Carbene-Dichlorosilylene Stabilized Phosphinidenes Exhibiting Strong Intramolecular Charge Transfer Transition

The unstable species dichlorosilylene was previously stabilized by carbene. The lone pair of electrons on the silicon atom of (carbene)­SiCl₂ can form a coordinate bond with metal–carbonyls. Herein we report that (carbene)­SiCl₂ can stabilize a phosphinidene (Ar–P, a carbone analogue) with the general formula carbene→SiCl₂→P–Ar (carbene = cyclic alkyl­(amino) carbene (cAAC; <b>2</b>) and N-heterocyclic carbene (NHC; <b>3</b>)). Compounds <b>2</b> and <b>3</b> are stable, isolable, and storable at 0 °C (<b>2</b>) to room temperature (<b>3</b>) under an inert atmosphere. The crystals of <b>2</b> and <b>3</b> are dark blue and red, respectively. The intense blue color of <b>2</b> arises due to the strong intramolecular charge transfer (ICT) transition from π_SiP→π*_cAAC. The electronic structure and bonding of <b>2</b>, <b>3</b> were studied by theoretical calculations. The HOMO of the molecule is located on the π_SiP bond, while the LUMO is located at the carbene moiety (cAAC or NHC). The dramatic change in color of these compounds from red (<b>3</b>, NHC) to blue (<b>2</b>, cAAC) is ascribed to the difference in energy of the LUMO within the carbenes (cAAC/NHC) due to a lower lying LUMO of cAAC

Acyclic Germylones: Congeners of Allenes with a Central Germanium Atom

The cyclic alkyl­(amino) carbene (cAAC:)-stabilized acyclic germylones (Me₂-cAAC:)₂Ge (<b>1</b>) and (Cy₂-cAAC:)₂Ge (<b>2</b>) were prepared utilizing a one-pot synthesis of GeCl₂(dioxane), cAAC:, and KC₈ in a 1:2:2.1 molar ratio. Dark green crystals of compounds <b>1</b> and <b>2</b> were produced in 75 and 70% yields, respectively. The reported methods for the preparation of the corresponding silicon compounds turned out to be not applicable in the case of germanium. The single-crystal X-ray structures of <b>1</b> and <b>2</b> feature the C–Ge–C bent backbone, which possesses a three-center two-electron π-bond system. Compounds <b>1</b> and <b>2</b> are the first acyclic germylones containing each one germanium atom and two cAAC: molecules. EPR measurements on compounds <b>1</b> and <b>2</b> confirmed the singlet spin ground state. DFT calculations on <b>1</b>/<b>2</b> revealed that the singlet ground state is more stable by ∼16 to 18 kcal mol^–1 than that of the triplet state. First and second proton affinity values were theoretically calculated to be of 265.8 (<b>1</b>)/267.1 (<b>2</b>) and 180.4 (<b>1</b>)/183.8 (<b>2</b>) kcal mol^–1, respectively. Further calculations, which were performed at different levels suggest a singlet diradicaloid character of <b>1</b> and <b>2</b>. The TD-DFT calculations exhibit an absorption band at ∼655 nm in <i>n</i>-hexane solution that originates from the diradicaloid character of germylones <b>1</b> and <b>2</b>

Acyclic Germylones: Congeners of Allenes with a Central Germanium Atom

The cyclic alkyl­(amino) carbene (cAAC:)-stabilized acyclic germylones (Me₂-cAAC:)₂Ge (<b>1</b>) and (Cy₂-cAAC:)₂Ge (<b>2</b>) were prepared utilizing a one-pot synthesis of GeCl₂(dioxane), cAAC:, and KC₈ in a 1:2:2.1 molar ratio. Dark green crystals of compounds <b>1</b> and <b>2</b> were produced in 75 and 70% yields, respectively. The reported methods for the preparation of the corresponding silicon compounds turned out to be not applicable in the case of germanium. The single-crystal X-ray structures of <b>1</b> and <b>2</b> feature the C–Ge–C bent backbone, which possesses a three-center two-electron π-bond system. Compounds <b>1</b> and <b>2</b> are the first acyclic germylones containing each one germanium atom and two cAAC: molecules. EPR measurements on compounds <b>1</b> and <b>2</b> confirmed the singlet spin ground state. DFT calculations on <b>1</b>/<b>2</b> revealed that the singlet ground state is more stable by ∼16 to 18 kcal mol^–1 than that of the triplet state. First and second proton affinity values were theoretically calculated to be of 265.8 (<b>1</b>)/267.1 (<b>2</b>) and 180.4 (<b>1</b>)/183.8 (<b>2</b>) kcal mol^–1, respectively. Further calculations, which were performed at different levels suggest a singlet diradicaloid character of <b>1</b> and <b>2</b>. The TD-DFT calculations exhibit an absorption band at ∼655 nm in <i>n</i>-hexane solution that originates from the diradicaloid character of germylones <b>1</b> and <b>2</b>

