Reactions of β-diketiminato magnesium and calcium hydrides with 1 atm of CO result in a reductive coupling process to produce the corresponding derivatives of the cis-ethenediolate dianion. ...Computational (DFT) analysis of this process mediated by Ca, Sr, and Ba highlights a common mechanism and a facility for the reaction that is enhanced by increasing alkaline earth atomic weight. Reaction of CO with PhSiH3 in the presence of the magnesium or calcium hydrides results in catalytic reduction to methylsilane and methylene silyl ether products, respectively. These reactions are proposed to ensue via the interception of initially formed group 2 formyl intermediates, an inference which is confirmed by a DFT analysis of the magnesium-centered reaction. The computational results identify the rate-determining process, requiring traversal of a 33.9 kcal mol–1 barrier, as a Mg–H/C–O σ-bond metathesis reaction, associated with the ultimate cleavage of the C–O bond. The carbonylation reactivity is extended to a variety of magnesium and calcium amides. With primary amido complexes, which for calcium include a derivative of the parent NH2− anion, CO insertion is facile and ensues with subsequent nitrogen-to-carbon migration of hydrogen to yield a variety of dinuclear and, in one case, trinuclear formamidate species. The generation of initial carbenic carbamoyl intermediates is strongly implicated through the isolation of the CO insertion product of a magnesium N-methylanilide derivative. These observations are reinforced by a DFT analysis of the calcium-centered reaction with aniline, which confirms the exothermicity of the formamidate formation (ΔH = −67.7 kcal mol–1). Stoichiometric reduction of the resultant magnesium and calcium formamidates with pinacolborane results in the synthesis of the corresponding N-borylated methylamines. This takes place via a sequence of reactions initiated through the generation of amidatohydridoborate intermediates and a cascade of reactivity that is analogous to that previously reported for the deoxygenative hydroboration of organic isocyanates catalyzed by the same magnesium hydride precatalyst. Although a sequence of amine formylation and deoxygenation may be readily envisaged for the catalytic utilization of CO as a C1 source in the production of methylamines, our observations demonstrate that competitive amine–borane dehydrocoupling is too facile under the conditions of 1 atm of CO employed.
The two-coordinate cationic Ni(I) bis-N-heterocyclic carbene complex Ni(6-Mes)2Br (1) 6-Mes =1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene has been structurally characterized ...and displays a highly linear geometry with a C–Ni–C angle of 179.27(13)°. Density functional theory calculations revealed that the five occupied metal-based orbitals are split in an approximate 2:1:2 pattern. Significant magnetic anisotropy results from this orbital degeneracy, leading to single-ion magnet (SIM) behavior.
A β-diketiminato magnesium alkyl complex is shown to be an effective pre-catalyst for the first reported catalytic hydroboration of organic isonitriles, RNC, with HBpin. The reaction proceeds under ...mild conditions when R = alkyl and provides access to the corresponding 1,2-diborylated amine products.
The site-selective functionalization of an indole template offers exciting possibilities for the derivatization of molecules with useful biological properties. Herein, we report the remote ...C6-selective C–H alkylation of indole derivatives enabled by dual cyclometalation/redox ruthenium catalysis. Remote alkylation was achieved using N-pyrimidinyl indoles with an ancillary ester directing group at the C3 position. This ancillary directing group proved pivotal to reactivity at C6, with yields up to 92% achieved. A one-pot procedure to install this directing group followed by remote C6 functionalization has also been reported; both processes are shown to proceed via ruthenium redox catalysis. Computationally calculated Fukui indices elucidated that the C6 position was the most reactive vacant C–H site toward potential functionalization. When this investigation was coupled with deuterium incorporation studies, a C2-cyclometalation/remote σ-activation pathway was deduced.
An acyclic aluminyl anion Jackson, Ross A; Matthews, Aidan J. R; Vasko, Petra ...
