Early Main Group Metal Catalysis: How Important is the Metal?

Penafiel, Johanne; Maron, Laurent; Harder, Sjoerd

doi:10.1002/anie.201408814

Cited by 57 publications

(43 citation statements)

References 51 publications

(23 reference statements)

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“…9,10 Some key breakthroughs in the eld which highlight the synergistic power of these bimetallic partnerships include Knochel's Turbo Grignard reagents RMgCl$LiCl (R ¼ alkyl) which allow the functionalisation of a wide range of organic molecules via Mg-halogen exchange 2 or Mulvey and O'Hara's template metallation, where mixed Na/Mg macrocyclic bases enable remote di-magnesiation of aromatic molecules. 4,5 Despite the increasing interest that sblock metal catalysis is currently attracting, 9,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] catalytic applications of these bimetallic systems have hardly been researched. 31 Breaking new ground in this area, we recently reported sodium tris(alkyl)magnesiate NaMg(CH 2 SiMe 3 ) 3 32 as an efficient precatalyst for hydroamination of a variety of carbodiimides and isocyanates.…”

Section: Introductionmentioning

confidence: 99%

s-Block cooperative catalysis: alkali metal magnesiate-catalysed cyclisation of alkynols

et al. 2019

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Section: Introductionmentioning

confidence: 99%

s-Block cooperative catalysis: alkali metal magnesiate-catalysed cyclisation of alkynols

et al. 2019

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“…First of all, the only and extremely stable +2 oxidation state which makes impossible for alkaline‐earth complexes the oxidative addition and reductive elimination reactions. The reactivity of these compounds is based solely on the sequence of redox neutral reactions such as σ‐bond metathesis and insertion of a polarized unsaturated substrate into the M–X bond . Another peculiarity of heteroleptic alkaline earth metal complexes is their tendency to undergo Schlenk‐type equilibrium resulted from their electropositivity and high degree of ionicity of M–ligand bonding .…”

Section: Introductionmentioning

confidence: 99%

“…The reactivity of these compounds is based solely on the sequence of redox neutral reactions such as σbond metathesis and insertion of a polarized unsaturated substrate into the M-X bond. [1][2][3]28] Another peculiarity of heteroleptic alkaline earth metal complexes is their tendency to undergo Schlenk-type equilibrium resulted from their electropositivity and high degree of ionicity of M-ligand bonding. [29] This issue together with high electropositivity and polarizability of M 2+ ions [30] puts forward a number of requirements towards the design of ligands intended for use in the synthesis of isolable complexes of these elements.…”

Section: Introductionmentioning

confidence: 99%

Calcium Amido Complexes Coordinated by Tridentate Amidinate Ligands: Synthesis, Structures and Catalytic Activity in Olefin Hydrophosphination and Polymerization of Cyclic Esters

et al. 2019

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The reactions of [(Me 3 Si) 2 N] 2 Ca(thf ) 2 with amidines 2-(Ph 2 P=NPh)C 6 H 4 NHC(tBu)=N(2,6-R 2 C 6 H 3 ) {R = iPr (L 1 H); R = Me (L 2 H)} afford heteroleptic calcium amido complexes (1); R = Me (2)} featuring tridentate coordination of the amidinate ligands. Complexes 1 and 2 proved to be efficient catalysts for intermolecular hydrophosphination of styrene, αmethylstyrene, divinylbenzene and phenylacetylene with Ph 2 PH and PhPH 2 . Compounds 1 and 2 exhibit high catalytic activity in the ring-opening polymerization of ε-caprolactone and enable quantitative conversion of 500 equiv. of monomer in 5 seconds [a] G. A. Razuvaev

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“…Further reaction with H 2 may cause precipitation of insoluble (CaH 2 ) n , but catalyst loss is partly prevented by aggregation to soluble but undefined Ca x Bn y H z species. Despite a lack of d orbitals, alkene activation proceeds through a weak electrostatic calciumalkene interaction, recently shown to be of importance in calcium catalysis 18 . The benzylic calcium intermediate formed after insertion may, after successive styrene insertions, form polystyrene 19 , but high H 2 pressure (20-100 bar) can prevent this side reaction by promoting σ-bond metathesis.…”

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Imine hydrogenation with simple alkaline earth metal catalysts

et al. 2018

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W ith molecular hydrogen being one of the cleanest reducing agents, catalytic hydrogenation using the more noble transition metals is among the most studied of all chemical processes 1 . Increasing social pressure towards a sustainable society, however, dictates replacement of costly, and often harmful, precious metals by more abundant first-row transition metals or even biocompatible redox inactive main group metals [2][3][4][5][6] . The alkaline earth metal calcium does not possess partially filled d orbitals for substrate activation, but has recently shown catalytic activities in the hydrogenation of C= C double bonds with molecular H 2 (ref. 7 ). Although restricted to conjugated C= C bonds, this example strikingly broke the dogma that transition metals are needed for alkene hydrogenation. This was followed by the development of metal-free frustrated Lewis pair (FLP) catalysts [8][9][10][11] and, most recently, cationic calcium hydride catalysts that are also able to hydrogenate unactivated alkenes 12 . Figure 1a shows a working hypothesis for styrene hydrogenation with a dibenzylcalcium catalyst (CaBn 2 ) 7 . The first step is the generation of a calcium hydride species, for which ample precedence exists [13][14][15][16][17] . Further reaction with H 2 may cause precipitation of insoluble (CaH 2 ) n , but catalyst loss is partly prevented by aggregation to soluble but undefined Ca x Bn y H z species. Despite a lack of d orbitals, alkene activation proceeds through a weak electrostatic calciumalkene interaction, recently shown to be of importance in calcium catalysis 18 . The benzylic calcium intermediate formed after insertion may, after successive styrene insertions, form polystyrene 19 , but high H 2 pressure (20-100 bar) can prevent this side reaction by promoting σ-bond metathesis. The latter step in the cycle is, like the initiation reaction, formally a deprotonation of H 2 by a resonance-stabilized benzylic carbanion. Considering the high pK a of H 2 (≈ 49) 20 , this reaction seemed questionable. Stoichiometric conversions of model systems, however, underscored the feasibility of this pathway 7 . Independent theoretical calculations illustrate that the final σ-bond metathesis step is indeed highly endergonic: Gibbs free energy of activation Δ G ‡ (60 °C, 20 bar) = 25.7 kcal mol −1 (ref. 21 ).As the highly atom-efficient catalytic reduction of imines by H 2 received much less attention than alkene or ketone hydrogenation [22][23][24] , it remained an important question whether calcium-catalysed hydrogenation can be extended to imine reduction. Current stateof-the-art imine hydrogenation catalysts can be divided into four categories that vary in terms of substrate activation and nucleophilic power ( Fig. 2a-d). Figure 2a shows organometallic metal hydrides that rely on hydride nucleophilicity. Apart from few early transition metal catalysts (Ti 25 , lanthanides 26 ), these are generally based on late transition metals (Rh, Ir) 22 . The aluminium hydride compound (iso-butyl) 2 AlH is an odd example of a ...

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Early Main Group Metal Catalysis: How Important is the Metal?

Cited by 57 publications

References 51 publications

s-Block cooperative catalysis: alkali metal magnesiate-catalysed cyclisation of alkynols

s-Block cooperative catalysis: alkali metal magnesiate-catalysed cyclisation of alkynols

Calcium Amido Complexes Coordinated by Tridentate Amidinate Ligands: Synthesis, Structures and Catalytic Activity in Olefin Hydrophosphination and Polymerization of Cyclic Esters

Imine hydrogenation with simple alkaline earth metal catalysts

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