Dinuclear Rare‐Earth Metal Alkyl Complexes Supported by Indolyl Ligands in μ‐η²:η¹:η¹ Hapticities and their High Catalytic Activity for Isoprene 1,4‐cis‐Polymerization

Abstract

Two series of new dinuclear rare-earth metal alkyl complexes supported by indolyl ligands in novel μ-η(2) :η(1) :η(1) hapticities are synthesized and characterized. Treatment of [RE(CH2 SiMe3 )3 (thf)2 ] with 1 equivalent of 3-(tBuN=CH)C8 H5 NH (L1 ) in THF gives the dinuclear rare-earth metal alkyl complexes trans-[(μ-η(2) :η(1) :η(1) -3-{tBuNCH(CH2 SiMe3 )}Ind)RE(thf)(CH2 SiMe3 )]2 (Ind=indolyl, RE=Y, Dy, or Yb) in good yields. In the process, the indole unit of L1 is deprotonated by the metal alkyl species and the imino C=N group is transferred to the amido group by alkyl CH2 SiMe3 insertion, affording a new dianionic ligand that bridges two metal alkyl units in μ-η(2) :η(1) :η(1) bonding modes, forming the dinuclear rare-earth metal alkyl complexes. When L1 is reduced to 3-(tBuNHCH2 )C8 H5 NH (L2 ), the reaction of [Yb(CH2 SiMe3 )3 (thf)2 ] with 1 equivalent of L2 in THF, interestingly, generated the trans-[(μ-η(2) :η(1) :η(1) -3-{tBuNCH2 }Ind)Yb(thf)(CH2 SiMe3 )]2 (major) and cis-[(μ-η(2) :η(1) :η(1) -3-{tBuNCH2 }Ind)Yb(thf)(CH2 SiMe3 )]2 (minor) complexes. The catalytic activities of these dinuclear rare-earth metal alkyl complexes for isoprene polymerization were investigated; the yttrium and dysprosium complexes exhibited high catalytic activities and high regio- and stereoselectivities for isoprene 1,4-cis-polymerization.

The behaviour of β-triketimine cobalt complexes in the polymerization of isoprene

“…12,13 These effects can be modied by changing the steric and electronic properties of the ligands. While industrial catalysis has tended to move towards lanthanide (Yb) catalysts for highcis polydienes, cognisance of the medium-term competing uses of these elements for their magnetic and photochemical properties combined with their limited mineral reserves has refocused academic attention on the rst-row d-block elements due to their greater long-term availability; 14 while earlier examples using these elements were far inferior to lanthanides in the degrees of activity and/or stereocontrol offered, 9,[15][16][17][18][19][20] ligand design offers an opportunity to tailor the properties of the base elements (Co, Ni, Fe), so that, even if they cannot surpass the remarkably high degrees of cis-1,4-selectivity of isoprene enchainment offered by some lanthanide catalysts of over 96%, [21][22][23][24][25][26][27] they may still have their activity tailored to produce alternative potentially useful polymers unknown in Nature. It is now possible to obtain high trans-1,4 polymer, 16,[28][29][30] high 3,4isotactic polymer [31][32][33] and high 3,4 atactic or syndiotactic polymer, 34 mostly with lanthanides, but it is also possible to obtain unique cis-1,4-alt-3,4 polyisoprene with cobalt phosphine complexes.…”

N-Containing Ligands as Universal Coordination Environments for Rare-Earth Alkyl and Bis(alkyl) Complexes

“…Subseqeuntly, a series of rare-earth alkyl complexes with a bulky isopropyl guanidinate ligand were synthesized [47,48]. (50), Me (51)), coordinated by a monoanionic bidentate pyrrolcarbaldiminate ligand, by the exchange reactions between the corresponding chloride derivatives and alkyllithium reagents in toluene at low temperature ( Fig. 2).…”

“…Zhang et al used substituted imino-indoles as coordination environments for rare-earth alkyl complexes [50][51][52] (68) and Y (69)) were isolated from the reaction mixtures (Scheme 12). Complexes 68 and 69 contain two µ-bridging dianionic imino-indole ligands bound to the metal centres in a µη 6 :η 1 :η 1 -fashion, and two terminal monoanionic imino-indole ligands η 1 :η 1 -coordinated to the metal atoms [52].…”

Cis-1,4-Polymerization of Isoprene by 1,3-Bis(oxazolinymethylidene)isoindoline-Ligated Rare-Earth Metal Dialkyl Complexes

“…In general, the practical and most common synthesis method of C PIP is the coordination–insertion polymerization of isoprene (IP) by using homogeneous organometallic catalysts based on rare-earth metals [12,13,14,15,16,17,18]. So far, a large number of the rare-earth metal catalyst precursors bearing a different chelating ligand have been reported for the cis -1,4-polymerization of IP [19,20,21,22,23,24,25,26,27]. Among these, the nonmetallocene pincer-type rare-earth metal complexes bearing the monoanionic tridentate C 2 -symmetric ligands usually exhibit both high activities and high cis -1,4 selectivities in the polymerization of IP [28,29,30] (Chart 1).…”