Mohammed Ghalib

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 1 with CuCl, CuBr, or Cu(SMe2)Br in THF at room temperature provides sparingly soluble [Cu7(μ(2)-L6)(μ(2)-X7)](+)[CuX2](-) cluster complexes 2a,b (L indicates coordinated 1, a X = Cl, 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 2a·4THF and the dimers 3b [{Cu(η(1)-L)2(μ(2)-Br)}2], 4b [{Cu(μ(2)-L)(η(1)-L)(κBr)}2], 5a·2MeOH, and 5b·2MeOH [{Cu(μ(2)-L)(η(1)-L)(κX···HOMe)}2] generally display μ(2)-P- and/or tilted η(1)-P-coordination, contrasting with the preference for the η(1)-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 3b and 4b, 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 4b 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 4b, indicating the absence of weak cuprophilic interactions in this compound.

Phosphanyl-substituted π-excess σ2P heterocycles: Coordination behaviour of 2-di-tert-butylphosphanyl-1-neopentyl-1,3-benzazaphosphole towards CuCl, HgCl2 and [Rh(COD)2]BF4

Reaction of the heterocyclic –PC(PtBu2)–N– hybrid ligand 1 with CuCl or HgCl2 in THF provided the metal complexes 2 and 3. The crystal structure analysis showed dimeric η1-phosphanyl and μ-chloro-coordinated species with the dicoordinated P-atom remote from the metal. In solution broadened phosphorus resonances are observed indicating low kinetic stability and ligand exchange reactions. The reaction of 1 with [Rh(COD)2]BF4 was much slower, required heating and led finally to the four-membered dihydrobenzazaphosphole Rh(COD) P⁁P′-chelate complex 4. The initial Rh(COD)+ complex proved very labile and added moisture traces at the PC bond, whereas the free ligand is stable to aqueous acids and bases.

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

GRAPHICAL ABSTRACT Abstract Coordination chemical studies of 1H-1,3-benzazaphospholes, π-excess aromatic σ2P-ligands, demonstrate similar ligand properties to those of phosphabenzenes toward MVI(CO)n but marked differences toward nonzerovalent transition metals. Benzazaphosphole d8-metal halide complexes are more strongly destabilized and undergo consecutive reactions, whereas benzazaphosphole coinage metal halide and HgCl2 complexes generally display μ2P- and/or bent η1P-coordination with π-P donor bond contribution, contrasting with the preference of phosphinine CuX complexes for η1P-coordination within the ring plane.

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

GRAPHICAL ABSTRACT ABSTRACT 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.

π-Rich σ2P-Heterocycles: d10-Transition Metal Complexes of 1H-1,3-Benzazaphospholes with Unusual Coordination

GRAPHICAL ABSTRACT Abstract 1H-1,3-Benzazaphospholes are aromatically stabilized σ2P heterocycles1,2 with increased π-density at phosphorus. This is caused by delocalization of the σ3N lone pair in the five-membered ring and disfavors π-back bonding from d10 transition metal cations to the ligand within the ring plane. The crystal structures of benzazaphosphole AgCl2c and CuX complexes2f display unusual bent or μ-bridging coordination although σ2P-phosphabenzene (phosphinine) ligands typically coordinate CuX groups in the σ-mode within the ring plane.3 Exceptions are complexes with pyridyl-phosphinine pincer ligands4a or 2-hydroxyphosphinines that acquire increased π-density by the +M-effect of the hydroxy group in o-position.4b

π-Rich σ2P-Heterocycles: Syntheses, Reactivity, and Application Potential of 1,3-Benzazaphospholes

GRAPHICAL ABSTRACT Abstract 1H-1,3-Azaphospholes and their benzo-fused derivatives are a particular class of aromatically stabilized σ2P heterocycles1,2 that differ from the well-known phosphabenzenes1a,3 and other types of azaphospholes1c by their increased π-density at phosphorus. This is caused by delocalization of the σ3N lone pair in the five-membered ring, the position of N in conjugation to phosphorus, the lack of P-N bonds, and the absence of electron-withdrawing σ2N atoms, and leads to a specific reactivity pattern, in many aspects different from that of other P = C compounds (Figure 1). We present a short overview on new routes to mono- and bidentate benzazaphospholes, substitution reactions at P, C2, and N and also on solvent/additive-dependent addition reactions of tBuLi, which provide access to sterically demanding and P-basic phosphine ligands. In addition, the application potential of bap-W(CO)5/Ag(+) initiators for ring-opening-polymerization of 3-5 membered cyclic ethers and of dihydro-benzazaphosphol-2-carboxylate Ni catalysts for the oligomerization of ethylene is shown.