9 research outputs found
Group 10 Metal Complexes with Chelating Macrocyclic Dicarbene Ligands Bearing a 2,6-Lutidinyl Bridge: Synthesis, Reactivity, and Catalytic Activity
PalladiumÂ(II) and platinumÂ(II) complexes
of the title ligands have
been prepared; the two carbene moieties of the ligand coordinate to
the metal in <i>cis</i> fashion, while the bridging pyridyl
group remains outside the metal coordination sphere but close to the
metal center. In this peculiar situation, the pyridyl group can assist
the oxidation of the metal center to the +IV oxidation state upon
coordination to the metal in the product. Furthermore, the pyridyl
group is found to promote the catalytic role of the palladiumÂ(II)
complexes in copper- and amine-free Sonogashira reactions
Group 10 Metal Complexes with Chelating Macrocyclic Dicarbene Ligands Bearing a 2,6-Lutidinyl Bridge: Synthesis, Reactivity, and Catalytic Activity
PalladiumÂ(II) and platinumÂ(II) complexes
of the title ligands have
been prepared; the two carbene moieties of the ligand coordinate to
the metal in <i>cis</i> fashion, while the bridging pyridyl
group remains outside the metal coordination sphere but close to the
metal center. In this peculiar situation, the pyridyl group can assist
the oxidation of the metal center to the +IV oxidation state upon
coordination to the metal in the product. Furthermore, the pyridyl
group is found to promote the catalytic role of the palladiumÂ(II)
complexes in copper- and amine-free Sonogashira reactions
Chelate Palladium(II) Complexes with Saturated <i>N</i>âPhosphanyl-N-Heterocyclic Carbene Ligands: Synthesis and Catalysis
<i>N</i>-Phosphanyl-N-heterocyclic
carbenes (NHCPs) featuring
a saturated imidazolin-2-ylidene or tetrahydropyrimid-2-ylidene ring
have been synthesized and characterized. The free carbenes exhibit
good stability and can be stored in the solid state for months at
ambient temperature without decomposition. Contrary to imidazoline-based
NHCPs, which decompose by ring opening, <i>N</i>-phosphanylÂtetrahydropyrimid-2-ylidenes
isomerize to 2-phosphanyl tetrahydropyrimidines upon heating. The
free carbenes are capable of acting as chelating ligands toward palladiumÂ(II),
forming very stable mononuclear complexes that have been structurally
characterized. The catalytic potential of the complexes has been preliminarily
assessed in cross-coupling reactions, most notably in the Suzuki coupling
of aryl chlorides, where these complexes display promising activity,
and in the copper- and amine-free Sonogashira coupling of aryl bromides
Blue-Emitting Dinuclear N-heterocyclic Dicarbene Gold(I) Complex Featuring a Nearly Unit Quantum Yield
Dinuclear N-heterocyclic dicarbene goldÂ(I) complexes
of general
formula [Au<sub>2</sub>(RIm-Y-ImR)<sub>2</sub>]Â(PF<sub>6</sub>)<sub>2</sub> (R = Me, Cy; Y = (CH<sub>2</sub>)<sub>1â4</sub>, <i>o</i>-xylylene, <i>m</i>-xylylene) have been synthesized
and screened for their luminescence properties. All the complexes
are weakly emissive in solution whereas in the solid state some of
them show significant luminescence intensities. In particular, crystals
or powders of the complex with R = Me, Y = (CH<sub>2</sub>)<sub>3</sub> exhibit an intense blue emission (λ<sub>max</sub> = 450 nm)
with a high quantum yield (Ί<sub>em</sub> = 0.96). The X-ray
crystal structure of this complex is characterized by a rather short
intramolecular Au···Au distance (3.272 Ă
Ì).
Time dependent density functional theory (TDDFT) calculations have
been used to calculate the UV/vis properties of the ground state as
well as of the first excited state of the complex, the latter featuring
a significantly shorter Au···Au distance
Stable NâPhosphorylated 1,2,4-Triazol-5-ylidenes: Novel Ligands for Metal Complexes
Synthetic routes to novel N-phosphorylated 1,2,4-triazolium
salts
have been developed. Treatment of the specified salts with strong
base produces new stable N-phosphorylated 1,2,4-triazol-5-ylidenes,
which add Se in two stages (first at the carbene carbon and then at
phosphorus) and rearrange to C-phosphorylated triazoles with heating.
The capacity of such N-phosphorylated triazol-5-ylidenes to act as
bidentate ligands toward transition-metal centers has also been demonstrated;
in particular, the formation of two dinuclear silver carbene complexes
is described herein. The structures of one representative carbene
and of one carbene complex were determined by an X-ray study
Stable NâPhosphorylated 1,2,4-Triazol-5-ylidenes: Novel Ligands for Metal Complexes
Synthetic routes to novel N-phosphorylated 1,2,4-triazolium
salts
have been developed. Treatment of the specified salts with strong
base produces new stable N-phosphorylated 1,2,4-triazol-5-ylidenes,
which add Se in two stages (first at the carbene carbon and then at
phosphorus) and rearrange to C-phosphorylated triazoles with heating.
