Facing Unexpected Reactivity Paths with Zr^IV–Pyridylamido Polymerization Catalysts

Abstract

This work provides original insights to the better understanding of the complex structure–activity relationship of ZrIV–pyridylamido‐based olefin polymerization catalysts and highlights the importance of the metal‐precursor choice (Zr(NMe2)4 vs. Zr(Bn)4) to prepare precatalysts of unambiguous identity. A temperature‐controlled and reversible σ‐bond metathesis/protonolysis reaction is found to take place on the ZrIV‐amido complexes in the 298–383 K temperature range, changing the metal coordination sphere dramatically (from a five‐coordinated tris‐amido species stabilized by bidentate monoanionic {N,N−} ligands to a six‐coordinated bis‐amido–mono‐amino complexes featured by tridentate dianionic {N−,N,C−} ligands). Well‐defined neutral ZrIV–pyridylamido complexes have been prepared from Zr(Bn)4 as metal source. Their cationic derivatives [ZrIV{N−,N,C−}Bn]+[B(C6F5)4]− have been successfully applied to the room‐temperature polymerization of 1‐hexene with productivities up to one order of magnitude higher than those reported for the related HfIV state‐of‐the‐art systems. Most importantly, a linear increase of the poly(1‐hexene) Mn values (30–250 kg mol−1) has been observed upon catalyst aging. According to that, the major active species (responsible for the increased Mn polymer values) in the aged catalyst solution, has been identified.

Benzoimidazole‐Pyridylamido Zirconium and Hafnium Alkyl Complexes as Homogeneous Catalysts for Tandem Carbon Dioxide Hydrosilylation to Methane

“…The κ 3 { N − , N , N − } NL bimid and κ 3 { N − , N , N } NL bimid‐Alk ligands are nearly planar with an average deviation of the Zr center from the plane intercepted by the three N sites of 0.038 Å (0.033 and 0.042 Å in 6 b and 10 a , respectively). The main Zr−N and Zr−C bond lengths fall typically in the range described for related systems . Compounds 9 b and 12 a crystallize in the triclinic P space group, both with a distorted square‐pyramidal coordination geometry (coordination number=5) .…”

“…In our previous studies, we investigated a variety of structurally and electronically diverse early‐transition‐metal complexes stabilized by multidentate N‐containing ligands as homogeneous catalysts for the upgrading of unactivated olefins as well as for the intramolecular hydroamination reaction . As an example of a challenging application of highly electrophilic coordination compounds in homogeneous catalysis, Matsuo and Kawaguchi have described the use of a κ 3 { O − , O , O − } Zr IV (Bn) 2 phenoxide complex in combination with the strong Lewis acid B(C 6 F 5 ) 3 for the tandem hydrosilylation of CO 2 to CH 4 .…”

Unusual Hafnium–Pyridylamido/ERn Heterobimetallic Adducts (ERn=ZnR2 or AlR3)

“…

NMR spectroscopy and DFT studies indicate that the Symyx/Dow Hf(IV)-pyridylamido catalytic system for olefin polymerization, [{N À ,N,C Nph À }HfMe][B(C 6 F 5 ) 4 ] (1, Nph = naphthyl), interacts with ER n (E = Al or Zn, R = alkyl group) to afford unusual heterobimetallic adducts [{N À ,N}HfMe(m-C Nph )(m-R)ER nÀ1 ][B(C 6 F 5 ) 4 ] in which the cyclometalated Nph acts as a bridge between Hf and E. 1 H VT (variable-temperature) EXSY NMR spectroscopy provides direct evidence of reversible alkyl exchanges in heterobimetallic adducts, with ZnR 2 showing a higher tendency to participate in this exchange than AlR 3 . Initially reported as the first industrially relevant systems to yield highly isotactic polypropylene with solution-process technology, [4][5][6] they subsequently attracted even greater attention for their propensity to undergo reversible transalkylation with metal alkyls, thereby opening the door to novel olefin block copolymers through "chain shuttling", that is, tandem catalysis under coordinative chaintransfer polymerization (CCTP) conditions. Nevertheless, a slight increase in the temperature (to > 265 K) initiates 1hexene polymerization.

Discovered by means of high-throughput screening in the framework of a Dow/Symyx collaboration, [1][2][3] Hf IV -pyridylamido-based olefin polymerization catalysts have several unique features.

…”

Imidazole‐Bridged Tetrameric Group(IV) Heteroleptic Complexes from the Spontaneous Metal‐Ligand Assembly of a Potentially N4‐Tetradentate Ligand

“…In recent years, our group has been extensively working on the preparation of multidentate heteroleptic N‐ligands and their related κ 3 {N,N,N}M 3+/4+ coordination compounds (or κ 3 {N,C,N}M 3+/4+ /κ 3 {N,N,C}M 3+/4+ organometallics) based on highly electrophilic metal ions (from group IV elements of the periodic table or from lanthanides, ) for applications in homogeneous catalysis. In a recent report, we have described the synthesis, characterization and catalytic application of a series of Zr IV /Hf IV alkyl/amido complexes stabilized by a tridentate N‐ligand containing a benzoimidazole fragment .…”