Reactivity of Stable Heteroleptic Silylene PhC(N<i>t</i>Bu)₂SiNPh₂ toward Diazobenzene and <i>N</i>‑Benzylidineaniline

The reaction of heteroleptic silylene LSiNPh₂ [L = PhC­(N<i>t</i>Bu)₂] with diazobenzene afforded product <b>6</b>. This involves one <i>o</i>-C–H bond activation at one of the phenyl groups of diazobenzene and migration of this hydrogen atom from the phenyl ring to one of the nitrogen atoms, which leads to the formation of the new C–Si and N–Si bonds. The reaction of benzylidineaniline with LSiNPh₂ results in the oxidative addition of the three-membered silaaziridine derivative <b>7</b>. Compounds <b>6</b> and <b>7</b> were fully characterized by elemental analysis, multinuclear NMR spectroscopy, and EI-MS spectrometry. The molecular structures of compounds <b>6</b> and <b>7</b> were established unequivocally by single-crystal X-ray structural analysis

Influence of Donor–Acceptor Distance Variation on Photoinduced Electron and Proton Transfer in Rhenium(I)–Phenol Dyads

A homologous series of four molecules in which a phenol unit is linked covalently to a rhenium­(I) tricarbonyl diimine photooxidant via a variable number of <i>p</i>-xylene spacers (<i>n</i> = 0–3) was synthesized and investigated. The species with a single <i>p</i>-xylene spacer was structurally characterized to get some benchmark distances. Photoexcitation of the metal complex in the shortest dyad (<i>n</i> = 0) triggers release of the phenolic proton to the acetonitrile/water solvent mixture; a H/D kinetic isotope effect (KIE) of 2.0 ± 0.4 is associated with this process. Thus, the shortest dyad basically acts like a photoacid. The next two longer dyads (<i>n</i> = 1, 2) exhibit intramolecular photoinduced phenol-to-rhenium electron transfer in the rate-determining excited-state deactivation step, and there is no significant KIE in this case. For the dyad with <i>n</i> = 1, transient absorption spectroscopy provided evidence for release of the phenolic proton to the solvent upon oxidation of the phenol by intramolecular photoinduced electron transfer. Subsequent thermal charge recombination is associated with a H/D KIE of 3.6 ± 0.4 and therefore is likely to involve proton motion in the rate-determining reaction step. Thus, some of the longer dyads (<i>n</i> = 1, 2) exhibit photoinduced proton-coupled electron transfer (PCET), albeit in a stepwise (electron transfer followed by proton transfer) rather than concerted manner. Our study demonstrates that electronically strongly coupled donor–acceptor systems may exhibit significantly different photoinduced PCET chemistry than electronically weakly coupled donor–bridge–acceptor molecules

Influence of Donor–Acceptor Distance Variation on Photoinduced Electron and Proton Transfer in Rhenium(I)–Phenol Dyads

A homologous series of four molecules in which a phenol unit is linked covalently to a rhenium­(I) tricarbonyl diimine photooxidant via a variable number of <i>p</i>-xylene spacers (<i>n</i> = 0–3) was synthesized and investigated. The species with a single <i>p</i>-xylene spacer was structurally characterized to get some benchmark distances. Photoexcitation of the metal complex in the shortest dyad (<i>n</i> = 0) triggers release of the phenolic proton to the acetonitrile/water solvent mixture; a H/D kinetic isotope effect (KIE) of 2.0 ± 0.4 is associated with this process. Thus, the shortest dyad basically acts like a photoacid. The next two longer dyads (<i>n</i> = 1, 2) exhibit intramolecular photoinduced phenol-to-rhenium electron transfer in the rate-determining excited-state deactivation step, and there is no significant KIE in this case. For the dyad with <i>n</i> = 1, transient absorption spectroscopy provided evidence for release of the phenolic proton to the solvent upon oxidation of the phenol by intramolecular photoinduced electron transfer. Subsequent thermal charge recombination is associated with a H/D KIE of 3.6 ± 0.4 and therefore is likely to involve proton motion in the rate-determining reaction step. Thus, some of the longer dyads (<i>n</i> = 1, 2) exhibit photoinduced proton-coupled electron transfer (PCET), albeit in a stepwise (electron transfer followed by proton transfer) rather than concerted manner. Our study demonstrates that electronically strongly coupled donor–acceptor systems may exhibit significantly different photoinduced PCET chemistry than electronically weakly coupled donor–bridge–acceptor molecules

Facile Access to the Functionalized N-Donor Stabilized Silylenes PhC(N<i>t</i>Bu)₂SiX (X = PPh₂, NPh₂, NCy₂, N<i>i</i>Pr₂, NMe₂, N(SiMe₃)₂, O<i>t</i>Bu)

