Neuartige basische Liganden für die homogenkatalytische Methanolcarbonylierung, XXXI Kationische Bis(Ether-Phosphan)metall-Komplexe der Nickeltriade mit fluktuierendem Verhalten / Novel Basic Ligands for the Homogeneous Catalytic Methanol Carbonylation, XXXI Cationic Bis(Ether-Phosphine)Metal Complexes of the Nickel Triad with Fluxional Behavior

Abstract

The (ether-phosphine) ligands R2PCH2C5H9O (1a-c) [R = Ph (a), Cy (= cyclo-C6H11) (b), n-C3H7 (c); C5H9O = tetrahydropyranyl] are obtained from the corresponding alkali metal phosphides MPR2 (M = Li, Na) and 2-chloromethyltetrahydropyran in ether. Reaction of 1 a-c with either Cl2M(COD) (COD = 1,5-cyclooctadiene) or [Ni(OH2)6]Cl2 in a2:1 ratio leads to the bis(ether-phosphine)metal complexes Cl2M(R2P∾O)2 trans-2b,c, trans-3b, cis-2a,b, cis-3a, and 4a [M = Pd (2), Pt (3), Ni (4)], in which the ligands 1a-c are η1-P-coordinated. In 2—4 Cl- is abstracted by AgClO4 to give the cationic trans-bis(ether-phosphine) complexes [ClM(R2P ∾ O)(R2P~O)][ClO4] (5a, 6a-c, 7a) [M = Ni (5), Pd (6), Pt (7); P∾O = η1-P-coordinated; P~O = η2-O,P-coordinated]. In contrast to 7a, the nickel and palladium complexes 5a and 6a-c show fluxional behavior as demonstrated by temperature dependent 31P{1H} NMR spectra. The coalescence temperatures and estimated free energie enthalpies ΔG≉ of 5a and 6a-c are compared with the corresponding data of the complexes [ClPd(Ph2P ∾ O)(Ph2~O)][ClO4] (8a-10a) [O,P ligand = Ph2PCH2C4H7O (8a), Ph2PCH2C4H7O2 (9a), Ph2PCH2CH2OCH3 (10a)] and give an insight into the relative basicity of the ether oxygen atoms.