Search

Identifying intermediates of Ni-containing reactions can be challenging due to the high reactivity of Ni complexes and their sensitivity toward air and moisture. Many Ni bidentate phosphine complexes are diamagnetic and can be analyzed in situ via 31P NMR spectroscopy, but the oxidation state of Ni is difficult to determine using 31P chemical shift analysis alone. The J-coupling between P atoms, JPP, has been proposed to correlate with oxidation state, but few investigations have looked at how JPP is affected by parameters such as length of the linker or identity of the phosphine or other ligands. The present investigation into the JPP values of Ni bidentate phosphine complexes with two-carbon and three-carbon linkers shows that the JPP values observed in 31P NMR spectra, |JPP|, are competent indicators of the oxidation state at Ni. For complexes with two-carbon linkers, |JPP| > 40 Hz is typical of Ni0 while |JPP| < 30 Hz is typical of NiII; this trend is reversed for complexes with three-carbon linkers. Additionally, the Lewis acidity of the Ni and Lewis basicity of the phosphine ligand affect JPP predictably. For example, increased P-to-Ni donation arising from more-donating phosphines or more-withdrawing ligands trans to the P atoms causes a more negative JPP. These results should enable the oxidation state of Ni and properties of ligands in Ni bidentate phosphine complexes to be determined in situ during reactions containing these species.

Identifying intermediates of Ni-containing reactions can be challenging due to the high reactivity of Ni complexes and their sensitivity toward air and moisture. Many Ni bidentate phosphine complexes are diamagnetic and can be analyzed in situ via (31)P NMR spectroscopy, but the oxidation state of Ni is difficult to determine using (31)P chemical shift analysis alone. The J-coupling between P atoms, J(PP), has been proposed to correlate with oxidation state, but few investigations have looked at how J(PP) is affected by parameters such as length of the linker or identity of the phosphine or other ligands. The present investigation into the J(PP) values of Ni bidentate phosphine complexes with two-carbon and three-carbon linkers shows that the J(PP) values observed in (31)P NMR spectra, ∣J(PP)∣, are competent indicators of the oxidation state at Ni. For complexes with two-carbon linkers, ∣J(PP)∣ > 40 Hz is typical of Ni(0) while ∣J(PP)∣ < 30 Hz is typical of Ni(II); this trend is reversed for complexes with three-carbon linkers. Additionally, the Lewis acidity of the Ni and Lewis basicity of the phosphine ligand affect J(PP) predictably. For example, increased P-to-Ni donation arising from more-donating phosphines or more-withdrawing ligands trans to the P atoms causes a more negative J(PP). These results should enable the oxidation state of Ni and properties of ligands in Ni bidentate phosphine complexes to be determined in situ during reactions containing these species.

Polymers that depolymerize back to monomers can be repeatedly chemically recycled, thereby reducing their environmental impact. Polyphthalaldehyde is a metastable polymer that is rapidly and quantitatively depolymerized due to its low ceiling temperature. However, the effect of substitution on the physical and chemical properties of polyphthalaldehyde derivatives has not been systematically studied. Herein, we investigate the cationic polymerization of seven distinct o‑phthalaldehyde derivatives and demonstrate that judicious choice of substituents results in materials with a wide range of ceiling temperatures (from < –60 to 106 °C) and decomposition temperatures (109–196 °C). We anticipate that these new polymers and their derivatives will enable researchers to access degradable materials with tunable thermal, physical, and chemical properties.

Catalyst-transfer polymerization has enabled synthesizing conjugated polymers with unmatched control over both polymer sequence and end-group identity. These attributes provide access to complex materials, including conjugated–conjugated and conjugated–nonconjugated block copolymers, gradient copolymers, nonlinear copolymers, and hybrid materials. This review discusses these materials, highlighting their syntheses as well as their applications.