Facile Synthesis of Dibenzo-7λ³‑phosphanorbornadiene Derivatives Using Magnesium Anthracene

Unprotected dibenzo-7λ³-phosphanorbornadiene derivatives RP<b>A</b> (<b>A</b> = C₁₄H₁₀ or anthracene; R = ^<i>t</i>Bu, dbabh = N<b>A</b>, HMDS = (Me₃Si)₂N, ^<i>i</i>Pr₂N) are synthesized by treatment of the corresponding phosphorus dichloride RPCl₂ with Mg<b>A</b>·3THF, in cold THF (∼20% to 30% isolated yields). Anthracene and the corresponding cyclic phosphane (RP)_<i>n</i> form as coproducts. Characteristic NMR features of the RP<b>A</b> derivatives include a doublet near 4 ppm in their ¹H NMR spectra and a triplet peak in the 175–212 ppm region of the ³¹P NMR spectrum (²<i>J</i>_PH ∼14 Hz). The X-ray structures of the <b>A</b>N–P<b>A</b> and (HMDS)­P<b>A</b> derivatives are discussed. Thermolysis of RP<b>A</b> benzene-<i>d</i>₆ solutions leads to anthracene extrusion. This process has a unimolecular kinetic profile for the ^<i>i</i>Pr₂NP<b>A</b> derivative. The 7-phosphanorbornene <i>anti</i>-^<i>i</i>Pr₂NP­(C₆H₈) could be synthesized (70% isolated yield) by thermolysis of ^<i>i</i>Pr₂NP<b>A</b> in 1,3-cyclohexadiene

Facile Synthesis of Dibenzo-7λ³‑phosphanorbornadiene Derivatives Using Magnesium Anthracene

Unprotected dibenzo-7λ³-phosphanorbornadiene derivatives RP<b>A</b> (<b>A</b> = C₁₄H₁₀ or anthracene; R = ^<i>t</i>Bu, dbabh = N<b>A</b>, HMDS = (Me₃Si)₂N, ^<i>i</i>Pr₂N) are synthesized by treatment of the corresponding phosphorus dichloride RPCl₂ with Mg<b>A</b>·3THF, in cold THF (∼20% to 30% isolated yields). Anthracene and the corresponding cyclic phosphane (RP)_<i>n</i> form as coproducts. Characteristic NMR features of the RP<b>A</b> derivatives include a doublet near 4 ppm in their ¹H NMR spectra and a triplet peak in the 175–212 ppm region of the ³¹P NMR spectrum (²<i>J</i>_PH ∼14 Hz). The X-ray structures of the <b>A</b>N–P<b>A</b> and (HMDS)­P<b>A</b> derivatives are discussed. Thermolysis of RP<b>A</b> benzene-<i>d</i>₆ solutions leads to anthracene extrusion. This process has a unimolecular kinetic profile for the ^<i>i</i>Pr₂NP<b>A</b> derivative. The 7-phosphanorbornene <i>anti</i>-^<i>i</i>Pr₂NP­(C₆H₈) could be synthesized (70% isolated yield) by thermolysis of ^<i>i</i>Pr₂NP<b>A</b> in 1,3-cyclohexadiene

Facile Synthesis of Dibenzo-7λ³‑phosphanorbornadiene Derivatives Using Magnesium Anthracene

