Silylene and Germylene Intermediates in the Reactions of Silole and Germole Dianions with N,N′‐Di‐tert‐butylethylenediimine

Toulokhonova, Irina S.; Timokhin, Vitaly I.; Bunck, David N.; Guzei, Ilia A.; West, Robert; Müller, Thomas

doi:10.1002/ejic.200800083

Cited by 11 publications

(9 citation statements)

References 29 publications

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“…We first interpreted this to suggest the other resonances in the 31 P NMR ChemCatChem spectrum might reflect the catalytically active species, which comprised a doublet of quartets around 6.3 ppm. Addition of (MeO) 2 P(= O)H to a sample of compound 3 [17] followed by a depolymerisation reaction under standard conditions resulted in a 31 P NMR spectrum containing an equivalent resonance at 6.3 ppm which we thus identify as compound 4, the open-chain partial methanolysis product of 2 (see SI, Figure S40). With these data in hand, we inferred that 4 may be the active species, however addition of an isolated sample of 3 to PLA in the presence of methanol produced rapid depolymerisation at 80 °C.…”

Section: Resultsmentioning

confidence: 98%

“…[14b] Compound 3, N,N'-di-tert-butylethene-1,2-diamine was synthesised via modified literature conditions using methanol. [17] Synthetic Procedures and Characterisation 2-(hydroxy)-1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaphosphole, 2. Potassium hydroxide (829 mg, 14.8 mmol) was dried in vacuo and transferred into a Schlenk flask containing 2-bromo-1,3di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaphosphole (2.75 g, 9.85 mmol) followed by ~40 mL of toluene.…”

Section: Experimental Section General Informationmentioning

confidence: 99%

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N‐Heterocyclic Phosphines as Precatalysts for the Highly Selective Degradation of Poly(lactic acid)

2022

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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.

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Section: Resultsmentioning

confidence: 98%

Section: Experimental Section General Informationmentioning

confidence: 99%

N‐Heterocyclic Phosphines as Precatalysts for the Highly Selective Degradation of Poly(lactic acid)

2022

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“…A proposed mechanism of the reaction includes metalation of N,N 0 -di-tert-butylethylenediimine and the formation of an intermediate silylene or germylene. 58 Based on the crystal structures of PMDTA coordinated lithiosilanes, the bend of aromatic substituents in anionic Group 14 and neutral Group 15 compounds has been explained by means of quantum chemical calculations, which indicate the deformation to be a result of Pauli-repulsion of the electrons in the occupied frontier orbitals. 59 Group 15 donor ligands A phenylalanine lithium salt has been found to be an effective catalyst for asymmetric Michael addition of isobutyraldehyde with b-nitroalkenes to give quaternary carbon-containing nitroalkanes.…”

Section: Group 14 Donor Ligandsmentioning

confidence: 99%

Alkali and alkaline-earth metals

Hill

2009

Annu. Rep. Prog. Chem., Sect. A: Inorg. Chem.

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“…6−8,10−16,19,22−24 In addition, their strong reducing properties dominate their reactivity versus dienes, heterodienes, and aromatic carbonyl compounds. 25,26 Despite these promising initial results, the development of the chemistry of silole and germole dianions has been disappointingly slow. In our opinion, their synthetic potential remained severely underexplored.…”

Section: Introductionmentioning

confidence: 99%

Trialkylsilyl-Substituted Silole and Germole Dianions as Precursors for Unusual Silicon and Germanium Compounds

2020

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Conspectus Group 14 element heteroles are the heavier analogues of cyclopentadienes in which a heavier group 14 element atom replaces the sp3 carbon atom. In particular siloles and, to a somewhat smaller degree, germoles attracted considerable attention since the early 1990s due to their favorable photophysical properties which allowed the construction of OLEDs using group 14 element heteroles as emissive or electron-transport layers. Anions and in particular dianions derived from group 14 element heteroles have been of substantial interest due to the possible occurrence of Hückel aromaticity involving the heavier main group atom. Aromaticity is not the only notable electronic feature of silole and germole dianions; the spatial and energetic alignment of their frontier orbitals is equally remarkable. With a high lying lone pair at the heteroatom, which is orthogonal to a delocalized π-system, their frontier orbital sequence closely resembles that of N-heterocyclic carbene analogues. Despite these intriguing parallels between carbene analogues and silole and germole dianions, disappointingly little is known about their reactivity. The installation of trialkylsilyl substituents in the 2,5-positions of the heterocyclopentadiene ring as in K2[I] has a remarkable effect on the stability of silole and germole dianions and allows us to study their reactivity and to evaluate their synthetic potential in detail. Simple double salt metathesis reactions with different dihalides provided heterofulvenes. These were detected either as intermediates or, in the case of carbon dihalides, isolated in the form of their ylidic isomers II. In other cases, the heterofulvenes were the starting point for complex reaction sequences leading to novel binuclear complexes of titanium and zirconium III or for simple isomerization reactions that lead to bicyclohexene-type tetrylenes (BCH-tetrylenes) IV, a novel class of heavier carbenes. These bicyclic carbene analogues are significantly stabilized by homoconjugation between the electron deficient tetrel atom and the remote CC double bond. Compound IV with E′R2SiR2 and E = Si is a valence isomer of disilabenzene and is a stable derivative of the global minimum of the Si2C4H6 potential energy surface. With group 13 dihalides, as for example with boron dichlorides, topological closely related compounds V were isolated. These Ge(II) complexes of borole dianions are isolobal to half-sandwich complexes of main group elements such as aluminum(I) cyclopentadienide or can be viewed as nido-type clusters. These analogies already open a broad field for future investigations of their reactivity. Trialkylsilyl-substituted heterole dianions I provide a facile synthetic approach to several novel intriguing compound classes with the tetrel element in unusual coordination states. The reactivity and the synthetic potential of these new compounds is however widely unexplored and calls for future systematic studies. Gratifyingly, the periodic table of the elements stills holds a lot of potential for future ...

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Silylene and Germylene Intermediates in the Reactions of Silole and Germole Dianions with N,N′‐Di‐tert‐butylethylenediimine

Cited by 11 publications

References 29 publications

N‐Heterocyclic Phosphines as Precatalysts for the Highly Selective Degradation of Poly(lactic acid)

N‐Heterocyclic Phosphines as Precatalysts for the Highly Selective Degradation of Poly(lactic acid)

Alkali and alkaline-earth metals

Trialkylsilyl-Substituted Silole and Germole Dianions as Precursors for Unusual Silicon and Germanium Compounds

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