Neuartige basische Liganden für die homogenkatalytische Methanolcarbonylierung, XXXVIII. Synthese, Eigenschaften und fluktuierendes Verhalten von (Ether‐Phosphan)palladium‐Komplexen

Novel Basic Ligands for the Homogeneous Catalytic Carbonylation of Methanol, XXVIII. — Synthesis, Properties and Fluxional Behavior of (Ether‐Phosphine)palladium Complexes Cl 2 Pd(COD) ( 1 ) (COD = 1,5‐cyclooctadiene) reacts with 1 equiv, of the (ether‐phosphine) ligand Ph 2 P∼D ( 2a–c ) (D = CH 2 C 4 H 7 O ( a ), CH 2 C 4 H 7 O 2 ( b ), CH 2 CH 2 OCH 3 ( c )] to give the dimeric complexes [μ‐ClPdCl(Ph 2 P∼D)] 2 ( 3a–c ) (P∼D = η 1 ‐ P ‐coordinated). According to the field‐desorption mass spectra which show only one peak for the monomeric moieties ClPd(Ph 2 P∼D), 3a–c have a very weak Pd 2 Cl 2 bridge. trans ‐Cl 2 Pd(Ph 2 P∼D) 2 ( 4a–c ) is obtained either from 3a–c and 2a–c by cleaving the Pd 2 Cl 2 bridge or from 1 and 2 equiv. of the ligands 2a–c. 4c crystallizes in the monoclinic space group P 2 1 /c with Z = 2. AgClO 4 selectively abstracts one Cl⊖ ligand from 4a–c which results in the formation of the cationic complexes [ trans ‐(Ph 2 P∩D)(Ph 2 P∼D)PdCl]⊕ ( 5a–c ) (P∩D = η 2 ‐ D,P ‐coordinated) containing one chelated and one η 1 1 ‐ P ‐bonded (ether‐phosphine) ligand. 5a–c show fluxional behavior which is demonstrated by temperature‐dependent 31 P{ 1 H}‐NMR investigations. The coalescence points have been determined and are at 253 ( 5a ), 303 ( 5b ), and 283 K ( 5c ). The activation enthalpies ΔG‡ are estimated at 48, 58, and 54 kJ/mol. The abstraction of the second Cl ⊖ ligand from 5a–c succeeds only in the presence of AgSbF 6 yielding the dicationic bis(chelate) complexes [ trans ‐(Ph 2 P∩D) 2 Pd] 2⊕ ( 6a–c ). The latter are also obtained from 4a–c ) and AgSbF 6 . The hydrogenating properties of 3a–c and 4a–c toward 1‐hexyne are investigated in comparison with trans ‐Cl 2 Pd(Ph 2 P‐CH 2 CH 2 CH 3 ) 2 .