Reactions of silylenes with organic substrates generally lead to silicon­(IV) compounds. Ligand substitution at the silicon­(II) atom of silylene, without changing the formal +2 oxidation state, is very rare. We report herein a straightforward route to functionalized silylenes LSiX (L = PhC­(NtBu)2 and X = PPh2 (1), NPh2 (2), NCy2(3), NiPr2 (4), NMe2 (5), N­(SiMe3)2 (6), OtBu (7)). Silylenes 1–7 have been prepared in quantitative yield by a modified ligand exchange reaction of PhC­(NtBu)2SiCl (LSiCl) with the corresponding lithium or potassium salts. Compounds 1–7 were characterized by spectroscopic and spectrometric techniques. Single-crystal X-ray structures of 1, 3, and 4 were determined

Facile Access to the Functionalized N-Donor Stabilized Silylenes PhC(N<i>t</i>Bu)₂SiX (X = PPh₂, NPh₂, NCy₂, N<i>i</i>Pr₂, NMe₂, N(SiMe₃)₂, O<i>t</i>Bu)

Reactions of silylenes with organic substrates generally lead to silicon­(IV) compounds. Ligand substitution at the silicon­(II) atom of silylene, without changing the formal +2 oxidation state, is very rare. We report herein a straightforward route to functionalized silylenes LSiX (L = PhC­(N<i>t</i>Bu)₂ and X = PPh₂ (<b>1</b>), NPh₂ (<b>2</b>), NCy₂(<b>3</b>), N<i>i</i>Pr₂ (<b>4</b>), NMe₂ (<b>5</b>), N­(SiMe₃)₂ (<b>6</b>), O<i>t</i>Bu (<b>7</b>)). Silylenes <b>1</b>–<b>7</b> have been prepared in quantitative yield by a modified ligand exchange reaction of PhC­(N<i>t</i>Bu)₂SiCl (LSiCl) with the corresponding lithium or potassium salts. Compounds <b>1</b>–<b>7</b> were characterized by spectroscopic and spectrometric techniques. Single-crystal X-ray structures of <b>1</b>, <b>3</b>, and <b>4</b> were determined

Facile Access to the Functionalized N-Donor Stabilized Silylenes PhC(N<i>t</i>Bu)₂SiX (X = PPh₂, NPh₂, NCy₂, N<i>i</i>Pr₂, NMe₂, N(SiMe₃)₂, O<i>t</i>Bu)

Reactions of silylenes with organic substrates generally lead to silicon­(IV) compounds. Ligand substitution at the silicon­(II) atom of silylene, without changing the formal +2 oxidation state, is very rare. We report herein a straightforward route to functionalized silylenes LSiX (L = PhC­(N<i>t</i>Bu)₂ and X = PPh₂ (<b>1</b>), NPh₂ (<b>2</b>), NCy₂(<b>3</b>), N<i>i</i>Pr₂ (<b>4</b>), NMe₂ (<b>5</b>), N­(SiMe₃)₂ (<b>6</b>), O<i>t</i>Bu (<b>7</b>)). Silylenes <b>1</b>–<b>7</b> have been prepared in quantitative yield by a modified ligand exchange reaction of PhC­(N<i>t</i>Bu)₂SiCl (LSiCl) with the corresponding lithium or potassium salts. Compounds <b>1</b>–<b>7</b> were characterized by spectroscopic and spectrometric techniques. Single-crystal X-ray structures of <b>1</b>, <b>3</b>, and <b>4</b> were determined

Stabilization of Low Valent Silicon Fluorides in the Coordination Sphere of Transition Metals

Silicon­(II) fluoride is unstable; therefore, isolation of the stable species is highly challenging and was not successful during the last 45 years. SiF₂ is generally generated in the gas phase at very high temperatures (∼1100–1200 °C) and low pressures and readily disproportionates or polymerizes. We accomplished the syntheses of stable silicon­(II) fluoride species by coordination of silicon­(II) to transition metal carbonyls. Silicon­(II) fluoride compounds L­(F)­Si·M­(CO)₅ {M = Cr (<b>4</b>), Mo (<b>5</b>), W­(<b>6</b>)} (L = PhC­(N<i>t</i>Bu)₂) were prepared by metathesis reaction from the corresponding chloride with Me₃SnF. However, the chloride derivatives L­(Cl)­Si·M­(CO)₅ {M = Cr (<b>1</b>), Mo (<b>2</b>), W­(<b>3</b>)} (L = PhC­(N<i>t</i>Bu)₂) were prepared by the treatment of transition metal carbonyls with L­(Cl)­Si. Direct fluorination of L­(Cl)Si with Me₃SnF resulted in oxidative addition products. Compounds <b>4</b>–<b>6</b> are stable at ambient temperature under an inert atmosphere of nitrogen. Compounds <b>4</b>–<b>6</b> were characterized by NMR spectroscopy, EI-MS spectrometry, and elemental analysis. The molecular structures of <b>4</b> and <b>6</b> were unambiguously established by single-crystal X-ray diffraction. Compounds <b>4</b> and <b>6</b> are the first structurally characterized fluorides, after the discovery of SiF₂ about four and a half decades ago

