Rare-Earth-Metal Complexes Bearing Phosphazene Ancillary Ligands: Structures and Catalysis toward Highly Trans-1,4-Selective (Co)Polymerizations of Conjugated Dienes

Abstract

The bis-arylated phosphazene compounds [HN(PPh2NAr)2] (Ar = phenyl (HL1), 2,6-dimethylphenyl (HL2), 2,6-diisopropylphenyl (HL3)) and the imidodiphosphinate compound HN(PPh2O)2 (HL4) have been prepared via the Staudinger reaction. Treatment of the neutral compounds HL1, HL2, and HL3 with Ln(CH2SiMe3)3(THF)2 (Ln = Sc, Y, Lu) generated the solvent-free bis(alkyl) complexes L1Ln(CH2SiMe3)2 (Ln = Sc (1a), Y (1b), Lu (1c)), L2Sc(CH2SiMe3)2 (2a), L3Y(CH2SiMe3)2 (3b), and L3Lu(CH2SiMe3)2 (3c), respectively. The reaction between HL4 and Y(CH2SiMe3)3(THF)2 gave the rare zwitterionic complex 4b. Lithiation of the ligand HL1 by nBuLi followed by a metathesis reaction with Nd(BH4)3(THF)3 afforded the corresponding complex L1Nd(BH4)2(THF)2 (5). Complexes 1 upon incorporation of [Ph3C][B(C6F5)4] and AliBu3 led to ternary systems that initiated isoprene polymerization with high activities, among which complex 1a was the first example of a scandium catalytic precursor providing trans-1,4-selectivity (90.0%), while the lutetium analogue 1c had medium trans-1,4-selectivity (54.3%) and the yttrium complex 1b exhibited high cis-1,4-selectivity (76.3%). The ternary system based on the zwitterion 4b displayed the highest activity for the isoprene polymerization among these complexes and gave cis-1,4-regularity-enriched polyisoprene (70.6%). Highly stereospecific homopolymerizations of isoprene (trans-1,4-content: 97.0%) and butadiene (trans-1,4-content: 94.0%) were achieved by using the borohydrido complex 5 upon the activation of dibutylmagnesium. The copolymerization of isoprene and butadiene with 1a/[Ph3C][B(C6F5)4/AliBu3] gave randomly arranged trans-1,4-regulated polybutadiene and polyisoprene sequences. The kinetics study displayed competitive polymerization rates of r BD = 2.89 and r IP = 0.41. The thermal behaviors of the (co)polymers were investigated.

Fine‐Tuning of Lewis Acidity: The Case of Borenium Hydride Complexes Derived from Bis(phosphinimino)amide Boron Precursors

“…Eur.J.2016, 22,1 1035 -11041 www.chemeurj.org relative to the ligand L'H( d = 7.20 ppm). [20] The 11 BNMR spectrum of 3 gave ab road signal at d = À3.4 ppm.…”

“…In the 1 H NMR spectrum of 3 , B−H appeared as a broad signal at δ =3.23 ppm. The 31 P{ 1 H} NMR spectrum of compound 3 showed a signal ( δ =20.1 ppm) that is significantly downfield shifted relative to the ligand L′H ( δ =7.20 ppm) . The 11 B NMR spectrum of 3 gave a broad signal at δ =−3.4 ppm.…”

Precisely Controlled Polymerization of Styrene and Conjugated Dienes by Group 3 Single‐Site Catalysts

“…A new family of bisarylated phosphazene (NPNPN‐type) and imidodiphosphinate (OPNPO‐type) rare‐earth metal complexes 100 – 102 were reported by Cui's group in 2013 as the first active zwitterionic complexes for IP polymerization . In combination with [Ph 3 C][B(C 6 F 5 ) 4 ] and Al i Bu 3 , the complex 101 showed the highest activity among these complexes, attributed to the larger Y metal ion as well as the smaller steric hindrance of the ligand.…”

Lanthanides and actinides: Annual survey of their organometallic chemistry covering the year 2013

“…The bis-arylated phosphazene compounds HN(PPh 2 NAr) 2 (Ar = phenyl (HL 1 ), 2,6-dimethylphenyl (HL 2 ), 2,6-diisopropylphenyl (HL 3 )) and the imidodiphosphinate compound HN(PPh 2 O) 2 (HL 4 ) have been prepared via the Staudinger reaction. Treatment of the neutral compounds HL 1 , HL 2 , and HL 3 with Ln(CH 2 SiMe 3 ) 3 (THF) 2 (Ln = Sc, Y, Lu) generated the solvent-free bis(alkyl) complexes L 1 Ln(CH 2 SiMe 3 ) 2 (Ln = Sc, Y, Lu), L 2 Sc(CH 2 SiMe 3 ) 2 , L 3 Y(CH 2 SiMe 3 ) 2 , and L 3 Lu(CH 2 SiMe 3 ) 2 , respectively [15].…”

“…A kinetics study displayed competitive polymerization rates of r BD = 2.89 and r IP = 0.41. The thermal behaviors of the (co)polymers were also investigated [15]. Bis(oxazolinyl)phenylligated rare-earth metal complexes have been reported to be highly regioselective catalysts for the cis-1,4-polymerization of isoprene.…”