Synthesis and Properties of Compressed Dihydride Complexes of Iridium:  Theoretical and Spectroscopic Investigations

Abstract

Reaction of [Cp*Ir(P-P)Cl][B(C6F5)4] (P-P = bisdimethydiphosphinomethane (dmpm), bisdiphenyldiphosphinomethane (dppm)) with [Et3Si][B(C6F5)4] in methylene chloride under 1 atm of hydrogen gas affords the dicationic compressed dihydride complexes [Cp*Ir(P-P)H2][B(C6F5)4]2. These dicationic complexes are highly acidic and are very readily deprotonated to the corresponding monohydride cations. When the preparative reaction is carried out under HD gas, the hydride resonance exhibits JHD = 7-9 Hz, depending upon the temperature of observation, with higher values of JHD observed at higher temperatures. A thermally labile rhodium analogue, [CpRh(dmpm)(H2)][B(C6F5)4]2, was prepared similarly. A sample prepared with HD gas gave JHD = 31 Hz and J(HRh) = 31 Hz, allowing the Rh complex to be identified as a dihydrogen complex. Quantum dynamics calculations on a density functional theory (DFT) potential energy surface have been used to explore the structure of the Ir complexes, with particular emphasis on the nature of the potential energy surface governing the interaction between the two hydride ligands and the Ir center.

Elongated Dihydrogen Versus Compressed Dihydride Complexes: The Temperature Dependence of the H–D Spin–Spin Coupling Constant as a Criterion To Distinguish between Them

“…[8] In this study it was found that 1 J HD depended not only on R HÀH , as is well known, but also that it has a certain dependence on R MÀH 2 . Hence we think it is preferable, if possible, to compute 1 J HD directly and compare it to experimental data, especially since it has been previously demonstrated in several cases of elongated dihydrogen/compressed dihydride complexes that MÀH 2 and HÀH motions are inextricably coupled.…”

“…However, as is known for this family of complexes, the experimentally resolved geometry cannot be compared directly to that of a direct minimization of the potential energy, as is customary with most other systems, because the flatness of the potential energy surface describing the motion within the MÀH 2 unit makes it necessary to consider nuclear motion quantum dynamically. Thus, following the same procedure as in previous studies [4,29,8] we determined the relaxed potential energy surface as a function of HÀH and MÀH 2 stretches, which are represented in Figure 1.…”

“…In a subsequent theoretical study, it was found that its PES had two minima, the most stable one matching the description of a dihydride (R HÀH = 1.63 ). [8] A simplified one-dimensional nuclear dynamics study described the geometry of the Ir À H 2 unit and also showed that the mean thermal R HÀH decreased with increasing temperature, thus indirectly explaining the experimental observations. The fact that the most stable minimum on the Born-Oppenheimer potential energy surface (i.e.…”

Activation of Hydrogen by Palladium(0): Formation of the Mononuclear Dihydride Complextrans‐[Pd(H)2(IPr)(PCy3)]

“…The value for the H-D coupling constant is consistent with the formation of the trans isomer. [23] Interestingly, in addition to the resonance of complex [D]-2, the hydride resonance of complex 2 was also present in the 1 H NMR spectrum. Comparison of the integration value of the two hydride signals with the integration of the isopropyl CH resonance of the IPr ligand (3 vs. 12), strongly suggested the presence of the bis-deuterated complex [D 2 ]-2.…”

Characterization of a Palladium Dihydrogen Complex

“…[15] The partially deuterated analogue of complex 1 was prepared by 1 Ha nd 2 HNMR spectra are shown in Figure 2). This 1 J HD value corresponds to a d HH of 0.81 AE 0.02 .…”