“…Theoretically, the IPR shifts can be to either higher or lower field with respect to the reference isotopomer, 34a,37c, and in transition metal agostic alkyls and related systems they can be as large as −1 ppm, 3c, particularly at low temperatures (IPR effects are normally very sensitive to temperature 37c ). In transition metals, polyhydrides' Δδ 1 is normally in the approximate range from 0 to −50 ppb, d,40,41 although some abnormal low-field shifts (Δδ 1 = 10−230 ppb) have been observed, 40c, the first example being apparently that reported by Harrod et al in 1979. , Some of them, particularly those of the [Tp‘IrH(H 2 )(PR 3 )] + system of Heinekey et al, 5a,b are clearly derived from an IPR effect, but others have been explained on the basis of the higher transoid influence of D as compared with 1 H, which can give rise, in certain H(H 2 ) systems, to low-field chemical shifts upon deuteration. 40c,42a,b Although in some cases this last explanation may be open to discussion, we believe that, in special instances, there are examples of small, low-field shifts that cannot be explained by IPR; i.e., Δδ 1 for Tp Me2 IrH 2 (thiophene) is +20 ppb, and this may be a cisoid influence of the D or an intrinsic deuterium effect of anomalous sign. , 3 Variation of Δδ n values in the 1* - d n species as a function of temperature (acetone- d 6 ). The dotted lines have been drawn only as a guide for the eye.…”
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.
“…Theoretically, the IPR shifts can be to either higher or lower field with respect to the reference isotopomer, 34a,37c, and in transition metal agostic alkyls and related systems they can be as large as −1 ppm, 3c, particularly at low temperatures (IPR effects are normally very sensitive to temperature 37c ). In transition metals, polyhydrides' Δδ 1 is normally in the approximate range from 0 to −50 ppb, d,40,41 although some abnormal low-field shifts (Δδ 1 = 10−230 ppb) have been observed, 40c, the first example being apparently that reported by Harrod et al in 1979. , Some of them, particularly those of the [Tp‘IrH(H 2 )(PR 3 )] + system of Heinekey et al, 5a,b are clearly derived from an IPR effect, but others have been explained on the basis of the higher transoid influence of D as compared with 1 H, which can give rise, in certain H(H 2 ) systems, to low-field chemical shifts upon deuteration. 40c,42a,b Although in some cases this last explanation may be open to discussion, we believe that, in special instances, there are examples of small, low-field shifts that cannot be explained by IPR; i.e., Δδ 1 for Tp Me2 IrH 2 (thiophene) is +20 ppb, and this may be a cisoid influence of the D or an intrinsic deuterium effect of anomalous sign. , 3 Variation of Δδ n values in the 1* - d n species as a function of temperature (acetone- d 6 ). The dotted lines have been drawn only as a guide for the eye.…”
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.
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