Asymmetric Bis(formamidinate) Group 4 Complexes: Synthesis, Structure and Their Reactivity in the Polymerization of α-Olefins

Guerbet upgrading of ethanol to n-butanol using Ru(iii) catalysts under air

A series of in situ prepared Ru(iii) complexes supported by easily accessible N-donor organic pincer ligands were used as catalysts in the Guerbet upgrading reaction of ethanol under aerobic conditions.

2-(Arylimino)benzylidene-8-arylimino-5,6,7-trihydroquinoline Cobalt(II) Dichloride Polymerization Catalysts for Polyethylenes with Narrow Polydispersity

A series of 2-(arylimino)benzylidene-8-arylimino-5,6,7-trihydroquinoline cobalt(II) chlorides (Co1–Co6) containing a fused ring and a more inert phenyl group as the substituent at the imino-C atom has been synthesized using a one-pot synthesis method and fully characterized by FT-IR and elemental analysis. The molecular structures of Co2 and Co5 have been confirmed by X-ray diffraction as having a distorted square pyramidal geometry around a cobalt core with a tridentate N,N,N-chelating ligand and two chlorides. On activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), Co1–Co6 exhibited high activities for ethylene polymerization. The least sterically hindered Co2 showed a maximum activity of 16.51 × 106 g (PE) mol−1 (Co) h−1 at a moderate temperature 50 °C. Additionally, ortho-fluoride Co6 was able to maintain a high activity not only at 70 °C but also after 60 min at 50 °C, highlighting its excellent thermal-stability and long catalytic lifetime. The resultant polyethylene showed clearly narrower molecular weight distribution (PDI: 1.3–3.1) than those produced by structurally related cobalt counterparts, indicating the positive influence of benzhydryl substitution on the catalysis. Moreover, the molecular weight (1.7–386.6 kg mol−1) of vinyl- or n-propyl-terminated polyethylene can be finely regulated by controlling polymerization parameters.

LLDPE-like Polymers Accessible via Ethylene Homopolymerization Using Nitro-Appended 2-(Arylimino)pyridine-nickel Catalysts

Four examples of para-nitro substituted 2-(arylimino)pyridine-nickel(II) bromide complexes of general formula, [2-{(2,6-R-4-NO2C6H2)N=CMe}C5H4N]NiBr2, but differentiable by the steric/electronic properties displayed by the ortho-groups [R = i-Pr (Ni1), Et (Ni2), CHPh2 (Ni3), CH(4-FPh)2 (Ni4)], have been prepared in good yield. For comparative purposes, the meta-nitro complex, [2-{(2,6-i-Pr2-3-NO2-4-(4-FPh)2C6H)N=CMe}C5H4N]NiBr2 (Ni5), has also been synthesized. The molecular structures of mononuclear Ni3·xH2O (x = 2, 3) and bromide-bridged dinuclear Ni4 and Ni5 are disclosed. Upon activation with either ethylaluminum dichloride (EtAlCl2) or modified methylaluminoxane (MMAO), all precatalysts displayed good catalytic performance at operating temperatures between 30 °C and 60 °C with higher activities generally seen using EtAlCl2 [up to 4.7 × 106 g PE (mol of Ni)−1 h−1]: Ni2 ~ Ni5 > Ni1 ~ Ni4 > Ni3. In terms of the resultant polyethylene (PE), Ni4/EtAlCl2 formed the highest molecular weight of the series (Mw up to 1.4 × 105 g mol−1) with dispersities (Mw/Mn) ranging from narrow to broad (Mw/Mn range: 2.2–24.4). Moreover, the melting temperatures (Tm) of the polymers generated via EtAlCl2 activation fell in a narrow range, 117.8–126.0 °C, which resembles that seen for industrial-grade linear-low density polyethylene (LLDPE). Indeed, their 13C NMR spectra revealed significant amounts of uniformly distributed long-chain branches (LCBs), while internal vinylene groups constituted the major type of chain unsaturation [vinylene:vinyl = 5.3:1 (EtAlCl2) and 9.9:1 (MMAO)].

Synthesis of Ti, Zr, and Hf complexes with a new tetra-azane ligand by one-pot HCl-elimination and their properties as catalysts for production of UHMWPE

The first example for the HCl-elimination reaction being applied in the attachment of an amido-containing ligand to Zr and Hf.

Group 4 alkoxide complexes containing [NNO]-type scaffold: synthesis, structural characterization and polymerization studies

A series of new dinuclear group 4 complexes containing [NNO]-type ligands are utilized as catalysts for polymerization reactions.

Metal-free access of bulky N,N′-diarylcarbodiimides and their reduction: bulky N,N′-diarylformamidines

A facile synthetic protocol for the preparation of N,N′-diarylcarbodiimides and their reduction with sodium borohydride in ethanol to obtain N,N′-diarylformamidines has been demonstrated.

Intermolecular hydroaminoalkylation of alkenes and dienes using a titanium mono(formamidinate) catalyst

An easily accessible formamidinate ligand-bearing titanium complex initially synthesized by Eisen et al. is used as catalyst for intermolecular hydroaminoalkylation reactions of unactivated, sterically demanding 1,1- and 1,2-disubstituted alkenes and styrenes with secondary amines. The corresponding reactions, which have never been achieved with titanium catalysts before, take place with excellent regioselectivity (up to 99 : 1) and in addition, corresponding reactions of 1,3-butadienes with N-methylbenzylamine are also described for the first time.