Overview of our work

Our research work addresses the following topics:

I. High valent transition metal complexes as catalysts for reduction reactions

Transition metal complexes with M=O bonds have found numerous applications in organic chemistry as catalysts for oxidation and oxygen transfer reactions. Aside from oxidation reactions, applications of oxo-metal complexes to other organic transformations are rare. Recently, an unconventional pathway for hydrosilylation of carbonyl groups with a high-valent rhenium oxide as catalyst has been disclosed. Our team has recently shown the excellent efficiency of MoO₂Cl₂ in the hydrosilylation of carbonyls by means of Si-H bond activation and has developed  this study to other dioxomolybdenum(VI) complexes. Now, we have extend the role of high-valent oxides as catalysts for reductive processes replacing silanes by a cheaper and more convenient reducing agent, H₂. Several Mo(VI) and Re(V) and (VII) oxo coumpounds catalyzed the selective hydrogenation of alkynes to alkenes and in the deoxygenation of of sulfoxides using hydrogen. The procedure replaces phosphines, expensive metals and environmentally hazardous reducing agents, which may have important advantages in terms of green chemistry.

 References: 

• Chemoselective hydrogenation of nitroarenes and deoxygenation of pyridine N-oxides with H2 catalyzed by MoO₂Cl₂, P. M. Reis, B. Royo, Tetrahedron Lett. 2009, 50, 949-952.
• Hydrogen activation by high-valent metal oxo-molybdenum(VI) and -rhenium(VII) and -(IV) compounds, P. M. Reis, P. J. Costa, C. C. Romão, J. A. Fernandes, M. J. Calhorda, B. Royo, Dalton Trans. 2008, 1727-1733. Inside Cover, Highlighted in Chemical Science, 2008, 5, issue 4.

• Perrhenic acid as catalyst for hydrosilylation of aldehydes and ketones and dehydrogenative silylation of alcohols, P. M. Reis, B. Royo, Catal. Commun. 2007, 8, 1057-1059.
• Catalyzing Aldehyde Hydrosilylation with a Molybdenum(VI) Complex: A density Functional Theory Study, P. J. Costa, C. C. Romão, A. C. Fernandes, B. Royo, P. M. Reis, M. J. Calhorda, Chem. Eur. J. 2007, 13, 3934-3941.

• Dioxomolybdenum(VI) complexes as catalysts for the hydrosilylation of aldehydes and ketones, P. M. Reis, C. C. Romão, B. Royo, Dalton Trans. 2006, 1842-1846.

• [MoO₂Cl₂] as catalyst for hydrosilylation of aldehydes and ketones, A. C. Fernandes, R. Fernandes, C. C. Romão, B. Royo, Chem. Commun. 2005, 213-214. "Hot paper" Highlighted in Chemical Science, 2005, 2, issue 2.
  
• Reduction of carbonyl groups by high-valent rhenium oxides, J. Mol. Catal. A: Chemical 2005, 236, 107.

II.  N-heterocyclic carbene complexes

The chemistry of N-heterocyclic carbene complexes (NHC) has developed rapidly since the first synthesis of an isolable carbene species of this type by Arduengo et al. in 1991. Advantages on the use of NHCs are that they provide improved catalysts and offer the possibilty of  topological  modifications. In our group we are exploring the use of NHCs as ligands for high-oxidation-state metal complexes and the functionalization of NHCs with cyclopentadienyl ligands. A novel cyclopentadienyl functionalized NHC has been recently prepared in our group and has been coordinated to different metal centers.

References:

• Easy preparation of Cp*-Functionalized N-Heterocyclic Carbenes and their Coordination to Rhodium and Iridium, A. Pontes da Costa, M. Sanaú, E. Peris, B. Royo, Dalton Trans. 2009, accepted.
• First Cp*-Functionalized N-Heterocyclic Carbene and Its Coordination to Iridium. Study of the Catalytic Properties, A. Pontes da Costa, M. Viciano, M. Sanaú, S. Merino, J. Tejeda, E. Peris, B. Royo, Organometallics, 2008, 27, 1305-1309.
• Dioxomolybdenum(VI) complexes containing N-heterocyclic carbenes, E. Mas-Marzá, P. M. Reis, E. Peris, B. Royo, J. Organomet. Chem. 2006, 691, 2708-2712.