A series of chiral mononuclear dialkyl
complexes [(S,S)-BOPA]Ln(CH2SiMe3)2 (1, 2) (BOPA = (S,S)-bis(oxazolinylphenyl)amido;
Ln = Sc (1); Ln = Lu (2)) and binuclear
alkyl complexes [ο-(S)-OPA–C6H4–(CH2SiMe3)CN–CH(
i
Pr)CH2–O]Ln(CH2SiMe3)}2 (3,
4) (OPA = (oxazolinylphenyl)amine; Ln = Y (3);
Ln = Tm (4)) have been synthesized in moderate yields
via one-pot acid–base reactions by use of the tris(trimethylsilylmethyl)
rare earth metal complexes with the chiral tridentate (S,S)-bis(oxazolinylphenyl)amine ligand. In the presence
of activator with or without a small amount of Al
i
Bu3, the dialkyl complexes 1 and 2 exhibit very high activities (up to 6.8 × 105 g molLn
–1 h–1) and trans-1,4-selectivity (up to 100%) in the quasi-living polymerization
of isoprene, yielding the trans-1,4-PIPs with moderate
molecular weights (M
n = (0.2–1.0)
× 105 g/mol) and narrow molecular weight distributions
(M
w/M
n = 1.02–2.66).
in 65-85% isolated yields. X-ray analyses show these complexes have decreasing steric hindrance in the coordination spheres of the metal centers in the order 1 > 2 > 3 > 4 > 5 > 6. A mechanism involving intramolecular alkyl and hydrogen migration is supported on the basis of DFT calculations to account for ligand alkylation. Activated by [Ph 3 C]-[B(C 6 F 5 ) 4 ], all of these iminoamido rare earth metal dialkyl complexes are active for living polymerization of isoprene, with activity and selectivity being significantly dependent on the steric hindrance around the metal center to yield homopolyisoprene materials with different microstructures and compositions. The sterically crowded complexes 1-3 give a mixture of 3,4-and trans-1,4-polyisoprenes (3,4-selectivities: 48-82%, trans-1,4-selectivities: 50-17%), whereas the less sterically demanding complexes 4-6 show high 3,4-selectivities (3,4-selectivities: 90-100%). In the presence of 2 equiv of Al i Bu 3 , the complexes 1-6/activator systems exhibit higher activities and 3,4-selectivities in the living polymerization of isoprene. A similar structure-reactivity relationship in polymerization catalysis can be also observed in these ternary systems. A possible mechanism of the isoprene polymerization processes is proposed on the basis of the DFT calculations.
Carbon dioxide (CO2), as a waste of manufacture, is a cheap and abundant C1 source. Utilization of CO2 for synthesis of carboxylic acids has been developed. Transition-metal complexes play a key role in catalytic carboxylation reactions employing CO2. This review summarizes recent advances in copper-catalyzed carboxylation reactions using CO2. The contents are arranged based on various substrates: organometallic reagents, aryl iodides, sodium sulfinates, terminal alkynes, arenes, heteroarenes, and unsaturated substrates.
Carbonylation of o-arylanilines utilizing CO2 as a carbonyl source for the synthesis of important phenanthridinones with a free (NH)-lactam motif has been described under metal-free condition. A range of o-arylanilines were transformed to the corresponding phenanthridinones in high yields.
The polymerization of ocimene has been first achieved by half-sandwich rare-earth metal dialkyl complexes in combination with activator and Al(i) Bu3 . The regio- and stereoselectivity in the ocimene polymerization can be controlled by tuning the cyclopentadienyl ligand and the central metal of the complex. The chiral cyclopentadienyl-ligated Sc complex 1 prepares syndiotactic cis-1,4-polyocimene (cis-1,4-selectivity up to 100%, rrrr = 100%), while the corresponding Lu, Y, and Dy complexes 2-4 and the achiral pentamethylcyclopentadienyl Sc, Lu, and Y complexes 5-7 afford isotactic trans-1,2-polyocimenes (trans-1,2-selectivity up to 100%, mm = 100%).
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