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Reactions of 2,6-(ArNCH)2C6H3Li with CrCl2(THF)2afford two trinuclear bis(imino)aryl NCN pincer Cr(II) complexes {[2,6-(ArNCH)2C6H3]Cr(μ-Cl)2}2Cr [Ar = 2,6-Me2C6H3(1a), 2,6-Et2C6H3(1b)], and a mononuclear bis(imino)aryl NCN pincer Cr(II) complex [2,6-(ArNCH)2C6H3]Cr(μ-Cl)2Li(THF)2[Ar = 2,6-iPr2C6H3(1c)], respectively. Similar reactions of 2,6-(ArNCH)2C6H3Li with CrCl3(THF)3produce only mononuclear bis(imino)aryl NCN pincer Cr(III) complexes [2,6-(ArNCH)2C6H3]CrCl2(THF) [Ar = 2,6-Me2C6H3(2a), 2,6-Et2C6H3(2b), 2,6-iPr2C6H3(2c)]. X-ray crystallographic analysis reveals that the terminal Cr(II) atoms in 1aand 1band the Cr(II) atom in 1cpossess a distorted trigonal bipyramidal coordination environment with the Cipsoatom of the pincer ligand and two chloride atoms in the equator and the two imine nitrogen atoms in the apical positions, while the Cr(III) complexes 2a, 2b, and 2call adopt a distorted octahedral geometry around the chromium metal. Upon activation with trialkylaluminum and [Ph3C][B(C6F5)4]−, the Cr(III) complexes show high catalytic activity for isoprene polymerization and afford polyisoprene with predominately trans-1,4 units, whereas the Cr(II) complexes are inert under the same conditions. [ABSTRACT FROM AUTHOR]

A series of new half-sandwich chromium(III) complexes chelated with (2-((arylimino)methyl)phenyl)tetramethylcyclopentadienyl ligands, 2-(ArNCH)C6H4Me4CpCrCl2(Ar = 2,6-Me2C6H3(1), 2,6-Et2C6H3(2), 2,6-iPr2C6H3(3), 4-MeC6H4(4)), have been synthesized from the reaction of CrCl3with the lithium salt of the corresponding ligand 2-(ArNCH)C6H4Me4CpLi (Ar = 2,6-Me2C6H3(LiL1), 2,6-Et2C6H3(LiL2), 2,6-iPr2C6H3(LiL3), 4-MeC6H4(LiL4)). Free ligands HL1−HL4were prepared by the condensation reaction of 2-(tetramethylcyclopentadienyl)benzaldehyde with 2,6-dialkylaniline. The free ligands were characterized by 1H NMR spectroscopy, while the chromium(III) complexes were characterized by elemental analyses and single-crystal X-ray crystallography. The X-ray crystallographic analysis indicates that the imine N atom in these complexes coordinates to the central chromium atom. Upon activation with AlR3and Ph3CB(C6F5)4, these complexes exhibit high catalytic activity for ethylene polymerization and produce polyethylene with moderate to high molecular weights. These chromium(III) complexes can also be activated with AlR3alone. In the latter case, they show slightly lower catalytic activity for ethylene polymerization in comparison to the AlR3/Ph3CB(C6F5)4activated catalyst systems. The effects of ligand structure, polymerization temperature, AlR3, and Al/Cr molar ratio on the catalytic behavior of these complexes were examined. [ABSTRACT FROM AUTHOR]

