Organocalcium-mediated nucleophilic alkylation of benzene Wilson, Andrew S. S.; Hill, Michael S.; Mahon, Mary F. ...
Science (American Association for the Advancement of Science),
12/2017, Letnik:
358, Številka:
6367
Journal Article
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The electrophilic aromatic substitution of a C–H bond of benzene is one of the archetypal transformations of organic chemistry. In contrast, the electron-rich π-system of benzene is highly resistant ...to reactions with electron-rich and negatively charged organic nucleophiles. Here, we report that this previously insurmountable electronic repulsion may be overcome through the use of sufficiently potent organocalcium nucleophiles. Calcium n-alkyl derivatives—synthesized by reaction of ethene, but-1-ene, and hex-1-ene with a dimeric calcium hydride—react with protio and deutero benzene at 60°C through nucleophilic substitution of an aromatic C–D/H bond. These reactions produce the n-alkyl benzenes with regeneration of the calcium hydride. Density functional theory calculations implicate an unstabilized Meisenheimer complex in the C–H activation transition state.
β‐Diketiminato (BDI) calcium alkyl derivatives undergo hydrogenolysis with H2 to regenerate (BDI)CaH2, allowing the catalytic hydrogenation of a wide range of 1‐alkenes and norbornene under very mild ...conditions (2 bar H2, 298 K). The reactions are deduced to take place with the retention of the dimeric structures of the calcium hydrido‐alkyl and alkyl intermediates via a well‐defined sequence of Ca−H/C=C insertion and Ca−C hydrogenation events. This latter deduction is strongly supported by DFT calculations (B3PW91) performed on the 1‐hexene/H2 system, which also indicates that the hydrogenation transition states display features which discriminate them from a classical σ‐bond metathesis mechanism. In particular, NBO analysis identifies a strong second order interaction between the filled α‐methylene sp3 orbital of the n‐hexyl chain and the σ* orbital of the H2 molecule, signifying that the H−H bond is broken by what is effectively the nucleophilic displacement of hydride by the organic substituent.
Hydrogen gets nuked: Hydrogenation of dimeric β‐diketiminato calcium alkyls occurs by nucleophilic attack and heterolysis of the H−H bond.
A Stable Calcium Alumanyl Schwamm, Ryan J.; Coles, Martyn P.; Hill, Michael S. ...
Angewandte Chemie International Edition,
March 2, 2020, Letnik:
59, Številka:
10
Journal Article
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A seven‐membered N,N′‐heterocyclic potassium alumanyl nucleophile is introduced and utilised in the metathetical synthesis of Mg−Al and Ca−Al bonded derivatives. Both species have been characterised ...by experimental and theoretical means, allowing a rationalisation of the greater reactivity of the heavier group 2 species implied by an initial assay of their reactivity.
AlCan Wrap: The Reaction of a seven‐membered cyclic alumanyl anion with a β‐diketiminato calcium tetraphenylborate provides facile access to a stable, but highly reactive, calcium alumanyl.
Playing tag with MOFs: Zinc metal–organic frameworks with pendant aldehyde and methoxy groups are prepared. The aldehyde‐tagged MOF takes up 2,4‐dinitrophenylhydrazine, reacting to form a ...hydrazone‐functionalized MOF which is crystallographically characterized. Use of both aldehyde‐ and methoxy‐functionalized dicarboxylates leads to MOFs containing both ligands, of which the aldehyde groups can be selectively reacted.
Beryllium-centred C-H activation of benzene Pearce, Kyle G; Hill, Michael S; Mahon, Mary F
Chemical communications (Cambridge, England),
02/2023, Letnik:
59, Številka:
11
Journal Article
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Reaction of BeCl
2
with the dilithium diamide, {SiN
Dipp
}Li
2
({SiN
Dipp
} = {CH
2
SiMe
2
NDipp}
2
), provides the dimeric chloroberyllate, {SiN
Dipp
BeCl}Li
2
, en route to the 2-coordinate ...beryllium amide, SiN
Dipp
Be. Lithium or sodium reduction of SiN
Dipp
Be in benzene, provides the relevant organoberyllate products, {SiN
Dipp
BePh}M (M = Li or Na),
via
the presumed intermediacy of transient Be(
i
) radicals.
Lithium or sodium reduction of SiN
Dipp
Be in benzene, provides the organoberyllate products, {SiN
Dipp
BePh}M (M = Li or Na).
