Iridium complexes dienes

The mechanistic basis of iridium-complex-catalyzed enantioselective hydrogenation is less secure than in the rhodium case. It is well known that square-planar iridium complexes exhibit a stronger affinity for dihydrogen than their rhodium counterparts. In earlier studies, Crabtree et al. investigated the addition of H2 to their complex and observed two stereoisomeric intermediate dihydrides in the hydrogenation of the coordinated cycloocta-1,5-diene. The observations were in contrast to the course of H2 addition to Ms-phosphine iridium complexes [69]. 

The complexes of the composition [ Ir( t-X)(diene) 2], where X = halogen, OH, OMe (e.g. [IrCl(CO)(cod)]) appeared to be very effective catalysts for the hydrosilylation of allyl chloride by trialkoxy- and alkylalkoxy-silanes [22]. Other iridium complexes have been subsequently reported as catalysts for the synthesis of silane... 

Dihapto 7>ligands, in copper complexes, 2, 174 Dihydride iridium complexes, preparation, 7, 396 Dihydrido clusters, with decarutheniums, 6, 1036 Dihydrobenzofuran, carbene C-H insertions, 10, 193 Dihydrobenzopyran, carbene C-H insertions, 10, 193 ring-closing diene metathesis,... 

The square pyramidal complexes of group 9 iridium cyclopropylbis( / -diene) complexes were recently synthesized in poor yields (3-5%) by metathesis reaction between diene)2 IrCl and cyclopropyllithium or cyclopropylmagnesium bromide (equation 16)" ... 

The complex has enjoyed relatively little use in organic synthesis. For iridium-catalyzed homogeneous hydrogenation of alkenes, Crabtree s iridium complex ((1,5-Cycloocta-diene)(tricyclohexylphosphine)(pyridine)iridium(I) Hexafluoro-phosphate) is generally preferred, although this readily prepared Ir complex is active. It is more reactive than its rhodium counterpart in the catalytic isomerization of butenyl- to allylsilanes. ... 

An NMR study (597) of ligand exchange in the system (diene)MCl(L) (diene = norbornadiene or 1,5-cyclooctadiene M = Rh or Ir L = tertiary phosphine, arsine, or stibene) shows a first-order dependence of the rate upon both L and the olefin complex in the temperature range from —70° to —10°C. The exchange involves an 8 2 mechanism with the five-coordinate complex (diene)MCl(L)2 as intermediate. The intermediate iridium complexes (l,5-CgHi2)IrCl(L)2 can be isolated from ethanolic solution. The activation energy for the process ranges from 4 to 10 kcal/mole (597). 

A limited amount of work has been done with complexes of diethylene-triamine 61). Treatment of bis-diethylenetriaminerhodium(III) iodide with potassium amide in liquid ammonia resulted in the isolation of solid [Rh(dien-H)2]I and [Rh(dien-H)(dien-2H)]. For the corresponding iridium complex, similar treatment resulted in the isolation of [Ir(dien-H)-(dien-2H)]. Further deprotonation presumably occurs, at least in the case of the rhodium complex, as evidenced by the fact that the solid [Rh(dien-H)(dien-2H)], which precipitates upon adding slightly more than three molar equivalents of potassium amide, dissolves completely when a total of six molar equivalents of potassium amide is added. 

Reviews have appeared of the photophysics of molybdenum complexes, primary and secondary processes in organometallic chemistry, flash photolysis of Pe(CO)5 and Cr(CO)g, dinuclear manganese carbonyl compounds, the photochemistry of metal complexes isolated in low temperature matrices, cluster complexes, diene complexes, photoproduction of coordinativeiy unsaturated species containing rhodium or iridium, and redox chemiluminescence of organometallic compounds.Synthetic and metal organic photochemistry in industry has also been reviewed. 

Cyclometallapolyselanes, 27 59 Cyclometallation reactions, 26 171 Cycloocta-1,5-diene, iridium complex, 26 122, 27 23... 

The lower reactivity of iridium complexes requires the use of more activated precursors. Thus, the neutral square-planar derivatives Zra .v- IrCI =C=C=C(R)Ph (Pz -Prs)2] (R = Ph, f-Bu) have been prepared from [IrH2Cl(Pz-Pr3)2] and the appropriate alkynol, via UV-promoted or CF3CO2H-catalyzed dehydration of the initially formed hydride-alkynyl intermediates [IrHCl C=CC(R)Ph(OH) (Pz-Pr3)2] [78, 81]. The cationic species [Ir(=C=C=CPh2)(/ -diene)( PR3) [BF4] (diene = COD, PR3 = PCys diene - TFB, PR3 - PCys, P/-Prs) are also known [211], They were synthesized by reacting the methoxo compounds [Ir(OMe)(z/ -diene)(PRs) with l,l-diphenyl-2-propyn-l-ol, followed by dehydration of the resulting alkynyl derivatives [Ir C=CCPh2(OH) (77 -diene)(PRs)] with stoichiometric amounts of HBF4. 

Representative products are XLII and XLIV . With butadiene in benzene the rhodium complex XLIIIa reacts fast at RT, whereas the iridium complex XLIIIb requires 2 h at reflux. Other dienes give complex products with XLIIIa. The complex XLIIIb reacts with isoprene (12 h at reflux) but fails to react with cyclic dienes. 

In contrast, the iridium complex XLVb is more reactive than the corresponding rhodium complex XLVa. Furthermore, the reaction rates in this reaction are independent of the diene (cyclooctadiene isoprene 2,3-dimethylbutadiene) . 

Partial or complete displacement of the coordinated acetonitrile ligands may be achieved with monodentate ligands (e.g., phosphines ), bidentate ligands (e.g., dienes), or tridentate ligands, providing a convenient entry to a range of (i -pentamethylcyclopentadienyl)rhodium and -iridium complexes. 

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