Synthesis, Characterization, and Dehydrogenation Activity of an Iridium Arsenic Based Pincer Catalyst

Abstract

A new arsenic-based pincer (AsOCOAs) dehydrogenation catalyst has been synthesized, IrHCl{2,6-C 6 H 3 -(O-AsBu t 2 )} (3). Treatment with an equivalent of base (NaO-tert-butoxide) under an atmosphere of hydrogen gas affords the dihydride catalyst IrH 2 {2,6-C 6 H 3 -(O-AsBu t2 )} ( 4). The activity of 3 was explored under transfer dehydrogenation conditions with cyclooctane and tert-butyl ethylene, giving a maximum turnover number of 960 at 175 °C in 24 h. Acceptorless dehydrogenations were also explored with pyrrolidine-based molecules, ethylperhydrocarbazole ( 5), methylperhydroindole ( 6), and butylpyrrolidine (7), in which all results indicate 3 is roughly half as active as the analogous phosphine-based pincer catalyst 2. Akin to the phosphine pincer catalysts the activity was seen to steadily improve with increasing temperature, peaking at 175 °C, upon which thermal decomposition sets in.

Recent Advances in Alkane Dehydrogenation Catalyzed by Pincer Complexes

“…1 Examples of pincer-iridium complexes that have been investigated for alkane dehydrogenation Recent Advances in Alkane Dehydrogenation Catalyzed by Pincer Complexes groups have been modified (Fig. 1) [58][59][60][61][62][63][64][65][66][67][68][69][70]. The Brookhart and Jensen groups reported a new class of catalysts wherein the benzylic CH 2 linkers of the PCP backbone were replaced by O linkers to obtain the ( R POCOP)Ir (21, R¼t-Bu;22, R¼i-Pr) systems [58][59][60]66].…”

“…Notably, ( tBu4 POCOP)IrH 2 (21-H 2 ) showed greater activity than ( tBu4 PCP)IrH 2 (11-H 2 ) for COA/TBE transfer dehydrogenation, although the latter was found to be significantly more active for the transfer dehydrogenation of linear alkanes [46][47][48]71]. As will be discussed later in this chapter, these phosphine, phosphinite, and mixed phosphine-phosphinite-based systems have found widespread utility as catalysts for alkane metathesis , [48,67,[71][72][73][74], alkyl group metathesis [62], dehydroaromatization reactions [61,75,76], alkane-alkene coupling reactions [77,78], and dehydrogenation of several other substrates [64,68,69,[79][80][81].…”

Dehydrogenation of n-Alkanes by Solid-Phase Molecular Pincer-Iridium Catalysts. High Yields of α-Olefin Product

“…3 Catalysts 1 and 2 were also found to be effective for the acceptorless dehydrogenation of alkanes. 2,4 Work with these complexes has been followed by reports of numerous catalytically active variants with the (PCP)Ir motif, [5][6][7][8][9] including other bis-phosphines, [10][11][12][13][14] bis-phosphinites (POCOP), [15][16][17][18] hybrid phosphine-phosphinites (PCOP), 19,20 arsines (AsOCOAs), 21 hybrid phosphine-thiophosphinites (PSCOP) 22 and hybrid amine-phosphinites (NCOP) 23 . In addition to simple alkane dehydrogenation, these complexes have been employed for numerous other catalytic transformations of hydrocarbons, including alkane metathesis, 6,8,9,20,[24][25][26] alkyl group metathesis, 27 dehydroaromatization, 19,28,29 alkanealkene coupling reactions, [30][31][32] borylation of alkanes 23 and the dehydrogenation of several non-alkane substrates.…”

Recent Advances on the Chemistry of POCOP–Nickel Pincer Compounds

“…This structural diversity is only matched by the numerous applications that these complexes have found so far, particularly in the case of homogeneous catalysis [30][31][32][33][34][35][36][37][38][39][40][41][42][43].…”