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

Abstract

The complexes [Ir(H)2(eta1-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(eta1-N-L)(PPh3)2 (L = py, 4; iQ, 5) and IrH(Cl)2(eta1-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(eta1-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)(eta1-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(mu-S)2MoS2]- (13). All the new complexes were characterized by analytical and spectroscopic methods. The X-ray structures of , 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.

Para-Hydrogen Induced Polarization without Incorporation ofPara-Hydrogen into the Analyte

“…The crystal structure of 2a with a BF 4 − counterion is illustrated in Figure . Previously Rosales et al reported the same structure with the PF 6 − counterion . We note that with BF 4 − the P−Ir−P bond angle is 163.44(7)° but with PF 6 − it is 161.00(4)°.…”

“…When H 2 was bubbled through a solution of [Ir(COD)(PPh 3 ) 2 ]BF 4 (1a) in dichloromethane, in the presence of a 2-fold excess pyridine, complex [Ir(PPh 3 ) 2 (py) 2 (H) 2 ] + (2a) was generated. Complex 2a was isolated, and appropriate NMR based spectroscopic data obtained to confirm its identity on the basis of agreement with previously described data of Rosales et al 29 The NMR parameters for 2a can be found in Table 1.…”

“…Tri(phenyl)phosphine (Aldrich), tri( p -tolyl)phosphine (Strem), tri(anisolyl)phosphine (Strem), pyridine (Aldrich), and 15 N-pyridine (Cambridge Isotopes) were used as supplied and stored under N 2 . [Ir(COD)(PPh 3 ) 2 ]BF 4 ( 1a ) and [Ir(COD)(NCMe) 2 ]BF 4 were prepared by literature methods. ,,, …”

Detection of Picomole Amounts of Biological Substrates by para-Hydrogen-Enhanced NMR Methods in Conjunction with a Suitable Receptor Complex

“…This complex has been partially characterized previously. 9 To learn about the methods sensitivity to detecting pyridine appropriate samples were prepared. After 32 scans at 325 K and 400 MHz (∼1 min of acquisition), a signal-to-noise ratio of 11 was obtained for the hydride resonances of 1 when the pyridine concentration was 0.1 µM, diagnostic of 50 pmol of substrate.…”

“…Key NMR data for 1 can be found in the Supporting Information. This complex has been partially characterized previously 1 Formation of IrCl(H) 2 (PPh 3 ) 2 (pyridine) 1 …”