Synthesis and properties of Tp(Me2)IrH(4) and Tp(Me2)IrH(3)(SiEt3): Ir(V) polyhydride species with C-3V geometry

The hydrogenation of Tp(Me2)Ir(C2H4)(2) under forcing conditions (C6H12, 90 degrees C, 2 atm, 3 days) affords the tetrahydride TpM(e2)IrH(4) (1*) in v ery high yield. TpM(e2)Ir(R)(R')(L) complexes (R = R' = H, alkyl, aryl; L = labile ligand) can also be used for the synthesis of 1*, but their hydroge nation is not as clean as that of the bis(ethylene) complex. TpIrH(4) (1) h as also been obtained from TpIr(C2H4)(2) by a similar procedure but only in less than or equal to 10% yield. Tp(Me2)IrH(4) is a very stable molecule, and both its chemical behavior and T-1 relaxation studies are in accord wit h a classical. highly fluxional, tetrahydride structure. H-1 and H-2 NMR sp ectroscopic studies carried out with mixtures of Tp(Me2)IrHr(4-n)D(n) (n = 0-4) species reveal the existence of a very unusual isotopic perturbation o f resonance (IPR) effect that is best reconciled with 1* land, by extension , with 1), possessing in solution a ground-state C(3 nu)structure in which a hydride ligand caps the face of the remaining hydrides in an otherwise di storted octahedral structure. Due to the existence of two kinds of Ir-H bon ds, a nonstatistical fractionation of D in the two types of hydride sites a vailable is observed upon deuteration, and this constitutes a very rare exa mple 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 easil y its hydrides with deuteriums not only in deuterated protolytic solvents b ut also in C6D6 and other substrates albeit under somewhat more forcing con dition. This behavior has been exploited in a somewhat limited catalytic de uteration of THF by D2O. The very stable compound Tp(Me2)IrH(3)(SiEt3) (2*) can be easily obtained from (TPIrH2)-Ir-Me2(C2H4) or Tp(Me2)Ir(C2H4)(2) an d neat HSiEt3 at 80 degrees C. Spectroscopic studies, including those of th e deuterated species Tp(Me2)IrH(3-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 nu geometry in which the SiEt3 group acts as the capping ligand. This assumpt ion is supported by a single-crystal X-ray study.