Palladium Pincer Complex-Catalyzed Trimethyltin Substitution of Functionalized Propargylic Substrates. An Efficient Route to Propargyl- and Allenyl-Stannanes

Abstract

Palladium pincer complex-catalyzed reaction of functionalized propargyl chloride (and mesylate) derivatives with hexamethylditin gives allenyl- and propargyl-stannane products. This catalytic activity is in sharp contrast with the reactivity of commonly used palladium(0) catalysts inducing addition of hexamethylditin to the triple bond. The product distribution of the pincer complex-catalyzed reaction is controlled by the substituent effects of the propargylic substrate: electron-withdrawing functionalities give mainly allenyl stannane products, while with electron-donating groups the main product is propargyl stannane. The catalytic reaction proceeds under very mild conditions tolerating many functionalities such as OH, OAc, NR3, and NR2Ac groups. Our mechanistic studies indicate that the key intermediate of the reaction is a monotrimethylstannane palladium pincer complex. A remarkable feature of the studied catalytic process is that the palladium catalyst does not undergo redox reactions, but its oxidation state is restricted to palladium(II). Since palladium(0) intermediates does not occur in this process, the catalyst is very stable and highly chemoselective.

Palladium Pincer Complex Catalyzed Cross‐Coupling of Vinyl Epoxides and Aziridines with Organoboronic Acids

“…This observation indicated that the application of chloride salts is necessary to form a stable complex, such as 9, otherwise the (h . [32][33][34] However, in 1 a and 1 c there is only a single free coordination site available on the metal atom; and the oxidation state of palladium is restricted to + 2 (features i) and ii) above), and therefore formation of an (h of complex 10 is also in line with our previous mechanistic results [15] on the trimethyltin transfer reactions catalyzed by 1 b. In this reaction the active catalyst is formed by transmetalation of hexamethylditin with the pincer-complex catalyst.…”

“…Thus, we have shown that allylic and propargylic substrates undergo substitution reactions with dimetallic reagents (such as distannane and silylstannane reagents) to give allyl and propargyl stannanes and silanes. [15,16,18] In these reactions, we exploited three important features of the palladium-pincer complex catalysts: i) high redox stability of the palladium(ii) central atom; ii) very strong terdentate ligand-metal bonding; and iii) presence of a s-donating aryl ligand. Because of these features application of pincer-complex catalysts have a great potential to open new synthetic routes in palladium-catalyzed transformations.…”

Novel silica immobilized NCN-pincer palladium(II) and platinum(II) complexes: Application as Lewis acid catalysts

“…Current efforts focus on the use of organometallic pincersiloxane reagents for surface modification and on the use of pincer-metal silica hybrid materials for other catalytic conversions (e.g., C-C and C-X bond formation) [45,[64][65][66][67][68][69]. The integrity and stability of the silica support will be another important aspect of these studies.…”

Unsymmetrical, oxazolinyl-containing achiral and chiral NCN pincer ligand precursors and their complexes with palladium(II)

“…Much of the research has focused on symmetrical NCN pincer palladium complexes, which are symmetrical with two identical N donors such as amines [5][6][7], imines [8,9], pyridines [10][11][12], oxazolines [13][14][15][16][17][18][19][20] or other N-containing heterocycles [21,22] and 2 equiv. five-membered palladacycles (Scheme 1).…”

“…five-membered palladacycles (Scheme 1). Some of the complexes have been successfully applied as catalysts for stannylation of allyl [5] or propargylic substrates [6], Diels-Alder reaction [15], Heck [8,10,21,22], Suzuki and Sonogashira [22] coupling reactions. And the chiral complexes proved to be effective in asymmetric Michael reaction between a-cyanocarboxylates and methyl vinyl ketone (up to 83% ee) [8,17].…”