Group 10 Metal Complexes with Chelating Macrocyclic Dicarbene Ligands Bearing a 2,6-Lutidinyl Bridge: Synthesis, Reactivity, and Catalytic Activity

Palladium­(II) and platinum­(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 palladium­(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

Palladium­(II) and platinum­(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 palladium­(II) complexes in copper- and amine-free Sonogashira reactions

Chelate Palladium(II) Complexes with Saturated <i>N</i>‑Phosphanyl-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>-phosphanyl­tetrahydropyrimid-2-ylidenes isomerize to 2-phosphanyl tetrahydropyrimidines upon heating. The free carbenes are capable of acting as chelating ligands toward palladium­(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 gold­(I) complexes of general formula [Au₂(RIm-Y-ImR)₂]­(PF₆)₂ (R = Me, Cy; Y = (CH₂)_1–4, <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 = (CH₂)₃ exhibit an intense blue emission (λ_max = 450 nm) with a high quantum yield (Φ_em = 0.96). The X-ray crystal structure of this complex is characterized by a rather short intramolecular Au···Au distance (3.272 Ǻ). 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 N‑Phosphorylated 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 N‑Phosphorylated 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>-CNC₆H₄O)₂Y (diNC-1: Y = P­(O)­Ph; diNC-2: Y = <i>o</i>-C­(O)­C₆H₄C­(O); diNC-3: Y = <i>m</i>-C­(O)­C₆H₄C­(O); diNC-4: Y = C­(O)­C₂H₄C­(O); diNC-5: Y = <i>trans</i>-C­(O)­C₂H₂C­(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 platinum­(II) complexes of general formula [PtX₂(diNC)]_1,2 (X = Cl, Me; diNC = diisocyanide ligand) were isolated by simple substitution of 1,5-cyclooctadiene in the starting [PtX₂(COD)] complexes. The structure of the complexes, mononuclear or dinuclear, was confirmed by single-crystal X-ray analysis. A dinuclear complex of formula {(μ-diNC)­[<i>cis</i>-PtCl₂(PPh₃)]₂} 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>-CNC₆H₄O)₂Y (diNC-1: Y = P­(O)­Ph; diNC-2: Y = <i>o</i>-C­(O)­C₆H₄C­(O); diNC-3: Y = <i>m</i>-C­(O)­C₆H₄C­(O); diNC-4: Y = C­(O)­C₂H₄C­(O); diNC-5: Y = <i>trans</i>-C­(O)­C₂H₂C­(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 platinum­(II) complexes of general formula [PtX₂(diNC)]_1,2 (X = Cl, Me; diNC = diisocyanide ligand) were isolated by simple substitution of 1,5-cyclooctadiene in the starting [PtX₂(COD)] complexes. The structure of the complexes, mononuclear or dinuclear, was confirmed by single-crystal X-ray analysis. A dinuclear complex of formula {(μ-diNC)­[<i>cis</i>-PtCl₂(PPh₃)]₂} 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

N‑Phosphorylated Azolylidenes: Novel Ligands for Dinuclear Complexes of Coinage Metals

Dinuclear silver­(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 copper­(I) complexes with N-phosphorylated imidazolylidene ligands display notable catalytic efficiency in nitrene transfer reactions