The synthesis, isolation and full characterisation of a Cu(IPr)(OC(H)(CF
)
) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) complex are reported. This new Cu(I) complex is a versatile ...synthon and can activate numerous X-H bonds including C-H, N-H and S-H bonds. Cu(IPr)(OC(H)(CF
)
) was investigated as a pre-catalyst in several catalytic reactions.
An N‐heterocyclic phosphine (NHP) has been investigated as a catalyst for transesterification of a range of commercial polymer samples. NHP catalysed degradation of poly(lactic acid) with methanol ...provides access to methyl lactate (MeLA) in high yields over the course of days. In situ NMR spectroscopy and kinetic analysis has provided quantitative assessment of the catalyst, and a solvent screen is reported. Surprisingly attempts to depolymerise polycaprolactone (PCL) and polyethylene terephthalate (PET) were unsuccessful, and reactions mixed PLA/PCL and PLA/PET provided completely specific degradation of the PLA alone. NMR analysis of the catalyst provides insight into its solution speciation, indicating that the NHP does not remain intact under the transesterification conditions. The enediamine, tBuN(H)CH=CHN(H)tBu, was shown to be formed via methanolysis of the NHP and proved to be a selective catalyst for PLA degradation. Assessment of the depolymerisation activity of by‐products of the NHP methanolysis suggest this is the active catalyst.
Organocatalysis: An N‐heterocyclic phosphine has been assessed for its transesterification activity towards poly(lactic acid). The catalyst produces methyl lactate in good yield in the presence of methanol, and is completely selective for poly(lactic acid) depolymerisation. In situ NMR spectroscopy has given insight into the catalyst speciation and shows the N‐heterocyclic phosphine does not remain intact.
Acyclic Boryl Complexes of Copper(I) Charman, Rex S. C.; Hobson, Josie A.; Jackson, Ross A. ...
Chemistry : a European journal,
January 2, 2024, Letnik:
30, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Reaction of (6‐Dipp)CuOtBu (6‐Dipp=C{NDippCH2}2CH2, Dipp=2,6‐iPr2C6H3) with B2(OMe)4 provided access to (6‐Dipp)CuB(OMe)2 via σ‐bond metathesis. (6‐Dipp)CuB(OMe)2 was characterised by NMR ...spectroscopy and X‐ray crystallography and shown to be a monomeric acyclic boryl of copper. (6‐Dipp)CuB(OMe)2 reacted with ethylene and diphenylacetylene to provide insertion compounds into the Cu‐B bond which were characterised by NMR spectroscopy in both cases and X‐ray crystallography in the latter. It was also competent in the rapid catalytic deoxygenation of CO2 in the presence of excess B2(OMe)4. Alongside π‐insertion, (6‐Dipp)CuB(OMe)2 reacted with LiNMe2 to provide a salt metathesis reaction at boron, giving (6‐Dipp)CuB(OMe)NMe2, a second monomeric acyclic boryl, which also cuproborated diphenylacetylene. Computational interrogation validated these acyclic boryl species to be electronically similar to (6‐Dipp)CuBpin.
A ring‐expanded NHC, 6‐Dipp ((6‐Dipp=C{NDippCH2}2CH2, Dipp=2,6‐iPr2C6H3)), has been shown to support two acyclic boryls. Reaction of (6‐Dipp)CuOtBu with B2(OMe)4 provided access to (6‐Dipp)CuB(OMe)2, the first acyclic boryl of copper, which was shown to react similarly to its cyclic cousins. Remarkably, however, it could also be subjected to salt metathesis to access (6‐Dipp)CuB(OMe)NMe2, the second acyclic boryl of copper.
Liquid assisted ball milling of NHCHBr (NHC = N-heterocyclic carbene) salts with copper(
i
) chloride, and a range of alkali metal complexes was shown to efficiently produce (NHC)CuX (NHC = normal or ...RE-NHC, X = halide, alkoxide, amide, alkyl, aryl; RE-NHC = ring-expanded NHC).
