title: Aluminium complexes of bidentate N,O- and N,N-ligands derived from oxidative functionalization of amido phosphines: synthesis, structure and reactivity.
abstract: A series of amido phosphinoxide and amido phosphinimine ligands that are electronic variations of monoanionic N,O- and N,N-ketiminates have been prepared and employed to examine the coordination chemistry of aluminium. Oxidation of the previously established N-(2-diphenylphosphinophenyl)-2,6-dialkylaniline in the presence of H(2)O(2) or organic azides RN(3) (R = 2,6-C(6)H(3)(i)Pr(2), SiMe(3)) led to phosphinoxides (H[NO] 1a-b) and phosphinimines (H[NN] 1c-d), respectively. Alkane elimination reactions of these protio-ligand precursors with trialkylaluminium in toluene or pentane solutions afforded cleanly the corresponding organoaluminium complexes, including dimethyl 2a-d, diethyl 3a-d and diisobutyl derivatives 4a-b and 4d. Solution NMR studies revealed Cs symmetry for these organoaluminium species, in which the α-hydrogen atoms are all diastereotopic. The correlation between the steric congestion of these molecules and the degree of resolution of the multiplet signals corresponding to the diastereotopic α-hydrogen atoms observed by the (1)H NMR spectroscopy is of particular interest. Dichloroaluminium complexes 5c-d were prepared in high yields by protonolysis of MeAlCl(2) with 1c-d. Single-crystal X-ray diffraction analyses of 2c-d, 3a, 3d, 4a, and 4d elucidated a mononuclear, distorted tetrahedral core for all of these aluminium species. Interestingly, complexes 2c-d are active initiators for catalytic ring-opening oligomerization of ε-caprolactone, whereas 2a-b are rather inactive, highlighting the significance of the steric hindrance imposed by the amido phosphinimine ligands, as compared to that imposed by the phosphinoxide counterparts.
authors.affiliation: Department of Chemistry and Center for Nanoscience & Nanotechnology, National Sun Yat-sen University, Kaohsiung 80424, Taiwan. lcliang@mail.nsysu.edu.tw
authors.forename: Lan-Chang
authors.initials: LC
authors.lastname: Liang
authors.forename: Feng-Yi
authors.initials: FY
authors.lastname: Chen
authors.forename: Mei-Hui
authors.initials: MH
authors.lastname: Huang
authors.forename: Liang-Chien
authors.initials: LC
authors.lastname: Cheng
authors.forename: Chun-Wei
authors.initials: CW
authors.lastname: Li
authors.forename: Hon Man
authors.initials: HM
authors.lastname: Lee