Yuushou Nakayama

Recent Trends in the Polymerization of α-Olefins Catalyzed by Organometallic Complexes of Early Transition Metals

This review article describes recent progress in the field of homogeneous organometallic catalysts for olefin polymerization and focuses on the metal-carbon bonding character of the transition metal complexes used as catalysts. Most catalysts of this kind are based on metallocene derivatives of Group 4 metals, their catalytic behavior (such as activity and stereospecificity) and the molecular weights of the resulting polymers are surveyed on the basis of the molecular structure of the catalyst precursors. Advanced mechanistic studies on the catalyst systems are also summarized. Some examples of the related polymerization of functionalized olefins are also presented. Not only the Group 4 metal catalysts but also the polymerization catalysts of many other early transition metals and late transition metals are reviewed including our recent study on the mono(cyclopentadienyl)mono(diene) complexes of Group 5 metals.

Reaction courses for formation of early transition metal phenoxides

Abstract The 1 : 1 and 1 : 2 reactions of TiCl4 with Me3SiO-2,6-(CH3)2C6H3 produced TiCl3[O-2,6-(CH3)2C6H3]2(THF)2 (1) and TiCl2[O-2,6-(CH3)2C6H3]2(THF)2 (2), respectively, bearing six-coordinated geometry around Ti. The compound 2 assumes the cis-geometry regarding the two phenoxy groups and THF is coordinated in the trans position of the phenoxy groups. Similarly, the 1 : 1 and 1 : 2 reactions of NbCl5 with the trimethylsilyl phenyl ether provided NbCl4[O-2,6-(CH3)2C6H3]2(THF) (7) and NbCl3[O-2,6-(CH3)2C6H3]2(THF) (8), respectively, with octahedron structure. The THF molecule again locates in the trans position of a phenoxy group in both cases and the two phenoxy groups of 8 locate in the cis position. Tungsten mono-phenoxide, WCl5[O-2,6-(CH3)2C6H3]2 (12), also has octahedron structure. In cases of tungsten bis-phenoxides, WCl4[O-2,6-(CH3)2C6H3]2 (13) and WCl4[O-2,6-(i-C3H7)C6H3]2 (14), the former has trans structure while the latter has cis structure regarding the phenoxy groups. A unique square pyramidal geometry has been observed in the tetrakis(phenoxy) tungsten, WCl[O-2,6(CH3)2C6H3]4 (16).

A new convenient preparation of monocyclooctatetraenyl-lanthanide complexes from metallic lanthanides and oxidants

Abstract Treatment of lanthanide metals with cyclooctatetraene in the presence of an equimolar amount of iodine afforded cyclooctatetraenyl-iodolanthanide(III) complexes, LnI(η 8 -cot)(thf) n . (cot = cyclooctatetraenyl; 1a : Ln ue5fb La, n = 3; 1b : Ln ue5fb Ce, n = 3; 1c : Ln ue5fb Pr, n = 3; 1d : Ln ue5fb Nd, n = 2; 1e : Ln ue5fb Sm, n = 1), in modest yields. Bromo and chloro-bridged dinuclear complexes of samarium, [Sm(μ-X)(cot)(thf)] 2 ( 2 : X ue5fb Br; 3 : X ue5fb Cl), are also prepared by the reaction of samarium metal with cyclooctatetraene in the presence of 1,2-dibromoethane or Ph 3 PCl 2 , respectively. The reaction of metallic samarium with cyclooctatetraene and diaryl disulfide or diphenyl diselenide in THF afforded cyclooctatetraenyl-thiolate or -selenolate complexes of samarium(III), [Sm(μ-EAr)(η 8 -cot)(thf) n ] 2 ( 4a : EAr ue5fb SPh, n = 2; 4b : SC 6 H 2 Me 3 -2,4,6, n = 2; 4c : SC 6 H 2 i Pr 3 -2,4,6, n = 1; 5 : SePh, n = 2). The dimeric structure of 5 was revealed by X-ray. crystallography [monoclinic, space group P 2 1 / n with a = 8.500(5), b = 21.805(6), c = 12.042(5) A, β = 105.98(4)°, V = 2145(1) A 3 , Z = 2, R = 0.055 for 2061 reflections with I > 3σ-( I ) and 235 parameters].A samarium (II) complex, [Sm(η 8 -cot)(thf)] n , ( 6 ), was also obtained by the direct reaction of samarium metal with cyclooctatetraene in THF with a catalytic amount of iodine. Reaction of 6 with iodine and diphenyl disulfide afforded 1e and 4a , respectively.

