Ligand environment and the structure of schiff base adducts and tetracoordinated metal-chelates

FI catalysts for olefin polymerization--a comprehensive treatment.

The search for newR-olefin polymerization catalysts based on transition metal complexes is a field of major interest involving many academic and industrial research groups. The ligands surrounding the metal play a crucial role in determining the activity as well as the stereospecifity of the catalyst, by affecting the steric and electronic properties at the metal. Over the last two decades, this field has been dominated by the metallocene complexes of group IV metals. Especially, ansa-metallocenes of C2 symmetry were found to induce isospecificity in the resulting polymers. 1 Recently, there has been a growing interest in the development ofnon-cyclopentadienyl ligands for the polymerization of R-olefins.2 Most attention was drawn to chelating di(amido) ligands, 3 some of whose group IV transition metal complexes induce polymerization in a liVing manner, 3a-c whereas chelating di(alkoxo) ligands 4 drew a more limited attention. The number of nonmetallocene systems, which were found to induce tacticity in the resulting polymer, is, however, quite small. 5 In this communication we introduce a novel family of di(alkoxo) complexes, one member of which is the first nonmetallocene C2symmetrical complex, which, upon activation, leads to a highly isospecific living polymerization of 1-hexene. Recently, we introduced the amine bis(phenolate) family of ligands to group IV transition metals. 6 We found that the presence of an extra donor group on a sidearm leads to octahedral LigMX 2type complexes, in which the two labile X groups are forced into a cis geometry. 6a Catalysts derived from these complexes (e.g. 1a) lead to highly reactive 1-hexene polymerization catalysts. 6b The Cs-symmetry of1a allows olefin approach from the two possible directions in each active position without preference, thus the polymer obtained is atactic. Therefore, we aimed at complexes of a different symmetry which may induce tactic polymerization, that incorporate ligands having similar functional groups yet having a different connectivity. Our approach is based on replacing the “branched” mode of connectivity of donor atoms with a sequential connectivity mode, namely diamine bis(phenolate) ligands. This new family of dianionic tetradentate chelating ligands is easily synthesized by a one-pot Mannich condensation between readily available di(secondary) amines, formaldehyde, and substituted phenols as demonstrated in eq 2. 2, a structural isomer

Isospecific Living Polymerization of 1-Hexene by a Readily Available Nonmetallocene C2-Symmetrical Zirconium Catalyst

Calixarene and resorcinarene ligands in transition metal chemistry

Recent advances in utilization of transition metal complexes and lanthanides as diagnostic tools

A Sensitive Spectroscopic Probe for Monitoring Changes in the Coordination Sphere of Titanium: Eight-Membered Dioxatitanacycles and Their Organometallic Derivatives†

Mononuclear tungsten(VI) calix[4]arene complexes

The reaction of MCl4·2thf (thf = tetrahydrofuran) with the sodium salt of quadridentate Schiff bases [L =N,N′-ethylenebis(acetylacetoneiminate)(acen), N,N′-ethylenebis(salicylideneiminate)(salen), N,N′-ethylenebis(α-methylsalicylideneiminate)(dmsalen), or N,N′-o-phenylenebis(salicylideneiminate)(salphen)] yields the complexes [MLCl2(thf)]. X-Ray analyses showed for all of them that the metal ion is seven-co-ordinate with a pseudo-pentagonal bipyramidal geometry. Details of the structures of [Zr(acen)Cl2(thf)](5), [Zr(salphen)Cl2(thf)]·0.5thf (10), and of the corresponding isostructural hafnium complex [Hf(salphen) Cl2(thf)]·0.5thf (11) are reported. The equatorial plane of the bipyramid is defined by the N2O2 donor atoms and by the oxygen atom from thf, while the two chlorine atoms are trans to each other [Cl–Zr–Cl 169.1 (1), (5); 165.2(1), (10); Cl–Hf–Cl 166.3(1)°, (11)]. Recrystallization of the seven-co-ordinate complexes from toluene removed the thf leading to six-co-ordinate complexes. The structural determination of the isostructural [Zr(acen)Cl2](12) and [Hf(acen)Cl2](13) showed the six-co-ordination of the metal with the two chlorines assuming a cis arrangement [Cl–Zr–Cl 87.2(1), (12); Cl–Hf–Cl 87.4(1)°, (13)]. Bond lengths within the co-ordination sphere are significantly shorter in the six-co-ordinate complexes. The cis and trans isomers do not interconvert in solutions of non-co-ordinating solvents, i.e. C6H6 or CH2Cl2, as shown by their distinctive 1H n.m.r. spectra. In the absence of geometrical constraints zirconium(IV) prefers six-co-ordination and a cis arrangement of the chloride ligands. This was confirmed by synthesizing [Zr(msal)2Cl2](15)(msal =N-methylsalicylideneiminate), [Cl–Zr–Cl 97.9(1)°] containing a bidentate Schiff-base ligand. Its crystallization from thf gave the unsolvated six-co-ordinated form. Crystallographic details: complex (5), space group P, a= 8.401 (1), b= 15.987 (2), c= 7.805(1)A, α= 98.41 (1), β= 90.32(1), γ= 76.65(1)°, Z= 2, and R 0.042 for 3 713 observed reflections; (10), space group P, a= 12.759(2), b= 13.332(2), c= 7.587(1)A, α= 91.60(2), β= 98.45(1), γ= 85.30(1)°, Z= 2, and R 0.033 for 3 813 observed reflections; (11), space group P, a= 12.737(7), b= 13.269(7), c= 7.564(4)A, α= 91.48(1), β= 98.56(1), γ= 85.26(1)°Z= 2, and R 0.027 for 4 227 observed reflections; (12), space group P21/n, a= 24.150(5), b= 9.160(2), c= 7.282(1)A, β= 90.90(1)°, Z= 4, and R 0.034 for 1 894 observed reflections; (13), space group P21/n, a= 24.096(10), b= 9.161 (4), c= 7.262(3)A, β= 90.87(1)°, Z= 4, and R 0.024 for 2 124 observed reflections; (15), space group P, a= 13.024(3), b= 14.522(3), c= 9.797(2)A, α= 90.10(1), β= 93.14(1), γ= 96.09(1)°, Z= 4, and R 0.044 for 3 294 observed reflections.

cis- and trans-Dichloro-derivatives of six- and seven-co-ordinate zirconium and hafnium bonded to quadridentate Schiff-base ligands. Crystal structures of [Zr(acen)Cl2(thf)], [M(salphen)Cl2(thf)]·0.5thf, [M(acen)Cl2], (M = Zr or Hf), and [Zr(msal)Cl2][acen =N,N′-ethylenebis(acetylacetoneiminate), salphen =N,N′-o-phenylenebis(salicylideneiminate), msal =N-methylsalicylideneiminate, and thf = tetrahydrofuran]

Titanium(IV) and zirconium(IV) tetrahydroborate moieties supported by a phenoxo ligand

A trans‐Dimethyl Derivative of Octahedral TiIV: Alkylation and Arylation of TiIV‐Schiff Base Complexes

Fabio Corazza

Papers

A Sensitive Spectroscopic Probe for Monitoring Changes in the Coordination Sphere of Titanium: Eight-Membered Dioxatitanacycles and Their Organometallic Derivatives†

Mononuclear tungsten(VI) calix[4]arene complexes

Titanium(IV) and zirconium(IV) tetrahydroborate moieties supported by a phenoxo ligand

A trans‐Dimethyl Derivative of Octahedral TiIV: Alkylation and Arylation of TiIV‐Schiff Base Complexes