The para‐selective C−H alkylation of aniline derivatives furnished with a pyrimidine auxiliary is herein reported. This reaction is proposed to take place via an N−H‐activated cyclometalate formed in ...situ. Experimental and DFT mechanistic studies elucidate a dual role of the ruthenium catalyst. Here the ruthenium catalyst can undergo cyclometalation by N−H metalation (as opposed to C−H metalation in meta‐selective processes) and form a redox active ruthenium species, to enable site‐selective radical addition at the para position.
Para‐normal activity: The para‐selective C−H alkylation of aniline derivatives is reported. The methodology is proposed to proceed by a dual role ruthenium process: cycloruthenation at N−H and redox radical generation. This strategy leads to para‐selective alkylations using pyrimidine and quinazoline auxiliaries.
Ambiphilic Al−Cu Bonding Liu, Han‐Ying; Schwamm, Ryan J.; Hill, Michael S. ...
Angewandte Chemie (International ed.),
June 21, 2021, Letnik:
60, Številka:
26
Journal Article
Recenzirano
Odprti dostop
Copper‐alumanyl complexes, LCu‐Al(SiNDipp), where L=carbene=NHCiPr (N,N′‐diisopropyl‐4,5‐dimethyl‐2‐ylidene) and Me2CAAC (1‐(2,6‐diisopropylphenyl)‐3,3,5,5‐tetramethyl‐pyrrolidin‐2‐ylidene) and ...featuring unsupported Al−Cu bonds, have been prepared. Divergent reactivity observed with carbodiimides and CO2 implies an ambiphilicity in the Cu–Al interaction that is dependent on the identity of the carbene co‐ligand.
Cu(ts) both ways: Carbene‐supported copper‐alumanyl complexes, LCu‐Al(SiNDipp), display divergent reactivity with carbodiimides and CO2, implying an ambiphilicity in the Cu–Al interaction that is dependent on the identity of the carbene co‐ligand.
A selective catalytic meta sulfonation of 2-phenylpyridines was found to occur in the presence of (arene)ruthenium(II) complexes upon reaction with sulfonyl chlorides. The 2-pyridyl group facilitates ...the formation of a stable Ru–Caryl σ bond that induces a strong para-directing effect. Electrophilic aromatic substitution proceeds with the sulfonyl chloride to furnish a sulfone at the position meta to the chelating group. This new catalytic process offers access to atypical regioselectivity for reactions involving chelation-assisted cyclometalation.
A β‐diketiminato magnesium alkyl complex, CH{C(Me)NDipp}2}MgnBu (Dipp=2,6‐iPr2C6H3), was shown to be an effective pre‐catalyst for the first reported catalytic hydroboration of alkyl‐ and ...aryl‐substituted carbodiimides with pinacol borane (HBpin). The catalytic reactions proceed under mild conditions to afford the corresponding N‐borylated formamidine compounds in good yields. The reactions were observed to proceed through the intermediacy of magnesium amidinate and formamidinatoborate intermediates and an example of one of these latter species has been structurally characterised by an X‐ray diffraction analysis. Crucially, no formation of the N‐boryl formamidine products was observed in the absence of additional equivalents of the carbodiimide and HBpin substrates. This observation, supported by the evolution of a sigmoidal kinetic profile for the hydroboration of dicyclohexylcarbodiimide, has been rationalised as the consequence of an allosteric effect of the pinacol borane and carbodiimide on the magnesium formamidinatoborate intermediates.
The first carbodiimide hydroboration reactions, which proceed efficiently with pinacol borane under magnesium catalysis and under mild reaction conditions, are described. Reduction was observed to occur only once and with complete selectivity to give the borylated formamidine (see scheme) and to proceed through the intermediacy of magnesium formamidinatoborate intermediates.
Reported is the reaction of a series of iron(II) bisphosphine complexes with PH3 in the presence of NaBArF 4 where BArF 4 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate. The iron(II) ...bisphosphine reagents bear two chlorides or a hydride and a chloride motif. We have isolated six different cationic terminal-bound PH3 complexes and undertaken rigorous characterization by NMR spectroscopy, single crystal X-ray diffraction, and mass spectrometry, where the PH3 often remains intact during the ionization process. Unusual bis- and tris-PH3 complexes are among the compounds isolated. Changing the monophosphine from PH3 to PMe3 results in the formation of an unusual Fe7 cluster, but with no PMe3 being ligated. Finally, by using an iron(0) source, we have provided a rare example of a terminally bound iron–PH2 complex.
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