Enantiomerically Pure N Chirally Substituted 1,3-Benzazaphospholes: Synthesis, Reactivity toward <i>t</i>BuLi, and Conversion to Functionalized Benzazaphospholes and Catalytically Useful Dihydrobenzazaphospholes

Catalytic C–P coupling of chiral <i>o</i>-bromoanilines <b>1a</b>–<b>c</b> to the corresponding <i>o</i>-phosphonoanilines <b>2a</b>–<b>c</b>, reduction to the phosphines <b>3a</b>–<b>c</b>, and final acid-catalyzed cyclocondensation represents a convenient access to the title compounds <b>4a</b>–<b>c</b>. Reaction of <b>4a</b>,<b>b</b> with <i>t</i>BuLi allows solvent-dependent directed lithiation leading either to 2-lithiobenz­azaphospholes with a −PCLi–NR– substructure (in Et₂O/KO<i>t</i>Bu), in the case of anisyl substitution accompanied by partial additional lithiation in <i>o</i>-position of the MeO-group, or to regiospecific “normal” addition with formation of −P­(<i>t</i>Bu)–CHLi–NR– species. These were trapped by ClSiMe₃, CO₂, or MeOH to give the corresponding substitution products <b>7b</b>, <b>8b</b>, <b>10b</b>, <b>11a</b>,<b>b</b> and <b>12a</b>,<b>b</b>, respectively. <b>12a</b>,<b>b</b>, containing the P–C–COOH structural unit, forms with Ni­(COD)₂ in THF very efficient ethylene oligomerization catalysts with high selectivity for linear α-olefins. The structure elucidation of the products is based on conclusive solution NMR data and crystal structure analyses of the 1-(1<i>S</i>)-anisylethyl compounds <b>3b</b> and <b>4b</b>

Enantiomerically Pure N Chirally Substituted 1,3-Benzazaphospholes: Synthesis, Reactivity toward <i>t</i>BuLi, and Conversion to Functionalized Benzazaphospholes and Catalytically Useful Dihydrobenzazaphospholes

Catalytic C–P coupling of chiral <i>o</i>-bromoanilines <b>1a</b>–<b>c</b> to the corresponding <i>o</i>-phosphonoanilines <b>2a</b>–<b>c</b>, reduction to the phosphines <b>3a</b>–<b>c</b>, and final acid-catalyzed cyclocondensation represents a convenient access to the title compounds <b>4a</b>–<b>c</b>. Reaction of <b>4a</b>,<b>b</b> with <i>t</i>BuLi allows solvent-dependent directed lithiation leading either to 2-lithiobenz­azaphospholes with a −PCLi–NR– substructure (in Et₂O/KO<i>t</i>Bu), in the case of anisyl substitution accompanied by partial additional lithiation in <i>o</i>-position of the MeO-group, or to regiospecific “normal” addition with formation of −P­(<i>t</i>Bu)–CHLi–NR– species. These were trapped by ClSiMe₃, CO₂, or MeOH to give the corresponding substitution products <b>7b</b>, <b>8b</b>, <b>10b</b>, <b>11a</b>,<b>b</b> and <b>12a</b>,<b>b</b>, respectively. <b>12a</b>,<b>b</b>, containing the P–C–COOH structural unit, forms with Ni­(COD)₂ in THF very efficient ethylene oligomerization catalysts with high selectivity for linear α-olefins. The structure elucidation of the products is based on conclusive solution NMR data and crystal structure analyses of the 1-(1<i>S</i>)-anisylethyl compounds <b>3b</b> and <b>4b</b>

Pyrido-anellated 1,3-azaphospholes-current state and future challenges

<p>A short overview of the syntheses, properties and some reactions of pyrido-anellated 1.3-azaphospholes is presented. Except for 2-phosphaindolizines, which have been intensively studied with respect to syntheses, electrophilic substitution and cycloadditions, this is a class of compound that has still been only sparingly investigated. Preliminary results and hints as to possible perspectives are included to encourage further research on these novel P,N hybrid ligands.</p

Π-Rich σ²P-Ligands: Unusual Coordination Behavior of <i>1H</i>-1,3-Benzazaphospholes Toward Late Transition Metals

<div><p>GRAPHICAL ABSTRACT</p><p></p></div

π‑Rich σ²P‑Heterocycles: Bent η¹‑P- and μ²‑P-Coordinated 1,3-Benzazaphosphole Copper(I) Halide Complexes

The reaction of 1-neopentyl-1,3-benzazaphosphole <b>1</b> with CuCl, CuBr, or Cu­(SMe₂)Br in THF at room temperature provides sparingly soluble [Cu₇(μ²-L₆)­(μ²-X₇)]⁺[CuX₂]⁻ cluster complexes <b>2a</b>,<b>b</b> (L indicates coordinated <b>1</b>, <b>a</b> X = Cl, <b>b</b> X = Br), with loosely bound THF, in high yields. The conversions proceed via transient THF-soluble labile [(L₂CuX)₂] complexes. Separation before complete conversion, combined with suitable conditions for crystallization, allowed these intermediates to be trapped. Depending on the reactant ratios, crystals of the clusters or of dimeric L₂CuX complexes were formed. The crystal structure analyses of <b>2a</b>·4THF and the dimers <b>3b</b> [{Cu­(η¹-L)₂­(μ²-Br)}₂], <b>4b</b> [{Cu­(μ²-L)­(η¹-L)­(κBr)}₂], <b>5a</b>·2MeOH, and <b>5b</b>·2MeOH [{Cu­(μ²-L)­(η¹-L)­(κX···HOMe)}₂] generally display μ²-P- and/or tilted η¹-P-coordination, contrasting with the preference for the η¹-P in-plane coordination mode of phosphinine ligands in their copper­(I) halide complexes. DFT studies of geometry-optimized monomers LCuBr, L­(CuBr)₂, L₂CuBr, and the dimers <b>3b</b> and <b>4b</b>, calculated at the ωB97xD/cc-PVDZ level, suggest that weak competing interactions with the solvent THF and the entropy factor of the dimerization result in lability and a subtle balance between the different complexes in solution, whereas the particular coordination observed in the crystals is attributable to conservation of the delocalized π-system in the ligand. The HOMO of <b>4b</b> is composed of Cu d orbitals and the π-type HOMO of the bridging ligand. Interestingly, despite the rather short Cu···Cu interatomic separation (2.726 Ǻ), no bond critical point could be located in <b>4b</b>, indicating the absence of weak cuprophilic interactions in this compound

