New κ 3-PNN′- and κ 4-PNN′O-polydentate ligands: Synthesis, coordination and structural studies

Abstract

The three-step synthesis of new mixed P/N/N′/O-donor ligands C 6H 3(OH){2-NHC(O)CH 2N CHC 6H 4PPh 2}(4-CH 3) 3a· HH and C 6H 4(OH){3-NHC(O)CH 2N CHC 6H 4PPh 2} 3b· HH, by Schiff base condensation of the 1° amines C 6H 3(OH){2-NHC(O)CH 2NH 2}(4-CH 3) 2a or C 6H 4(OH){3-NHC(O)CH 2NH 2} 2b with C 6H 4(CHO)(2-PPh 2) in refluxing EtOH, is described. Reaction of 1 equiv. of 3a· HH or 3b· HH with MCl 2(cod) (M = Pt, Pd; cod = cycloocta-1,5-diene) affords the κ 2-PN-chelate complexes MCl 2( 3a· HH) (M = Pd 4a; M = Pt 4b) and MCl 2( 3b· HH) (M = Pt 4c). The dichlorometal(II) complexes 4d and 4e, bearing instead a pendant 4-phenolic group, were similarly prepared (in >90% yield). Chloro-bridge cleavage of [Pd(μ-Cl)(η 3-C 3H 5)] 2 with 3a· HH or 3b· HH gave the monocationic κ 2-PN-chelate complexes [Pd(η 3-C 3H 5)( 3a· HH)]Cl 5a or [Pd(η 3-C 3H 5)( 3b· HH)]Cl 5b, respectively. Elimination of cod, and single CH 3 protonation, from Pt(CH 3) 2(cod) upon reaction with 1 equiv. of 3a· HH or 3b· HH in C 7H 8 at room temperature afforded the neutral complexes C 6H 3(OH){2-NC(O)CH 2N CHC 6H 4PPh 2Pt(CH 3)}(4-CH 3) 6a and C 6H 4(OH){3-NC(O)CH 2N CHC 6H 4PPh 2Pt(CH 3)} 6b, respectively bearing a monoanionic ( 3a· H − or 3b· H −) κ 3-PNN′-tridentate ligand. Amide and phenol deprotonation were readily achieved, using KO t Bu as base, to give high yields of the κ 4-PNN′O-tetradentate complexes C 6H 3(O){2-NC(O)CH 2N CHC 6H 4PPh 2Pd}(4-CH 3) 7a and C 6H 3(O){2-NC(O)CH 2N CHC 6H 4PPh 2Pt}(4-CH 3) 7b bearing the dianionic ligand 3a 2− . All new compounds have been characterised by multinuclear NMR, FTIR, mass spectroscopy and microanalysis. Single crystal X-ray studies have been performed on compounds 1b·1.5CH 2Cl 2, 3b· HH·0.5Et 2O, 6b·CHCl 3 and 7b·0.5Et 2O.