| Autor: |
Schnabel, R. C., Carroll, P. S., Roddick, D. M. |
| Zdroj: |
Organometallics; January 23, 1996, Vol. 15 Issue: 2 p655-662, 8p |
| Abstrakt: |
The synthesis and reactivity properties of new dimeric iridium polyhydrides incorporating the acceptor ligand (C2F5)2PCH2CH2(C2F5)2 (dfepe) are reported. Hydrogenolysis of (dfepe)Ir(η3-C3H5) (prepared by metathesis of [(dfepe)Ir(μ-Cl)]2 with allylmagnesium chloride) afforded (dfepe)2Ir2(μ-H)3(H) (3) in high yield as an air-stable red crystalline solid. A triply bridged ground-state geometry for 3 was deduced from low-temperature NMR data and was confirmed by X-ray crystallography. Hydride site exchange mechanisms are proposed which are consistent with VT 1H and 31P NMR data. Although 3 is formally coordinatively saturated, hydride bridge dissociation readily occurs and leads to ligand addition reactions. Thus, treatment of tetrahydride 3 with 1 atm of H2 at 20 °C quantitatively affords the hexahydride dimer [(dfepe)Ir(μ-H)2(H)2]2 (5). In the absence of H2, 5 rapidly loses H2 in solution at 20 °C to re-form 3. The structure of 5 has been determined by X-ray crystallography. 3 also reacts with CO to give (dfepe)Ir(CO)2H (6), which loses CO under 1 atm of H2 to reversibly afford (dfepe)Ir(CO)H3 (7). The trihydride undergoes thermal H/D exchange with both D2 (20 °C) and benzene-d6 (120 °C), presumably via the intermediacy of (dfepe)Ir(CO)H. The tetrahydride 3 also undergoes H/D exchange with D2 and benzene-d6 under similar conditions. In the presence of tert-butylethylene, dehydrogenation of cyclopentane by 3 at 120 °C quantitatively affords CpIr(dfepe); a likely intermediate in this process is the dihydride dimer [(dfepe)Ir(μ-H)]2. (dfepe)Ir(η3-C3H5) also reacts directly with cyclopentane at 120 °C to give CpIr(dfepe). |
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