Premium
Rationalizing and Disrupting Fluxional Processes in Agostically Stabilized 14‐Electron Alkyliridium Hydride Complexes
Author(s) -
Phillips Nicholas,
Treasure Lucinda,
Rees Nicholas H.,
Tirfoin Rémi,
McGrady John E.,
Aldridge Simon
Publication year - 2014
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201402516
Subject(s) - chemistry , agostic interaction , iridium , hydride , oxidative addition , reactivity (psychology) , carbene , cationic polymerization , medicinal chemistry , alkyl , reductive elimination , stereochemistry , pincer movement , proton nmr , photochemistry , crystallography , polymer chemistry , catalysis , hydrogen , organic chemistry , metal , medicine , alternative medicine , pathology
We have investigated the fundamental patterns of reactivity for the cationic Ir III complexes [(6‐Mes)(6‐Mes′)Ir(H)] + and [(7‐Mes)(7‐Mes′)Ir(H)] + [6‐Mes, 7‐Mes = ring‐expanded N‐heterocyclic carbene (NHC) ligands, ′ indicates that NHC is tethered through an iridium‐bound CH 2 group], each of which undergoes degenerate fluxional exchange between an iridium‐bound agostic C–H bond and the discrete alkyl/hydride ligands resulting from C–H activation. A comparison between the activation parameters Δ H ‡ and Δ S ‡ determined by variable‐temperature NMR (VT‐NMR) spectroscopy line‐shape analysis and those obtained from DFT calculations on model systems offers a basis to discriminate between different possible exchange mechanisms, and an oxidative addition pathway gives the lowest barrier and also the best agreement between experiment and theory. The addition of neutral Lewis base donors to [(6‐Mes)(6‐Mes′)Ir(H)] + resulted in the displacement of the weak agostic C–H ··· Ir interaction and the generation of static (alkyl)iridium(III) hydride complexes such as [(6‐Mes)(6‐Mes′)Ir(H)(CN t Bu) 2 ] + . The analogous carbonyl complex is more labile, with the enhanced π‐acceptor properties of the ancillary ligands leading to C–H reductive elimination and to the formation of the Ir I complex [(6‐Mes) 2 Ir(CO) 2 ] + , which incorporates unactivated NHC donors and has the ability to reversibly take up H 2 .