Reaction of bis(pinacolato)diboron with (6-Dipp)CuO
t
Bu generates a ring-expanded N-heterocyclic carbene supported copper(
i
) boryl, (6-Dipp)CuBpin. This compound showed remarkable stability and ...was characterised by NMR spectroscopy and X-ray crystallography. (6-Dipp)CuBpin readily dechalcogenated a range of heterocumulenes such as CO
2
, isocyanates and isothiocyanates to yield (6-Dipp)CuXBpin (X = O, S). In the case of CO
2
catalytic reduction to CO is viable in the presence of excess bis(pinacolato)diboron. In contrast, in the case of iso(thio)cyanates, the isocyanide byproduct of dechalcogenation reacted with (6-Dipp)CuBpin to generate a copper(
i
) borylimidinate, (6-Dipp)CuC(&z.dbd;NR)Bpin, which went on to react with heterocumulenes. This off-cycle reactivity gives selective access to a range of novel boron-containing heterocycles bonded to copper, but precludes catalytic reactivity.
A copper(
i
) boryl supported by a ring-expanded N-heterocyclic carbene has been synthesised and its reactivity towards heterocumulenes has been investigated.
Philip Power at 65: an icon of organometallic chemistry Fischer, Roland C; Hill, Michael S; Liptrot, David J
Dalton transactions : an international journal of inorganic chemistry,
04/2018, Letnik:
47, Številka:
16
Journal Article
Recenzirano
Odprti dostop
We are delighted to present this collection of articles to celebrate the work of Philip Power on the occasion of his 65th birthday.
Heavier group 2 (Mg, Ca) bis(trimethylsilyl)amides are catalysts for the formation of unsymmetrical diaminoboranes, (R(2)N)BH(NR'(2)), by dehydrocoupling of amine boranes and protic amines; a process ...which is proposed to occur by a sequential metal-centred elimination-insertion-elimination mechanism.
Frustrated Lewis pairs (FLPs) have evolved from a revolutionary concept to widely applied catalysts. We recently reported the ring-expanded N-heterocyclic carbene supported copper(I) ...boryliminomethanide, (6-Dipp)CuC(=NtBu)Bpin and noted it reacted with heterocumulenes in a fashion reminiscent of FLPs. We thus set out to explore its reactivity with a range of other substrates known to react with FLPs. This was undertaken by a series of synthetic studies using NMR spectroscopy, mass spectrometry, IR spectroscopy, and single crystal X-ray crystallography. (6-Dipp)CuC(=NtBu)Bpin was investigated for its reactivity towards water, hydrogen, and phenylacetylene. Its solution stability was also explored. Upon heating, (6-Dipp)CuC(=NtBu)Bpin decomposed to (6-Dipp)CuCN, which was characterised by SC-XRD and NMR spectroscopy, and pinBtBu. Although no reaction was observed with hydrogen, (6-Dipp)CuC(=NtBu)Bpin reacted with water to form (6-Dipp)CuC(=N(H)tBu)B(OH)pin, which was structurally characterised. In contrast to its FLP-reminiscent heterolytic cleavage reactivity towards water, (6-Dipp)CuC(=NtBu)Bpin acted as a Brønsted base towards phenyl acetylene generating (6-Dipp)CuCCPh, which was characterised by SC-XRD, IR, and NMR spectroscopy, and HC(=NtBu)Bpin
The reaction of diphenyltin dihydride with LiAlH4 gives access to a set of charged tin cages as their lithium salts. Variation in the ratio of reactants provides a perstannabicyclooctane dianion and ...a perstannanorbornane as the di- and monoanions. These compounds can be synthesised selectively by careful stoichiometric control and have been characterised by single crystal X-ray diffractometry, NMR and UV-vis spectroscopy. Computational exploration of the electronic structures of these compounds was undertaken and, in agreement with structural and spectroscopic features, indicated significant σ-delocalisation in the tin skeletons.
