Carbon nanobelts are molecules of
high fundamental and technological
interest due to their structural similarity to carbon nanotubes, of
which they are molecular cutouts. Despite this attention, synthetic
accessibility is a major obstacle, such that the few known strategies
offer limited structural diversity, functionality, and scalability.
To address this bottleneck, we have developed a new strategy that
utilizes highly fused monomer units constructed via a site-selective
[2 + 2 + 2] cycloaddition and a high-yielding zirconocene-mediated
macrocyclization to achieve the synthesis of a new carbon nanobelt
on large scale with the introduction of functional handles in the
penultimate step. This nanobelt represents a diagonal cross section
of an armchair carbon nanotube and consequently has a longitudinally
extended structure with an aspect ratio of 1.6, the highest of any
reported nanobelt. This elongated structure promotes solid-state packing
into aligned columns that mimic the parent carbon nanotube and facilitates
unprecedented host–guest chemistry with oligo-arylene guests
in nonpolar solvents.
High-valent Ru V -oxo intermediates have long been proposed in catalytic oxidation chemistry, but investigations into their electronic and chemical properties have been limited due to their reactive nature and rarity. The incorporation of Ru into the [Co 3 O 4 ] subcluster via the singlestep assembly reaction of Co II (OAc) 2 (H 2 O) 4 (OAc = acetate), perruthenate (RuO 4 − ), and pyridine (py) yielded an unprecedented Ru(O)Co 3 (μ 3 -O) 4 (OAc) 4 (py) 3 cubane featuring an isolable, yet reactive, Ru Voxo moiety. EPR, ENDOR, and DFT studies reveal a valence-localized [Ru V (S = 1/2)Co III 3 (S = 0)O 4 ] configuration and non-negligible covalency in the cubane core. Significant oxyl radical character in the Ru V -oxo unit is experimentally demonstrated by radical coupling reactions between the oxo cubane and both 2,4,6-tri-tert-butylphenoxyl and trityl radicals. The oxo cubane oxidizes organic substrates and, notably, reacts with water to form an isolable μ-oxo bis-cubane complex [(py) 3 (OAc) 4 Co 3 (μ 3 -O) 4 Ru]-O-[RuCo 3 (μ 3 -O) 4 (OAc) 4 (py) 3 ]. Redox activity of the Ru Voxo fragment is easily tuned by the electron-donating ability of the distal pyridyl ligand set at the Co sites demonstrating strong electronic communication throughout the entire cubane cluster. Natural bond orbital calculations reveal cooperative orbital interactions of the [Co 3 O 4 ] unit in supporting the Ru V -oxo moiety via a strong π-electron donation.
Expanded helicenes are large, structurally
flexible π-frameworks
that can be viewed as building blocks for more complex chiral nanocarbons.
Here we report a gram-scale synthesis of an alkyne-functionalized
expanded [11]helicene and its single-step transformation into two
structurally and functionally distinct types of macrocyclic derivatives:
(1) a figure-eight dimer via alkyne metathesis (also gram scale) and
(2) two arylene-bridged expanded helicenes via Zr-mediated, formal
[2+2+n] cycloadditions. The phenylene-bridged helicene
displays a substantially higher enantiomerization barrier (22.1 kcal/mol)
than its helicene precursor (<11.9 kcal/mol), which makes this
a promising strategy to access configurationally stable expanded helicenes.
In contrast, the topologically distinct figure-eight retains the configurational
lability of the helicene precursor. Despite its lability in solution,
this compound forms homochiral single crystals. Here, the configuration
is stabilized by an intricate network of two distinct yet interconnected
helical superstructures. The enantiomerization mechanisms for all
new compounds were probed using density functional theory, providing
insight into the flexibility of the figure-eight and guidance for
future synthetic modifications in pursuit of non-racemic macrocycles.
Copper boryl species have been widely invoked as reactive intermediates in Cu-catalysed C−H borylation reactions, but their isolation and study have been challenging. Use of the robust dinucleating ligand DPFN...
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