Nitration Under Continuous Flow Conditions: Convenient Synthesis of 2‑Isopropoxy-5-nitrobenzaldehyde, an Important Building Block in the Preparation of Nitro-Substituted Hoveyda–Grubbs Metathesis Catalyst

Herein, we describe the use of continuous flow chemistry for selective, efficient and reproducible nitration of 2-isopropoxybenzaldehyde to produce the desired 2-isopropoxy-5-nitrobenzaldehyde, an important building block in the preparation of a ligand of nitro-substituted Hoveyda–Grubbs metathesis catalyst. Nitration was done with red fuming HNO₃, and this challenging and hazardous process was performed using a flow-through silicon-glass microreactor equipped with a set of temperature sensors, and with a productivity of 13 g/h, providing us with a reproducible chemical process amenable for production of sufficient quantities of 2-isopropoxy-5-nitrobenzaldehyde for ongoing large-scale synthesis of nitro-substituted Hoveyda–Grubbs metathesis catalyst

Rational and Then Serendipitous Formation of Aza Analogues of Hoveyda-Type Catalysts Containing a Chelating Ester Group Leading to a Polymerization Catalyst Family

Analogues of the well-known Hoveyda–Grubbs catalyst bearing both a chelating ester function and a chelating nitrogen atom were obtained. These complexes behave differently depending on the character of the chelating amine. Complexes containing a secondary amine underwent unexpected spontaneous oxidation of the amine group, leading to the Schiff base analogues. In contrast, complexes containing a tertiary amine were prone to intramolecular cyclization in the presence of a base (Et₃N). Probing the activity of such (pre)­catalysts in ring-closing metathesis reactions (RCMs) revealed their dormant character and excellent thermo-switchability. In particular, complexes bearing an iminium nitrogen fragment were found to be very useful in a delayed ring-opening metathesis polymerization (ROMP) and were therefore commercialized

Raman, Surface-Enhanced Raman, and Density Functional Theory Characterization of (Diphenylphosphoryl)(pyridin-2‑, -3‑, and -4-yl)methanol

This work presents near-infrared Raman spectroscopy (FT-RS) and surface-enhanced Raman scattering (SERS) studies of three pyridine-α-hydroxymethyl biphenyl phosphine oxide isomers: (diphenylphosphoryl)­(pyridin-2-yl)­methanol (α-Py), (diphenylphosphoryl)­(pyridin-3-yl)­methanol (β-Py), and (diphenylphosphoryl)­(pyridin-4-yl)­methanol (γ-Py) adsorbed onto colloidal and roughened in oxidation–reduction cycles silver surfaces. The molecular geometries in the equilibrium state and vibrational frequencies were calculated by density functional theory (DFT) at the B3LYP 6-311G­(df,p) level of theory. The results imply that the most stable structure of the investigated molecules is a dimer created by two intermolecular hydrogen bonds between the H atom of the α-hydroxyl group (in up (HO_U) or down (HO_D) stereo bonds position) and the O atom of tertiary phosphine oxide (O) of the two monomers. Comparison the FT-RS spectra with the respective SERS spectra allowed us to predict the orientation of the hydroxyphosphonate derivatives of pyridine that depends upon both the position of the substituent relative to the ring N atom (in α-, β-, and γ-position, respectively) and the type of silver substrate