Highly 3,4-Selective Living Polymerization of Isoprene with Rare Earth Metal Fluorenyl N-Heterocyclic Carbene Precursors

Abstract

Fluorenyl modified N-heterocyclic carbene ligated rare earth metal bis(alkyl) complexes, (Flu-NHC)Ln(CH 2 SiMe 3 ) 2 (Flu-NHC ) (C 13 H 8 CH 2 CH 2 (NCHCCHN)C 6 H 2 Me 3 -2,4,6); Ln ) Sc (1a); Ln ) Y (1b); Ln ) Ho (1c); Ln ) Lu (1d)), were synthesized and fully characterized by NMR and X-ray diffraction analyses. Complexes 1b-d with the activation of Al i Bu 3 and [Ph 3 C][B(C 6 F 5 ) 4 ] exhibited high activity, medium syndiobut remarkably high 3,4-regio-selectivity, and the unprecedented livingness for the polymerization of isoprene. Such distinguished catalytic performances could be maintained under various monomer-to-initiator ratios (500-5000) and broad polymerization temperatures (25-80°C). The resultant polymers are crystalline, having syndiotactically enriched (racemic enchainment triad rr ) 50%, pentad rrrr ) 30%) 3,4-regulated (99%) microstructure and high glass-transition temperatures (40-49°C). In contrast, complex 1a was almost inert, while complexes bearing indenyl modified N-heterocyclic carbene moiety, (Ind-NHC)Ln(CH 2 SiMe 3 ) 2 (Ind-NHC ) C 9 H 6 CH 2 CH 2 (NCHCCHN)C 6 H 2 Me 3 -2,4,6; Ln ) Sc (2a); Ln ) Y (2b); Ln ) Ho (2c); Ln ) Lu (2d)), also showed low activity or selectivity. These differences in catalytic performance could be attributed mainly to the electronics and spacial sterics of the metal center of these precursors.

Tuning the catalytic properties of rare earth borohydrides for the polymerisation of isoprene

“…43 Furthermore, one can also propose that the carbene moiety would help to dissociate the cluster structure -possibly of 1b′ type -of 1b after storage, since dry batches of precatalyst was not established. 44,45 Adding an additional equivalent L 1 led to a lower activity but similar 3,4-preference (run 2.12). When the half-sandwich 1a is associated to HL 2-Mes the activity is even lower but the selectivity remains unchanged (run 2.13).…”

Synthetic rubbers prepared by lanthanide coordination catalysts

“…The cis-1,4 contents in the polyisoprenes prepared by various neodymium catalysts are usually in the range of 94%-95% (Table 6) [16] , various coordination ligands used in the neodymium compounds do not make appreciable difference. Cui et al [30] synthesized two lanthanide metallocenes: which can efficiently catalyze 3,4-polymerization of isoprene when combined with [Ph 3 C][B(C 6 F 5 ) 4 ] and Al(iBu) 3 , as shown in Table 7. The results in Table 7 illustrate that all catalysts have high polymerization activities except 1a, 2a (no activity), 2b (medium) and 2d (low).…”

“…Higher molar ratio of 30 3.9 99 Nd(naph) 3 -Al(i-Bu) 2 ClAl(i-Bu) 3 The following is a scheme for alkyl group transfer.…”

Tunable regioselectivity in 1,3-butadiene polymerization by using 2,6-bis(dimethyl-2-oxazolin-2-yl)pyridine incorporated transition metal (Cr, Fe and Co) catalysts

“…Industry applied systems such as tianium tetraethoxides/AlEt 3 [6], vandium trichloride/AlR 3 [7][8], Co(acac) 3 /CS 2 or Ph 3 P [9-10] and recently emerged rare earth catalysts [11,12] are notable for their unique catalytic properties, in particular, polymers with high level of regioregularity such as trans-1,4 [11][12][13], cis-1,4 [14][15][16][17][18][19][20][21][22][23] and 3,4 (1,2) [24][25] regio-and/or stereoselectivity, as such, 1,2-syndiotactic [23] for polybutadiene, and syndiotactic 3,4 (1,2) [24], isotactic 3,4 [25] for polyisoprene as well as their block combinations have been unprecedently achieved.…”