, Inc. Copyright
Thermoregulated phase-separable catalysis for rh nanoparticle catalyzed selective hydrogenation of 1,5-cyclooctadiene
Xu, Yicheng,Wang, Yanhua,Zeng, Yan,Song, Ying,Zhao, Jiaqi,Jiang, Jingyang,Jin, Zilin
, p. 1871 - 1876 (2012)
Through the study of the critical solution temperature of ionic liquids [CH3(OCH2CH2)nN+Et 3][CH3SO3-] (ILPEG, n = 12, 16, 22), ILPEG-stabilized Rh nanoparticle catalysts have been found to function as thermoregulated phase-separable catalysts and have been shown to be efficient and recyclable for the selective hydrogenation of 1,5-cyclooctadiene (1,5-COD) to cyclooctene (COE). Under optimized conditions, the conversion of 1,5-COD and selectivity for COE were 99% and 90%, respectively. The Rh catalyst could be recovered by simple phase separation and reused for ten times without loss of activity or selectivity.
Synthesis and coordination chemistry of new asymmetric donor/acceptor pincer ligands, 1,3-C6H4(CH2PtBu(Rf))2 (Rf = CF3, C2F5)
Debnath, Suman,Venegas, Gabriel,Arulsamy, Navamoney,Roddick, Dean M.
, p. 12420 - 12430 (2018)
Syntheses of new asymmetric pincer precursors 1,3-C6H4{CH2P(tBu,X)}2 (tBu,XPCPH; X = Cl, SiMe3, OPh) and a new class of hybrid donor/acceptor pincer ligands 1,3-C6H4{CH2P(tBu,Rf)}2 (tBu,RfPCPH; Rf = CF3, C2F5) are reported. All tBu,XPCPH compounds are obtained as mixtures of meso and rac diastereomers in varying ratios (meso?:?rac ～ 4?:?1 to 3?:?2) which were used without separation. Treatment of Ru(cot)(cod) with tBu,CF3PCPH under 1 atm H2 in acetone at 20 °C produced the hydride solvate (tBu,CF3PCP)Ru(acetone)xH which was not isolated, but could be trapped as stable diene complexes (tBu,CF3PCP)Ru(L)2H (L2 = cod (1), nbd (2)). Catalytic cyclooctane dehydrogenation studies demonstrate that 2 has ～50% the activity of (CF3PCP)Ru(cod)(H), but significantly higher catalyst stability and is able to operate at higher catalyst loading concentrations without deactivation via bimolecular decomposition.
Solvent- and phase-controlled photochirogenesis. Enantiodifferentiating photoisomerization of (Z)-cyclooctene sensitized by cyclic nigerosylnigerose-based nanosponges crosslinked by pyromellitate
Wei, Xueqin,Liang, Wenting,Wu, Wanhua,Yang, Cheng,Trotta, Francesco,Caldera, Fabrizio,Mele, Andrea,Nishimoto, Tomoyuki,Inoue, Yoshihisa
, p. 2905 - 2912 (2015)
Cyclic nigerosylnigerose (CNN), a saucer-shaped cyclic tetrasaccharide with a shallow concave surface, was reacted with pyromellitic dianhydride in 1 : 2 and 1 : 4 ratios to give two CNN-based polymers of different degrees of crosslinking, both of which swelled upon soaking in water, acting as a 'nanosponge' (NS). These NSs evolved several phases from isotropic solution to flowing and rigid gels via suspension by gradually increasing the concentration in water. The CNN-NSs thus prepared effectively mediated the enantiodifferentiating photoisomerization of (Z)-cyclooctene (1Z) to chiral (E)-isomer (1E). The enantiomeric excess (ee) of 1E obtained was a critical function of the solvent composition and the phase evolved at different CNN-NS concentrations in water. In isotropic solution, the enantioselectivity was generally low (-4% to +6% ee) but the chiral sense of 1E was inverted by increasing the methanol content. Interestingly, the product's ee was controlled more dramatically by the phase evolved, as was the case with the cyclodextrin-based nanosponge (CD-NS) reported previously. Thus, the ee of 1E was low in solution and suspension, but suddenly leaped at the phase border of flowing gel and rigid gel to give the highest ee of 22-24%, which are much higher than those obtained with CD-NSs (6-12% ee), revealing the positive roles of the chiral void space formed upon gelation of the crosslinked saccharide polymer.
Subnanoscale size effect of dendrimer-encapsulated Pd clusters on catalytic hydrogenation of olefin
Maeno, Zen,Kibata, Takayuki,Mitsudome, Takato,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
, p. 180 - 181 (2011)
Dendrimer-encapsulated subnano Pd clusters catalyze selective hydrogenation of 1,3-cyclooctadiene to cyclooctene. The catalytic activity increases with the size of the subnano Pd clusters. The activity of the threefold hollow sites of the subnano Pd clust
Catalytic Dehydrogenation of Alkanes by PCP-Pincer Iridium Complexes Using Proton and Electron Acceptors
Shada, Arun Dixith Reddy,Miller, Alexander J. M.,Emge, Thomas J.,Goldman, Alan S.
, p. 3009 - 3016 (2021)
Dehydrogenation to give olefins offers the most broadly applicable route to the chemical transformation of alkanes. Transition-metal-based catalysts can selectively dehydrogenate alkanes using either olefinic sacrificial acceptors or a purge mechanism to remove H2; both of these approaches have significant practical limitations. Here, we report the use of pincer-ligated iridium complexes to achieve alkane dehydrogenation by proton-coupled electron transfer, using pairs of oxidants and bases as proton and electron acceptors. Up to 97% yield was achieved with respect to oxidant and base, and up to 15 catalytic turnovers with respect to iridium, using t-butoxide as base coupled with various oxidants, including oxidants with very low reduction potentials. Mechanistic studies indicate that (pincer)IrH2 complexes react with oxidants and base to give the corresponding cationic (pincer)IrH+ complex, which is subsequently deprotonated by a second equivalent of base; this affords (pincer)Ir which is known to dehydrogenate alkanes and thereby regenerates (pincer)IrH2.
Synthesis and characterization of PBP pincer iridium complexes and their application in alkane transfer dehydrogenation
Shih, Wei-Chun,Ozerov, Oleg V.
, p. 228 - 233 (2017)
This work reports on the synthesis of several new complexes of Ir supported by a diarylboryl/bis(phosphine) PBP pincer ligand. The previously reported complexes (PBP)Ir(Ph)- (Cl) (1) and (PBP)Ir(H)(Cl) (2) were converted to the new complexes (PBP)IrH4 (3) and (PBP)Ir(Ph)(H) (4). Complexes 3 and 4 serve similarly as precatalysts for transfer dehydrogenation of cyclooctane. The turnover numbers achieved were relatively modest but were increased (to 220 at 200 °C) when 1-hexene was used as a sacrificial hydrogen acceptor vs tertbutylethylene. The dicarbonyl complex (PBP)Ir(CO)2 (6) was also synthesized, by the reaction of CO with either 3 or 4. Intermediates (PBPhP)Ir(H)(CO)2 (5) and (PBP)IrH2(CO) (7) were observed in these reactions. Complex 7 could be obtained in pure form by comproportionation of 3 and 6. Solid-state structures of 3 and 6 were determined by X-ray crystallography.