Ball milling of 5-, 6-, and 7-membered N-heterocyclic carbene (NHC) salts, copper(
i
) chloride and alkali metal bases including alkoxides, amides, and organolithium produces to 12 NHC-copper complexes in moderate to good yields.
The structures and bonding in the heavier group 14 element olefin analogues E{CH(SiMe
)
}
and E{N(SiMe
)
}
(E = Ge, Sn, or Pb) and their dissociation into :E{CH(SiMe
)
}
and :E{N(SiMe
)
}
monomers ...were studied computationally using hybrid density functional theory (DFT) at the B3PW91 with basis set superposition error and zero point energy corrections. The structures were reoptimized with the dispersion-corrected B3PW91-D3 method to yield dispersion force effects. The calculations generally reproduced the experimental structural data for the tetraalkyls with a few angular exceptions. For the alkyls, without the dispersion corrections, dissociation energies of -2.3 (Ge), +2.1 (Sn), and -0.6 (Pb) kcal mol
were calculated, indicating that the dimeric E-E bonded structure is favored only for tin. However, when dispersion force effects are included, much higher dissociation energies of 28.7 (Ge), 26.3 (Sn), and 15.2 (Pb) kcal mol
were calculated, indicating that all three E-E bonded dimers are favored. Calculated thermodynamic data at 25 °C and 1 atm for the dissociation of the alkyls yield Δ
values of 9.4 (Ge), 7.1 (Sn), and -1.7 (Pb) kcal mol
, indicating that the dimers of Ge and Sn, but not Pb, are favored. These results are in harmony with experimental data. The dissociation energies for the putative isoelectronic tetraamido-substituted dimers E{N(SiMe
)
}
without dispersion correction are -7.0 (Ge), -7.4 (Sn), and -4.8 (Pb) kcal mol
, showing that the monomers are favored in all cases. Inclusion of the dispersion correction yields the values 3.6 (Ge), 11.7 (Sn), and 11.8 (Pb) kcal mol
, showing that dimerization is favored but less strongly so than in the alkyls. The calculated thermodynamic data for the amido germanium, tin, and lead dissociation yield Δ
values of -12.2, -3.7, and -3.6 kcal mol
at 25 °C and 1 atm, consistent with the observation of monomeric structures. Overall, these data indicate that, in these sterically-encumbered molecules, dispersion force attraction between the ligands is of greater importance than group 14 element-element bonding, and is mainly responsible for the dimerization of the metallanediyls species to give the dimetallenes. In addition, calculations on the non-dissociating distannene Sn{SiMe
Bu
}
show that the attractive dispersion forces are key to its stability.
A range of N-heterocyclic carbene-supported copper diphenylphosphides (NHC = IPr, 6-Dipp, SIMes and 6-Mes) were synthesised. These include the first reports of ring-expanded NHC-copper(
i
) ...phosphides. The compounds were characterised by NMR spectroscopy and X-ray crystallography. Reaction of (6-Dipp)CuPPh
2
with isocyanates, isothiocyanates and carbon disulfide results in the insertion of the heterocumulene into the Cu-P bond. The NHC-copper phosphides were found to be the most selective catalysts yet reported for the hydrophosphination of isocyanates. They provide access to a broad range of phosphinocarboxamides in excellent conversion and good yield.
The first copper(
i
) phosphides supported by ring-expanded N-heterocyclic carbenes have been synthesised and react readily with heterocumulenes. These copper(
i
) phosphides are highly active and selective in the hydrophosphination of isocyanates.
The alkaline‐earth element bis(trimethylsilyl)amides, Ae{N(SiMe3)2}2(thf)2 Ae=Mg, Ca, Sr, are effective precatalysts for boron–nitrogen bond formation through the desilacoupling of amines, RR′NH ...(R=alkyl, aryl; R′=H, alkyl, aryl), and pinBSiMe2Ph. This reactivity also yields a stoichiometric quantity of Me2PhSiH and provides the first example of a catalytic main‐group element–element coupling that is not dependent on the concurrent elimination of H2.