Synthesis and characterization of cationic pyridine-2-thiolate complexes of lanthanoid(III): crystal structures of pentagonal bipyramidal [Ln(SC5H4N)2(hmpa)3]I (Ln = Sm, Yb; hmpa = hexamethylphosphoric triamide)

The cationic thiolate complexes of general formula [Ln(SC5H4N)2(hmpa)3]I (1; Ln = Pr, Nd, Sm, Eu, Er, Yb; hmpa = hexamethylphosphoric triamide) were prepared in modest yields by the reaction of metallic lanthanoids with 2,2′-dipyridyl disulfide and iodine in the presence of HMPA. The structure of 1 is a pentagonal bipyramidal seven-coordinated geometry consisting of two apical HMPA together with two chelating pyridine-2-thiolate ligands and one HMPA ligand in the pentagonal plane, which was confirmed by X-ray analysis for the samarium complex 1c (monoclinic, space group P21c with a = 16.614(3), b = 13.350(4), c = 21.302(3)A, β = 100.14(1)°, V = 4650(1)A3, Z = 4, R = 0.039 for 4247 reflections with I > 3σ-(I) and 442 parameters) and the ytterbium complex 1f (monoclinic, space group C2 with a = 19.909(4), b = 11.140(3), c = 21.273(3)A, β = 105.20(1)°, V = 4553(1)A3, Z = 4, R = 0.038 for 4746 reflections with I > 3σ(I) and 442 parameters).

Half-sandwich complexes of niobium and tantalum bearing o-xylylene, anthracene, or cyclooctatetraene: crystal structures of (η5-C5Me5)Nb{o-(CH2)2C6H4}Cl2, (η5-C5Me5)Ta(η4-anthracene)(CH2Ph)2, and (η5-C5Me5)Nb(η4-butadiene)(η3-cyclooctatetraene)

Abstract Half-sandwich complexes of niobium and tantalum having an extended conjugated 1,3-diene ligand such as o-xylylene, anthracene, and cyclooctatetraene have been synthesized and characterized. The molecular structures of Cp*Nb{o-(CH2)2C6H4}Cl2 (1) (Cp*=η5-pentamethylcyclopentadienyl), Cp*Ta(η4-C14H10)(CH2Ph)2 (14), and Cp*Nb(η4-C4H6)(η3-C8H8) (16) were determined by X-ray crystallographic studies. Complexes 1 and 14 adopted a four-legged piano stool geometry and their o-xylylene and anthracene ligands coordinated to the metal center in the η4-coordination mode. X-ray analysis together with their NMR spectral data revealed that the o-xylylene complex 1 has a large contribution of the 2σ–1π canonical form, but otherwise the anthracene complexes have an increased contribution of 2π–η4-diene canonical form compared with the butadiene complexes. Thus, the electronic structures of η4-o-xylylene and η4-anthracene ligands are deviated from that of η4-butadiene into the opposite direction. The 1H NMR singlet signal of the cyclooctatetraene ligand in 16 indicated the presence of the dynamic fluxionality in solution, while it coordinated to the metal in η3-fashion in the crystal.

Polymerization of ethylene catalyzed by half-metallocene complexes of niobium, tantalum, and zirconium bearing o-xylylene or anthracene as an auxiliary ligand: molecular structure of [Mg2Cl3(THF)6][ZrCl2(η5-C5Me5) (η-1–4-anthracene)]

Abstract Polymerization of ethylene catalyzed by half-metallocene complexes of niobium and tantalum MR2(η5-C5Me5)(L) (1: M=Ta, R=Cl, L=o-xylylene; 2: M=Nb, R=Cl, L=o-xylylene; 3: M=Ta, R=Cl, L=η-1–4-anthracene; 4: M=Ta, R=CH2Ph, L=η-1–4-anthracene) as well as by a new anthracene–zirconium complex [Mg2Cl3(THF)6][ZrCl2(η5-C5Me5)(η-1–4-anthracene)] (5), whose structure was revealed by X-ray analysis, was studied and the results were compared with the reported results using 1,3-butadiene complexes of niobium and tantalum. The catalytic activity of niobium and tantalum complexes was found to be in the order of o-xylylene>butadiene ⪢anthracene, whereas the anthracene complex of zirconium 5 showed much lower activity and broad polydispersity.