The capacity of such N-phosphorylated triazol-5-ylidenes to act as
bidentate ligands toward transition-metal centers has also been demonstrated;
in particular, the formation of two dinuclear silver carbene complexes
is described herein. The structures of one representative carbene
and of one carbene complex were determined by an X-ray study
Platinum(II) Complexes with Novel Diisocyanide Ligands: Catalysts in Alkyne Hydroarylation
A series of novel diisocyanide ligands
(<i>o</i>-CNC<sub>6</sub>H<sub>4</sub>O)<sub>2</sub>Y (diNC-1:
Y = PÂ(O)ÂPh; diNC-2:
Y = <i>o</i>-CÂ(O)ÂC<sub>6</sub>H<sub>4</sub>CÂ(O); diNC-3:
Y = <i>m</i>-CÂ(O)ÂC<sub>6</sub>H<sub>4</sub>CÂ(O); diNC-4:
Y = CÂ(O)ÂC<sub>2</sub>H<sub>4</sub>CÂ(O); diNC-5: Y = <i>trans</i>-CÂ(O)ÂC<sub>2</sub>H<sub>2</sub>CÂ(O)) was successfully synthesized
by reaction of lithium 2-isocyanophenate (generated in situ from benzoxazole
and <i>n</i>-BuLi) and a diacylic or phosphonic dichloride.
The corresponding platinumÂ(II) complexes of general formula [PtX<sub>2</sub>(diNC)]<sub>1,2</sub> (X = Cl, Me; diNC = diisocyanide ligand)
were isolated by simple substitution of 1,5-cyclooctadiene in the
starting [PtX<sub>2</sub>(COD)] complexes. The structure of the complexes,
mononuclear or dinuclear, was confirmed by single-crystal X-ray analysis.
A dinuclear complex of formula {(ÎŒ-diNC)Â[<i>cis</i>-PtCl<sub>2</sub>(PPh<sub>3</sub>)]<sub>2</sub>} could also be obtained
with the diisocyanide ligand having a rigid fumaryl bridge and consequently
the isocyanide moieties pointing in opposite directions. All the complexes
were employed as catalysts in the hydroarylation of alkynes, showing
generally good activity and selectivity toward the <i>trans</i>-hydroarylation product. With <i>N</i>-methylindole as
aromatic substrate the major product was instead a heterocycle:alkyne
2:1 adduct
Platinum(II) Complexes with Novel Diisocyanide Ligands: Catalysts in Alkyne Hydroarylation
A series of novel diisocyanide ligands
(<i>o</i>-CNC<sub>6</sub>H<sub>4</sub>O)<sub>2</sub>Y (diNC-1:
Y = PÂ(O)ÂPh; diNC-2:
Y = <i>o</i>-CÂ(O)ÂC<sub>6</sub>H<sub>4</sub>CÂ(O); diNC-3:
Y = <i>m</i>-CÂ(O)ÂC<sub>6</sub>H<sub>4</sub>CÂ(O); diNC-4:
Y = CÂ(O)ÂC<sub>2</sub>H<sub>4</sub>CÂ(O); diNC-5: Y = <i>trans</i>-CÂ(O)ÂC<sub>2</sub>H<sub>2</sub>CÂ(O)) was successfully synthesized
by reaction of lithium 2-isocyanophenate (generated in situ from benzoxazole
and <i>n</i>-BuLi) and a diacylic or phosphonic dichloride.
The corresponding platinumÂ(II) complexes of general formula [PtX<sub>2</sub>(diNC)]<sub>1,2</sub> (X = Cl, Me; diNC = diisocyanide ligand)
were isolated by simple substitution of 1,5-cyclooctadiene in the
starting [PtX<sub>2</sub>(COD)] complexes. The structure of the complexes,
mononuclear or dinuclear, was confirmed by single-crystal X-ray analysis.
A dinuclear complex of formula {(ÎŒ-diNC)Â[<i>cis</i>-PtCl<sub>2</sub>(PPh<sub>3</sub>)]<sub>2</sub>} could also be obtained
with the diisocyanide ligand having a rigid fumaryl bridge and consequently
the isocyanide moieties pointing in opposite directions. All the complexes
were employed as catalysts in the hydroarylation of alkynes, showing
generally good activity and selectivity toward the <i>trans</i>-hydroarylation product. With <i>N</i>-methylindole as
aromatic substrate the major product was instead a heterocycle:alkyne
2:1 adduct
NâPhosphorylated Azolylidenes: Novel Ligands for Dinuclear Complexes of Coinage Metals
Dinuclear silverÂ(I) complexes with bridging N-phosphorylated
azolylidene
ligands have been synthesized. Subsequent transfer of the ligands
to other group 11 metal centers (Cu, Au) has been accomplished, highlighting
the usefulness of the silver complexes as an easy to handle, air-
and moisture-stable source of these ligands. Preliminary results indicate
that dinuclear copperÂ(I) complexes with N-phosphorylated imidazolylidene
ligands display notable catalytic efficiency in nitrene transfer reactions