Stabilization of Low Valent Silicon Fluorides in the Coordination Sphere of Transition Metals

Silicon­(II) fluoride is unstable; therefore, isolation of the stable species is highly challenging and was not successful during the last 45 years. SiF₂ is generally generated in the gas phase at very high temperatures (∼1100–1200 °C) and low pressures and readily disproportionates or polymerizes. We accomplished the syntheses of stable silicon­(II) fluoride species by coordination of silicon­(II) to transition metal carbonyls. Silicon­(II) fluoride compounds L­(F)­Si·M­(CO)₅ {M = Cr (<b>4</b>), Mo (<b>5</b>), W­(<b>6</b>)} (L = PhC­(N<i>t</i>Bu)₂) were prepared by metathesis reaction from the corresponding chloride with Me₃SnF. However, the chloride derivatives L­(Cl)­Si·M­(CO)₅ {M = Cr (<b>1</b>), Mo (<b>2</b>), W­(<b>3</b>)} (L = PhC­(N<i>t</i>Bu)₂) were prepared by the treatment of transition metal carbonyls with L­(Cl)­Si. Direct fluorination of L­(Cl)Si with Me₃SnF resulted in oxidative addition products. Compounds <b>4</b>–<b>6</b> are stable at ambient temperature under an inert atmosphere of nitrogen. Compounds <b>4</b>–<b>6</b> were characterized by NMR spectroscopy, EI-MS spectrometry, and elemental analysis. The molecular structures of <b>4</b> and <b>6</b> were unambiguously established by single-crystal X-ray diffraction. Compounds <b>4</b> and <b>6</b> are the first structurally characterized fluorides, after the discovery of SiF₂ about four and a half decades ago

Stabilization of Low Valent Silicon Fluorides in the Coordination Sphere of Transition Metals

Silicon­(II) fluoride is unstable; therefore, isolation of the stable species is highly challenging and was not successful during the last 45 years. SiF₂ is generally generated in the gas phase at very high temperatures (∼1100–1200 °C) and low pressures and readily disproportionates or polymerizes. We accomplished the syntheses of stable silicon­(II) fluoride species by coordination of silicon­(II) to transition metal carbonyls. Silicon­(II) fluoride compounds L­(F)­Si·M­(CO)₅ {M = Cr (<b>4</b>), Mo (<b>5</b>), W­(<b>6</b>)} (L = PhC­(N<i>t</i>Bu)₂) were prepared by metathesis reaction from the corresponding chloride with Me₃SnF. However, the chloride derivatives L­(Cl)­Si·M­(CO)₅ {M = Cr (<b>1</b>), Mo (<b>2</b>), W­(<b>3</b>)} (L = PhC­(N<i>t</i>Bu)₂) were prepared by the treatment of transition metal carbonyls with L­(Cl)­Si. Direct fluorination of L­(Cl)Si with Me₃SnF resulted in oxidative addition products. Compounds <b>4</b>–<b>6</b> are stable at ambient temperature under an inert atmosphere of nitrogen. Compounds <b>4</b>–<b>6</b> were characterized by NMR spectroscopy, EI-MS spectrometry, and elemental analysis. The molecular structures of <b>4</b> and <b>6</b> were unambiguously established by single-crystal X-ray diffraction. Compounds <b>4</b> and <b>6</b> are the first structurally characterized fluorides, after the discovery of SiF₂ about four and a half decades ago

Facile Access to the Functionalized N-Donor Stabilized Silylenes PhC(N<i>t</i>Bu)₂SiX (X = PPh₂, NPh₂, NCy₂, N<i>i</i>Pr₂, NMe₂, N(SiMe₃)₂, O<i>t</i>Bu)

Reactions of silylenes with organic substrates generally lead to silicon­(IV) compounds. Ligand substitution at the silicon­(II) atom of silylene, without changing the formal +2 oxidation state, is very rare. We report herein a straightforward route to functionalized silylenes LSiX (L = PhC­(N<i>t</i>Bu)₂ and X = PPh₂ (<b>1</b>), NPh₂ (<b>2</b>), NCy₂(<b>3</b>), N<i>i</i>Pr₂ (<b>4</b>), NMe₂ (<b>5</b>), N­(SiMe₃)₂ (<b>6</b>), O<i>t</i>Bu (<b>7</b>)). Silylenes <b>1</b>–<b>7</b> have been prepared in quantitative yield by a modified ligand exchange reaction of PhC­(N<i>t</i>Bu)₂SiCl (LSiCl) with the corresponding lithium or potassium salts. Compounds <b>1</b>–<b>7</b> were characterized by spectroscopic and spectrometric techniques. Single-crystal X-ray structures of <b>1</b>, <b>3</b>, and <b>4</b> were determined