Aluminum Compounds Containing η¹‐ and/or η⁵‐Bidentate Dianionic Pyrrolyl–Methylamide Ligands

Abstract

A series of dialuminum compounds have been synthesized and their reactivity and application for lactide polymerization have been studied. The reaction of AlH3 x NMe3 with [C4H3NH(2-CH2NHtBu)] in diethyl ether generated a dimeric aluminum hydride compound, [[[C4H3N(2-CH2NtBu)]AlH]2] (1). The structure of 1 was confirmed by spectroscopy of a deuterated analogue of 1 with an Al--D function. Direct treatment of [C4H3NH(2-CH2NHtBu)] with LiAlH4 in diethyl ether resulted in colorless crystals of [[Li[micro-eta1:eta5-C4H3N(2-CH2NtBu)]2Al]2] (2) in 80 % yield after recrystallization from a toluene solution. The micro-eta1:eta5-pyrrolyl protons exhibit high-field shifts at delta=5.73, 6.15, and 6.72 comparable to a similar eta5-bonding mode in the literature. Treatment of 1 with 1 equiv acetone oxime or acetone in dichloromethane gave [[[C4H3N(2-CH2NtBu)]Al[varkappaO,varkappaN-(ON==CMe2)]]2] (3) and [[[C4H3N(2-CH2NtBu)]Al(O--CHMe2)]2] (4) in 67 % and 60 % yield, respectively. Compounds 1-4 have been characterized by X-ray diffractometry and were used as catalysts for epsilon-caprolactone polymerization.

Reactions of Dimeric Aluminium Hydride Compounds Containing Bidentate Dianionic Pyrrolyl Ligands and Their Applications in Ring‐Opening Polymerization of ϵ‐Caprolactone

“…[{C 4 H 3 N(2-CH 2 NtBu)}AlH] 2 (1) was prepared according to a previously reported procedure. [13] All the chemicals (Aldrich, Acros) were used as received.…”

“…Metal hydride induced benzil reduction to diphenylethenediolate is even less well explored. [11] Previously dialuminium compounds were generated with mono-or bidentate orientation of acetone or acetone oxime into [{C 4 H 3 N(2-CH 2 NtBu)}AlH] 2 , [13] whereas in this work we prepared two dialkoxy-bridged dialuminium compounds by insertion of 1-indanone and 9-fluorenone into the aluminium hydride bonds. …”

“…[13] The reactions of 1 with mono-and diketones are summarized in Scheme 1 and Scheme 2, respectively. The reactions of 1 with 2 equiv.…”

“…The Al-N(pyrrolyl) bond lengths are rather similar to those of previously reported aluminium pyrrolyl compounds. [13] The solid-state structures of compounds 4-7 were determined similarly and their molecular structures are shown in Unlike the geometry of 8, compound 9 exhibits a center of symmetry in which the Al 2 N 2 forms a perfect plane. Compound 9 consists of two five-coordinate aluminium centers, which can be described as distorted trigonal bipyramidal.…”

“…The range of the polydispersity index (PDI) of the poly(ε-caprolactone) product (1.26-1.47) is comparable to or a little broader than that of polymers obtained with other aluminium catalysts. [13,21] [20]…”