9 research outputs found
Borole-Derived Spirocyclic Tetraorganoborate
Preparation of a novel conjugated tetraorganoborate is
presented
in a facile two-step procedure. Successful utilization as a halide
abstraction reagent is demonstrated in a metathesis reaction with
the platinumÂ(II) boryl complex [(Cy<sub>3</sub>P)<sub>2</sub>PtÂ(Br)Â(BC<sub>4</sub>Ph<sub>4</sub>)], which was obtained by oxidative addition
of 1-bromo-2,3,4,5-tetraphenylborole to a platinum(0) species. The
novel compounds were investigated by means of spectroscopic and X-ray
diffraction techniques
Borole-Derived Spirocyclic Tetraorganoborate
Preparation of a novel conjugated tetraorganoborate is
presented
in a facile two-step procedure. Successful utilization as a halide
abstraction reagent is demonstrated in a metathesis reaction with
the platinumÂ(II) boryl complex [(Cy<sub>3</sub>P)<sub>2</sub>PtÂ(Br)Â(BC<sub>4</sub>Ph<sub>4</sub>)], which was obtained by oxidative addition
of 1-bromo-2,3,4,5-tetraphenylborole to a platinum(0) species. The
novel compounds were investigated by means of spectroscopic and X-ray
diffraction techniques
Si–H Bond Activation at the Boron Center of Pentaphenylborole
Si–H
bond activation is usually considered a domain of transition-metal
complexes, and only few metal-free systems have proven suitable for
this task. We have now found that
Et<sub>3</sub>SiH readily reacts with pentaphenylborole to afford
1-bora-3-cyclopentenes as the <i>syn</i> and <i>anti</i> addition products. Here, Si–H bond cleavage is accomplished
at a single boron center, a reactivity that is facilitated by a combination
of high electrophilicity and loss of antiaromaticity. The mechanism
of this transformation most likely involves a sequence of adduct formation,
σ-bond metathesis, and conrotatory ring closure, similar to
that observed for H/D exchange between H<sub>2</sub> and silanes mediated
by HBÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> and heterolytic H<sub>2</sub> splitting by boroles, respectively
Si–H Bond Activation at the Boron Center of Pentaphenylborole
Si–H
bond activation is usually considered a domain of transition-metal
complexes, and only few metal-free systems have proven suitable for
this task. We have now found that
Et<sub>3</sub>SiH readily reacts with pentaphenylborole to afford
1-bora-3-cyclopentenes as the <i>syn</i> and <i>anti</i> addition products. Here, Si–H bond cleavage is accomplished
at a single boron center, a reactivity that is facilitated by a combination
of high electrophilicity and loss of antiaromaticity. The mechanism
of this transformation most likely involves a sequence of adduct formation,
σ-bond metathesis, and conrotatory ring closure, similar to
that observed for H/D exchange between H<sub>2</sub> and silanes mediated
by HBÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> and heterolytic H<sub>2</sub> splitting by boroles, respectively
Tin-Bridged <i>ansa</i>-Metallocenes of the Late Transition Metals Cobalt and Nickel: Preparation, Molecular and Electronic Structures, and Redox Chemistry
Using
the flytrap approach, paramagnetic <i>ansa</i>-metallocenes
of the late transition metals cobalt and nickel containing a tetra-<i>tert</i>-butyldistannane bridge have been prepared. The complexes
were identified using a combination of analytical methods (NMR, EPR,
cyclic voltammetry, and X-ray crystallography) and further converted
to their corresponding cations by one-electron oxidation with ferrocenium
hexafluorophosphate. Spectral and structural analyses of the ionic
products are consistent with metal-based oxidations
Tin-Bridged <i>ansa</i>-Metallocenes of the Late Transition Metals Cobalt and Nickel: Preparation, Molecular and Electronic Structures, and Redox Chemistry
Using
the flytrap approach, paramagnetic <i>ansa</i>-metallocenes
of the late transition metals cobalt and nickel containing a tetra-<i>tert</i>-butyldistannane bridge have been prepared. The complexes
were identified using a combination of analytical methods (NMR, EPR,
cyclic voltammetry, and X-ray crystallography) and further converted
to their corresponding cations by one-electron oxidation with ferrocenium
hexafluorophosphate. Spectral and structural analyses of the ionic
products are consistent with metal-based oxidations
1‑Heteroaromatic-Substituted Tetraphenylboroles: π–π Interactions Between Aromatic and Antiaromatic Rings Through a B–C Bond
A series of 2,3,4,5-tetraphenylboroles substituted with
different
aromatic heterocycles (thiophene, furan, pyrrole, and dithiophene)
in the 1-position were synthesized and characterized by means of NMR,
elemental analysis, and X-ray crystallography. In contrast to known
2,3,4,5-tetraphenylboroles, X-ray diffraction revealed a nearly coplanar
arrangement of the aromatic heterocycles and the antiaromatic borole
scaffold as a result of π-conjugation, which could be substantiated
by DFT calculations. Furthermore, the 2,2′-dithiophene-bridged
bisborole (<b>14</b>) exhibits a large bathochromic shift in
the absorption spectrum, demonstrating the exceptional Lewis acidity
of the nonannulated borolyl moiety
1‑Heteroaromatic-Substituted Tetraphenylboroles: π–π Interactions Between Aromatic and Antiaromatic Rings Through a B–C Bond
A series of 2,3,4,5-tetraphenylboroles substituted with
different
aromatic heterocycles (thiophene, furan, pyrrole, and dithiophene)
in the 1-position were synthesized and characterized by means of NMR,
elemental analysis, and X-ray crystallography. In contrast to known
2,3,4,5-tetraphenylboroles, X-ray diffraction revealed a nearly coplanar
arrangement of the aromatic heterocycles and the antiaromatic borole
scaffold as a result of π-conjugation, which could be substantiated
by DFT calculations. Furthermore, the 2,2′-dithiophene-bridged
bisborole (<b>14</b>) exhibits a large bathochromic shift in
the absorption spectrum, demonstrating the exceptional Lewis acidity
of the nonannulated borolyl moiety
Synthesis of Functionalized 1,4-Azaborinines by the Cyclization of Di-<i>tert</i>-butyliminoborane and Alkynes
Di-<i>tert</i>-butyliminoborane is found to be a very
useful synthon for the synthesis of a variety of functionalized 1,4-azaborinines
by the Rh-mediated cyclization of iminoboranes with alkynes. The reactions
proceed via [2 + 2] cycloaddition of iminoboranes and alkynes in the
presence of [RhClÂ(P<i>i</i>Pr<sub>3</sub>)<sub>2</sub>]<sub>2</sub>, which gives a rhodium η<sup>4</sup>-1,2-azaborete
complex that yields 1,4-azaborinines upon reaction with acetylene.
This reaction is compatible with substrates containing more than one
alkynyl unit, cleanly affording compounds containing multiple 1,4-azaborinines.
The substitution of terminal alkynes for acetylene also led to 1,4-azaborinines,
enabling ring substitution at a predetermined location. We report
the first general synthesis of this new methodology, which provides
highly regioselective access to valuable 1,4-azaborinines in moderate
yields. A mechanistic rationale for this reaction is supported by
DFT calculations, which show the observed regioselectivity to arise
from steric effects in the B–C bond coupling en route to the
rhodium η<sup>4</sup>-1,2-azaborete complex and the selective
oxidative cleavage of the B–N bond of the 1,2-azaborete ligand
in its subsequent reaction with acetylene