Hyperconjugation Involving Strained Carbon–Carbon Bonds. Structural Analysis of Ester and Ether Derivatives and One-Bond ¹³C–¹³C Coupling Constants of α- and β‑Nopinol

σ_C–C–σ*_C–O interactions involving the strained carbon–carbon bonds of α- and β-nopinol, and their ester and ether derivatives have been demonstrated in the solid state using the variable oxygen probe. These hyperconjugative interactions are manifested as a strong response of the C–OR bond distance to the electron demand of the OR substituent. Although the effects upon the donor C–C bond distances are not large enough to be measurable by X-ray crystallography, they do result in systematic and measurable effects on the ¹³C–¹³C one-bond coupling constants. For the donor C–C bond, coupling constants decrease, consistent with weakening of this bond, while the intervening C–C bond coupling constants increase, consistent with bond strengthening, as the electron demand of OR increases

Hyperconjugation Involving Strained Carbon–Carbon Bonds. Structural Analysis of Ester and Ether Derivatives and One-Bond ¹³C–¹³C Coupling Constants of α- and β‑Nopinol

σ_C–C–σ*_C–O interactions involving the strained carbon–carbon bonds of α- and β-nopinol, and their ester and ether derivatives have been demonstrated in the solid state using the variable oxygen probe. These hyperconjugative interactions are manifested as a strong response of the C–OR bond distance to the electron demand of the OR substituent. Although the effects upon the donor C–C bond distances are not large enough to be measurable by X-ray crystallography, they do result in systematic and measurable effects on the ¹³C–¹³C one-bond coupling constants. For the donor C–C bond, coupling constants decrease, consistent with weakening of this bond, while the intervening C–C bond coupling constants increase, consistent with bond strengthening, as the electron demand of OR increases

Solution and Gas-Phase Investigations of Trimethylsilylpropyl-Substituted Pyridinium Ions. Manifestation of the Silicon δ Effect

Computational studies on the <i>N</i>-methyl-2-trimethyl-M-propylpyridinium ions <b>15a</b> (M = Si), <b>15b</b> (M = Ge), <b>15c</b> (M = Sn), and <b>15d</b> (M = Pb) and <i>N</i>-methyl-4-trimethyl-M-propylpyridinium ions <b>16a</b> (M = Si), <b>16b</b> (M = Ge), <b>16c</b> (M = Sn), and <b>16d</b> (M = Pb) provide evidence for a significant through-bond (double hyperconjugative) interaction between the M–CH₂ bond and the low-lying π* orbital of the pyridinium ion. The strength of this interaction increases in the order Si < Ge < Sn < Pb, in line with the σ-donor abilities of the C–M bond. The through-bond interaction for M = Si has been studied in solution using ¹³C and ²⁹Si NMR studies; however, the effect is small. The collision-induced dissociation fragmentation reactions of <b>15a</b> and <b>16a</b> are strongly influenced by the through-bond interaction, with the major fragmentation pathway proceeding via extrusion of ethylene to yield the trimethylsilylmethyl-substituted pyridinium ions <b>1a</b> and <b>2a</b>

Hyperconjugation Involving Strained Carbon–Carbon Bonds. Structural Analysis of Ester and Ether Derivatives and One-Bond ¹³C–¹³C Coupling Constants of α- and β‑Nopinol

σ_C–C–σ*_C–O interactions involving the strained carbon–carbon bonds of α- and β-nopinol, and their ester and ether derivatives have been demonstrated in the solid state using the variable oxygen probe. These hyperconjugative interactions are manifested as a strong response of the C–OR bond distance to the electron demand of the OR substituent. Although the effects upon the donor C–C bond distances are not large enough to be measurable by X-ray crystallography, they do result in systematic and measurable effects on the ¹³C–¹³C one-bond coupling constants. For the donor C–C bond, coupling constants decrease, consistent with weakening of this bond, while the intervening C–C bond coupling constants increase, consistent with bond strengthening, as the electron demand of OR increases

Hyperconjugation Involving Strained Carbon–Carbon Bonds. Structural Analysis of Ester and Ether Derivatives and One-Bond ¹³C–¹³C Coupling Constants of α- and β‑Nopinol

