Synthesis and reactivity of iridium complexes with pyridine and piperidine ligands: models for hydrodenitrogenation

Abstract

The complexes [Ir(H)₂(η¹-N-L)₂(PPh₃)₂]PF₆, L = py (1), iQ (2) and pip (3) (py = pyridine, iQ = isoquinoline, pip = piperidine) have been synthesized in high yields by hydrogenation of [Ir(cod)(PPh₃)₂]PF₆ in the presence of the appropriate nitrogen compound. When hydrogen is bubbled through 1,2-dichloroethane solutions of 1 or 2, two new species were formed in each case by C–Cl bond activation of the solvent, Ir(H)₂Cl(η¹-N-L)(PPh₃)₂ (L = py, 4; iQ, 5) and IrH(Cl)₂(η¹-N-L)(PPh₃)₂ (L = py, 6; iQ, 7). Reaction of 3 with py or iQ yielded complexes 1 and 2, respectively, while under a slow stream of carbon monoxide the complex [Ir(H)₂(η¹-N-pip)(CO)(PPh₃)₂]PF₆ (8) was produced. Complex 3 also reacts with halide and 4-bromothiophenolate anions leading to the corresponding neutral species Ir(H)₂(X)(η¹-N-pip)(PPh₃)₂, X = Cl (9), I (10) and 4-BrC₆H₄S (11), or with [MoS₄]²⁻ to yield the hetero-bimetallic complex [Ir(H)(PPh₃)₂(μ-S)₂MoS₂]⁻ (13). All the new complexes were characterized by analytical and spectroscopic methods. The X-ray structures of 1, 2 and 8 consist of distorted octahedra with a mutually cis disposition of the two hydrides and mutually trans phosphines. Complexes 1, 2 and 3 and their derivatives are of interest as models for the chemisorption step in hydrodenitrogenation reactions on solid catalysts.