Ethylene polymerization catalyzed by group 4 metal complexes of tridentate heteroscorpionate ligands

Abstract

Considerable attention has been recently devoted to group 4 metal complexes of N,O polydentate ligands exhibiting electronic properties comparable to those of the cyclopentadienyl ligand: among these the heteroscorpionates are attractive candidates. Herein we review the results reached in olefin polymerization catalysis promoted by group 4 metals complexes of heteroscorpionate ligands, with particular reference to the work carried out in our research group. The ethylene polymerization catalyzed by titanium and zirconium complexes of the (3,5-t Bu 2 -2-phenoxo)bis(3,5-Me 2 -pyrazol-1-yl)methane ligand has been investigated in great detail. A solution structure of the active species was proposed on the basis of variable temperature 1 H NMR spectroscopic evidences. Kinetic mechanisms accounting for the formation of linear and branched polyethylenes obtained by the zirconium complexes have been proposed in the light of the ionic interactions of the active species and steric hindrance at metal centre determined by the heteroscorpionate ligands.

Hydridotris(3,5-dimethylpyrazolyl)borate Dimethylamido Imido Niobium and Tantalum Complexes: Synthesis, Reactivity, Fluxional Behavior, and C–H Activation of the NMe2 Function

“…During the 1990s, the development of scorpionate or hydridotris(pyrazolyl)borate chemistry of the heavier group 5 metals was hampered by the lack of simple methods to synthesize suitable starting materials. This anionic tridentate chelate ligand has been widely used in coordination chemistry as a stabilizing group, due to its strong electron donor ability that renders it capable of forming stable complexes with metals in a high oxidation state. ,, For example, group 4 metal alkyl derivatives are difficult to prepare by alkylation of [MXCl 3 ] complexes (M = Ti, Zr, Hf; X = Tp = HB(C 3 H 3 N 2 ) 3 ; X = Tp* = HB(3,5-Me 2 C 3 HN 2 ) 3 ), although neutral trialkyl [MXR 3 ] (R = CH 2 Ph, NMe 2 ) complexes have been isolated and their reactivity toward cationic species has been investigated . More recently, a series of aryloxide derivatives [TiTpX 2 (OAr)] have been prepared and used as catalysts in olefin polymerization.…”

Group 4 Metal Complexes Supported by [ONNO]-Type Bis(o-aminophenolato) Ligands: Synthesis, Structure, and α-Olefin Polymerization Activity

“…In the post-metallocene era, there is a continuing interest in the development of new transition metal-based catalysts for α-olefin polymerization, which is fueled by the search for new ligand frameworks that improve the understanding of structure−property relationships. − Rational ligand design based upon this knowledge leads to better control over polymerization parameters such as activity, selectivity, livingness, and comonomer incorporation ability and may open access to polymeric materials otherwise unavailable. ,, An emerging class of non-metallocene catalysts are group 4 metal complexes based on aryloxide ligands functionalized with heteroatom donors. These ligands allow tuning of the electronic and steric properties of the resulting precatalysts. ,− …”

Heteroscorpionate-Based Co2+, Zn2+, and Cu2+ Complexes: Coordination Behavior, Aerobic Oxidation, and Hydrogen Sulfide Detection

“…6 In our research group we devoted particular attention to the phenol-substituted bis(pyrazolyl)methane derivatives. [7][8][9][10][11][12][13][14] Recently the coordination of (3,5-t Bu 2 -2-phenol)bis(3,5-Me 2 -pyrazol-1-yl)methane ligand (L1-H) to the acidic Zn 2þ center has been described. 7 The complexes exhibit a tetrahedral *To whom correspondence should be addressed.…”

“…In our research group we devoted particular attention to the phenol-substituted bis(pyrazolyl)methane derivatives. − Recently the coordination of (3,5- t Bu 2 -2-phenol)bis(3,5-Me 2 -pyrazol-1-yl)methane ligand ( L1- H) to the acidic Zn 2+ center has been described . The complexes exhibit a tetrahedral geometry in which the ligand is N,N-κ 2 -coordinated to the metal and the hydroxyl phenyl group is not coordinated but is involved in extended intermolecular hydrogen bonding.…”