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Research interests of the Frost Group lie in the area of mechanistic organometallic chemistry and catalysis. The current focus of the group is centered on the design and synthesis of new water-soluble phosphines, kinetic and mechanistic studies of catalytic processes, small molecule activation (H₂, CO₂, etc), and organometallic chemistry in alternative solvents (water in particular). Our research program ties together aspects of inorganic, organic, organometallic, and green chemistry.

Novel water-soluble phosphine derivatives:

Our group has focused on the air-stable and water-soluble phosphine 1,3,5-triaza-7-phosphaadamantane (PTA). We have been active in developing methods to tune PTA's properties to generate a range of water-soluble phosphines with the goal of designing new monodentate and bidentate water-soluble phosphines based on the PTA framework. In particular we have been interested in exploring the possibility of selectively modifying either the upper or lower rim of the PTA ligand.

We reported the first modification of the "upper rim" of PTA through lithiation of an alpha phosphorus methylene followed by reaction with ClPPh₂. (Inorg. Chem. 2006, 45, 6748-6755). To see the article click here. Of interest is that modifications of this type lead to chiral phosphines with the chiral center in close proximity to the phosphorus and; therefore, any coordinated metal center. We are currently working on methodologies to generate optically active versions of these PTA derivatives. One method for the straightforward generation of a library of chiral phosphine ligands is through the insertion of CO₂, aldehydes, or ketones into the C-Li bond of PTA-Li (Inorg. Chem. 2008, 47, 612 - 620). To see our article on this chemistry click here.

We have also described the development of a series of "lower rim" PTA derivatives through reaction of P(CH₂NH₂)₃ with various aldehydes (Inorg. Chem. 2007, 46, 10962-10964). To see the communication click here.

Ruthenium Half-Sandwich Chemistry:

Ruthenium half-sandwich complexes have been utilized in a variety of reactions. Our group has been interested in the synthesis and reactivity of a series of water-soluble complexes of the type Cp'Ru(PTA)₂X and the related mixed phosphine derivatives Cp'Ru(PTA)(PPh₃)X, where Cp' = Cp, Ind, Tp, Dp; and X = Cl or H. The Cp'Ru(PTA)(PR₃)H complexes undergo an interesting H/D exchange reaction with D₂O (and CD₃OD depending on the complex) (Organometallics, 2004, 23, 5317-5323). To see the article click here.

 

Selective hydrogenation using the Cp'Ru(PTA)(PR₃)X complexes has been explored in our group. The Ru-H complexes in particular have been most interesting as they are active catalysts in the biphasic hydrogenation of alpha,beta-unsaturated ketones. Spectroscopic studies of the nature of CpRu(PTA)2H under the reaction conditions enabled the identification of mono- and dihydride intermediates; [CpRu(PTA)(PTAH)H]⁺ and [CpRu(PTA)₂(H)₂]⁺ respectively. The distribution of these intermediates as a function of pH has been determined and related to the rate of catalysis; TOF increases with an increase in the concentration of [CpRu(PTA)(PTAH)H]⁺ the presumed active catalytic species. The catalytic activity under various conditions, such as pH, salt, and hydrogen pressure, has been explored (Organometallics, 2005, 24, 2339-2346). To see the article click here.

Coordination Chemistry of PTA:

Coordination chemistry of PTA has interesting potential, with both phosphorus and nitrogen coordination possible. PTA preferentially coordinates to metals through phosphorus; prior to late 2005, no examples of a nitrogen bound PTA complex had been reported. Amine functionalities of PTA, however, are the preferred sites of alkylation; protonation; and, as we have shown, borane addition (Eur. J. Inorg. Chem. 2006, 1182-1189, article). In an ongoing project carried out largely by undergraduates the general coordination chemistry of PTA is undergoing investigation, specifically the requirement for N versus P coordination. Recently we reported the first transition metal complex of PTA in which only the N of PTA is coordinated to the metal center: Mn(OH₂)₂PTA₂Cl₂ (Inorg. Chem. 2006, 45, 3481-3483). To see the article click here.