Polyhydride (Fluoroalkyl)phosphine Complexes of Iridium. Synthesis, Dynamics, and Reactivity Properties of (dfepe) 2 Ir 2 (μ-H) 3 (H)
1996; American Chemical Society; Volume: 15; Issue: 2 Linguagem: Inglês
10.1021/om950722c
ISSN1520-6041
AutoresR. Chris Schnabel, Patrick S. Carroll, Dean M. Roddick,
Tópico(s)Ammonia Synthesis and Nitrogen Reduction
ResumoThe 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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