Unprotected dibenzo-7λ³-phosphanorbornadiene derivatives RP<b>A</b> (<b>A</b> = C₁₄H₁₀ or anthracene; R = ^<i>t</i>Bu, dbabh = N<b>A</b>, HMDS = (Me₃Si)₂N, ^<i>i</i>Pr₂N) are synthesized by treatment of the corresponding phosphorus dichloride RPCl₂ with Mg<b>A</b>·3THF, in cold THF (∼20% to 30% isolated yields). Anthracene and the corresponding cyclic phosphane (RP)_<i>n</i> form as coproducts. Characteristic NMR features of the RP<b>A</b> derivatives include a doublet near 4 ppm in their ¹H NMR spectra and a triplet peak in the 175–212 ppm region of the ³¹P NMR spectrum (²<i>J</i>_PH ∼14 Hz). The X-ray structures of the <b>A</b>N–P<b>A</b> and (HMDS)­P<b>A</b> derivatives are discussed. Thermolysis of RP<b>A</b> benzene-<i>d</i>₆ solutions leads to anthracene extrusion. This process has a unimolecular kinetic profile for the ^<i>i</i>Pr₂NP<b>A</b> derivative. The 7-phosphanorbornene <i>anti</i>-^<i>i</i>Pr₂NP­(C₆H₈) could be synthesized (70% isolated yield) by thermolysis of ^<i>i</i>Pr₂NP<b>A</b> in 1,3-cyclohexadiene

Synthesis, Characterization, and Thermolysis of Dibenzo-7-dimethylgermanorbornadiene

The dibenzo-7-dimethylgermanorbornadiene Me₂Ge<b>A</b> (<b>A</b> <i> = </i> C₁₄H₁₀) has been synthesized in one step by treatment of Mg<b>A</b>·3THF with Me₂GeCl₂ in tetrahydrofuran (−35 °C) and isolated in 69% yield. The thermolysis of Me₂Ge<b>A</b> in toluene leads to the effective expansion of the bicyclic framework to the dibenzo-7,8-tetramethyldigermabicyclo[2.2.2]­octadiene (Me₂Ge)₂<b>A</b>, isolated in 71% yield (based on germanium). The bicyclic compounds Me₂Ge<b>A</b> and (Me₂Ge)₂<b>A</b> have been characterized by single-crystal X-ray diffraction studies and their structures discussed

Synthesis, Characterization, and Thermolysis of Dibenzo-7-dimethylgermanorbornadiene

The dibenzo-7-dimethylgermanorbornadiene Me₂Ge<b>A</b> (<b>A</b> <i> = </i> C₁₄H₁₀) has been synthesized in one step by treatment of Mg<b>A</b>·3THF with Me₂GeCl₂ in tetrahydrofuran (−35 °C) and isolated in 69% yield. The thermolysis of Me₂Ge<b>A</b> in toluene leads to the effective expansion of the bicyclic framework to the dibenzo-7,8-tetramethyldigermabicyclo[2.2.2]­octadiene (Me₂Ge)₂<b>A</b>, isolated in 71% yield (based on germanium). The bicyclic compounds Me₂Ge<b>A</b> and (Me₂Ge)₂<b>A</b> have been characterized by single-crystal X-ray diffraction studies and their structures discussed

Dipalladium(I) Terphenyl Diphosphine Complexes as Models for Two-Site Adsorption and Activation of Organic Molecules

A <i>para</i>-terphenyl diphosphine was employed to support a dipalladium­(I) moiety. Unlike previously reported dipalladium­(I) species, the present system provides a single molecular hemisphere for binding of ligands across two metal centers, enabling the characterization and comparison of the binding of a wide variety of saturated and unsaturated organic molecules. The dipalladium­(I) terphenyl diphosphine toluene-capped complex was synthesized from a dipalladium­(I) hexaacetonitrile precursor in the presence of toluene. The palladium centers display interactions with the π-systems of the central ring of the terphenyl unit and that of the toluene. Exchange of toluene for anisole, 1,3-butadiene, 1,3-cyclohexadiene, thiophenes, pyrroles, or furans resulted in well-defined π-bound complexes which were studied by crystallography, nuclear magnetic resonance (NMR) spectroscopy, and density functional theory. Structural characterization shows that the interactions of the dipalladium unit with the central arene of the diphosphine does not vary significantly in this series allowing for a systematic comparison of the binding of the incoming ligands to the dipalladium moiety. Several of the complexes exhibit rare μ–η²:η² or μ–η²:η¹(O or S) bridging motifs. Hydrogenation of the thiophene and benzothiophene adducts was demonstrated to proceed at room temperature. The relative binding strength of the neutral ligands was determined by competition experiments monitored by NMR spectroscopy. The relative equilibrium constants for ligand substitution span over 13 orders of magnitude. This represents the most comprehensive analysis to date of the relative binding of heterocycles and unsaturated ligands to bimetallic sites. Binding interactions were computationally studied with electrostatic potentials and molecular orbital analysis. Anionic ligands were also demonstrated to form π-bound complexes

