Calcium Hydride Reduction of Polycyclic Aromatic Hydrocarbons

Wilson, Andrew S. S.; Dinoi, Chiara; Hill, Michael S.; Mahon, Mary F.; Maron, Laurent; Richards, Emma

doi:10.1002/anie.201913895

Cited by 28 publications

(27 citation statements)

References 55 publications

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“…Although an exchange spectroscopy (EXSY) NMR experiment demonstrated that 2 and 2’ are in equilibrium at room temperature, attempts to quantify this process by variable temperature 1 H NMR studies were frustrated by the competitive redistribution to the homoleptic ytterbium complex, [(BDI Dipp ) 2 Yb] 36 , and facile Yb–H/D exchange with the deuterobenzene solvent. In this latter regard, the signal associated with the hydride ligand of 2 was observed to decrease if left in benzene- d 6 for extended periods of time (>6 h), concomitant with the formation of a new signal in the 2 H NMR spectrum centred at 7.92 ppm, which was assigned as the ytterbium deuteride [BDI Dipp YbD] 2 , 2- d 7 , 37 .…”

Section: Resultsmentioning

confidence: 99%

Hydroarylation of olefins catalysed by a dimeric ytterbium(II) alkyl

et al. 2021

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Although the nucleophilic alkylation of aromatics has recently been achieved with a variety of potent main group reagents, all of this reactivity is limited to a stoichiometric regime. We now report that the ytterbium(II) hydride, [BDIDippYbH]2 (BDIDipp = CH[C(CH3)NDipp]2, Dipp = 2,6-diisopropylphenyl), reacts with ethene and propene to provide the ytterbium(II) n-alkyls, [BDIDippYbR]2 (R = Et or Pr), both of which alkylate benzene at room temperature. Density functional theory (DFT) calculations indicate that this latter process operates through the nucleophilic (SN2) displacement of hydride, while the resultant regeneration of [BDIDippYbH]2 facilitates further reaction with ethene or propene and enables the direct catalytic (anti-Markovnikov) hydroarylation of both alkenes with a benzene C-H bond.

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Section: Resultsmentioning

confidence: 99%

Hydroarylation of olefins catalysed by a dimeric ytterbium(II) alkyl

et al. 2021

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“…In a third set of calculations the pathway for benzene hydrogenation with the most active (TRIP) 2 NBaH catalyst has been evaluated (Scheme b). The cycle starts with benzene complexation followed by formation of a Meisenheimer anion which is surprisingly exothermic (Ar3: −3.5 kcal mol −1 ); breaking benzene's aromaticity by formation of the Meisenheimer anion is generally endothermic . Two possible transition states for the reaction with H 2 have been located (Ar5* and Ar6*).…”

Section: Resultsmentioning

confidence: 99%

Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings

et al. 2020

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Two series of bulky alkaline earth (Ae) metal amide complexes have been prepared: Ae[N(TRIP)2]2 (1‐Ae) and Ae[N(TRIP)(DIPP)]2 (2‐Ae) (Ae=Mg, Ca, Sr, Ba; TRIP=SiiPr3, DIPP=2,6‐diisopropylphenyl). While monomeric 1‐Ca was already known, the new complexes have been structurally characterized. Monomers 1‐Ae are highly linear while the monomers 2‐Ae are slightly bent. The bulkier amide complexes 1‐Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1‐Ba can reduce internal alkenes like cyclohexene or 3‐hexene and highly challenging substrates like 1‐Me‐cyclohexene or tetraphenylethylene. It is also active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species, which can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate size but it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has a noticeable influence on the thermodynamics for formation of the (amide)AeH species. Complex 1‐Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts, the substrate scope in hydrogenation catalysis could be extended to challenging multi‐substituted unactivated alkenes and even to arenes among which benzene.

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“…Thec ycle starts with benzene complexation followed by formation of aM eisenheimer anion which is surprisingly exothermic (Ar3: À3.5 kcal mol À1 ); breaking benzenesa romaticity by formation of the Meisenheimer anion is generally endothermic. [5,29,49] Tw opossible transition states for the reaction with H 2 have been located (Ar5* and Ar6*). Thet ransition state for formation of 1,3-cyclohexadiene (Ar5*) is 1.6 kcal mol À1 lower in energy than that for 1,4-cyclohexadiene formation (A6*).…”

Section: Methodsmentioning

confidence: 98%

“…[27] Stock demonstrated that LiN(iPr) 2 or KN(SiMe 3 ) 2 catalyze the reduction of activated PA H 'sl ike anthracene or naphthalene under drastic conditions (25 mol %c atalyst, 200 8 8C, 70 bar H 2 , 18 h). [28] TheH ill group very recently demonstrated the stoichiometric reduction of activated PA H'sw ith Ca hydride complex IV [29] but the catalytic hydrogenation of aromatic rings with Ae metal catalysts has hitherto not been reported.…”

Section: Introductionmentioning

confidence: 99%

Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings

et al. 2020

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Tw oseries of bulkyalkaline earth (Ae) metal amide complexes have been prepared:A e[N(TRIP) 2 ] 2 (1-Ae) and Ae[N(TRIP)(DIPP)] 2 (2-Ae) (Ae = Mg, Ca, Sr,B a; TRIP = SiiPr 3 ,D IPP = 2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized.M onomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene.I ti sa lso active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species,w hich can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate sizeb ut it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has an oticeable influence on the thermodynamics for formation of the (amide)AeH species.C omplex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts,t he substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene. Scheme 4. Energy profiles (DH in kcal mol À1 )for a) the hydrogenation of ethylene by catalysts 1-Ca(orange), 1-Ba (black) and CaN'' 2 (red), and b) benzene hydrogenation by 1-Ba;B3PW91/def2tzvpp including correction for dispersion (GD3BJ) and solvent (PCM = benzene).

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Calcium Hydride Reduction of Polycyclic Aromatic Hydrocarbons

Abstract: A molecular calcium hydride effects the two electron reduction of polyaromatic hydrocarbons, including naphthalene (E0=−3.1 V).

Cited by 28 publications

References 55 publications

Hydroarylation of olefins catalysed by a dimeric ytterbium(II) alkyl

Hydroarylation of olefins catalysed by a dimeric ytterbium(II) alkyl

Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings

Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings

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