Synthesis and Structure of Neutral and Cationic Aluminum Complexes Supported by Bidentate O,P-Phosphinophenolate Ligands and Their Reactivity with Propylene Oxide and ε-Caprolactone

Abstract

The O,P-type phosphinophenol ligands 1a-c were found to readily react with 1 equiv of AlMe 3 to afford in high yields the corresponding Al chelate complexes {η 2 3c) also formed quantitatively upon reaction of phosphinophenols 1b,c with 0.5 equiv of AlMe 3 . Both the mono-and bis-adduct Al methyl species 2a-c and 3b,c are stable monomeric species whether in solution or in the solid state and remain stable in coordinating solvents such as thf. In contrast, the bis-adduct Al methyl complex 3c undergoes a ligand exchange reaction in the presence of an alcohol source ( i PrOH, BnOH) to generate the homoleptic tris-adduct Al complex {η 2 -O,P-(2-PPh 2 -4-Me-6-t Bu-C 6 H 3 O)} 3 Al (5c), as determined from X-ray crystallographic studies. Both the mono-and bis-adduct Al methyl species 2b,c and 3b,c react fast with B(C 6 F 5 ) 3 via a methide abstraction reaction to afford the stable and well-defined Al cationic species {η 2 -O,P-( 2, respectively, which were found to be highly active in propylene oxide polymerization to afford atactic poly(propylene oxide). These cations also readily initiate the ring-opening polymerization of ε-caprolactone via successive ring-opening insertions of the monomer into the Al-O phenoxide bond of the phosphinophenolate chelating ligand to exclusively afford linear poly(ε-caprolactone) capped, at the ester end, with a (phosphino oxide)phenolate group, as deduced from NMR and MALDI-TOF data. In these cationic systems, the POchelating moiety may thus act as both a supporting ligand and an initiating group for the ROP of ε-CL.

Coordination chemistry of the main group elements with phosphine, arsine and stibine ligands

“…23) [161,162]. 2-Diphenylphosphinophenols form mono-, bis-and tris-adducts on reaction with AlMe 3 in which the ligands chelate (P,O) as monoanions to the aluminium, with the Al-P distances increasing with increased coordination number as expected [164]. Chelating C,P coordination is found…”

Synthesis, structure, and reactivity of AlMe2(1-Me-CB11F11): An AlMe2+ cation-like species bonded to a superweak anion

“…Cationic aluminum complexes are of considerable interest due to their potential use in a variety of organic and catalytic transformations [1][2][3][4][5][6][7]. The most reactive are undoubtedly the cation-like species AlR 2 + bonded to carborane and borane superweak anions, which have been isolated and characterized by Reed and co-workers (AlEt 2 (CB 11 H 6 Cl 6 ) and AlEt 2 (CB 11 H 6 Br 6 )) [7] and by Knapp and co-workers ((AlMe 2 ) 2 (B 12 Cl 12 ) and (AlEt 2 ) 2 (B 12 Cl 12 )) [2].…”

Synthesis, Structure, and Ring‐Opening Polymerization Catalysis of Zinc Complexes Containing Amido Phosphinimine Ligands

“…Interestingly, the alkyl derivatives 3a-c and 4a-c are all quite active (93 % to quantitative conversion) under the conditions investigated. In general, the (corrected) [64,65] number-averaged molecular weights (M n ) of PCL measured by gel permeation chromatography (GPC) are comparatively higher than those expected (Entries 1-11). Nevertheless, they are approximately proportional to the theoretical values or to the monomer-to-catalyst ratios (Entries 6-11, Figures S2 and S3), which indicates that the propagating chains grow in a reasonably controlled manner.…”

“…[13,51,58] It has been shown that the steric hindrance imposed by the β-diketiminate ligands in {[BDI]Zn(μ-OAc)} 2 is essential to encourage the formation of catalytically active [BDI]Zn(μ-OAc) in solution. [51] Given that 6a is mononuclear, even in the solid state, its low activity in ROP catalysis thus reflects intrinsic discrepancy between [64,65] [f] Conducted in the presence of 2-propanol (2.0 mm).…”