Dipalladium(I) Terphenyl Diphosphine Complexes as Models for Two-Site Adsorption and Activation of Organic Molecules

A <i>para</i>-terphenyl diphosphine was employed to support a dipalladium­(I) moiety. Unlike previously reported dipalladium­(I) species, the present system provides a single molecular hemisphere for binding of ligands across two metal centers, enabling the characterization and comparison of the binding of a wide variety of saturated and unsaturated organic molecules. The dipalladium­(I) terphenyl diphosphine toluene-capped complex was synthesized from a dipalladium­(I) hexaacetonitrile precursor in the presence of toluene. The palladium centers display interactions with the π-systems of the central ring of the terphenyl unit and that of the toluene. Exchange of toluene for anisole, 1,3-butadiene, 1,3-cyclohexadiene, thiophenes, pyrroles, or furans resulted in well-defined π-bound complexes which were studied by crystallography, nuclear magnetic resonance (NMR) spectroscopy, and density functional theory. Structural characterization shows that the interactions of the dipalladium unit with the central arene of the diphosphine does not vary significantly in this series allowing for a systematic comparison of the binding of the incoming ligands to the dipalladium moiety. Several of the complexes exhibit rare μ–η²:η² or μ–η²:η¹(O or S) bridging motifs. Hydrogenation of the thiophene and benzothiophene adducts was demonstrated to proceed at room temperature. The relative binding strength of the neutral ligands was determined by competition experiments monitored by NMR spectroscopy. The relative equilibrium constants for ligand substitution span over 13 orders of magnitude. This represents the most comprehensive analysis to date of the relative binding of heterocycles and unsaturated ligands to bimetallic sites. Binding interactions were computationally studied with electrostatic potentials and molecular orbital analysis. Anionic ligands were also demonstrated to form π-bound complexes

A Retro Diels–Alder Route to Diphosphorus Chemistry: Molecular Precursor Synthesis, Kinetics of P₂ Transfer to 1,3-Dienes, and Detection of P₂ by Molecular Beam Mass Spectrometry

The transannular diphosphorus bisanthracene adduct P₂<b>A</b>₂ (<b>A</b> = anthracene or C₁₄H₁₀) was synthesized from the 7-phospha­dibenzo­norborna­diene Me₂NP<b>A</b> through a synthetic sequence involving chloro­phosphine ClP<b>A</b> (28–35%) and the tetracyclic salt [P₂<b>A</b>₂Cl]­[AlCl₄] (65%) as isolated intermediates. P₂<b>A</b>₂ was found to transfer P₂ efficiently to 1,3-cyclohexadiene (CHD), 1,3-butadiene (BD), and (C₂H₄)­Pt­(PPh₃)₂ to form P₂(CHD)₂ (>90%), P₂(BD)₂ (69%), and (P₂)­[Pt­(PPh₃)₂]₂ (47%), respectively, and was characterized by X-ray diffraction as the complex [CpMo­(CO)₃(P₂<b>A</b>₂)]­[BF₄]. Experimental and computational thermodynamic activation parameters for the thermolysis of P₂<b>A</b>₂ in a solution containing different amounts of CHD (0, 4.75, and 182 equiv) have been obtained and suggest that P₂<b>A</b>₂ thermally transfers P₂ to CHD through two competitive routes: (<i>i</i>) an associative pathway in which reactive intermediate [P₂<b>A</b>] adds the first molecule of CHD before departure of the second anthracene, and (<i>ii</i>) a dissociative pathway in which [P₂<b>A</b>] fragments to P₂ and <b>A</b> prior to addition of CHD. Additionally, a molecular beam mass spectrometry study on the thermolysis of solid P₂<b>A</b>₂ reveals the direct detection of molecular fragments of only P₂ and anthracene, thus establishing a link between solution-phase P₂-transfer chemistry and production of gas-phase P₂ by mild thermal activation of a molecular precursor

