Rh(III) Pyridinium Substituted Bipyridine Complexes as Catalysts for Arene H/D Exchange

Highlights of C (sp2)–H hydrogen isotope exchange reactions

“…In a second example, Sanford has reported on pyridinium‐substituted bipyridine complexes as catalysts for H–D exchange in arenes . One such catalyst was synthesized from RhCl 3 ·H 2 O and a dicationic bipyridine ligand (Figure 29).…”

Electrophilic RhI catalysts for arene H/D exchange in acidic media: Evidence for an electrophilic aromatic substitution mechanism

“…Developing reactivity with earlier transition metals (i.e., earlier than the Ni, Pd and Pt triad) could provide more tolerance of Lewis basic groups, but major challenges include avoiding oxidation of the metal to higher valent states that are incapable of C-H activation and developing complexes that possess electrophilic hydrocarbyl ligands (after C-H activation) [42][43][44][45][46][47][48][49][50][51][52][53]. Recently, a number of catalysts based on Ir and Rh have been shown to be active for benzene C−H activation [50][51][52][53][54][55][56][57][58][59][60][61]. Rhodium complexes are particularly attractive due to the possibility of C−H activation by Rh I [62] or Rh III [55].…”

Hydride‐Rhodium(III)‐N‐Heterocyclic Carbene Catalysts for Vinyl‐Selective H/D Exchange: A Structure–Activity Study

“…Since the pioneering works of Garnett4 and Shilov5 in the 1960s, a plethora of transition‐metal‐based homogeneous catalytic systems for H/D exchange have been developed, including those based on iridium,4c, 6 rhodium,4d, 6g,t, 7 palladium,7h, 8 platinum,4a,b, 5, 7h, 8a,c, 9 ruthenium,7i, 10 cobalt,11 and osmium 7i. 10h, 12 The versatility of these organometallic catalysts is shown by their ability to deuterate different CH groups of aliphatic,2b, 6k,m, 7b,f, 10b,e,i aromatic,2b, 4a, 6k,m,o,s–u, 7b,g,k, 9d, 10e,h,j, 12 and vinylic substrates 6a,n. 7a,d,e,i, 10g However, the control of regio‐ and stereoselectivity still remains an important challenge, especially for the deuteration of olefins in the presence of aromatic groups.…”

“…In this context, a key issue to take into account is that most transformations mediated by transition‐metal‐based catalytic systems proceed according to a CH activation mechanism (Scheme a) 6. 7f,g,k, 8b,c, 9d, 10a–f,h, 12, 13 The selectivity of the reaction depends on the activation energies of the relevant CH moieties, which are related to their dissociation energies. Thus, the observed reactivity order is generally: C sp H>C sp2 H>C sp3 H.…”