Synthesis of Amido-quinoline Hafnium and Zirconium Complexes with Improved Performances toward Ethylene/1-Octene Copolymerization

Molecular magnesium hydrides and hydride-rich clusters are of significant interest for applications ranging from catalysis and small molecule activation to hydrogen storage. Here, we investigate the 2-anilidomethylpyridine framework NNL as an ancillary support for magnesium organometallics with a special emphasis on hydrides. The proligand NNLH (N-[2,6-bis(1-methylethyl)phenyl]-α,6-diphenyl-2-pyridinemethanamine) gives [(NNL)Mg( n Bu)(thf)] (1) by n butane elimination from Mg( n Bu)2(thf) n . A stronger donor such as DMAP replaces the THF from 1 to give [(NNL)Mg( n Bu)(dmap)] (2). Both are air-sensitive, and 1 is adventitiously oxidized into [(NNL)Mg(μ-O n Bu)]2 (3 2 ). The homoleptic [(NNL)2Mg] (8) is made from 1 and a second equiv of NNLH. 1’s terminal n Bu group is selectively protonated by HN(SiMe3)2 to give [(NNL)MgHMDS] (4; HMDS = N(SiMe3)2), whereas Ph3SiOH partially protonates the backbone anilide as well to give a mixture of [(NNL)Mg(OSiPh3)(thf)] (5) and free NNLH. Like HN(SiMe3)2, aprotic MeOTf also reacts by selectively abstracting the n Bu group from 1 to give [(NNL)Mg(μ:κ2-O,O’-OTf)(thf)]2 (6 2 ). Interestingly, screening the common synthetic routes for magnesium hydrides leads to diverse outcomes upon varying the Mg precursors and hydride sources. 1 and PhSiH3 give the hydride cluster [{(NNL)2Mg2(μ-H)}2(μ-H)4Mg] (7), whereas 2 and PhSiH3 give the molecular complex [(NNLde)Mg(dmap)2] (9) with a dearomatized pyridyl backbone. 1 and HBpin (pinacolborane) give a product mixture, from which a different hydride cluster [(NNL)2Mg2(μ-H)}2(μ:κ2-O,O’-O2C2Me4)] (10) is identified, showing a rare instance of complete deborylation of a HBpin molecule. 1 and HBcat (catecholborane) also give a product mixture, one of which is the borylated ligand [(NNL)Bcat] (11). HBpin with 4 as the Mg precursor takes the ligand borylation route more selectively to give [(NNL)Bpin] (12). Last, 1 reacts with i PrNH2BH3 to give [(NNL)Mg{NH( i Pr)BH3}] (13), which shows a slow and fractional conversion into the dinuclear mixed hydrido amidoborane [(NNL)2Mg2(μ-H){(μ-NH( i Pr)BH3}] (14) by partial β-hydride elimination. In comparison, [(NNL)Mg( i PrNHBH3)(dmap)] (15) arising from the DMAP-bound 2 and i PrNH2BH3 is stable toward such elimination.

Heteroleptic Magnesium n-Butyl on a Chemically Non-innocent 2-Anilidomethylpyridine Ligand Leading to Diverse Magnesium Hydrides

Mandal,

Joshi,

Mishra

et al. 2024

Development of Group IV Metal Complexes Bearing Thioether-Amido Ligands with Enhanced High-Temperature Catalytic Performance toward Olefin Copolymerization

Liu,

Feng,

Liu

et al. 2024

The development of homogeneous metal catalysts with both high activity and exceptional thermal stability is crucial for the efficient synthesis of polyolefin elastomers (POEs) through solution-phase olefin polymerization. In this study, a series of Hf (Hf1−Hf5), Zr (Zr1), and Ti (Ti1) complexes featuring thioether-amido ligands were synthesized and carefully characterized using advanced techniques such as 1 H and 13 C NMR spectroscopy as well as single-crystal X-ray diffraction analysis for Hf4 and Hf5. The results revealed that the catalytic activity and 1-octene incorporation efficiency of these metal complexes followed the trend Hf > Zr > Ti, underscoring the significant impact of the metal center on catalytic performance. Furthermore, the choice of ligands was found to play a critical role in dictating the catalytic properties, with ligands bearing less steric hindrance on the sulfur atom proving to be more favorable for copolymerization reactions. Notably, the Hf complex Hf1, featuring a methyl group on the sulfur atom, displayed exceptional catalytic activity as high as 21,060 kg(polymer)•mol −1 (Hf)•h −1 toward ethylene/1-octene copolymerization at 120 °C and produced POE with a high molecular weight (M w = 6.3 × 10 4 g•mol −1 ), relatively narrow distribution (Đ = 2.4), and high incorporation of 1-octene (34.1 mol %). This study demonstrates the potential of tailored ligand design in developing efficient metal catalysts for the production of high-value-added POEs.

Zirconium and Hafnium Complexes Bearing Tridentate ONN-Ligands: Extremely High Activity toward Ethylene (Co)Polymerization

Gao,

Tian,

Han

et al. 2024