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The bis(imino)pyridine iron complex, [[2,6-(MeC=N-2,6-iPr2C6H3)2C5H)N]FeCl2] (1), in combination with MAO and ZnEt2 (> 500 equiv.), is shown to catalyze polyethylene chain growth on zinc. The catalyzed chain growth process is characterized by an exceptionally fast and reversible exchange of the growing polymer chains between the iron and zinc centers. Upon hydrolysis of the resultant ZnR2 product, a Poisson distribution of linear alkanes is obtained; linear alpha-olefins with a Poisson distribution can be generated via a nickel-catalyzed displacement reaction. Other dialkylzinc reagents such as ZnMe2 and ZniPr2 also show catalyzed chain growth; in the case of ZnMe2 a slight broadening of the product distribution is observed. The products obtained from Zn(CH2Ph)2 show evidence for chain transfer but not catalyzed chain growth, whereas ZnPh2 shows no evidence for chain transfer. The Group 13 metal alkyl reagents AlR3 (R = Me, Et, octyl, IBu) and GaR3 (R = Et, nBu) act as highly efficient chain transfer agents, whereas GaMe3 exhibits behavior close to catalyzed chain growth. LinBu, MgnBu2 and BEt3 result in very low activity catalyst systems. SnMe4 and PbEt4 give active catalysts, but with very little chain transfer to Sn or Pb. The remarkably efficient iron catalyzed chain growth reaction for ZnEt2 compared to other metal alkyls can be rationalized on the basis of: (1) relatively low steric hindrance around the zinc center, (2) their monomeric nature in solution, (3) the relatively weak Zn-C bond, and (4) a reasonably close match in Zn-C and Fe-C bond strengths.

Highly active transition metal ethylene polymerization catalysts across the transition series have been investigated for their ability to catalyze chain growth on zinc. In reactions of various catalysts with ZnEt(2), product distributions range from Schulz-Flory to Poisson, with several catalysts showing intermediate behavior. A statistical modeling program is introduced to correlate product distributions with the relative rates of propagation, chain transfer to zinc, and beta-H transfer. Six regimes have been identified, ranging from Schulz-Flory to pure Poisson where chain transfer to metal is the only termination process, through to combined alkane/alkene distributions where beta-H transfer is competitive with chain transfer to metal. It is concluded that, while catalyzed chain growth (CCG) is favored by a reasonable match between the bond dissociation energies of both the main group and transition metal alkyl species, the M-C bond energies of the bridging alkyl species, and hence the stabilities of any hetero-bimetallic intermediates or transition states, are key. The latter are strongly influenced by the steric environment around the participating metal centers, more bulky ligands leading to a weakening of the bonds to the bridging alkyl groups; CCG is thus usually more favored for sterically hindered catalysts.

The synthesis and an X-ray diffraction study of bis(pentamethylcyclopentadienyl)(ethylene)titanium 2Ti(?j-C2H4)] are reported. This complex represents the first example of an isolable ethylene adduct of titanium. Titanium-olefin complexes have been widely invoked as key intermediates in Ziegler-Natta olefin polymerization schemes. Whereas treatment of (7j-C5Me5)2Ti(?;-C2H4) with ethylene leads to only traces of polymer after months, (n-C5Me5)2Ti(7)-C2H4) participates in a range of stoichiometric and catalytic reactions. These include the catalytic conversion of ethylene specifically to butadiene and ethane and the catalytic isomerization of alkenes.'H, 12H, and 13C NMR spectra were recorded on Varían T-60 and EM-390, JEOL FX90Q, and Bruker WM-500 spectrometers. Spectra were taken in benzene or toluene solutions, and data are referenced to

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This study explored self-reported changes in caregiving intensity (CI) and caregiver burden (CB) among informal caregivers due to the COVID-19 pandemic overall and by gender. Informal caregivers for someone age 50+ completed a survey via Amazon’s MTurk in June 2020. Participants reported changes in CI and CB due to COVID-19 and provided demographic information. Multinomial logistic regression models assessed changes in CI and CB attributed to the COVID-19 pandemic overall and by gender. The sample ( n = 835) was 68.5% male and had an average age of 34 years ( SD 9.8); 55.7% had increased CI, and 53.1% had increased CB attributed to the pandemic. Increased CB due to COVID-19 was associated with increased CI (OR 5.67, 95% CI 3.92–8.00). Male caregivers with decreased CI due to COVID-19 were nearly seven times as likely as those with no change in CI to have reduced CB due to COVID-19 (OR 6.91, 95% CI 3.29–14.52). Women with decreased CI due to COVID-19 were over eight times as likely to have reduced CB due to COVID (OR 8.30, 95% CI 2.66–25.91). Results indicate that many caregivers experienced increases in CI and CB since the start of the COVID-19 pandemic, and that these changes are complex and vary by gender.