The major research activities derived from this grant have focused on reactivity of metal complexes of the water-soluble and air-stable 1, 3, 5-triaza-7-phosphadamantane (PTA). Related to this have been efforts in our laboratories aimed at the design and synthesis of novel phosphine ligands based on the PTA framework. This report covers the work of one undergraduate and two graduate students working on two separate but related projects at the University of Nevada. Students working on these projects have been trained in synthetic inorganic and organometallic chemistry and catalysis. As part of their training student have been directly involved with presenting their work at group meetings and conferences as well as writing manuscripts for publication. Research results have been published in a number of peer reviewed journals and presented at conferences and seminars around the country.

The earliest reports on the synthesis and catalytic activity of PTA complexes involved the ruthenium compound, cis-[Ru(PTA)₄Cl₂] (cis-1), synthesized in essentially quantitative yield by reaction of PTA with RuCl₃¥3H₂O in ethanol. During a reinvestigation of some of the chemistry of 1 we isolated orange crystals of trans-1 from a dichloromethane solution. In organic solvents trans-1 undergoes a relatively clean isomerization to cis-1. In aqueous environments trans-1 undergoes a more complicated transformation involving isomerization, protonation, and ligand substitution affording cis-1 and a series of structurally related molecules. From these results we conclude that the synthesis of [Ru(PTA)₄Cl₂] (1), affords trans-1 not cis-1. This study and others show that the ligand exchange chemistry of 1 and related compounds in water is complicated and affords a wide variety of species. These results have helped lead us to more robust complexes such as CpRu(PR₃)₂X, discussed below.

We have synthesized and characterized a series of Cp'Ru(PTA)(PPh₃)X complexes bearing cyclopentadienyl (C₅H₅^-, Cp), 1,2-dihydropentalenyl (η⁵-C₈H₉^-, Dp), or indenyl (η⁵-C₉H₇^-, = Ind) ancillary ligands; X = Cl or H. The air stable Cp'Ru(PTA)(PPh₃)Cl complexes (Cp' = Cp, Dp, Ind) exhibit activity in the regioselective transfer hydrogenation of a,b unsaturated carbonyls in aqueous media employing HCO₂H, HCO₂Na, or H₂ as the reducing agent. Most recently we have developed the use of these Cp'Ru(PTA)PPh₃)Cl complexes as air stable and highly reactive catalyst precursors for the atom transfer radical addition (ATRA) of carbon tetrachloride, p-Toluenesulfonyl chloride, or chloroform to styrene. The catalyst performance depends upon the electron richness at the ruthenium center and the facile dissociation of one phosphine ligand. The pronounced electron donating ability of Cp* ligand renders Cp*Ru(PTA)(PPh₃)Cl the most efficient  catalyst among those investigated. We are currently developing more advanced systems for this reaction.

Most recently an undergraduate in my laboratory has worked on the synthesis of chiral derivatives of the PTA ligand. We have shown that PTA may be deprotonated by n-BuLi yielding PTA-Li. Carbon dioxide, ketones, and aldehydes may be inserted into the C-Li bond of PTA-Li resulting in a library of chiral water-soluble phosphine ligands. Efforts are currently underway to utilize these new ligands in catalysis.