Practical Gas Cylinder-Free Preparations of Important Transition Metal-Based Precatalysts Requiring Gaseous Reagents

Abstract

A simple and safe setup for the synthesis of a selection of important transition metal-based precatalysts is reported, all requiring low-molecular weight gaseous reagents for their preparation. Hydrogen, carbon monoxide, ethylene, and acetylene are each liberated in a controlled manner from a corresponding easy-to-handle precursor in a closed two-chamber reactor. Gas cylinders and elaborate setups/techniques connected to handling toxic and/or flammable gases as reported in the literature can thus be avoided. The corresponding precatalysts are of high relevance in the active research fields of C–H bond activation, dehydrogenation, hydrogenation, and coupling reactions. The selection of complexes shown is meant to serve as examples for the usefulness and broadness of the presented methods, allowing precatalysts requiring gaseous reagents to become available for the research community.

Transformation of Acetylene to Ethenylidene, Carbene, Acetylide, Vinyl, and Olefin Groups with Cp*Fe(1,2-Cy2PC6H4S)

“…Experimental methods and syntheses of 1,2-Cy 2 PC 6 H 4 SH, H­(Et 2 O)­BAr 4 F (Ar F = 3,5-(CF 3 ) 2 C 6 H 3 ), [Cp 2 Fe]­[BAr 4 F ], and 2,4,6-tri- tert -butylphenoxyl radical have been recently described. ,, Acetylene gas and all other reagents were purchased from commercial suppliers and used without further purification. Deuterated acetylene, C 2 D 2 , was prepared by reacting calcium carbide with D 2 O in a two-chamber reactor, , as described in the Deuterium Labeling Experiment section.…”

ThioCORMates: Tunable and Cost‐Effective Carbon Monoxide‐Releasing Molecules

“… [12] Alternatively, some existing CORMs that had previously been used for in situ delivery were shown to work for ex situ CO formation, such as Larhed and co‐workers demonstrating that Mo(CO) 6 could also be used as an external source of CO [13] . Because of the ease and general reaction compatibility in using a two‐chamber/ex situ delivery approach, these reagents have been widely used in carbonylative cross‐coupling and more recently in inorganic synthesis [9,14] . Nonetheless, these existing methods carry some disadvantages, including the elevated temperatures necessary for CO release in nearly all cases, [15] expensive reagents that are difficult to recycle, or complex conditions necessary to trigger gas evolution.…”

“…[22] This requirement provides an example of why a tunable release rate is a useful feature of a CORM in practice, since the choice of thioCORMate and base can act in an analogous way to a regulator on a CO gas tank. ThioCORMate 2 a was used to conveniently generate the steady stream of CO gas over the necessary timescale by reaction with DABCO (see Table 1, entry 3), forming Vaska's complex (14) itself, as well as a Vaska-type complex with tris[3,4bis(trifluoromethyl) phenyl]phosphine ligands (15). The IR carbonyl stretches and NMR data for these complexes matched those reported in the literature.…”

Pd‐Catalyzed Difluoromethylations of Aryl Boronic Acids, Halides, and Pseudohalides with ICF2H Generated ex Situ

“…In our efforts to develop chemical techniques for the safe handling of gaseous compounds, and to demonstrate their successful use as stoichiometric reagents, we have earlier reported the application of a two‐chamber reactor in combination with easy‐to‐handle gas surrogates [22–29] . Others have reported its use for the expedient preparation of SO 2 F 2 [30] .…”

“…[21] In our efforts to develop chemical techniques for the safe handling of gaseous compounds, and to demonstrate their successful use as stoichiometric reagents, we have earlier reported the application of a two-chamber reactor in combination with easy-to-handle gas surrogates. [22][23][24][25][26][27][28][29] Others have reported its use for the expedient preparation of SO 2 F 2 . [30] Here, we report on a set-up for the simple synthesis of DFIM and its stoichiometric use in the Suzuki coupling with aryl boronic acids and derivatives thereof.…”