Iridium dibromide complexes of the phenyldiimine ligand 2,6-bis(1-((2,6-dimethylphenyl)imino)ethyl)phenyl, trans-(XyPhDI)IrBr2L, have been synthesized, and relative Ir-L BDFEs have been experimentally determined for a wide range of corresponding adducts of ligands L. An estimate of the absolute enthalpy of Ir-L binding has been obtained from dynamic NMR measurements. The results of DFT calculations are in very good agreement with the relative and absolute experimental values. Computational studies were extended to the formation of adducts of (XyPhDI)IrH2 and (XyPhDI)Ir(I), as well as other (pincer)Ir(I) fragments, (Phebox)Ir(I) and (PCP)Ir(I), to enable a comparison of electronic and steric effects with these archetypal pincer ligands. Attempts to reduce (XyPhDI)IrBr2(MeCN) to a hydride or an Ir(I) complex yielded a dinuclear CN-bridged complex with a methyl ligand on the cyanide-C-bound Ir center (characterized by scXRD), indicating that C-CN bond cleavage took place at that Ir center. DFT calculations indicate that the C-CN bond cleavage occurs at one Ir center with strong assistance by coordination of the CN nitrogen to the other Ir center.
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Pincer-ligated iridium complexes have been widely developed, and (pincer)Ir(III) complexes, particularly five-coordinate, are central to their chemistry. Such complexes typically bear two formally anionic ligands in addition to the pincer ligand itself. Yet despite the prevalence of halides as anionic ligands in transition metal chemistry there are relatively few examples in which both of these ancillary anionic ligands are halides or even other monodentate low-field anions. We report a study of the fragment (iPrPCP)IrCl2 (iPrPCP = 3-2,6-C6H3(CH2PiPr2)), and adducts thereof. These species are found to be thermodynamically disfavored relative to the corresponding hydridohalides. For example, DFT calculations and experiment indicate that one Ir-Cl bond of (iPrPCP)IrCl2 complexes will undergo reaction with H2 to give the (iPrPCP)IrHCl or an adduct thereof. In the presence of aqueous HCl, (iPrPCP)IrCl2 adds a chloride ion to give an unusual example of an anionic transition metal complex ((iPrPCP)IrCl3–) with a Zundel cation (H5O2+). (iPrPCP)IrCl2 is not stable as a monomer at room temperature but exists in solution as a mixture of clusters which can add various small molecules. DFT calculations indicate that dimerization of (iPrPCP)IrCl2 is more favorable than dimerization of (iPrPCP)IrHCl, in accord with its observed tendency to form clusters.
more » « less- Award ID(s):
- 2117792
- PAR ID:
- 10529779
- Publisher / Repository:
- ChemRxiv
- Date Published:
- Format(s):
- Medium: X
- Institution:
- Rutgers University
- Sponsoring Org:
- National Science Foundation
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