Well-shuffled: An unexpected substituent distribution reaction via alkyldiarylsilylium ions leads to a distribution of substituents. Starting from alkyldiaryl silanes, this reaction provides a facile synthetic approach to sterically highly hindered triarylsilylium ions. These silylium ions can be applied in dihydrogen activation reactions.
Titanaaziridines or η(2)-imine titanium complexes are considered key intermediates of the titanium-catalyzed hydroaminoalkylation of alkenes. Herein, we present an efficient synthetic route to this class of compounds, starting from N-methylanilines and a bis(η(5):η(1)-pentafulvene)titanium complex. Consecutive reactions on the η(2)-methyleneaniline complexes, characterized for the first time, prove a high chemical versatility. In particular, hydroaminoalkylation products were found in reactions of the three-membered titanacycles with alkenes. For the first time, all the intermediates of the hydroaminoalkylation of alkenes were isolated and characterized.
The first tetrasilabuta‐1,3‐diene (2) was obtained as reddish‐brown crystals simply and unexpectedly by lithiation of disilene 1, partial bromination with an aryl bromide, and intermolecular cleavage of lithium bromide. The conjugation between the two SiSi double bonds of 2 was demonstrated by electron spectroscopy and X‐ray crystallography. Mes = 2,4,6‐Me3C6H2, Tip = 2,4,6‐iPr3C6H2.
The
reaction of diarylalkylsilanes and -germanes with trityl cation
in the presence of a weakly coordinating anion to give the corresponding
triarylsilylium or -germylium ions was investigated. This reaction
provides a facile access to a larger range of these sterically highly
hindered Lewis acids. The factors that promote the substituent exchange
were studied, and significant effects of the substituent, of the solvent,
and of the group 14 element were revealed. A combined solid-state
XRD and NMR investigation of the tris(pentamethylphenyl) silylium
borate [(Me5C6)3Si]2[B12Cl12] disclosed the trigonal planar coordination
environment of the silicon atom in this silylium ion. NMR investigations
indicate for 2,4,6-triisopropylphenyl-substituted silylium and germylium
ions the onset of C–H···E+ three-center
interactions (E = Si, Ge) between the distant CH bond of the isopropyl
group and the positively charged group 14 element atom.
This paper reports on the potential of titanium compounds as building blocks for supramolecular polygons. Self-assembly reactions of low-valent titanocene units and N-heterocyclic bridging ligands lead to novel titanium-based supramolecular squares. Pyrazine (3), 4,4'-bipyridine (4), and tetrazine (5) were used as bridging ligands, and the acetylene complexes [Cp2Ti{eta2-C2(SiMe3)2}] (1) and [(tBuCp)2Ti{eta2-C2(SiMe3)2}] (2) as sources of titanocene fragments. Molecular rectangles can be synthesized by stepwise reduction of the titanocene dichlorides [Cp(2)TiCl2] and [(tBuCp)2TiCl2] and consecutive coordination of two different bridging ligands. The resulting complexes are the first examples of molecular rectangles containing bent metallocene corner units. Single-crystal X-ray analyses of the tetranuclear compounds revealed the geometric properties of the molecular polygons in the solid state. Comparison of bond lengths and angles in coordinated and free ligands reveals the reduced state of the bridging ligand in the low-valent titanium compounds. The syntheses and properties of these novel, highly air- and moisture-sensitive compounds are discussed.
As you like it: The choice of solvents and substituents at the silicon atom determine what product is formed from carbon dioxide after electrophilic activation by silyl cations (see scheme). Benzoic acid as well as the C‐1 building blocks formic acid and methanol are on the product tableau.
The reaction of bis(cyclooctadiene)nickel with
Ga4[C(SiMe3)3]4 (1) yields a coordination compound
analogous to [Ni(CO)4], [Ni{Ga−C(SiMe3)3}4], which
shows a tetrahedral coordination of the central nickel
atom, linear Ni−Ga−C groups, and very short Ni−Ga
distances. Quantum-chemical DFT calculations on the
model complexes [Ni(EMe)4] (E = B, Al, Ga, In, Tl) verify
strong π back-donation of electron density from nickel
to the empty p(π) orbitals of the group 13 elements, which
is more effective than in tetracarbonylnickel itself.
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