It’s a Si→N: Alkaline‐earth element (Ae) bis(trimethylsilyl)amides, Ae{N(SiMe3)2}2(thf)2 (Ae=Mg, Ca, Sr), are precatalysts for boron–nitrogen bond formation through the desilacoupling of amines, RR′NH (R=alkyl, aryl; R′=H, alkyl, aryl), and pinBSiMe2Ph (pin=pinacolato; see scheme).
The transition metal tetra‐ and trinorbornyl bromide complexes, M(nor)4 (M=Fe, Co, Ni) and Ni(nor)3Br (nor=1‐bicyclo2.2.1hept‐1‐yl) and their homolytic fragmentations were studied computationally ...using hybrid density functional theory (DFT) at the B3PW91 and B3PW91‐D3 dispersion‐corrected levels. Experimental structures were well replicated; the dispersion correction resulted in shortened M−C bond lengths for the stable complexes, and it was found that Fe(nor)4 receives a remarkable 45.9 kcal mol−1 stabilization from the dispersion effects whereas the tetragonalized Co(nor)4 shows stabilization of 38.3 kcal mol−1. Ni(nor)4 was calculated to be highly tetragonalized with long Ni−C bonds, providing a rationale for its current synthetic inaccessibility. Isodesmic exchange evaluation for Fe(nor)4 confirmed that dispersion force attraction between norbornyl substituents is fundamental to the stability of these species.
Gecko‐fabulous: Dispersion‐corrected density functional theory analysis on first row transition metal(IV) complexes of the norbornyl ligand, M(nor)4 (M=Co, Fe, Ni) and Ni(nor)3Br, show that dispersion force attraction between these rigid substituents is fundamental to the stability of these unusually high oxidation state complexes.
Reactions of TEMPO (2,2,6,6‐tetramethyl‐1‐piperidinyloxy) with magnesium hydride species initiate oxidative hydrogen release, which may be elaborated to a catalytic regime within a manifold ...constructed about sequential TEMPO‐mediated redox and MgO/SiH metathesis processes.
Upping the tempo: Reactions of TEMPO (2,2,6,6‐tetramethyl‐1‐piperidinyloxy) with magnesium hydride species initiate catalytic hydrogen release through sequential TEMPO‐mediated redox and MgO/SiH metathesis processes (see scheme). This is the first example of catalytic single‐electron transfer reactivity involving an s‐block metal.
The (IPr)CuO
t
Bu catalysed reduction of 11 aryl and alkyl isocyanates with pinacolborane gave only the boraformamides, pinBN(R)C(O)H, in most cases. Overreduction, which hampers almost all ...isocyanate hydroborations, was restricted to electron poor aryl isocyanates (4-NC-C
6
H
4
NCO, 4-F
3
C-C
6
H
4
NCO, 3-O
2
N-C
6
H
4
NCO). Computational analysis showed stability of
(IPr)CuH
2
, which was proposed to be the catalyst resting state, drives selectivity, suggesting an approach to prevent overreduction in future work. In the case of iPrNCO, formation of this species renders overreduction kinetically inaccessible. For 4-NC-C
6
H
4
NCO, however, the barrier height for the first step of over-reduction is much lower, even relative to
(IPr)CuH
2
, resulting in unselective reduction.
The (IPr)CuO
t
Bu catalysed reduction of 11 aryl and alkyl isocyanates with pinacolborane gave only the boraformamides, pinBN(R)C(O)H, in the case of electron rich isocyanates. A computational study provided insight into this selectivity.
![An air-stable [Cu(NHC)(OR)]...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1359-7345/small "An air-stable [Cu(NHC)(OR)] (R = C(H)(CF 3 ) 2 ) complex for C-H, N-H and S-H bond activation")
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