Bifunctional Organometallic Catalysts Involving Proton Transfer or Hydrogen Bonding

Abstract

Inspired by the cooperativity displayed by metalloenzymes, bifunctional organometallic complexes featuring pendant basic functional groups are designed and evaluated as catalysts in reactions for which enzymes are not suited. Anti-Markovnikov hydration of terminal alkynes is the focus, as are hydrogen bonding and proton transfer facilitated by the pendant groups.

Structures, Mechanisms, and Results in Bifunctional Catalysis and Related Species Involving Proton Transfer

“…We have provided evidence for the profound effects of a substituent next to heterocyclic nitrogen on both chelate stability and catalytic ability [3,8,33,34,[39][40][41][42][43][44][45][46]. Ruthenium complexes 7a and 7b (Fig.…”

“…2) show dramatically different reactivity: 7a is static on the NMR time scale, showing sharp peaks in 1 H and 31 P NMR spectra even at 80°C, whereas its tert-butylated analog exhibits broad NMR resonances even near 0°C. Moreover, 7a is ineffective as an alkyne hydration catalyst whereas 7b (which becomes 4b during hydration reactions) shows excellent activity [8,33,38]. Our success in creating efficient and highly active catalysts for alkyne hydration and alkene isomerization ( Fig.…”

“…For alkene isomerization, an imidazolyl substituent in 6 offers rate accelerations of more than 10,000. Aspects of this work have already been published [33][34][35][36][37][38] and reviewed [8,39].…”

“…For about 10 years [2,3] our group has studied combining the ability of a transition metal to move electrons with ligands capable of proton transfer, examples in the wider field of bifunctional catalysis. For reviews of bifunctional catalysts, see [4][5][6][7][8][9][10][11][12]. Here we describe some fundamental studies of bifunctional catalysts and related complexes, with a focus on phosphines bearing an imidazolyl or pyridyl group and the roles the basic nitrogen substituent can play.…”

Bioinspired Catalyst Design and Artificial Metalloenzymes

“…In addition to the potential of the chirality of these natural building blocks in asymmetric reactions, [11c, 12] the potential for second-sphere ligand-substrate interactions may lead to the induction of enzyme-like regio-, chemo-, enantio-and substrate selectivities. [13] An additional advantage of this approach is the role separation between the metal centre, which typically dominates the chemical activity, and the biomolecular environment, which is used to induce selectivity in the reaction (Figure 1). This division of functionalities greatly simplifies the application of modular combinatorial synthesis approaches.…”