Mononuclear η8-cyclooctatetraenyl(thiolato)samarium(III) complexes (η8-C8H8)Sm(SR)(hmpa)2 (R=2,4,6-triisopropylphenyl and 2-pyridyl; HMPA=hexamethylphosphoric triamide) derived from metallic samarium, diaryl disulfide, and 1,3,5,7-cyclooctatetraene in the presence of HMPA

Abstract Treatment of metallic samarium with cyclooctatetracne in the presence of an equimolar amount of diaryl disulfide afforded mononuclear cyclooctatetraenyl(thiolato)samarium(III) complexes of the formula ( η 8 -C 8 H 8 )Sm(SR)L x ( 3a : R=2-pyridyl, L=THF, x =0.5; 3b : R=2-pyridyl, L=HMPA, x =2; 3c : R=2,4,6-triisopropylphenyl, L=HMPA, x =2; HMPA=hexamethylphosphoric triamide) in modest yields. These complexes have been characterized by 1 H-NMR spectroscopy and elemental analysis together with X-ray analysis for 3b and 3c . The complex 3b has a pseudo square pyramidal and four-legged piano-stool geometry coordinated by a planar η 8 -C 8 H 8 ring, a chelating pyridine-2-thiolato ligand, and two HMPA ligands, while the complex 3c has three-legged piano-stool geometry comprised of a planar η 8 -C 8 H 8 ring, a thiolato ligand, and two HMPA ligands.

Cationic monocyclooctatetraenyl-lanthanoid complexes derived from metallic lanthanoid: crystal structures of [Sm(η8−C8H8)(hmpa)3]I and [Sm(η8−C8H8)(hmpa)3][Sm(η8−C8H8)2] (HMPA = hexamethylphosphoric triamide)

Abstract Addition of an excess hexamethylphosphoric triamide (abbr. HMPA) to a neutral complex SmI( ν 8 −C 8 H 8 (thf) ( 1 ) (C 8 H 8 = 1,3,5,7-cyclooctatetraene), which was prepared by a direct reaction of metallic samarium with C 8 H 8 in the presence of iodine in THF, afforded a cationic samarium complex [Sm( η 8 −C 8 H 8 )(hmpa) 3 ]I ( 2 ). Complex 2 can also be prepared by a simple one-pot reaction of stoichiometric amounts of metallic samarium, cyclooctatetraene, and iodine in the presence of an excess HMPA at 50°C. With a catalytic amount of iodine, ionic complexes of general formula Ln (η 8 − C 8 H 8 )( hmpa ) n ][ Ln (η 8 − C 8 H 8 ) 2 ] [ Ln = La and n = 4 ( 6 ); Ln = Sm and n = 3 ( 7 ) ] were obtained by treating metallic lanthanum or samarium, respectively with cyclooctatetraene in the presence of HMPA. The structure of the diamagnetic complex 6 as well as the paramagnetic complexes 2 and 7 was determined by 1 H NMR spectroscopy. Crystal structures of 2 and 7 were revealed by X-ray analyses, indicating that these complexes comprised of a cationic [Sm( η 8 −C 8 H 8 )(hmpa) 3 ] + and an anionic part; for 2 and 7 being I − and [Sm( η 8 −C 8 H 8 ) 2 ] − , respectively.

Polymerization of acrylonitrile catalyzed by thiolate complexes of divalent and trivalent lanthanoids

Arenethiolate complexes of lanthanoid(II) and lanthanoid(III) metals were used as initiators for the polymerization of acrylonitrile at - 78°C in THF, giving atactic and high molecular mass (M n 10 5 ) polyacrylonitriles in good yield.

Characterization of lactone oligomers isolated by preparative SFC

Oligomerization of e-caprolactone and δ-valerolactone was performed by use of SmMe-(C 5 Me 5 ) 2 (THF) 2 initiator, and the 26-mer, 28-mer and 30-mer of e-caprolactone were isolated in pure form by preparative SFC. The MALDI-TOF mass spectrum of the 28-mer indicates that the parent peak (3256.1) emerges as 28-mer + 2Na - H (3256.9). The ESI mass spectrum of the 28-mer indicates that the molecular weight (3211.7) is consistent with the calculated value (3211.9). In a similar manner, the 19-, 25- and 32-mers of δ-valerolactone were isolated. The MALDI-TOF mass spectrum of the 19-mer indicates that the parent peaks (1896.6 and 1879.9) emerge as 19-mer + Na + K + MeOH - I-hexanol-5-one (1896.3) and 19-mer + 2Na + MeOH - I-hexanol-5-one (1880.2). Glass transition and melting temperatures (T g and T m ) of oligo-e-caprolactones and oligo-δ-valerolactones increase wh increasing degree of polymerization.