Synthesis and structure of two crowded trans-[PdCl2L2] complexes based on a chiral, calix[4]arene-fused phosphole. (8th January 2018)

• Record Type: Journal Article
• Authors: Elaieb, Fethi; Sémeril, David; Bauder, Claude; Matt, Dominique; Bailly, Corinne; Karmazin, Lydia
• Is Part Of: Polyhedron. Volume 139(2018)
• Page Start: 172
• Page End: 177
• Publication Date: 2018-01-08
• Subjects: Calixarene -- Phosphole -- Palladium -- Chiral ligands -- Bulky ligands; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2017.10.020
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: Reaction of a racemic calixarene-fused phosphole with PdCl2 results in a mixture of two diastereomeric trans -PdCl2 L2 complexes in which the calixarene fragments provide effective steric protection of the metal atoms, notably along their d z 2 axis, while at the same time adopting strongly pinched conformations. Abstract: The chiral, calix[4]arene-fused phosphole rac -1 reacts with [PdCl2 (PhCN)2 ] to afford a mixture of two diastereomeric complexes, trans -[PdCl2 {( P, R )-1 }{( M, S )-1 }] (2a ) and trans -[PdCl2 {( P, R )-1 }2 ]/ trans -[PdCl2 {( M, S )-1 }2 ] (2b ), which can be separated by column chromatography. Ligand1 contains an inherently chiral calix[4]arene skeleton (displaying either P or M helicity) as well as an inversion-stable phosphorus atom (with R or S configuration) having its lone pair located on the endo -face of the calixarene cavity. Both complexes, which equilibrate slowly in solution (2a :2b = 39:61 at equilibrium), have been isolated and characterised by single-crystal X-ray diffraction: Complex2a : triclinic, space group P 1 ¯, unit cell dimensions a = 11.0070(3), b = 21.9271(7), c = 23.2270(7) Å, α = 116.054(2)°, β = 95.823(2)°, γ = 92.956(2)°, Z = 2; Complex2b : triclinic, space group P 1 ¯, unit cell dimensions a = 14.2643(6), b = 17.3200(8), c = 22.6335(10) Å, α = 102.496(2)°, β = 103.774(2)°, γ = 95.034(2)°, Z = 2. The unit cell of2a contains two inequivalent centrosymmetric molecules, which differ only slightly from each other. Both palladium atoms have close to a square planar environment and are sterically protected along the d z 2 axis by the two bulky calixarene units, which adopt markedly pinched conformations. Each chlorine atom sits close to an equatorial H atom (Heq ) of a methylenic ArC H2 group (av. Heq …Cl separation 2.88 Å). Consistent with an Heq …Cl bonding interaction, the corresponding 1 H NMR signal undergoes an unusual downfield shift upon complex formation. In the solid, 2b consists of a racemic mixture of trans -[PdCl2 {( P, R )-1 }2 ] and trans -[PdCl2 {( M, S )-1 }2 ]. Similar Heq …Cl interactions to those seen in2a are found in2b .