Magnesium Complexes Containing η¹‐ and η³‐Pyrrolyl or Ketiminato Ligands: Synthesis, Structural Investigation and ϵ‐Caprolactone Ring‐Opening Polymerisation

Abstract

A series of dimeric magnesium derivatives containing substituted pyrrolyl or ketiminato ligands was synthesised and the application of these derivatives for the ring opening polymerisation of ϵ‐caprolactone has been carried out. Reactions of [Mg{N(SiMe3)2}]2 (1) with one equiv. of 2‐dimethylaminomethyl pyrrole and 2‐diethylaminomethyl pyrrole in toluene generates [Mg{C4H3N(2‐CH2NMe2)}{N(SiMe3)2}]2 (2) and [Mg{C4H3N(2‐CH2NEt2)}{N(SiMe3)2}]2 (3), respectively, in high yield. Similarly, the reaction of 1 with one equiv. of 2‐tert‐butylaminomethyl pyrrole in toluene at room temperature affords [Mg{C4H3N(2‐CH2NHtBu)}{N(SiMe3)2}]2 (4). Furthermore, reactions of 1 with one equiv. of HOCMeCHCMeN(C6H3‐2,6‐iPr2) or HOCMeCHCMeN(C6H4‐2‐OMe) in toluene yielded the dimeric magnesium complexes, [Mg{OCMeCHCMeN(C6H3‐2,6‐iPr2)}{N(SiMe3)2}]2 (5) and [Mg{OCMeCHCMeN(C6H4‐2‐OMe)}{N(SiMe3)2}]2 (6), respectively, in satisfactory yields by means of deamination. All the complexes were characterised by NMR spectroscopy and X‐ray diffraction analysis in the solid state. They show moderate reactivity towards the ring opening polymerisation of ϵ‐caprolactone in dichloromethane or tetrahydrofuran.

Effect of Substituents of Cerium Pyrazolates and Pyrrolates on Carbon Dioxide Activation

“…The Ce–N distances are slightly elongated compared with other Ce III ate complexes like [Ce{N(SiHMe 2 ) 2 } 4 ][Li(do) x ] (do, x = py, 4; tmeda, 2; 12-crown-4, 1 and thf, 4; Ce–N 2.377(6) to 2.438(6) Å), KCe[N(SiHMe 2 ) 2 ] 4 (2.3820(12) to 2.4379(12) Å), and [Ce{N(SiMe 3 ) 2 } 4 ][Na(thf) 4 (Et 2 O)] (Ce–N 2.434(6) to 2.448(6) Å), due to the higher coordination number CN of 4 (CN 8 vs. 4) [ 67 , 68 , 69 ]. The σ,π-bridging motif of the pyrrolato ligands has been detected previously, for example, in complexes [Me 2 In( µ -pyr)] n , [Me 2 Al 2 ( µ -Cl)]( µ -Me 4 pyr)Li, [Mg{ µ -C 4 H 2 N(2-CH 2 NH t Bu)}{N(SiMe 3 ) 2 }] 2 , and (AlMe 3 )( µ -C 4 H 3 N)[2-CH 2 NH( t Bu)Li(tmeda)] [ 70 , 71 , 72 , 73 ].…”

Alkaline and alkaline earth metals

“…148 Magnesium derivatives containing pyrrolyl or ketiminato ligands have been synthesised and applied in the ROP of caprolactone. 149…”

Ring-Opening Polymerization of ε-Caprolactone and Styrene Oxide–CO2 Coupling Reactions Catalyzed by Chelated Dehydroacetic Acid–Imine Aluminum Complexes

“…We have been involved in organometallic chemistry, which includes the synthesis, characterization and reactivity study of main and transition metal complexes and their catalytic activity toward cyclic esters ring-opening polymerization, for the past twenty years [ 25 , 26 , 27 ]. It is known that even minor changes of the ligands on metal complexes can have large effects on their catalytic activities.…”