Synthesis and Properties of Tp^Me2IrH₄and Tp^Me2IrH₃(SiEt₃):  Ir(V) Polyhydride Species withC_3vGeometry

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 T 1 relaxation studies are in accord with a classical, highly fluxional, tetrahydride structure. 1H and 2H NMR spectroscopic studies carried out with mixtures of TpMe2IrH4 - n D n (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 C 3 v 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 J HD 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 - n D n (SiEt3) (n = 1−3) (which show no IPR effect), are in accord with 2* being an Ir(V) species with a similar C 3 v geometry in which the SiEt3 group acts as the capping ligand. This assumption is supported by a single-crystal X-ray study.

Synthetic, Mechanistic, and Theoretical Studies on the Generation of Iridium Hydride Alkylidene and Iridium Hydride Alkene Isomers

“…Accordingly, observation of the rearrangement of the 2,6‐dimethyl‐substituted anisoles shown in Scheme prompted us to convert the chelating aryloxide alkene ligands of 4 o and 5 o into the corresponding 2‐ethyl‐6‐methylphenols ( 9 a and 9 b in Scheme ). This has been achieved by the two‐step synthesis shown in Scheme , which implies hydrogenation of 4 o and 5 o in the presence of HSiEt 3 , to give the known Ir V complex [(Tp Me2 )Ir(H) 3 (SiEt 3 )]22 plus the silyl ethers 8 a and 8 b , which are then readily hydrolyzed to the desired phenols.…”

Monoanionic NSiN-type ligands in transition metal coordination chemistry and catalysis

“…The catalytic dehydrogenative silylation of unactivated C−H bonds is a target of great importance due to the application of silyl arenes and vinyl silanes as reagents for organic synthesis and materials science [36]. The iridium complex containing isoelectronic ligands such as ƞ 5 -cyclopentadienyl [37] or κ 3trispyrazolylborate ligands [38] are known.…”

Structural and bonding characteristics in transition metal–silane complexes

“…A recently reported Tp Me2 Ir-(SiEt 3 )H 3 (Tp Me2 = HB(3,5-Me 2 -pz) 3 ) complex adopts a capped octahedron in which the silyl group caps the triangle face formed by the three hydride ligands (see 14). 33 However, the analogous Tp Me2 IrH 4 is believed to have an edge-bridged octahedral structure because of the absence of silyl-hydrido interactions. 34 To understand these types of silyl-hydrido interactions, one starts with a classical picture and then considers the additional interligand interactions between hydride and silyl ligands.…”