Hydrogen binding to and fluxional behavior of Ir(H)2X(P-tert-Bu2R)2 (X = Cl, Br, I; R = Me, Ph)

Mechanistic insight into novel sulfoxide containing SABRE polarisation transfer catalysts

“…53 The effects of H 2 pressure and DMSO concentration on these exchange processes were also studied in methanol-d 4 ; such indirect H 2 exchange, rather than direct H 2 loss, has been reported for several similar systems. 51,54 When similar EXSY data were collected in CD 2 Cl 2 , the rate of hydrogen and DMSO loss proved to be slower than those in methanol-d 4 , as summarised in Table 3.…”

Thermodynamic and kinetic studies of H2 and N2 binding to bimetallic nickel-group 13 complexes and neutron structure of a Ni(η2-H2) adduct

“…Activation barriers and rate constants for H 2 binding and loss have seldom been reported despite their relevance for many catalytic processes. Δ H ‡loss values for (η 2 -H 2 )NiML (9.3 to 11.3 kcal mol –1 ) are comparable to those reported (in kcal mol –1 ) for [Ru(η 2 -H 2 )H 3 (PPh 3 ) 3 ] + (8.8),31 Cr(η 2 -H 2 )(CO) 3 (PCy 3 ) 2 (12.1),10 Ir(η 2 -H 2 )(H) 2 X(P t Bu 2 Me) 2 (9.4 to 11.3 for X = Cl, Br, I),40 and Ir(η 2 -H 2 )(H) 2 X(P i Pr 3 ) 2 (10.1 to 11.4 for X = Cl, Br, I),51 and are significantly lower than those reported for W(η 2 -H 2 )(CO) 3 (PCy 3 ) 2 (16.9)44 and Ru(η 2 -H 2 )(H) 2 (PPh 3 ) 3 (17.9) 31. Perhaps the most thoroughly studied H 2 binding equilibrium is that of W(η 2 -H 2 )(CO) 3 (PCy 3 ) 2 , for which rate constants for both H 2 binding ( k bind ) and loss ( k loss ) have been directly measured to be ∼2 × 10 6 M –1 s –1 and 469 s –1 at 298 K, respectively 44,52.…”

Activation of Molecular Hydrogen

“…[187][188][189][190] The EIE values for H 2 versus D 2 addition are usually inverse over a large temperature range (260-360 K), showing that counterintuitively D 2 binds more strongly than H 2 . The values of K H /K D observed thus far are 0.36-0.77 for formation of H 2 complexes and 0.47-0.85 for complete OA.…”

“…It should be kept in mind that EIEs are temperature dependent because of the entropy differences. The EIE for the W analogue cannot be measured directly because of stronger W(H 2 ) bonding, but the equilibrium shown in Equation 5.7 provides a means of determining accurate EIE values: 187,188,192 Lower K H /K D of 0.36-0.50 occur here, possibly because of a secondary isotope effect due to the hydride ligands (values for MH x (D 2 )L n cannot be determined because of isotopic exchange, so values for MD x (D 2 )L n are used). D 2 loss from IrClD 2 (D 2 )(L) 2 is energetically $1 kcal/mol higher than H 2 loss from IrClH 2 (H 2 )(L) 2 (L ¼ P-t-Bu 2 Me).…”

“…D 2 loss from IrClD 2 (D 2 )(L) 2 is energetically $1 kcal/mol higher than H 2 loss from IrClH 2 (H 2 )(L) 2 (L ¼ P-t-Bu 2 Me). 188 …”