Cationic, Neutral, and Anionic Hydrides of Iridium with PSiP Pincers

Abstract

This work describes synthetic routes from the known precursor [IrClH{κP,P,Si-Si(Me)(CH-2-PiPr)}] (1) to new hydride and polyhydride derivatives. Substituting the chloride ligand with triflate leads to the five-coordinate complex [IrH{κO-OS(CF)}{κP,P,Si-Si(Me)(CH-2-PiPr)}] (2), which can undergo reversible coordination of water (HO) or dihydrogen (H) to generate respectively the cationic derivative [IrH{κP,P,Si-Si(Me)(CH-2-PiPr)}(OH)](CFSO) (3) or the neutral trans-hydride-dihydrogen [IrH{κO-OS(CF)}{κP,P,Si-Si(Me)(CH-2-PiPr)}(η-H)] (6) in equilibrium. The use of acetonitrile or carbon monoxide (CO) excess instead of water produces stable analogues of 3 (complexes 4 or 5, respectively). The reaction between 1 and NaBH affords the tetrahydroborate derivative [IrH{κH-HBH}{κP,P,Si-Si(Me)(CH-2-PiPr)}] (7), which can be protonated with triflic acid to form 2 or with HBF to give the dinuclear cationic derivative [(μ:κH,κH-BH)[IrH{κP,P,Si-Si(Me)(CH-2-PiPr)}]](BF) (8). The reactions of 7 with alcohols afford either the dihydride-carbonyl [IrH{κP,P,Si-Si(Me)(CH-2-PiPr)}(CO)] (9) or the known tetrahydride [IrH{κP,P,Si-Si(Me)(CH-2-PiPr)}] (10), depending on the ease of alcohol decarbonylation. NMR observations and density functional theory calculations on the fluxional behavior of 10 indicate that the spatial contour of the mer PSiP framework conditions hydride-ligand exchanges. Complex 10 reacts with NaH in tetrahydrofuran to form the anionic trihydride [IrH{κP,P,Si-Si(Me)(CH-2-PiPr)}]Na (11), which exists as a mixture of fac and mer isomers in equilibrium.

Detection of an Iridium–Dihydrogen Complex: A Proposed Intermediate in Ionic Hydrogenation

“…Upon cooling the NMR probe to −80 °C, two new singlet resonances were observed in the 1 H NMR spectrum at −2.38 (ω 1/2 = 134 Hz) and −13.64 ppm (ω 1/2 = 51 Hz) in an approximate 1.3:1 ratio, respectively. The broad resonance at −2.38 ppm is consistent with iridium-bound dihydrogen , and the resonance at −13.64 ppm is assigned as the Ir–H in [ (NMe2H)(tBu)4 (POCOP)­Ir­(CO)­(H 2 )­(H)]­(OTf) 2 ( 8 , Figure ). By 31 P NMR spectroscopy at −80 °C, a new major product was observed as a singlet resonance at 183.0 ppm; the ratio of the new product to unreacted 4 was approximately 5:1.…”

Transfer hydrogenation of aldehydes catalyzed by silyl hydrido iron complexes bearing a [PSiP] pincer ligand

“…Phosphine-based [PSiP] pincer complexes of transition metals have been studied extensively in recent years. [1][2][3][4][5] In particular, they are involved as key intermediates in a variety of catalytic reactions of silicon compounds such as hydrosilylation, hydrocarboxylation of allenes and transfer hydrogenation. 6 Because silyl ligands have stronger s-donating characters and show a more potent trans-inuence than commonly-used ligands in transition metal chemistry, 7 the introduction of strong electron-donating and trans-labilizing silyl groups into tridentate ligand architectures may promote the formation of electron-rich and coordinatively-unsaturated complexes that exhibit novel reactivity with s-bonds.…”

Access to FeII Bis(σ‐B−H) Aminoborane Complexes through Protonation of a Borohydride Complex and Dehydrogenation of Amine‐Boranes

“…A broad singlet at 47.9 ppm is observed in the 11 B NMR spectrum. This value significantly differs from that of free [BH 4 ] − (ca −40 ppm) but appears to be quite common when compared to structurally related iron borohydride complexes . Moreover, in the 31 P{ 1 H} NMR spectrum 2 displays an AB system centered at 166.5 ppm indicating non‐equivalence of the phosphorous donors.…”