As a continuation of our studies on biomimetic chemistry and butterfly cluster chemistry, two series of “closed” and “open” butterfly [2Fe2Se] cluster complexes have been prepared in satisfactory yields. Thus, treatment of Fe3(CO)12with (HSeCH2)2CHOH in toluene at reflux gave the expected “closed” butterfly [2Fe2Se] cluster complex [(μ-SeCH2)2CH(OH)]Fe2(CO)6(A), whereas the “open” butterfly cluster complex (μ-EtSe)[(μ-SeCH2CH(OH)(CH2Br)]Fe2(CO)6(B) was unexpectedly produced along with complex Avia a sequential reaction of (μ-Se2)Fe2(CO)6with Et3BHLi, followed by treatment with (BrCH2)2CHOH. The other “closed” and “open” cluster complexes 1−6could be further prepared by the hydroxy transformation and CO substitution reactions of complexes Aand B. For example, (i) reaction of Awith PPh3and decarbonylating agent Me3NO afforded PPh3-monosubstituted complex [(μ-SeCH2)2CH(OH)]Fe2(CO)5(PPh3) (1), (ii) further reaction of 1with the acylating agent PhC(O)Cl in the presence of Et3N produced the benzoate-functionalized complex [(μ-SeCH2)2CH(O2CPh)]Fe2(CO)5(PPh3) (2), (iii) treatment of Awith the phosphatizing agent Ph2PCl in the presence of Et3N or simply with PhPCl2yielded the phosphite-functionalized complexes [(μ-SeCH2)2CH(OPPh2-η1)]Fe2(CO)5(3) and [(μ-SeCH2)2CH(OPPhCl-η1)]Fe2(CO)5(4), and (iv) treatment of Bwith 4-pyridinecarboxylic chloride or Ph2PCl in the presence of Et3N resulted in formation of the “open” butterfly cluster complexes (μ-EtSe)[μ-SeCH2CH(CH2Br)(O2CC5H4N-4)]Fe2(CO)6(5) and (μ-EtSe)[μ-SeCH2CH(CH2Br)(OPPh2-η1)]Fe2(CO)5(6). All the new complexes have been characterized by elemental analysis and spectroscopy, as well as for A, 1−4, and 6by X-ray crystallography. Both 1H and 77Se NMR spectral studies demonstrated that complexes Band 5consist of three isomers of e-Et/a-R, e-Et/e-R, and a-Et/e-R, whereas complex 6exists only as one isomer of e-Et/a-R. On the basis of an electrochemical study, it was found that the “closed” and “open” complexes Aand Bcan catalyze the proton reduction of TsOH and HOAc to give hydrogen, respectively. [ABSTRACT FROM AUTHOR]

The tridentate ligand N-(2-((2,6-diisopropylphenylimino)methyl)phenyl)quinolin-8-amine ( HL) was prepared. Treatment of HLwith 1 equiv of Ln(CH 2SiMe 3) 3(THF) 2afforded the corresponding rare-earth metal bis(alkyl) complexes LLn(CH 2SiMe 3) 2(THF) n(Ln = Sc, n= 0 ( 1); Y, n= 1 ( 2); Lu, n= 0 ( 3)) in high yields. Variable-temperature 1H NMR spectral analysis showed that these complexes were fluxional at room temperature. Complexes 1and 3were THF-free, where the metal center adopted a square-pyramidal geometry, while in 2the metal center generated a distorted octahedral geometry owing to the coordination of a THF molecule. All these complexes catalyzed the ring-opening polymerization of ε-caprolactone with high activities in living fashion, among which the Lu complex was proved to be more active than its Sc and Y analogues. [ABSTRACT FROM AUTHOR]

A series of new rare-earth metal bis(alkyl) complexes [L1−3Ln(CH2SiMe3)2(THF)n] (L1= MeC4H2SCH2NC6H4(Ph)2PNC6H2Me3-2,4,6: Ln = Sc, n= 1 (1a); Ln = Lu, n= 1 (1b); L2= MeC4H2SCH2NC6H4(Ph)2PNC6H3Et2-2,6: Ln = Sc, n= 1 (2a); Ln = Lu, n= 1 (2b); Ln = Y, n= 1 (2c); L3= MeC4H2SCH2NC6H4(Ph)2PNC6H3iPr2-2,6: Ln = Sc, n= 0 (3a)) and L4Sc(CH2SiMe3)2(THF) (4a) (L4= C6H5CH2NC6H4(Ph)2PNC6H3Et2-2,6) have been prepared by reaction of rare-earth metal tris(alkyl)s with the corresponding HL1−4ligands via alkane elimination. Complexes 1a, 1b, 2a−2c, and 4aare monomeric with a coordinating THF molecule. Each metal ion is coordinated by a NPN ligand, two trans-located alkyl groups, and a THF molecule, forming a distorted trigonal-bipyramidal geometry. Complex 3ais THF-free, adopting a distorted tetrahedron geometry. In combination with AlR3and borate, these complexes have shown medium activity and good trans-1,4 selectivity for the polymerization of butadiene. The resultant polymer has moderate molecular weight (Mn= 10 000−18 000) with narrow molecular weight distribution (Mw/Mn< 1.6) and trans-1,4 regularity varying from 49.2% up to 91.3%. The catalyst performances are strongly dependent on the orthosubstituent of the N-aryl ring and the presence of the thiophene moiety of the ligands and the type of aluminum alkyls and the lanthanide metal used. The scandium complex 2adisplays the highest trans-1,4 selectivity. [ABSTRACT FROM AUTHOR]