Mansuk Kim

Structure and Reactivity of Alkynyl Ruthenium Alkylidenes

The isolation and structural characterization of alkynyl Ru-alkylidene species has been elusive owing to their rapid metallotropic shift and fast turnover. The enyne ring-closing metathesis and relay metathesis provides the platform to form a variety of alkynyl Ru-alkylidene species possessing a sterically and electronically different substituent on the carbenic carbon, which allowed their regio-controlled trapping and structural characterization.

Initiation and Termination Mode of Enyne Cross-Metathesis and Metallotropic [1,3]-Shift Controlled by Remote Substituents

The cross-metathesis of terminal alkyne and alkene using Ru-based Grubbs catalyst generally undergoes alpha-insertion. In this study, excellent control over alpha- and beta-insertion of ruthenium alkylidene into terminal alkynes has been achieved by using a substituent at a remote site from the reaction center. While the origin of this regioselectivity of insertion and metallotropic shift remains to be established, the trend indicates that the alpha-insertion with a concomitant metallotropic shift is favored with small substituents whereas the beta-insertion without a metallotropic shift is favored with bulky substituents such as tert-butyl and trialkyl silyl groups.

Nonmetathetic activity of ruthenium alkylidene complexes: 1,4-hydrovinylative cyclization of multiynes with ethylene.

An efficient 1,4-hydrovinylative cyclization reaction of triynes and tetraynes catalyzed by ruthenium alkylidene complexes under ethylene is described. The regioselectivity of vinyl group incorporation can be controlled by the nature of the substituent on the alkyne, and the Grubbs second-generation catalyst is the most effective among typical ruthenium alkylidene complexes.

Control of a reactive batch distillation process using an iterative learning technique

Quadratic criterion-based iterative learning control (QILC) was applied to a numerical reactive batch distillation process, in which methacrylic anhydride (MAN) is produced through the reaction of methacrylic acid with acetic anhydride. The role of distillation is to shift the equilibrium conversion toward the direction of the product by removing acetic acid (AcH), a by-product of the reaction. Two temperatures at both ends of the column were controlled by individual control loops. A nonlinear PID controller manipulating the reflux ratio was employed to regulate the top temperature at the boiling point of AcH. A constrained QILC was used for the tracking of the reactor temperature. A time-varying reference trajectory for the reactor temperature that satisfies the target conversion and purity of MAN was obtained through repeated simulations and confrimation experiments in the pilot plant. The QILC achieved satisfactory tracking in several batch runs with gentle control movements, while the PID control as a substitute of the QILC in a comparative study exhibited unacceptable performance.