N,N,O-Tridentate Mixed Lithium–Magnesium and Lithium–Aluminum Complexes: Synthesis, Characterization, and Catalytic Activities

The syntheses and crystal structures
of a series of heterobimetallic Li/Mg and Li/Al complexes prepared
from an N,N,O-tridentate ligand are described. The ligand HOC­(CH2)5CH2N­(Me)­CH2CH2NMe2 (LH) and nBu2Mg
were used to synthesize the homometallic magnesium alkoxide [{LMgOC­(CH2)5CH2N­(Me)­CH2CH2NMe2}2] (1), which
was reacted with nBuLi to afford the lithium alkylmagnesiate
[{Bu2Mg­{LiOC­(CH2)5CH2N­(Me)­CH2CH2NMe2}}2] (2). Complex 2 was then hydrolyzed to produce
[{BuMgOLi­{LiOC­(CH2)5CH2N­(Me)­CH2CH2NMe2}2}2] (3). The sequential reaction of LH in diethyl ether with RAlMe2 (R = Me, Cl) and nBuLi aforded two lithium aluminate complexes containing a
polymeric structure of one-dimensional chains [{−LiOC­(CH2)5CH2N­(Me)­CH2CH2NMe2}­Al­(Me)­(n-Bu)­CH3−}n] (4) and [{−LiOC­(CH2)5CH2N­(Me)­CH2CH2NMe2}­Al­(n-Bu)2CH2−}n] (5),
respectively. Each of the complexes 1–5 was structurally characterized and tested for its capability to
catalyze Meerwein–Ponndorf–Verley (MPV) reactions. Heterobimetallic
complexes 2 and 3 exhibited catalytic activities
better than those of homometallic magnesium complex 1 and heterobimetallic lithium aluminate complexes 4 and 5 for MPV reactions.