SNS-Ligands for Ru-Catalyzed Homogeneous Hydrogenation and Dehydrogenation Reactions

Abstract

A detailed study of literature-known and novel S-containing pincer-type ligands for ruthenium-catalyzed homogeneous hydrogenation and dehydrogenation reactions was carried out. The scope and limitations of these catalysts were carefully investigated, and it was shown that simple bench-stable SNS−Ru complexes can be used to facilitate the hydrogenation of a variety of different substrates at a maximum H 2 pressure of 20 bar under operationally simple, easy to scale up, gloveboxfree conditions by using starting materials and reagents that do not require any special purification prior to use. It was also shown that such complexes can be used to catalyze the dehydrogenative coupling of alcohols and amines to get amides as well as for the dehydrogenative dimerization of alcohols to esters.

Metal‐ligand cooperative activation of HX (X=H, Br, OR) bond on Mn based pincer complexes

“…Pincer complexes based on these ligands have been reported for various transition metals, including manganese (Figure 1b) [8,13,30,31,22–29] . SNS‐, [32–37] CNC‐, [38–43] and PCP‐ligands [44–48] are primarily known for their use in 4d and 5d transition metal catalysis (Figure 1a). Especially in 4d and 5d‐transition metal catalysis high turnover frequencies and turnover numbers are reported for the complexes [31,40,42,49] …”

La[N(SiMe3)2]3‐Catalyzed Hydroboration of Esters and Other Challenging Unsaturated Groups

“…Reduction of esters to corresponding alcohols is a fundamental transformation in organic chemistry . Conventionally, this transformation is realized by employing hydride sources or hydrogenation mediated by transition metal catalysts . The major demerit of metal hydride reduction is the handling of the intrinsically unsafe pyrophoric and moisture sensitive chemical agents, especially at large scale.…”

“…Moreover, quenching the excessive reactive metal hydrides during workup and the disposal of the effluent generated may pose additional cumbersome environmental burden [2a]. For transition metal mediated hydrogenation, usually harsh conditions with elevated reaction temperature accompanying with high pressure are mandatory [3a,b]. In recent years, catalytic hydroboration of unsaturated carbonyl compounds followed by hydrolysis offers a promising approach to the alcohol synthesis.…”

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

“…After the first family of PCP complexes was synthetized by Shaw in 1976 [7], numerous research groups have applied this concept for almost all types of homogeneously catalyzed chemical reactions. A myriad of novel complexes with different pincer arms have been synthetized and characterized, including a vast family of carbene pincers [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23], PNP [24][25][26][27][28][29], PNN [30,31], POP [32], PCP [33][34][35][36][37][38], SNS [39,40], NCN [41], NSiN [42], CNC [43], CNN [44], NNN [45], as well as sulfur- [46][47][48], silicon- [49,50], selenium- [51,52], and boron-functionalized [53,…”