Effect of Ligands on the Lewis Acidity of the Metal and the Binding of N‐Bases to Iridium Pincer Complexes

Abstract

The coordination of pyridine (Py) and benzonitrile (PhCN) to benzene based pincer hydridochlorides [(PCP)IrH(Cl)] (1), [(POCOP)IrH(Cl)] (2), [{EtO(O)C‐POCOP}IrH(Cl)] (3), and [(PCN)IrH(Cl)] (4) was studied spectroscopically and computationally to deduce the ligand influence. The variable temperature NMR (1H, 31P, 15N) and UV/Visible spectroscopic measurements revealed preferential coordination of these N‐donor ligands in the apical position of 1–4 and gave the formation enthalpies for the hexacoordinate complexes, which follow the order: 1 ≈ 4 > 3 > 2. This order nicely agrees with the order of Lewis acidity obtained for these complexes in DFT calculations. The orbital and electron density distribution analysis were performed at the DFT/M06 theory level for 1–4 and a series of p‐substituted PCP‐based hydridochlorides. The increasing Lewis acidity of iridium [as a maximum energy, VS,max, of molecular electrostatic potential (MEP)] correlates with decreasing basicity of Cl‐ligand (as MEP minimum, VS,min) as well as with Hammett σp parameters of p‐substituents. Importantly, these properties are conserved upon conversion into the corresponding dihydrides, as shown on the example of 1 and 4.

Stereoisomerism as an Origin of Different Reactivities of Ir(III) PC(sp3)P Pincer Catalysts

“…However, it gives colorless hexacoordinate species upon cooling in dichloromethane or upon addition of MeCN, which has much higher basicity − and stronger coordinating ability than dichloromethane. As was demonstrated for other iridium­(III) hydridochloride complexes, ,− there are two possibilities for a Lewis base binding to 1 an axial position trans to the hydride ligand and an equatorial position trans to the metalated carbon (Scheme ). The evidence of their formation can be found in variable temperature IR and NMR spectra.…”

Unravelling strong temperature-dependence of JHD in transition metal hydrides: solvation and non-covalent interactions versus temperature-elastic H–H bonds

“…3). 23 However, such a proposal suffers from multiple discrepancies (for example, it contradicts the data on the chemical shis of type V structures [30][31][32] ) and illustrates that without understanding the crucial role of solvation and non-covalent interactions, temperature-dependent J HD in transition metal hydrides cannot be properly addressed. The present comprehensive NMR data set (Table S4 †) for (X-POCOP)IrH 2 and the related complex (PCP) IrH 2 (PCP = 2,6-( t Bu 2 PCH 2 ) 2 C 6 H 3 ), together with crystallographic and computational data, allowed coming up with a quantitative model based on the discrete isomers with different r(H-H).…”