Chemical communications,
04/2023, Letnik:
59, Številka:
35
Journal Article
Recenzirano
Odprti dostop
The potassium aluminyl complex K
2
Al{N(Dipp)SiMe
3
}
2
2
was synthesised
via
reduction of AlI{N(Dipp)SiMe
3
}
2
(Dipp = 2,6-i-Pr
2
C
6
H
3
). This represents the first example of an aluminyl anion ...supported by an acyclic ligand framework. Attempts to yield the same structure with a larger ligand framework, {N(Dipp)Si(i-Pr)
3
}, led to C-H cleavage. K
2
Al{N(Dipp)SiMe
3
}
2
2
behaves as a nucleophilic source of aluminium; reaction with an electrophilic β-diketiminate supported magnesium(
ii
) iodide forms a monomeric, acyclic magnesium aluminyl complex.
The potassium aluminyl, K
2
Al{N(Dipp)SiMe
3
}
2
2
has been synthesised. Reaction with HC{(CH
3
)C(Dipp)N}
2
MgI(OEt
2
) forms HC{(CH
3
)C(Dipp)N}
2
MgAl{N(Dipp)SiMe
3
}
2
, a monomeric, acyclic, magnesium aluminyl complex.
A catalytic meta-selective C-H functionalization of 2-phenylpyridines using a range of tertiary halides is described. The protocol is simple to perform and uses commercially available reagents to ...construct challenging quaternary carbon centres in a regioselective manner. Preliminary studies suggest the C-H functionalization proceeds through a radical process directed via a remote σ-activation.
Organoboranes are some of the most synthetically valuable and widely used intermediates in organic and pharmaceutical chemistry. Their synthesis, however, is limited by the behaviour of common boron ...starting materials as archetypal Lewis acids such that common routes to organoboranes rely on the reactivity of boron as an electrophile. While the realization of convenient sources of nucleophilic boryl anions would open up a wealth of opportunity for the development of new routes to organoboranes, the synthesis of current candidates is generally limited by a need for highly reducing reaction conditions. Here, we report a simple synthesis of a magnesium boryl through the heterolytic activation of the B-B bond of bis(pinacolato)diboron, which is achieved by treatment of an easily generated magnesium diboranate complex with 4-dimethylaminopyridine. The magnesium boryl is shown to act as an unambiguous nucleophile through its reactions with iodomethane, benzophenone and N,N'-di-isopropyl carbodiimide and by density functional theory.
Reaction between a β‐diketiminato magnesium hydride and carbon monoxide results in the isolation of a dimeric cis‐enediolate species through the reductive coupling of two CO molecules. Under ...catalytic conditions with PhSiH3, an observable magnesium formyl species may be intercepted for the mild reductive cleavage of the CO triple bond.
I should COCO: Reaction between a β‐diketiminato magnesium hydride and carbon monoxide results in the isolation of a dimeric cis‐enediolate species through the reductive coupling of two CO molecules. Under catalytic conditions with PhSiH3, an observable magnesium formyl species may be intercepted for the mild reductive cleavage of the CO triple bond.
Reactions of dimeric β-diketiminato (BDI) magnesium and calcium hydrides with (BDI)Mg+Al{OC(CF3)3}4− provide ionic multimetallic hydride derivatives, which have been characterized by ...single-crystal X-ray diffraction analysis. The exclusively magnesium centered species comprises a cation in which two (BDI)Mg+ units are connected by a single μ2-bridging hydride. In contrast, the greater lability of the calcium-containing system is underscored by the isolation of a cyclic heterotrimetallic species in which a CaH2 moiety is coordinated by a molecule of benzene and an aryl substituent of a {(BDI)Mg}2H+ cation. The homometallic dimagnesium species displays a greater facility toward reaction with diphenylacetylene than neutral (BDI)MgH2, although the resultant crystallographically characterized vinyldimagnesium cation equilibrates into a complex mixture of neutral and ionic species in solution. An initial assessment of both systems for the hydrosilylation of 1-hexene and diphenylacetylene evidences an inferior catalytic performance of (BDI)MgH2 in isolation.