π‑Rich σ²P‑Heterocycles: Bent η¹‑P- and μ²‑P-Coordinated 1,3-Benzazaphosphole Copper(I) Halide Complexes

The reaction of 1-neopentyl-1,3-benzazaphosphole <b>1</b> with CuCl, CuBr, or Cu­(SMe₂)Br in THF at room temperature provides sparingly soluble [Cu₇(μ²-L₆)­(μ²-X₇)]⁺[CuX₂]⁻ cluster complexes <b>2a</b>,<b>b</b> (L indicates coordinated <b>1</b>, <b>a</b> X = Cl, <b>b</b> X = Br), with loosely bound THF, in high yields. The conversions proceed via transient THF-soluble labile [(L₂CuX)₂] complexes. Separation before complete conversion, combined with suitable conditions for crystallization, allowed these intermediates to be trapped. Depending on the reactant ratios, crystals of the clusters or of dimeric L₂CuX complexes were formed. The crystal structure analyses of <b>2a</b>·4THF and the dimers <b>3b</b> [{Cu­(η¹-L)₂­(μ²-Br)}₂], <b>4b</b> [{Cu­(μ²-L)­(η¹-L)­(κBr)}₂], <b>5a</b>·2MeOH, and <b>5b</b>·2MeOH [{Cu­(μ²-L)­(η¹-L)­(κX···HOMe)}₂] generally display μ²-P- and/or tilted η¹-P-coordination, contrasting with the preference for the η¹-P in-plane coordination mode of phosphinine ligands in their copper­(I) halide complexes. DFT studies of geometry-optimized monomers LCuBr, L­(CuBr)₂, L₂CuBr, and the dimers <b>3b</b> and <b>4b</b>, calculated at the ωB97xD/cc-PVDZ level, suggest that weak competing interactions with the solvent THF and the entropy factor of the dimerization result in lability and a subtle balance between the different complexes in solution, whereas the particular coordination observed in the crystals is attributable to conservation of the delocalized π-system in the ligand. The HOMO of <b>4b</b> is composed of Cu d orbitals and the π-type HOMO of the bridging ligand. Interestingly, despite the rather short Cu···Cu interatomic separation (2.726 Ǻ), no bond critical point could be located in <b>4b</b>, indicating the absence of weak cuprophilic interactions in this compound

π‑Rich σ²P‑Heterocycles: Bent η¹‑P- and μ²‑P-Coordinated 1,3-Benzazaphosphole Copper(I) Halide Complexes

The reaction of 1-neopentyl-1,3-benzazaphosphole <b>1</b> with CuCl, CuBr, or Cu­(SMe₂)Br in THF at room temperature provides sparingly soluble [Cu₇(μ²-L₆)­(μ²-X₇)]⁺[CuX₂]⁻ cluster complexes <b>2a</b>,<b>b</b> (L indicates coordinated <b>1</b>, <b>a</b> X = Cl, <b>b</b> X = Br), with loosely bound THF, in high yields. The conversions proceed via transient THF-soluble labile [(L₂CuX)₂] complexes. Separation before complete conversion, combined with suitable conditions for crystallization, allowed these intermediates to be trapped. Depending on the reactant ratios, crystals of the clusters or of dimeric L₂CuX complexes were formed. The crystal structure analyses of <b>2a</b>·4THF and the dimers <b>3b</b> [{Cu­(η¹-L)₂­(μ²-Br)}₂], <b>4b</b> [{Cu­(μ²-L)­(η¹-L)­(κBr)}₂], <b>5a</b>·2MeOH, and <b>5b</b>·2MeOH [{Cu­(μ²-L)­(η¹-L)­(κX···HOMe)}₂] generally display μ²-P- and/or tilted η¹-P-coordination, contrasting with the preference for the η¹-P in-plane coordination mode of phosphinine ligands in their copper­(I) halide complexes. DFT studies of geometry-optimized monomers LCuBr, L­(CuBr)₂, L₂CuBr, and the dimers <b>3b</b> and <b>4b</b>, calculated at the ωB97xD/cc-PVDZ level, suggest that weak competing interactions with the solvent THF and the entropy factor of the dimerization result in lability and a subtle balance between the different complexes in solution, whereas the particular coordination observed in the crystals is attributable to conservation of the delocalized π-system in the ligand. The HOMO of <b>4b</b> is composed of Cu d orbitals and the π-type HOMO of the bridging ligand. Interestingly, despite the rather short Cu···Cu interatomic separation (2.726 Ǻ), no bond critical point could be located in <b>4b</b>, indicating the absence of weak cuprophilic interactions in this compound