Manganese‐Mediated Formic Acid Dehydrogenation Anderson, Nickolas H.; Boncella, James; Tondreau, Aaron M.
Chemistry : a European journal,
August 9, 2019, Letnik:
25, Številka:
45
Journal Article
Recenzirano
Odprti dostop
A robust and rapid manganese formic acid (FA) dehydrogenation catalyst is reported. The manganese is supported by the recently developed, hybrid backbone chelate ligand tBuPNNOP ...(tBuPNNOP=2,6‐(di‐tert‐butylphosphinito)(di‐tert‐butylphosphinamine)pyridine) (1) and the catalyst is readily prepared with MnBrCO5 to form (tBuPNNOP)Mn(CO)2Br (2). Dehydrohalogenation of 2 generated the neutral five coordinate complex (tBuPNNOP)Mn(CO)2 (3). Dehydrogenation of FA by 2 and 3 was found to be highly efficient, exhibiting turnover frequencies (TOFs) exceeding 8500 h−1, rivaling many noble metal systems. The parent chelate, tBuPONOP (tBuPONOP=2,6‐bis(di‐tert‐butylphosphinito)pyridine) or tBuPNNNP (tBuPNNNP=2,6‐bis (di‐tert‐butylphosphinamine)pyridine), coordination complexes of Mn were synthesized, respectively affording (tBuPONOP)Mn(CO)2Br (4) and (tBuPNNNP)Mn(CO)2Br (5). FA dehydrogenation with the hybrid‐ligand supported 2 exhibits superior catalysis to 4 and 5.
Homogenous catalysis: A manganese formic acid dehydrogenation catalyst supported by a hybrid PNP chelate is reported. The pyridine‐based ligand contains an oxygen and an amine linkage to the phosphorous arms of the chelate, and the manganese complex displays heightened catalysis over the analogous complexes of the parent dioxo‐ or diamino‐ligands (see graphic).
Cycloadditions, such as the 4+2 Diels-Alder reaction to form six-membered rings, are among the most powerful and widely used methods in synthetic chemistry. The analogous 2+2 alkene cycloaddition to ...synthesize cyclobutanes is kinetically accessible by photochemical methods, but the substrate scope and functional group tolerance are limited. Here, we report iron-catalyzed intermolecular 2+2 cycloaddition of unactivated alkenes and cross cycloaddition of alkenes and dienes as regio- and stereoselective routes to cyclobutanes. Through rational ligand design, development of this base metal–catalyzed method expands the chemical space accessible from abundant hydrocarbon feedstocks.
Alkene hydrosilylation, the addition of a silicon hydride (Si-H) across a carbon-carbon double bond, is one of the largest-scale industrial applications of homogeneous catalysis and is used in the ...commercial production of numerous consumer goods. For decades, precious metals, principally compounds of platinum and rhodium, have been used as catalysts for this reaction class. Despite their widespread application, limitations such as high and volatile catalyst costs and competing side reactions have persisted. Here, we report that well-characterized molecular iron coordination compounds promote the selective anti-Markovnikov addition of sterically hindered, tertiary silanes to alkenes under mild conditions. These Earth-abundant base-metal catalysts, coordinated by optimized bis(imino) pyridine ligands, show promise for industrial application.
(PNHP)Mn(CO)2 (I) carboxylate complexes (PNHP = HN{CH2CH2(PiPr2)}2) were prepared via 1,2-addition of either formic or oxalic acid to (PNP)Mn(CO)2 (PNP = the deprotonated, amide form of the ...ligand –N{CH2CH2(PiPr2)}2). The structural and spectral properties of these complexes were compared. The manganese formate complex was found to be dimeric in the solid state and monomeric in solution. Half an equivalent of oxalic acid was employed to form the bridging oxalate dimanganese complex. The catalytic competencies of the carboxylate complexes were assessed, and the formate complex was found to decompose formic acid catalytically. Both dehydrogenation and dehydration pathways were active as assessed by the presence of H2, CO2, and H2O. The addition of LiBF4 exhibited a strong inhibitory effect on the catalysis.
A series of U(IV) complexes bearing alkyl and chloride ligands in the trans configuration was synthesized and characterized. Starting with the diastereopure U(IV) trans-dichloride complex meso-( ...tBu2PONO)UCl2(dtbpy) (1, tBu2PONO = 2,6-bis((di-tert-butylphosphino)methanolato)pyridine), four distinct alkyl groups were employed to prepare ( tBu2PONO)U(R)Cl(dtbpy), where R = (trimethylsilyl)methyl (neosilyl), 2a, R = 2,2-dimethyl propyl (neopentyl), 2b, and R = 2-methyl-2-phenyl propyl (neophyl), 2c. Alkylation occurs with specificity but generates a predominant species and a minor species corresponding to anti/syn regioisomers relative to the tBu2P groups of the ligand. For synthesis using R = methyl, the dimethyl complex ( tBu2PONO)U(Me)2(dtbpy), 2d, was prepared; the addition of 1 equiv of MeLi produced a mixture of products. Complexes 2a–2d were characterized using single crystal X-ray diffraction (SC-XRD), UV−vis-nIR, and 1H and 31P NMR spectroscopies.