Reactions of the seven-membered heterocyclic potassium diamidoalumanyl, K{Al(SiN
Dipp
)}
2
(SiN
Dipp
= {CH
2
SiMe
2
NDipp}
2
; Dipp = 2,6-di-isopropylphenyl), with a variety of Cu(
i
), Ag(
i
) and ...Au(
i
) chloride N-heterocyclic carbene (NHC) adducts are described. The resultant group 11-Al bonded derivatives have been characterised in solution by NMR spectroscopy and, in the case of {SiN
Dipp
}Al-Au(NHC
iPr
) (NHC
iPr
=
N
,
N
′-di-isopropyl-4,5-dimethyl-2-ylidene), by single crystal X-ray diffraction. Although similar reactions of LAgCl and LAuCl, where L is a more basic cyclic alkyl amino carbene (CAAC), generally resulted in reduction of the group 11 cations to the base metals, X-ray analysis of (
Cy
CAAC)AgAl(SiN
Dipp
) (
Cy
CAAC = 2-2,6-bis(1-methylethyl)phenyl-3,3-dimethyl-2-azaspiro4.5dec-1-ylidene) provides the first solid-state authentication of an Ag-Al σ bond. The reactivity of the NHC-supported Cu, Ag and Au alumanyl derivatives was assayed with the isoelectronic unsaturated small molecules,
N
,
N
′-di-isopropylcarbodiimide and CO
2
. While these reactions generally provided products consistent with nucleophilic attack of the group 11 atom at the electrophilic heteroallene carbon centre, treatment of the NHC-supported copper and silver alumanyls with
N
,
N
′-di-isopropylcarbodiimide yielded less symmetric Cu-
C
and Ag-
C
-bonded isomers. In contrast to the previously described copper and silver alumanyl derivatives, (NON)Al(O
2
C)M(P
t
-Bu
3
) (M = Cu or Ag; NON = 4,5-bis(2,6-di-isopropylanilido)-2,7-di-
tert
-butyl-9,9-dimethylxanthene), which were prone to facile CO extrusion and formation of carbonate derivatives, the NHC-supported dioxocarbene species, (NHC
iPr
)M(CO
2
)Al(SiN
Dipp
) (M = Cu, Ag, Au), are all stable at room and moderately elevated temperatures. The stabilising role of the NHC co-ligand was, thus, assessed by preparation of the
t
-Bu
3
P adducted copper-alumanyl, (
t
-Bu
3
P)CuAl(SiN
Dipp
). Treatment of this latter compound, which was also structurally characterised by X-ray analysis, with both
N
,
N
′-di-isopropylcarbodiimide and CO
2
again provided smooth heteroallene insertion and formation of the relevant Cu-
C
-bonded products. Although both compounds were quite stable at room temperature, heating of (
t
-Bu
3
P)Cu(CO
2
)Al(SiN
Dipp
) at 60 °C induced elimination of CO and formation of the analogous carbonate, (
t
-Bu
3
P)Cu(OCO
2
)Al(SiN
Dipp
), which was identified by
13
C and
31
P NMR spectroscopy. Reflective of the more reliable nucleophilic behaviour of the gold centres in these group 11 alumanyls, computational (QTAIM and NBO) analysis highlighted a lower level of covalency of the Al-Au linkage in comparison to the analogous Al-Cu and Al-Ag interactions. Although substitution of the co-ligand significantly perturbs the charge distribution across the Cu-Al bond of LCuAl(SiN
Dipp
) (L = NHC
iPr
or
t
-Bu
3
P), only a negligible difference is observed between the phosphine-coordinated copper systems derived from either the SiN
Dipp
- or (NON)-based alumanyl ligands. Computational mapping of the reaction profiles arising from treatment of the various group 11 alumanyls with
N
,
N
′-di-isopropylcarbodiimide indicates that the observed formation of the Cu-N and Ag-N bound isomers do not provide the thermodynamic reaction outcome. In contrast, examination of the CO
2
-derived reactions, and their potential toward CO extrusion and subsequent carbonate formation, implies that the identity of the co-ligand exerts a greater influence on this aspect of reactivity than the architecture of the diamidoalumanyl anion.
Reactions of the seven-membered cyclic potassium diamidoalumanyl, K{Al(SiN
Dipp
)}
2
(SiN
Dipp
= {CH
2
SiMe
2
NDipp}
2
; Dipp = 2,6-di-isopropylphenyl), with a variety of Cu(
i
), Ag(
i
) and Au(
i
) chloride N-heterocyclic carbene (NHC) adducts are described.
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