Kirkina Vladislava A, Silantyev Gleb A, De-Botton Sophie, Filippov Oleg A, Titova Ekaterina M, Pavlov Alexander A, Belkova Natalia V, Epstein Lina M, Gelman Dmitri, Shubina Elena S
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov Street 28, 119991 Moscow, Russia.
Institute of Chemistry, The Hebrew University, Edmond Safra Campus, Givat Ram, 91904 Jerusalem, Israel.
Inorg Chem. 2020 Sep 8;59(17):11962-11975. doi: 10.1021/acs.inorgchem.0c00797. Epub 2020 Aug 7.
Two stereoisomers of pentacoordinate iridium(III) hydridochloride with triptycene-based PC(sp)P pincer ligand (1,8-bis(diisopropylphosphino)triptycene), and , differ by the orientation of hydride ligand relative to the bridgehead ring of triptycene. According to DFT/B3PW91/def2-TZVP calculations performed, an equatorial Cl ligand can relatively easily change its position in , whereas that is not the case in . Both complexes and readily bind the sixth ligand to protect the empty coordination site. Variable temperature spectroscopic (NMR, IR, and UV-visible) studies show the existence of two isomers of hexacoordinate complexes ·MeCN, ·MeCN, and ·Py with acetonitrile or pyridine coordinated trans to hydride or trans to metalated C(sp), whereas only the equatorial isomer is found for ·Py. These complexes are stabilized by various intramolecular noncovalent C-H···Cl interactions that are affected by the rotation of isopropyls or pyridine. The substitution of MeCN by pyridine is slow yielding axial Py complexes as kinetic products and the equatorial Py complexes as thermodynamic products with faster reactions of ·L. Ultimately, that explains the higher activity of in the catalytic alkenes' isomerization observed for allylbenzene, 1-octene, and pent-4-enenitrile, which proceeds as an insertion/elimination sequence rather than through the allylic mechanism.