Reactions of equimolar quantities of secondary amine boranes, R(2)NH·BH(3), with the homoleptic group 2 alkyl compounds M{CH(SiMe(3))(2)}(2)(THF)(2) (M = Mg, Ca, Sr) provide the alkyl group 2 amido ...borane derivatives M{CH(SiMe(3))(2)}{NR(2)BH(3)}(THF)(2). While the strontium derivatives of reactions with dimethylamine and pyrrolidine borane are stable and isolable compounds, the analogous magnesium and calcium compounds are found to be unstable at room temperature. Studies of the thermolysis of the alkylstrontium derivatives have allowed this instability to be rationalised as a result of β-hydride elimination, the facility of which varies with changing M(2+) charge density, to form the products of M-C insertion of H(2)B=NR(2). Subsequent to this process, alkylaminoboranes, HB(NR(2)){CH(SiMe(3))(2)}, are observed to form through a further suggested β-hydride elimination reaction. This chemistry is also extended to the reaction of the primary amine borane (t)BuNH(2)·BH(3) with Sr{CH(SiMe(3))(2)}(2)(THF)(2). In this case the crystal structure of a heteroleptic species, which may be considered as a tetrameric aggregate of two Sr{CH(SiMe(3))(2)}{(NH(t)Bu)BH(3)}(2) anions and two cationic Sr{(NH(t)Bu)(BH(3))}(THF)(2) components, has been determined. Kinetic studies of the reactions of M{CH(SiMe(3))(2)}(2)(THF)(2) (M = Mg, Ca, Sr) with dimethylamine borane have also been undertaken and describe a complex mechanism in which the barriers to formation of the various intermediate species are a consequence of M(2+) radius and resultant charge density as well as the steric demands of the coordinated amidoborane ligands.
Bicycle race: Structurally complex bis(imidazolidine‐2,4‐dione) molecules may be synthesized with complete atom‐efficiency from simple building blocks by a kinetically controlled magnesium‐mediated ...cascade of intermolecular isocyanate insertion and intramolecular alkyne hydroamination reaction steps.
The reaction of diphenyltin dihydride with LiAlH4 gives access to a set of charged tin cages as their lithium salts. Variation in the ratio of reactants provides a perstannabicyclooctane dianion and ...a perstannanorbornane as the di- and monoanions. These compounds can be synthesised selectively by careful stoichiometric control and have been characterised by single crystal X-ray diffractometry, NMR and UV-vis spectroscopy. Computational exploration of the electronic structures of these compounds was undertaken and, in agreement with structural and spectroscopic features, indicated significant σ-delocalisation in the tin skeletons.
Alkylstrontium secondary amidoboranes are shown to undergo β-hydride elimination and Sr-C insertion reactions; observations which provide support for similar processes in d(0)-catalysed dialkylamine ...borane dehydrocoupling.
Marine invertebrate animals such as sponges, gorgonians, tunicates and bryozoans are sources of biomedicinally relevant natural products, a small but growing number of which are advancing through ...clinical trials. Most metazoan and anthozoan species harbour commensal microorganisms that include prokaryotic bacteria, cyanobacteria (blue-green algae), eukaryotic microalgae, and fungi within host tissues where they reside as extra- and intra-cellular symbionts. In some sponges these associated microbes may constitute as much as 40% of the holobiont volume. There is now abundant evidence to suggest that a significant portion of the bioactive metabolites thought originally to be products of the source animal are often synthesized by their symbiotic microbiota. Several anti-cancer metabolites from marine sponges that have progressed to pre-clinical or clinical-trial phases, such as discodermolide, halichondrin B and bryostatin 1, are thought to be products derived from their microbiotic consortia. Freshwater and marine cyanobacteria are well recognised for producing numerous and structurally diverse bioactive and cytotoxic secondary metabolites suited to drug discovery. Sea sponges often contain dominant taxa-specific populations of cyanobacteria, and it is these phytosymbionts (= photosymbionts) that are considered to be the true biogenic source of a number of pharmacologically active polyketides and nonribosomally synthesized peptides produced within the sponge. Accordingly, new collections can be pre-screened in the field for the presence of phytobionts and, together with metagenomic screening using degenerate PCR primers to identify key polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) genes, afford a biodiscovery rationale based on the therapeutic prospects of phytochemical selection. Additionally, new cloning and biosynthetic expression strategies may provide a sustainable method for the supply of new pharmaceuticals derived from the uncultured phytosymbionts of marine organisms.
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