σ_C–C–σ*_C–O interactions involving the strained carbon–carbon bonds of α- and β-nopinol, and their ester and ether derivatives have been demonstrated in the solid state using the variable oxygen probe. These hyperconjugative interactions are manifested as a strong response of the C–OR bond distance to the electron demand of the OR substituent. Although the effects upon the donor C–C bond distances are not large enough to be measurable by X-ray crystallography, they do result in systematic and measurable effects on the ¹³C–¹³C one-bond coupling constants. For the donor C–C bond, coupling constants decrease, consistent with weakening of this bond, while the intervening C–C bond coupling constants increase, consistent with bond strengthening, as the electron demand of OR increases

Hyperconjugation Involving Strained Carbon–Carbon Bonds. Structural Analysis of Ester and Ether Derivatives and One-Bond ¹³C–¹³C Coupling Constants of α- and β‑Nopinol

σ_C–C–σ*_C–O interactions involving the strained carbon–carbon bonds of α- and β-nopinol, and their ester and ether derivatives have been demonstrated in the solid state using the variable oxygen probe. These hyperconjugative interactions are manifested as a strong response of the C–OR bond distance to the electron demand of the OR substituent. Although the effects upon the donor C–C bond distances are not large enough to be measurable by X-ray crystallography, they do result in systematic and measurable effects on the ¹³C–¹³C one-bond coupling constants. For the donor C–C bond, coupling constants decrease, consistent with weakening of this bond, while the intervening C–C bond coupling constants increase, consistent with bond strengthening, as the electron demand of OR increases

Convergent Access to Polycyclic Cyclopentanoids from α,β-Unsaturated Acid Chlorides and Alkynes through a Reductive Coupling, Nazarov Cyclization Sequence

Reductive coupling of α,β-unsaturated acid chlorides <b>A</b> with alkynoyls <b>B</b> provides convergent access to Nazarov cyclization precursors, α-carboxy divinyl ketones <b>C</b>. Cyclization of <b>C</b> gives an intermediate oxyallyl cation intermediate <b>D</b>, which can be trapped with tethered arenes (Ar). The resultant products can be further cyclized through nucleophilic displacement of suitable leaving groups X by tethered OH groups to give lactones (in a subsequent step). Where X is a suitable chiral auxiliary (e.g., oxazolidinone) this strategy affords access to homochiral cyclopentanoids

Convergent Access to Polycyclic Cyclopentanoids from α,β-Unsaturated Acid Chlorides and Alkynes through a Reductive Coupling, Nazarov Cyclization Sequence

Reductive coupling of α,β-unsaturated acid chlorides <b>A</b> with alkynoyls <b>B</b> provides convergent access to Nazarov cyclization precursors, α-carboxy divinyl ketones <b>C</b>. Cyclization of <b>C</b> gives an intermediate oxyallyl cation intermediate <b>D</b>, which can be trapped with tethered arenes (Ar). The resultant products can be further cyclized through nucleophilic displacement of suitable leaving groups X by tethered OH groups to give lactones (in a subsequent step). Where X is a suitable chiral auxiliary (e.g., oxazolidinone) this strategy affords access to homochiral cyclopentanoids

Luminescent Iridium(III) Cyclometalated Complexes with 1,2,3-Triazole “Click” Ligands

A series of cyclometalated iridium­(III) complexes with either 4-(2-pyridyl)-1,2,3-triazole or 1-(2-picolyl)-1,2,3-triazole ancillary ligands to give complexes with either 5- or 6-membered chelate rings were synthesized and characterized by a combination of X-ray crystallography, electron spin ionization–high-resolution mass spectroscopy (ESI-HRMS), and nuclear magnetic resonance (NMR) spectroscopy. The electronic properties of the complexes were probed using absorption and emission spectroscopy, as well as cyclic voltammetry. The relative stability of the complexes formed from each ligand class was measured, and their excited-state properties were compared. The emissive properties are, with the exception of complexes that contain a nitroaromatic substituent, insensitive to functionalization of the ancillary pyridyl-1,2,3-triazole ligand but tuning of the emission maxima was possible by modification of the cyclometalating ligands. It is possible to prepare a wide range of optimally substituted pyridyl-1,2,3-triazoles using copper Cu­(I)-catalyzed azide alkyne cycloaddition, which is a commonly used “click” reaction, and this family of ligands represent an useful alternative to bipyridine ligands for the preparation of luminescent iridium­(III) complexes