Zhong-Xia Wang

Nickel-Catalyzed Cross-Coupling of Allyl Alcohols with Aryl- or Alkenylzinc Reagents

Nickel-catalyzed cross-coupling of allyl alcohols with aryl- and alkenylzinc chlorides through C-O bond cleavage was performed. Reaction of (E)-3-phenylprop-2-en-1-ol and 1-aryl-prop-2-en-1-ols with aryl- or alkenylzinc chlorides gave linear cross-coupling products. Reaction of 1-phenyl- or 1-methyl-substituted (E)-3-phenylprop-2-en-1-ol with aryl- or alkenylzinc chlorides resulted in 3-aryl/alkenyl-substituted (E)-(prop-1-ene-1,3-diyl)dibenzenes or 3-aryl/alkenyl-substituted (E)-(but-1-enyl)benzene. Reaction of allyl alcohol with p-Me2NC6H4ZnCl resulted in a mixture of normal coupling product 4-allyl-N,N-dimethylaniline and its isomerized product N,N-dimethyl-4-(prop-1-en-1-yl)aniline.

Crown ether complexes of potassium quinolin-8-olates: synthesis, characterization and catalysis toward the ring-opening polymerization of rac-lactide

A series of crown ether complexes of potassium quinolin-8-olates were synthesized and characterized. Catalysis of these complexes towards the ring-opening polymerization of rac-lactide was evaluated. The crown ether complexes of potassium quinolin-8-olate and potassium 2-methylquinolin-8-olate exhibited high catalytic activity and good molecular weight control. The 18-crown-6 complex of potassium 5-chloroquinolin-8-olate showed lower catalytic activity and poor molecular weight control; whereas the 18-crown-6 complex of potassium 5,7-dichloroquinolin-8-olate was inactive. Among the complexes, 18-crown-6 complex of potassium quinolin-8-olate showed the best selectivity of isotacticity, the Pm value achieving 0.75 when the polymerization was performed in toluene at 0 °C.

Ring-opening polymerization of rac-lactide catalyzed by crown ether complexes of sodium and potassium iminophenoxides

A series of iminophenoxide ligand precursors [2-(RNCH)C6H4OH] (HL1: R = C6H5; HL2: R = 2,6-iPr2C6H3) and [2-(RNCH)-4,6-tBu2C6H2OH] (HL3: R = C6H5; HL4: R = 2,6-iPr2C6H3) were synthesized. These compounds reacted with NaN(SiMe3)2/15-crown-5 or KN(SiMe3)2/18-crown-6 to afford corresponding crown ether complexes of sodium and potassium iminophenoxides (1, (15-C-5)NaL2; 2, (15-C-5)NaL3; 3, (15-C-5)NaL4; 4, (18-C-6)KL1; 5, (18-C-6)KL2; 6, (18-C-6)KL3; 7, (18-C-6)KL4). Catalysis of the complexes toward the ring-opening polymerization of rac-lactide was studied. Each of the complexes exhibited high catalytic activity at room temperature. Complexes 2, 3, 6 and 7 showed poor isotactic selectivity and relatively broad molecular weight distributions. Complexes 1 and 5 resulted in more stereoregular polymers with Pm values of 0.58 and 0.66, respectively. Complex 4 led to the best selectivity for isotacticity (Pm = 0.75) when the polymerization was performed in toluene at 0 °C.

Transition-Metal-Free Cross-Coupling of Aryl and Heteroaryl Thiols with Arylzinc Reagents

Cross-coupling of (hetero)arylthiols with arylzinc reagents via C-S cleavage was performed under transition-metal-free conditions. The reaction displays a wide scope of substrates and high functional-group tolerance. Electron-rich and -deficient (hetero)arylthiols and arylzinc reagents can be employed in this transformation. Mg2+ and Li+ ions were demonstrated to facilitate the reaction.

Synthesis of aluminum complexes supported by 2-(1,10-phenanthrolin-2-yl)phenolate ligands and their catalysis in the ring-opening polymerization of cyclic esters

A series of aluminum complexes supported by 2-(1,10-phenanthrolin-2-yl)phenolate ligands were synthesized and characterized. The reaction of o-bromophenol with n-butyllithium followed by nucleophilic addition to the phenanthroline and oxidation process gave the ligand precursors 2-(1,10-phenanthrolin-2-yl)phenol derivatives 1a–1d. Treatment of 1a–1d with an equiv. of AlR3 (R = Et, Bui) afforded the corresponding aluminum aryloxides 2a–2e. Treatment of 2b with 2 equiv. of benzyl alcohol formed complex 2f. All new compounds were characterized by 1H and 13C NMR spectroscopy and elemental analyses. The structure of complex 2c was further characterized by single crystal X-ray diffraction techniques. Complexes 2a–2e/BnOH and 2f were active to catalyze the ring-opening polymerization of e-caprolactone, leading to polycaprolactone with good molecular weight control and relatively narrow molecular weight distribution. Complexes 2a–2e/BnOH and 2f catalyzed the polymerization of rac-lactide and 2b, 2c, 2e and 2f were demonstrated to lead to isotactic enriched polylactides. The above catalysts also catalyzed the ROP of rac-β-butyrolactone and led to atactic poly(hydroxybutyrate). Complex 2f also catalyzed block copolymerization of the cyclic esters to form PCL-b-PHB, PCL-b-PLA, and PHB-b-PLA block copolymers.

Transition-Metal-Free Reaction of Aryltrimethylammonium Iodides with Arylzinc Reagents

Reaction of aryltrimethylammonium iodides with arylzinc chlorides in the absence of a transition-metal catalyst to form biaryl compounds was performed under mild conditions. The reaction was suitable for a broad scope of substrates and exhibited good compatibility of functional groups. The Mg2+ ion was demonstrated to markedly promote the reaction.