Synthesis and Properties of Tp^Me2IrH₄and Tp^Me2IrH₃(SiEt₃): Ir(V) Polyhydride Species with<i>C</i>₃<i>_v</i>Geometry

Abstract

The hydrogenation of TpMe2Ir(C2H4)2 under forcing conditions (C6H12, 90 °C, 2 atm, 3 days) affords the tetrahydride TpMe2IrH4 (1*) in very high yield. TpMe2Ir(R)(R‘)(L) complexes (R = R‘ = H, alkyl, aryl; L = labile ligand) can also be used for the synthesis of 1*, but their hydrogenation is not as clean as that of the bis(ethylene) complex. TpIrH4 (1) has also been obtained from TpIr(C2H4)2 by a similar procedure but only in ≤10% yield. TpMe2IrH4 is a very stable molecule, and both its chemical behavior and T1 relaxation studies are in accord with a classical, highly fluxional, tetrahydride structure. 1H and 2H NMR spectroscopic studies carried out with mixtures of TpMe2IrH4-nDn (n = 0−4) species reveal the existence of a very unusual isotopic perturbation of resonance (IPR) effect that is best reconciled with 1* (and, by extension, with 1), possessing in solution a ground-state C3v structure in which a hydride ligand caps the face of the remaining hydrides in an otherwise distorted octahedral structure. Due to the existence of two kinds of Ir−H bonds, a nonstatistical fractionation of D in the two types of hydride sites available is observed upon deuteration, and this constitutes a very rare example of an IPR effect on a classical polyhydride. It is also the first one that shows in addition resolved JHD couplings. Complex 1* exchanges easily its hydrides with deuteriums not only in deuterated protolytic solvents but also in C6D6 and other substrates, albeit under somewhat more forcing condition. This behavior has been exploited in a somewhat limited catalytic deuteration of THF by D2O. The very stable compound TpMe2IrH3(SiEt3) (2*) can be easily obtained from TpMe2IrH2(C2H4) or TpMe2Ir(C2H4)2 and neat HSiEt3 at 80 °C. Spectroscopic studies, including those of the deuterated species TpMe2IrH3-nDn(SiEt3) (n = 1−3) (which show no IPR effect), are in accord with 2* being an Ir(V) species with a similar C3v geometry in which the SiEt3 group acts as the capping ligand. This assumption is supported by a single-crystal X-ray study.