Acyclic Germylones: Congeners of Allenes with a Central Germanium Atom

The cyclic alkyl­(amino) carbene (cAAC:)-stabilized acyclic germylones (Me₂-cAAC:)₂Ge (<b>1</b>) and (Cy₂-cAAC:)₂Ge (<b>2</b>) were prepared utilizing a one-pot synthesis of GeCl₂(dioxane), cAAC:, and KC₈ in a 1:2:2.1 molar ratio. Dark green crystals of compounds <b>1</b> and <b>2</b> were produced in 75 and 70% yields, respectively. The reported methods for the preparation of the corresponding silicon compounds turned out to be not applicable in the case of germanium. The single-crystal X-ray structures of <b>1</b> and <b>2</b> feature the C–Ge–C bent backbone, which possesses a three-center two-electron π-bond system. Compounds <b>1</b> and <b>2</b> are the first acyclic germylones containing each one germanium atom and two cAAC: molecules. EPR measurements on compounds <b>1</b> and <b>2</b> confirmed the singlet spin ground state. DFT calculations on <b>1</b>/<b>2</b> revealed that the singlet ground state is more stable by ∼16 to 18 kcal mol^–1 than that of the triplet state. First and second proton affinity values were theoretically calculated to be of 265.8 (<b>1</b>)/267.1 (<b>2</b>) and 180.4 (<b>1</b>)/183.8 (<b>2</b>) kcal mol^–1, respectively. Further calculations, which were performed at different levels suggest a singlet diradicaloid character of <b>1</b> and <b>2</b>. The TD-DFT calculations exhibit an absorption band at ∼655 nm in <i>n</i>-hexane solution that originates from the diradicaloid character of germylones <b>1</b> and <b>2</b>

Acyclic Germylones: Congeners of Allenes with a Central Germanium Atom

The cyclic alkyl­(amino) carbene (cAAC:)-stabilized acyclic germylones (Me₂-cAAC:)₂Ge (<b>1</b>) and (Cy₂-cAAC:)₂Ge (<b>2</b>) were prepared utilizing a one-pot synthesis of GeCl₂(dioxane), cAAC:, and KC₈ in a 1:2:2.1 molar ratio. Dark green crystals of compounds <b>1</b> and <b>2</b> were produced in 75 and 70% yields, respectively. The reported methods for the preparation of the corresponding silicon compounds turned out to be not applicable in the case of germanium. The single-crystal X-ray structures of <b>1</b> and <b>2</b> feature the C–Ge–C bent backbone, which possesses a three-center two-electron π-bond system. Compounds <b>1</b> and <b>2</b> are the first acyclic germylones containing each one germanium atom and two cAAC: molecules. EPR measurements on compounds <b>1</b> and <b>2</b> confirmed the singlet spin ground state. DFT calculations on <b>1</b>/<b>2</b> revealed that the singlet ground state is more stable by ∼16 to 18 kcal mol^–1 than that of the triplet state. First and second proton affinity values were theoretically calculated to be of 265.8 (<b>1</b>)/267.1 (<b>2</b>) and 180.4 (<b>1</b>)/183.8 (<b>2</b>) kcal mol^–1, respectively. Further calculations, which were performed at different levels suggest a singlet diradicaloid character of <b>1</b> and <b>2</b>. The TD-DFT calculations exhibit an absorption band at ∼655 nm in <i>n</i>-hexane solution that originates from the diradicaloid character of germylones <b>1</b> and <b>2</b>

Electron-Induced Conversion of Silylones to Six-Membered Cyclic Silylenes

A silicon atom in the zero oxidation state stabilized by two carbene ligands is known as sila­dicarbene (silyl­one). There are two pairs of electrons on the silicon atom in silyl­one. This was recently confirmed by both experimental and theoretical charge density investigations. The silyl­one is stable up to 195 °C in an inert atmosphere. However, a substoichiometric amount (33 mol%) of potassium metal triggers the activation of the unsaturated C:Si:C backbone, leading to a selective reaction with a tertiary C–H bond in an atom-economical approach to form a six-membered cyclic silylene with three-coordinate silicon atom. Cyclic voltammetry shows that this reaction proceeds via the formation of a silyl­one radical anion intermediate, which is further confirmed by EPR spectroscopy

Electron-Induced Conversion of Silylones to Six-Membered Cyclic Silylenes

A silicon atom in the zero oxidation state stabilized by two carbene ligands is known as sila­dicarbene (silyl­one). There are two pairs of electrons on the silicon atom in silyl­one. This was recently confirmed by both experimental and theoretical charge density investigations. The silyl­one is stable up to 195 °C in an inert atmosphere. However, a substoichiometric amount (33 mol%) of potassium metal triggers the activation of the unsaturated C:Si:C backbone, leading to a selective reaction with a tertiary C–H bond in an atom-economical approach to form a six-membered cyclic silylene with three-coordinate silicon atom. Cyclic voltammetry shows that this reaction proceeds via the formation of a silyl­one radical anion intermediate, which is further confirmed by EPR spectroscopy