Iridium alkynyls

Anti-Markovnikov hydration, and iridium alkynyl complexes,... 

Dinuclear iridium alkynyl complexes, synthesis and characteristics, 7, 331... 

No relevant iridium alkynyls exist to date. However, the rhodium complexes Tp RhH(C = CPh)(PR3) (R = C6H5 (559), C6H4F-4 (560)) have been prepared by the addition of phenylacetylene to the respective bis(phosphine) complexes, and the ethyl propiolate complex Tp RhH(C = CC02Et)(PPh3) (561) has very recently been prepared in the same way. ... 

Iridium alkynyl complexes are involved in the catalytic hydrosilylation of Esteruelas... 

The main species in solution has been identified to be the hydrido-alkynyl complex [IrH(C2Ph)(cod)(//2-iPrPCH2CH2OMe)]+BF4 (23). This is, however, only a sink that results from direct reaction of 22 with the 1-alkyne, draining the active catalyst from the system. The catalysis proceeds via the dihydrido-diene intermediate [IrH2(cod)(//2- PrPCH2CH2OMe)]+ BF4 (24), which reacts reversibly with the alkyne to yield the hydrido-iridium-styryl complex 25, followed by a rate-determining reaction of this hydrido-vinyl species with hydrogen to re-... 

Addition to linear 1,1-disubstituted allylic acetates is slower than addition to monosubstituted allylic esters. Additions to allylic trifluoroacetates or phosphates are faster than additions to allylic carbonates or acetates, and reactions of branched allylic esters are faster than additions to linear allylic esters. Aryl-, vinyl, alkynyl, and alkyl-substituted allylic esters readily undergo allylic substitution. Amines and stabilized enolates both react with these electrophiles in the presence of the catalyst generated from an iridium precursor and triphenylphosphite. 

A plausible reaction pathway was suggested by an experiment using labels, where the reaction proceeded via the pathway shown in Scheme 10.1. First, the oxidative addition of terminal alkyne 8 to an iridium complex leads to an alkynyl-... 

Attempts to turn this acetylene dimerization reachon into a catalyhc polymeriza-hon process have failed thus far. In the presence of excess phenylacetylene, the iridium(I) complex 23 activates another Caikynyi—H bond and hansforms, after a hydrogen shift, to the stable (vinyl)(alkynyl) iridium(III) system 27 (Equahon 12.10). 

The transformation predominates in Group 9 (Rh, Ir) chemistry. Reactions of RhCl(L)2 2 with 1-alkynes give the q -alkyne complexes which slowly convert to the hydrido(alkynyl)s at room temperature. The latter are sensitive to air and not often isolated. Addition of pyridine affords RhHCl(C=CR)(py)(L)2, which readily lose pyridine in hydrocarbon solvents to give square-planar fran.s-RhCl(=C=CHR)(L)2. Alternatively, the Cp complexes Rh(=C=CHR)(L)Cp can be obtained by reaction of the chloro complexes vdth TlCp. In the iridium series, heating for 36h in refluxing toluene afforded the vinylidenes in 80-90% yields. Table 1.2 lists several examples of reactions in which the q -alkyne complexes have been detected. 

A novel hydrazepine formation is observed in the iridium-catalyzed reaction of alkynyl hydrazone 304 with Bu Me2SiH in excess under slightly forcing conditions (Equation (53))/ The transformation leading to 305 can be explained by continuous interaction of Bu MceSiH with a silylformylation product of 304 under the reaction conditions/ ... 

Mel, in Rh-catalyzed methanol carbonylation, 7, 256 to monocarbonyl iridium complexes, 7, 284 in mononuclear ruthenium and osmium alkynyl formations,... 

Reductive coupling of acrylates 521 and imines in the presence of iridium provides azetidin-2-ones bearing aromatic, alkenyl, and alkynyl side chains, with high diastereoselection (Equation 213) <2002OL2537>. The reaction has been proposed to occur through a reductive Mannich addition-cyclization mechanism. 

Iridium(m) hydrides catalyze a 6-endo-dig cyclization of ortho-alkynyl benzoic acids to afford isocoumarins (Equation 323) <2005OL5437>. Likewise, the intramolecular cyclization of ortho-alkynyl benzoic acids can be catalyzed by palladium(ll) and silver(ll) to afford isocoumarins as the major product along with formation of the 5-endo-dig cyclization product (Equation 323) <1999S1145, 2000T2533>. 

Vaska s complex, the square planar iridium(I) compound shown in equation 145, readily interacts with alkynyl(phenyl)iodonium triflates in toluene at room temperature21. Such reactions proceed with loss of iodobenzene and deliver octahedral Ir(III) complexes possessing (7-alkynyl and trifluoromethanesulfonato ligands in a Jnms-relationship. The rhodium(I) analog of Vaska s complex behaves in a similar way21. 

Since it is known that halo(phenyl)acetylenes add oxidatively to Vaska s complex to give (7-phenylethynyl iridium(III) halides, 32112, the intervention of phenyliodonium iridium(III) and rhodium(III) intermediates, 33, in the alkynyliodonium reactions seems plausible. In any case, the production of cr-alkynyl complexes with alkynyl(phenyl)-iodonium triflates appears to be both more general and efficient21. 

Iridacyclopentadienes 79 (R = Ph, -Tol, H, Me) on reaction with alkynes in the presence of a protonating agent in acetonitrile produce iridabenzenes by a C-C bond-forming reaction <2004GEJ4518>. (77 -Acetato)iridacyclopentadiene 80 reacts with alkynes RC=CH (R = Ph, />-Tol) to produce a variety of iridabenzenes via >-(alkynyl)(but-l,3-dien-l-yl)iridiums, which are protonated <2005OM4849>. 

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. 

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