Metal—ligand bonds hydrogen

In an effort to apply the cooperative principles of metalloenzyme reactivity, involving a combination of metal-ligand and hydrogen bonding, we have reported a ruthenium catalyst incorporating imidazolyl phosphine ligands that efficiently and selectively hydrates terminal alkynes (5). We subsequently found that application of pyridyl phosphines to the reaction resulted in a >10-fold rate enhancement and complete anti-Markovnikov selectivity, even in the... 

Today, iridium compounds find so many varied applications in contemporary homogeneous catalysis it is difficult to recall that, until the late 1970s, rhodium was one of only two metals considered likely to serve as useful catalysts, at that time typically for hydrogenation or hydroformylation. Indeed, catalyst/solvent combinations such as [IrCl(PPh3)3]/MeOH, which were modeled directly on what was previously successful for rhodium, failed for iridium. Although iridium was still considered potentially to be useful, this was only for the demonstration of stoichiometric reactions related to proposed catalytic cycles. Iridium tends to form stronger metal-ligand bonds (e.g., Cp(CO)Rh-CO, 46 kcal mol-1 Cp(CO)Ir-CO, 57 kcal mol ), and consequently compounds which act as reactive intermediates for rhodium can sometimes be isolated in the case of iridium. 

In this chapter, for space reasons, only a few paradigmatic examples of rotaxanes and catenanes based on donor-acceptor (charge transfer (CT)) and/or hydrogen bonding interactions (systems based on metal-ligand bonding are reviewed in another... 

Protonation. Electrophilic attack of a proton on a metal-ligand bond is another terminating step in catalytic cycles (equation 8). This is typical of ruthenium-catalyzed hydrogenation. 

Discrete supramolecular Pc-porphyrin-Pc assemblies have also been prepared using saddle distorted components, namely a protonated dodecaphenylporphyrin and octaphenyl Zn(II) phthalocyaninate complex, using 4-pyridinecarboxylate as a supramolecular linking unit. Both metal-ligand and hydrogen bonding interactions allow the assembly of the components [27],... 

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