A Retro Diels–Alder Route to Diphosphorus Chemistry: Molecular Precursor Synthesis, Kinetics of P₂ Transfer to 1,3-Dienes, and Detection of P₂ by Molecular Beam Mass Spectrometry

The transannular diphosphorus bisanthracene adduct P₂<b>A</b>₂ (<b>A</b> = anthracene or C₁₄H₁₀) was synthesized from the 7-phospha­dibenzo­norborna­diene Me₂NP<b>A</b> through a synthetic sequence involving chloro­phosphine ClP<b>A</b> (28–35%) and the tetracyclic salt [P₂<b>A</b>₂Cl]­[AlCl₄] (65%) as isolated intermediates. P₂<b>A</b>₂ was found to transfer P₂ efficiently to 1,3-cyclohexadiene (CHD), 1,3-butadiene (BD), and (C₂H₄)­Pt­(PPh₃)₂ to form P₂(CHD)₂ (>90%), P₂(BD)₂ (69%), and (P₂)­[Pt­(PPh₃)₂]₂ (47%), respectively, and was characterized by X-ray diffraction as the complex [CpMo­(CO)₃(P₂<b>A</b>₂)]­[BF₄]. Experimental and computational thermodynamic activation parameters for the thermolysis of P₂<b>A</b>₂ in a solution containing different amounts of CHD (0, 4.75, and 182 equiv) have been obtained and suggest that P₂<b>A</b>₂ thermally transfers P₂ to CHD through two competitive routes: (<i>i</i>) an associative pathway in which reactive intermediate [P₂<b>A</b>] adds the first molecule of CHD before departure of the second anthracene, and (<i>ii</i>) a dissociative pathway in which [P₂<b>A</b>] fragments to P₂ and <b>A</b> prior to addition of CHD. Additionally, a molecular beam mass spectrometry study on the thermolysis of solid P₂<b>A</b>₂ reveals the direct detection of molecular fragments of only P₂ and anthracene, thus establishing a link between solution-phase P₂-transfer chemistry and production of gas-phase P₂ by mild thermal activation of a molecular precursor

Mechanism and Scope of Phosphinidene Transfer from Dibenzo-7-phosphanorbornadiene Compounds

Dibenzo-7-phosphanorbornadiene compounds, RP<b>A</b> (<b>A</b> = C₁₄H₁₀ or anthracene), are investigated as phosphinidene sources upon thermally induced (70–90 °C) anthracene elimination. Analysis of substituent effects reveals that π-donating dialkylamide groups are paramount to successful phosphinidene transfer; poorer π-donors give reduced or no transfer. Substituent steric bulk is also implicated in successful transfer. Molecular beam mass spectrometry (MBMS) studies of each derivative reveal dialkylamide derivatives to be promising precursors for further gas-phase spectroscopic studies of phosphinidenes; in particular, we present evidence of direct detection of the dimethylamide derivative, [Me₂NP]. Kinetic investigations of ^<i>i</i>Pr₂NP<b>A</b> thermolysis in 1,3-cyclohexadiene and/or benzene-<i>d</i>₆ are consistent with a model of unimolecular fragmentation to yield free phosphinidene [^<i>i</i>Pr₂NP] as a transient reactive intermediate. This conclusion is probed by density functional theory (DFT) calculations, which favored a mechanistic model featuring free singlet aminophosphinidenes. The breadth of phosphinidene acceptors is expanded to unsaturated substrates beyond 1,3-dienes to include olefins and alkynes; this provides a new synthetic route to valuable amino-substituted phosphiranes and phosphirenes, respectively. Stereoselective phosphinidene transfer to olefins is consistent with singlet phosphinidene reactivity by analogy with the Skell hypothesis for singlet carbene addition to olefins