RESEARCH INTERESTS:

Much of my group´s research efforts revolves around the study of the transition-metal-mediated reactions of small, energy-rich molecules of fundamental significance in inorganic, bioinorganic, and organometallic chemistry. Specific projects include:

I. Preparation and Study of Metal Complexes of Nitroxyl (NH=O).
The nitrosonium cation (NO+), the nitroside anion (NO­), as well as the conjugate acid of NO­, nitroxyl (NH=O), are thought to be responsible for certain aspects of the rich biological chemistry of nitric oxide (NO). Moreover,NH=O is a common intermediate in Fe-catalyzed enzymaticprocess important in the nitrogen cycle, (i.e.,reduction of nitrite to ammonia and oxidation of ammoniaand hydroxylamine). In our studies of the coordinationchemistry of NH=O we have reported the preparationof a nitroxyl complex of Re by oxidation of ligatedhydroxylamine, and are now extending this chemistry toother NH₂OH systems.

Other studies concern mechanisticaspects of "protonation" reactions of NO ligandsthat give rise to stepwise reduction to NH=O and ultimatelyNH₂OH.

Our recent discovery that nitrosoniumtriflate can effect NO+ insertion into metal-hydride bondsprovides a general preparative route to M-NH=O complexes,a finding that should greatly facilitate our studiesof the reaction chemistry of NH=O.

II. Atom and Group-Transfer Reactions
Our group has a longstanding interest in reactions mediatedby transition metals in which an oxygen atom ornitrene (NR) fragment is transferred to an organic molecule.Our recent work in this area has centered on lateseriesmetals, particularly nickel. We have found that 3-coordinate Ni complexes containing Ni=L multiplebonds (L = CR₂, NR, PR) exhibit unique group-transferreactivity, for example to olefins, and will continue tofeature these and related reactions in our future researchefforts. Illustrated below is the conversion of a Ni(I)amide to a Ni(II)+ cation by oxidation; deprotonationyields the first imido complex of a d⁸ metal (structure isshown in the figure).

The nitrene fragment can subsequently be transferred tounsaturated substrates, as illustrated below in its reactionswith ethylene (to give an aziridine) and carbon monoxide(forming an isocyanate). Similar group-transfers areobserved for the related carbene and phosphinidenecomplexes (dtbpe)Ni=CPh₂ and (dtbpe)Ni=PR.

Selected References

Interactions of aziridines with nickel complexes: Oxidative-addition and reductive-elimination reactions that break and make C–N bonds. B. L. Lin, C. R. Clough, and G. L. Hillhouse, J. Am. Chem. Soc., 124, 2890 (2002).

Synthesis, structure, and reactions of a nitroxyl complex of iridium(III), cis,trans-IrHCl2(NH=O)(PPh3)2. R. Melenkivitz and G. L. Hillhouse, J. Chem. Soc., Chem. Commun., 660 (2002).

A new route to coordination complexes of nitroxyl (HN=O) via insertion reactions of nitrosonium triflate with transition-metal hydrides. R. Melenkivitz, J. S. Southern, G. L. Hillhouse, T. E. Concolino, L. M. Liable-Sands, and A. L. Rheingold, J. Am. Chem. Soc., 124, 12068 (2002).

Group transfer from nickel imido, phosphinidene, and carbene complexes to ethylene with formation of aziridine, phosphirane, and cyclopropane products. R. Waterman and G. L. Hillhouse, J. Am. Chem. Soc., 125, 13350 (2003).

Preparation of stable alkyl complexes of Ni(I) and their one-electron oxidation to nickel(II) complex cations. K. D. Kitiachvili, D. J. Mindiola, and G. L. Hillhouse, J. Am. Chem. Soc., 126, 10554 (2004).

Snapshots of the oxidative-addition process of silanes to nickel(0). V. M. Iluc and G. L. Hillhouse, Tetrahedron, 62, 7577 (2006).

η²-Organoazide complexes of nickel and their conversion to terminal imido complexes via dinitrogen extrusion. R. Waterman and G. L. Hillhouse, J. Am. Chem. Soc., 130, 12628 (2008).

Two-coordinate d9 complexes. Synthesis and oxidation of NHC nickel(I) amides. C. A. Laskowski and G. L. Hillhouse, J. Am. Chem. Soc., 130, 13846 (2008).