Ligated iridium complexes

Scheme 5 Proposed mechanism for borylation by bipyridine ligated iridium complexes...

Pincer-ligated iridium complexes have been used as homogeneous catalysts for the dehydrogenation of aliphatic polyalkenes to give partially unsaturated polymers. The catalyst appears to be selective for dehydrogenation in branches as compared with the backbone of the polymer.56 The mechanism shown in Scheme 1 has been suggested for an [IrCl(cod)]2-catalysed oxidative esterification reaction of aliphatic aldehydes and olefinic alcohols.57... 

Recently, metathesis of cyclooctane was reported using the tandem system having the pincer-ligated iridium complexes for hydrogenation/dehydrogenation and Schrock-type Mo-alkylidene complexes for olefin metathesis [78]. However,... 

Ray A, Zhu K, Kissin YV, Cherian AE, Coates GW, Goldman AS. Dehydrogenation of ahphatic polyolefins catalyzed by pincer-ligated iridium complexes. Chem Commun. 2005 (27) 3388-3390. 

Ugi s ferrocenylamine has also been used in the synthesis of chiral biden-tate NHC heterodonor ligands in which the second ligating unit is either a diphenylphosphino or phenylsulfid group [89]. Several rhodium(I) and iridium complexes have been prepared which are depicted in Scheme 33. 

Pincer-ligated metal complexes have displayed extraordinarily rich chemistry and have found widespread use in catalysis. Pincer complexes of numerous transition metals have been synthesized, but the most well-studied probably involve Ru, Rh, Ir, and Pd [1-7], Our group has largely focused on pincer-iridium complexes, which have shown a strong tendency toward the activation of C-H bonds. These complexes have been found to effect the oxidative addition of a variety of C-H bonds including those with sp - and sp-hybridized carbon [8-10], Most notable, however, has been the activation of C(sp )-H bonds, leading to alkane dehydrogenation [6, 7],... 

Krogstad DA, DeBoer AJ, Ortmeier WJ, Rudolf JW, Halfen JA (2005) l,3,5-Triaza-7-phosphaadamantane (PTA) ligated iridium(I) complexes as catalysts for the intramolecular hydroamination of 4-pentyn-l-amine in water. Inorg Chem Commun 8 1141-1144... 

A key feature of the mechanism of Wilkinson s catalyst is that catalysis begins with reaction of the solvated catalyst, RhCl(PPh3)2S (S=solvent), and H2 to form a solvated dihydride Rh(H)2Cl(PPh3)2S [1], In a subsequent step the alkene binds to the catalyst and then is transformed into product via migratory insertion and reductive elimination steps. Schrock and Osborn investigated solvated cationic complexes [M(PR3)2S2]+ (M=Rh, Ir and S= solvent) that are closely related to Wilkinson s catalyst. Similarly to Wilkinson s catalyst, the mechanistic sequence proposed by Schrock and Osborn features initial reaction of the catalyst with H2 followed by reaction of the dihydride with alkene for the case of monophosphine-ligated rhodium and iridium catalysts [12-17]. Such mechanisms commonly are characterized... 

Neutral formyl complexes which contain ligating CO often decompose by decarbonylation however, several exceptions exist. For instance, the osmium formyl hydride Os(H)(CO)2(PPh3)2(CHO) evolves H2(54). Although the data are preliminary, the cationic iridium formyl hydride 49 [Eq. (14)] may also decompose by H2 evolution (67). These reactions have some precedent in earlier studies by Norton (87), who obtained evidence for rapid alkane elimination from osmium acyl hydride intermediates Os(H)(CO)3(L)(COR) [L = PPh3, P(C2H5)3], Additional neutral formyls which do not give detectable metal hydride decomposition products have been noted (57, 65) however, in certain cases this can be attributed to the instability of the anticipated hydride under the reaction conditions (H2 loss or reaction with halogenated solvents). 

Iridium nanoparticles, preparation, 12, 82 Iridium(III) O-ligated complexes, preparation, 7, 315 Iridium polyhydrides, preparation and characteristics, 7, 405 Iridium pyrrolyl derivatives, reactivity, 7, 282 Iridium tetrahydrides, characteristics, 7, 407-408 Iridium trihydrides, preparation, 7, 405 Iridium vinylidenes, synthesis and characteristics, 7, 352 Iridium xyliphos complexes, properties, 7, 442 Iridoids, via Pauson-Khand reaction, 11, 360 Iron(arene) (cyclopentadienyl) cations, preparation and reactivity, 6, 166... 

Mixed donor tridentate [NPS] ligated derivatives, chromium(III) complexes, 5, 370 Mixed iridium carbonyl dimers, preparation, 7, 289 Mixed isonitrile acetylides, liquid crystals, 12, 281 Mixed isonitrile phenyl complexes, liquid crystals, 12, 282 Mixed ligand triangular Pt carbonyl clusters, characteristics, 8, 411... 

Several studies on A-frame complexes have demonstrated that, initially, hydrogen oxidatively adds across a single metal. " Iridium is always the favored site of attack in heteronuclear A-frames. Rearrangement may subsequently lead to monohydride ligation at both metal centers. Hydrogen addition to the iridium d species in Scheme 1 occurs with perpendicular orientation to the carbonyl. The initial product is observed only at low temperatures for R = Ph, however. Upon warming it rearranges to the parallel species, (7), by means of dissociation and reattack of H2, rather than an 17 -benzene. Parallel attack may be induced by the use of L = 7r-acceptor, e.g., tetracyanoethylene. These facts have been rational-... 

Balch, A.L. Catalano. V.J. Ligation-induced changes in metal-metal bonding in luminescent binuclear complexes containing gold(I) and iridium(I). Inorg. Chem. 1991, 30, 1302. 

The catalytic asymmetric hydroboration of 1,1-disubstituted alkenes R R C=CH2 with pinacolborane has been attained (<92% ee) by using complexes of iridium with chiral phospine-oxazolidines as catalysts (2.5 mol%). The same class of compounds has been shown to facilitate hydroboration (<98% ee) catalysed by chiral complexes of CuCl with a bidentate A)-heterocyclic carbene (NHC) containing SOg" as an additional ligating group. ... 

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