β‐Diketiminate‐supported magnesium alkyl: synthesis, structure and application as co‐catalyst for polymerizations mediated by a lanthanum half‐sandwich complex

Abstract

Mg(n‐Bu){η2‐HC[C(Me)NMes]2} (2) (Mes = mesityl, 2,4,6‐Me3C6H2), a new β‐diketiminate‐supported magnesium alkyl, has been synthesized and structurally characterized. The X‐ray analysis of the lanthanum half‐sandwich complex Cp*La(BH4)2(THF)2 (1) (Cp* = pentamethylcyclopentadienyl; THF = tetrahydrofuran) is also reported. Complex 2 has been assessed as both alkylating agent and chain transfer agent for the lanthanum‐catalysed polymerization and coordinative chain transfer polymerization of isoprene and styrene using 1 as the pre‐catalyst. The results are compared with those for n‐butylethylmagnesium (BEM) which is traditionally used for this purpose. The 1,4‐trans stereospecific polymerization of isoprene shows a more controlled character using 2 versus BEM, and higher activities are observed for the chain transfer polymerization of styrene when 2 is used as chain transfer agent. The activity is in turn lower than that observed using BEM when 1 equiv. of magnesium compound is used for the polymerization of styrene. The combination of 1, 2 and Al(i‐Bu)3 leads finally to a 1,4‐trans stereoselective coordinative chain transfer polymerization of isoprene, in a similar way to BEM. Copyright © 2015 John Wiley & Sons, Ltd.

Coordinative Chain Transfer and Chain Shuttling Polymerization

“…However, it produced highly stereoregular 1,4-trans polyisoprene (up to 98.8%) with a better match between calculated and measured molar masses than n-BuEtMg. 43 Isoprene CCTP activated with II and using i-Bu 3 Al as CTA resulted in a formation of 1,4-trans polyisoprenes (up to 97.9%) in good yields (73−94%) with transfer efficiency around 30% (29% when using n-BuEtMg instead of new Mg compound II). 43 Mechanism of ethene CCG on dialkylmagnesium was found to be a useful tool to produce telechelic polyethylenes.…”

“…A comparison of new magnesium alkyl ( II , Figure ) with the conventional n -BuEtMg as a cocatalyst showed generally lower activity when II was used. However, it produced highly stereoregular 1,4- trans polyisoprene (up to 98.8%) with a better match between calculated and measured molar masses than n -BuEtMg . Isoprene CCTP activated with II and using i -Bu 3 Al as CTA resulted in a formation of 1,4- trans polyisoprenes (up to 97.9%) in good yields (73–94%) with transfer efficiency around 30% (29% when using n -BuEtMg instead of new Mg compound II ) …”

“…Noteworthy is the 100% efficiency reported for PE-vinyl using a designed-on purpose bis­(exoalkenyl) magnesium CTA (bis­(10-undecenyl)­Mg, IIIa , Figure ), and the subsequent ability to reach 1,ω-heterodifunctional I-PE-vinyl and SC­(S) NEt 2 -PE-vinyl, with 96 and 87% functionalization efficiency for the second chain end. Other main advances in the field in the last 10 years include end functionalization of poly­(1-alkene) , and of highly stereoregular 1,4- trans polyisoprene (≤98% trans units), which are also not reachable by other polymerization techniques.…”

“…42 Novel magnesium alkyl compound bearing β-diketiminate ligand (II, Figure 8) was synthesized and used as a cocatalyst and/or CTA for CCTP of styrene and isoprene catalyzed by lanthanum complex (C 5 Me 5 )La(BH 4 ) 2 (THF) 2 (25, Figure 7). 43 A comparison of new magnesium alkyl (II, Figure 8) with the conventional n-BuEtMg as a cocatalyst showed generally lower activity when II was used. However, it produced highly stereoregular 1,4-trans polyisoprene (up to 98.8%) with a better match between calculated and measured molar masses than n-BuEtMg.…”

Rare Earth Starting Materials and Methodologies for Synthetic Chemistry

“… 465 This is exemplified by the variety of coordination motifs exhibited by this family of complexes: (1) monoring complexes, e.g. [RE(Cp R )(BH 4 ) 2 (THF)] ( 158 , Cp R = Cp*, RE = Sc; 466 159 , Cp R = Cp iPr5 ; RE = Dy 439 ) and [RE(Cp R )(BH 4 ) 2 (THF) 2 ] ( 160-RE , Cp R = Cp*, RE = La, 467 Nd; 453 , 468 161 , Cp R = Cp ttt , RE = La 436 ); (2) borohydride-bridged dimers, e.g. [{Ce(Cp ttt )(μ-BH 4 ) 2 (THF)} 2 ] ( 162 ); 436 (3) clusters, e.g.…”