TitleReactions of (PCP)Ir complexes with small molecules
NameKundu, Sabuj Kumar (author), Goldman, Alan (chair), Krogh- Jespersen, Karsten (co-chair), Warmuth, Ralf (co-chair), Glasser, Benjamin (outside member), Rutgers University, Graduate School - New Brunswick,
DescriptionIridium pincer complexes (R4PCP)IrHn (PCP=[k3-2,6-C6H3(CH2PR2)]) are effective catalysts for the dehydrogenation of alkanes. We wished to design pincer ligands in which the set of phosphinoalkyl groups would offer (a) maximal steric "protection" against cluster-formation (b) minimal hindrance to C-H addition, and (c) resistance to decomposition and self-dehydrogenation (unlike iPr groups). Thus, we have synthesized iridium complexes of ligands tBu3MePCP ([C6H3(CH2PtBuMe)(CH2PtBu2]). (tBu3MePCP)IrH4 (1) shows more efficiency in dehydrogenation of alkanes than either
(tBu4PCP)IrHn or (iPr4MePCP)IrHn. (tBu3MePCP)IrH4 was also found to be a very effective catalyst in alkane metathesis.
Although isocyanides are important building blocks in organic synthesis, their commercial availability is limited compared to other chemicals. (PCP)Ir complexes react with different secondary methyl amines and at ambient temperature to form
corresponding iridium isocyanide complexes (PCP)Ir(H)(H)(CNR), 3-1 (a-e) which react with CO forming (PCP)Ir(CO) to liberate the corresponding isocyanide.
The addition of PhCCH to highly stable complexes, (PCP)IrL (L = CO, CNR), is challenging. (PCP)IrL (L = CO, CNR) complexes react with PhCCH in presence of acid to form complex (PCP)Ir(CO)(H)(CCPh) (5-3) and (PCP)Ir(CNBz)(H)(CCPh) (5-1), respectively, in which hydride and acetylide group are trans to each other. The reaction proceeds via the cationic intermediate [(PCP)Ir(CO)(H)]+. Solid-supported catalysts have significant advantages over homogeneous systems, particularly with respect to product-catalyst separation. We have investigated several routes to the development of supported pincer-ligated iridium catalysts. The p-dimethylamino- substituted PCP complex is found to bind strongly to alumina while maintaining the same high activity (or even slightly greater) for alkane-dehydrogenation as found in the solution phase.
A broad range of (PCP)Ir complexes with widely varying steric and electronic effects have been synthesized and studied including (PCP)IrL, (PCP)Ir(H)(H)L and PCP)Ir(H)(Cl)L, (L = various P- and N-donors, N2, various olefins). The relative thermodynamics of these adducts have been detected by equilibrium measurements and calculated using DFT. Precursors of "(PCP)Ir" cleaves sp3 C--O bonds of various esters (RCO2R1, R1= alkyl) to give (PCP)Ir(R1)(O2CR) or, in cases where R1 has a b-hydrogen, (PCP)Ir(H)(O2CR) plus the corresponding alkene derived from R1.
NoteIncludes bibliographical references
Noteby Sabuj Kumar Kundu
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
RightsThe author owns the copyright to this work.