1255934-46-3Relevant academic research and scientific papers
Ligand survey results in identification of PNP pincer complexes of iridium as long-lived and chemoselective catalysts for dehydrogenative borylation of terminal alkynes
Lee, Chun-I,Demott, Jessica C.,Pell, Christopher J.,Christopher, Alyson,Zhou, Jia,Bhuvanesh, Nattamai,Ozerov, Oleg V.
, p. 6572 - 6582 (2015)
Following the report on the successful use of SiNN pincer complexes of iridium as catalysts for dehydrogenative borylation of terminal alkynes (DHBTA) to alkynylboronates, this work examined a wide variety of related pincer ligands in the supporting role in DHBTA. The ligand selection included both new and previously reported ligands and was developed to explore systematic changes to the SiNN framework (the 8-(2-diisopropylsilylphenyl)aminoquinoline). Surprisingly, only the diarylamido/bis(phosphine) PNP system showed any DHBTA reactivity. The specific PNP ligand (bearing two diisopropylphosphino side donors) used in the screen showed DHBTA activity inferior to SiNN. However, taking advantage of the ligand optimization opportunities presented by the PNP system via the changes in the substitution at phosphorus led to the discovery of a catalyst whose activity, longevity, and scope far exceeded that of the original SiNN archetype. Several Ir complexes were prepared in a model PNP system and evaluated as potential intermediates in the catalytic cycle. Among them, the (PNP)Ir diboryl complex and the borylvinylidene complex were shown to be less competent in catalysis and thus likely not part of the catalytic cycle.
Synthesis and reactivity of rhodium and iridium alkene, alkyl and silyl complexes supported by a phenyl-substituted PNP pincer ligand
Calimano, Elisa,Tilley, T. Don
, p. 9250 - 9263 (2011/01/06)
New rhodium and iridium complexes supported by the phenyl-substituted PNP pincer ligand PNPPhH (HN(2-PPh2-4-Me-C6H 3)2) (1) were synthesized. The reaction of 2 equiv. of 1 with [(COD)IrCl]2 afforded the coordination complex [(PNP PhH)Ir(COD)]Cl (2) featuring hydrogen bonding between the N-H group and the chloride anion, as characterized by NMR spectroscopy and X-ray crystallography. Reaction of 1 with [(COE)2IrCl]2 or [(COE)2RhCl]2 in benzene provided a mixture of complexes including (PNPPhH)MHCl2 (M = Ir (4), M = Rh (7)) and (PNP)M(COE) (M = Ir (5), M = Rh (8)). Alkene complexes of the type (PNP Ph)M(L) (M = Ir, L = COD (3) and COE (5); M = Rh, L = COE (8) and L = ethylene (9)) were synthesized by reaction of (PNPPh)Li with the appropriate alkene chloride complexes. Reactions of silanes with 5, 8 or 9 produced silyl hydride complexes (PNPPh)MH(SiR3) (M = Ir, R = Ph (16) and R = Et (17); M = Rh, R = Ph (18), Et (19) and Ph2Cl (20)) via Si-H oxidative addition. The JSiH coupling constants for rhodium complexes 18, 19 and 20 were determined to be ca. 35 Hz, while iridium complexes 16 and 17 exhibited coupling constants less than 10 Hz. X-Ray crystal structures of 16 and 18 reveal isostructural complexes featuring a trigonal bipyramidal geometry about iridium with a mer binding of the PNPPh ligand. A hydride ligand, located from the Fourier map for 18, has a short contact of 1.83(3) A with the silicon atom. Oxidative addition of iodomethane to 5 and 8 afforded (PNPPh)M(Me)(I)(THF) (M = Rh (14), M = Ir (12)), respectively. Arene C-H activation upon thermolysis of 12 in benzene produced (PNPPh)M(Ph)(I)(THF). Iridium silyl iodide complexes (PNPPh)IrI(SiR3) (SiR3 = SiPh3 (21), SiH2Mes (22) and SiH2Xyl (23)) resulted from addition of organosilanes to 12, via elimination of CH4. The Royal Society of Chemistry.