Phosphinidenes R‐P are convenient P1 building blocks for the synthesis of a plethora of organophosphorus compounds. Thus far, transition‐metal‐complexed phosphinidenes have been used for their ...singlet ground‐state reactivity to promote selective addition and insertion reactions. One disadvantage of this approach is that after transfer of the P1 moiety to the substrate, a challenging demetallation step is required to provide the free phosphine. We report a simple method that enables the Lewis acid promoted transfer of phenylphosphinidene, PhP, from NHC=PPh adducts (NHC=N‐heterocyclic carbene) to various substrates to produce directly uncoordinated phosphorus heterocycles that are difficult to obtain otherwise.
Pass it on: ZnCl2‐promoted phosphinidene transfer reactions of the sterically unencumbered carbene–phosphinidene adduct MeNHC=PPh to various substrates (S) are demonstrated. These unprecedented reactions provided access to new uncomplexed phosphorus heterocycles, which are difficult to obtain otherwise.
Bis(imino)pyridine iron dinitrogen and dialkyl complexes are well-defined precatalysts for the chemo- and regioselective reduction of aldehydes and ketones. Efficient carbonyl hydrosilylation is ...observed at low (0.1−1.0 mol %) catalyst loadings and with 2 equiv of either PhSiH3 or Ph2SiH2, representing one of the most active iron-catalyzed carbonyl reductions reported to date.
(iPrPNHP)Mn(CO)2(OH) (2; iPrPNHP = HN{CH2CH2(PiPr2)}2) was formed from the reversible 1,2-addition of water to (iPrPNP)Mn(CO)2 (1; iPrPNP = the deprotonated, amide form of the ligand, ...–N{CH2CH2(PiPr2)}2). This reversible reaction was probed via variable-temperature NMR experiments, and the energetics of the 1,2-addition/elimination was found to be slightly exothermic (−0.8 kcal/mol). The corresponding manganese hydroxide was found to react with aldehydes, yielding the corresponding manganese carboxylate complexes (iPrPNHP)Mn(CO)2(CO2R), where R = H, methyl, phenyl. While no reaction between 1 and neat benzaldehyde was observed, in the presence of water, conversion to the corresponding manganese-bound benzoate with formation of H2 was observed. The catalytic oxidation of benzaldehyde by water without additives was unsuccessful due to strong product inhibition, with the manganese benzoate formed under a variety of reaction conditions. Upon addition of base, a catalytic cycle for the conversion of aldehyde to carboxylate and hydrogen can be devised.
Related BAP BAP = bis(acyl)phosphide and Acac (Acac = β-diketonate) molecules perform as robust supports for both lanthanide and actinide metals. Here, a molecular bimetallic Eu2+ complex was ...successfully targeted and isolated by employing sodium bis(mesitoyl)phosphide Na(mesBAP) in a salt metathesis with EuI2, producing Eu( mes BAP) 2 (et 2 o) 2 (et2o = metal-coordinated diethyl ether). The corresponding Acac-Eu2+ complex was targeted using mesAcac– (1,3-dimesityl-1,3-propanedione), generating Eu( mes Acac) 2 (et 2 o) 2 . Both complexes were characterized by single-crystal X-ray diffraction, UV–vis, IR, and NMR spectroscopies, and variable-temperature magnetic susceptibility. Eu( mes BAP) 2 (et 2 o) 2 was persistent under anaerobic, anhydrous conditions, whereas the analogous Eu( mes Acac) 2 (et 2 o) 2 showed evidence of decomposition under identical conditions. Variable-temperature magnetic susceptibility and magnetization studies of Eu( mes BAP) 2 (et 2 o) 2 and Eu( mes Acac) 2 (et 2 o) 2 were performed, resulting in similar magnetic exchange coupling values of J ex = −0.018 and −0.023 cm–1 and axial zero-field-splitting D values of −0.38 and −0.51 cm–1, respectively.
A family of cationic, neutral, and anionic bis(imino)pyridine iron alkyl complexes has been prepared, and their electronic and molecular structures have been established by a combination of X-ray ...diffraction, Mössbauer spectroscopy, magnetochemistry, and open-shell density functional theory. For the cationic complexes, (iPrPDI)Fe-RBPh4 (iPrPDI = 2,6-(2,6-iPr2-C6H3NCMe)2C5H3N; R = CH2SiMe3, CH2CMe3, or CH3), which are known single-component ethylene polymerization catalysts, the data establish high spin ferrous compounds (S Fe = 2) with neutral, redox-innocent bis(imino)pyridine chelates. One-electron reduction to the corresponding neutral alkyls, (iPrPDI)Fe(CH2SiMe3) or (iPrPDI)Fe(CH2CMe3), is chelate-based, resulting in a bis(imino)pyridine radical anion (S PDI = 1/2) antiferromagnetically coupled to a high spin ferrous ion (S Fe = 2). The neutral neopentyl derivative was reduced by an additional electron and furnished the corresponding anion, Li(Et2O)3(iPrPDI)Fe(CH2CMe3)N2, with concomitant coordination of dinitrogen. The experimental and computational data establish that this S = 0 compound is best described as a low spin ferrous compound (S Fe = 0) with a closed-shell singlet bis(imino)pyridine dianion (S PDI = 0), demonstrating that the reduction is ligand-based. The change in field strength of the bis(imino)pyridine coupled with the placement of the alkyl ligand into the apical position of the molecule induced a spin state change at the iron center from high to low spin. The relevance of the compounds and their electronic structures to olefin polymerization catalysis is also presented.
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