Water-Soluble Ruthenium Alkylidenes:  Synthesis, Characterization, and Application to Olefin Metathesis in Protic Solvents

Abstract

Ruthenium alkylidenes 6 and 7 bearing cationically functionalized phosphine ligands are soluble and stable in protic solvents and initiate olefin metathesis reactions in methanol, water, and aqueous emulsions. NMR spectroscopy data and X-ray diffraction analyses of alkylidene 6 suggested that these new alkylidenes were structurally similar to previously reported complexes of the type (PR 3 ) 2 Cl 2 RudCHR, in which the alkylidene substituents lie in the Cl-Ru-Cl plane. The anionic chloride ligands of complexes 6 and 7 were found to undergo facile ligand exchange reactions with other anions in protic solution. Both alkylidenes initiate the ring-opening metathesis polymerization (ROMP) of strained, cyclic olefins in water. However, the propagating species in these reactions decompose prior to complete consumption of monomer. These complexes initiate the quantitative, living polymerization of functionalized monomers in water in the presence of a Brønsted acid. Both chain termination and chain transfer reactions were experimentally demonstrated to be absent on the time scale of these acid-activated polymerizations. Alkylidenes 6 and 7 react readily with acyclic olefins: alkylidene 6 reacted with trans-2-butene to yield a new ethylidene complex in either methanol or water, and the treatment of 6 with tri(ethylene glycol) methyl vinyl ether in water yielded water-soluble Fischer-carbene complex 16.

Salicylaldimine Ruthenium Alkylidene Complexes: Metathesis Catalysts Tuned for Protic Solvents

“…Complex 7c tolerates water, and remains <40% intact after 2 d in CD 3 OD/D 2 O (3:1) under air at 20 °C (according to integration of Ar-CH 3 and alkylidene 1 H NMR signals). In contrast, previous catalysts bearing ligands with cationic functional groups (such as 5 [12]) decompose in minutes when exposed to traces of oxygen in solution.…”

“…[6] For instance, aqueous olefin metathesis is attractive for carbon-carbon bond formation in biological applications [7] and green chemistry, [8,9] yet complexes 1-4a are insoluble in water and soluble versions such as 5 have proven to be unstable to air and incompatible with internal olefins. [10][11][12] Grubbs and coworkers have begun to address this challenge by modifying the local environment of the catalyst with a polyethylene glycol-bearing ligand, as in complex 4b. [9] Here, our intent is to complement this approach by tuning the primary coordination sphere of the catalyst to the demands of aqueous media.…”

Transition metal-based polymer chemistry: a critical micro-review

“…This requires the use of environmentally friendly alternatives. The most prominent ones are currently supercritical carbon dioxide [172 -177] as well as water itself [27,144,146,[178][179][180][181][182][183][184][185][186]. The latter is certainly not new in organic synthesis [187][188][189][190][191][192][193], yet still lacks comparable prominence in polymer chemistry.…”

Quasi-Nature Catalysis: Developing C−C Bond Formations Catalyzed by Late Transition Metals in Air and Water

“…Such advantages have been well demonstrated by the recent large volume of work with water-soluble catalysts, 6,7 such as catalytic hydrogenation, 8 hydroformylation (e.g., the well-known Rhone-Poulenc process), 9 palladium-catalyzed carboncarbon bond formation reactions, 10 and rutheniumcatalyzed metathesis reactions. 11 This Account describes the development of synthetically useful catalytic coupling reactions under the ambient conditions of both air and water, which comes down to the competitive reactivity of C-M bonds toward water (hydrolysis), air (oxidation), and organic substrates (often an electrophile to generate the desired product) (Figure 1). Through a delicate balance of these reactivities, this Account demonstrates that various air-and water-sensitive catalytic reactions can in fact be carried out in air and water.…”