3 research outputs found
Luminescent P‑Chirogenic Copper Clusters
P-chirogenic
clusters of the cubanes [Cu<sub>4</sub>I<sub>4</sub>L<sub>4</sub>]
(L = chiral phosphine) were prepared from (+)- and (−)-ephedrine
with L = (<i>S</i>)- or (<i>R</i>)-(R)(Ph)(<i>i</i>-Pr)P (with R = CH<sub>3</sub> (seven steps) or C<sub>17</sub>H<sub>35</sub> (10 steps)) with e.e. up to 96%. The X-ray structure
of [Cu<sub>4</sub>I<sub>4</sub>((<i>R</i>)-(CH<sub>3</sub>)(Ph)(<i>i</i>-Pr)P)<sub>4</sub>] confirmed the cubane
structure with average Cu···Cu and Cu···I
distances of 2.954 and 2.696 Å, respectively. The cubane structure
of the corresponding [Cu<sub>4</sub>I<sub>4</sub>((<i>S</i>)-(CH<sub>3</sub>)(Ph)(<i>i</i>-Pr)P)<sub>4</sub>] was
established by the comparison of the X-ray powder diffraction patterns,
and the opposite optical activity of the (<i>S</i>)- and
(<i>R</i>)-ligand-containing clusters was confirmed by circular
dichroism spectroscopy. Small-angle X-ray scattering patterns of one
cluster bearing a C<sub>17</sub>H<sub>35</sub> chain exhibit a weak
signal at 2θ ∼ 2.8° (<i>d</i> ∼
31.6 Å), indicating some molecular ordering in the liquid state.
The emission spectra exhibit two emission bands, both associated with
triplet excited states. These two bands are assigned as follows: the
high energy emission is due to a halide-to-ligand charge transfer,
XLCT, state mixed with LXCT (ligand-to-halide-charge-transfer). The
low energy band is assigned to a cluster-centered excited state. Both
emissions are found to be thermochromic with the relative intensity
changing between 77 and 298 K for the clusters in methylcyclohexane
solution. Several differences are observed in the photophysical parameters,
emission quantum yields and lifetimes for R = CH<sub>3</sub> and C<sub>17</sub>H<sub>35</sub>. The measurements of the polarization along
the emission indicate that the emission is depolarized, consistent
with an approximate tetrahedral geometry of the chromophores
Luminescent P‑Chirogenic Copper Clusters
P-chirogenic
clusters of the cubanes [Cu<sub>4</sub>I<sub>4</sub>L<sub>4</sub>]
(L = chiral phosphine) were prepared from (+)- and (−)-ephedrine
with L = (<i>S</i>)- or (<i>R</i>)-(R)(Ph)(<i>i</i>-Pr)P (with R = CH<sub>3</sub> (seven steps) or C<sub>17</sub>H<sub>35</sub> (10 steps)) with e.e. up to 96%. The X-ray structure
of [Cu<sub>4</sub>I<sub>4</sub>((<i>R</i>)-(CH<sub>3</sub>)(Ph)(<i>i</i>-Pr)P)<sub>4</sub>] confirmed the cubane
structure with average Cu···Cu and Cu···I
distances of 2.954 and 2.696 Å, respectively. The cubane structure
of the corresponding [Cu<sub>4</sub>I<sub>4</sub>((<i>S</i>)-(CH<sub>3</sub>)(Ph)(<i>i</i>-Pr)P)<sub>4</sub>] was
established by the comparison of the X-ray powder diffraction patterns,
and the opposite optical activity of the (<i>S</i>)- and
(<i>R</i>)-ligand-containing clusters was confirmed by circular
dichroism spectroscopy. Small-angle X-ray scattering patterns of one
cluster bearing a C<sub>17</sub>H<sub>35</sub> chain exhibit a weak
signal at 2θ ∼ 2.8° (<i>d</i> ∼
31.6 Å), indicating some molecular ordering in the liquid state.
The emission spectra exhibit two emission bands, both associated with
triplet excited states. These two bands are assigned as follows: the
high energy emission is due to a halide-to-ligand charge transfer,
XLCT, state mixed with LXCT (ligand-to-halide-charge-transfer). The
low energy band is assigned to a cluster-centered excited state. Both
emissions are found to be thermochromic with the relative intensity
changing between 77 and 298 K for the clusters in methylcyclohexane
solution. Several differences are observed in the photophysical parameters,
emission quantum yields and lifetimes for R = CH<sub>3</sub> and C<sub>17</sub>H<sub>35</sub>. The measurements of the polarization along
the emission indicate that the emission is depolarized, consistent
with an approximate tetrahedral geometry of the chromophores
Stereoselective Synthesis of <i>o</i>-Bromo (or Iodo)aryl P-Chirogenic Phosphines Based on Aryne Chemistry
The efficient synthesis of chiral or achiral tertiary
phosphines
bearing an <i>o</i>-bromo (or iodo)aryl substituent is described.
The key step of this synthesis is based on the reaction of a secondary
phosphine borane with the 1,2-dibromo (or diiodo)arene, owing to the
formation in situ of an aryne species in the presence of <i>n</i>-butyllithium. When P-chirogenic secondary phosphine boranes were
used, the corresponding <i>o</i>-halogeno-arylphosphine
boranes were obtained without racemization in moderate to good yields
and with ee up to 99%. The stereochemistry of the reaction, with complete
retention of the configuration at the P atom, has been established
by X-ray structures of P-chirogenic <i>o</i>-halogenophenyl
phosphine borane complexes. The decomplexation of the borane was easily
achieved without racemization using DABCO to obtain the free <i>o</i>-halogeno-arylphosphines in high yields