Vinylidenes with iridium

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. 

Vinylidene-mediated reactions involving rhodium and iridium are discussed separately from those involving Groups 10 and 11 transition metals. The reactions of Group 9 metal vinylidenes are more numerous and have more in common with one another. Extensive stoichiometric organometallic literature aids in the understanding of these processes. In contrast, reactions of Groups 10 and 11 metal vinylidenes are more scattered and often controversial. 

C-M bond addition, for C-C bond formation, 10, 403-491 iridium additions, 10, 456 nickel additions, 10, 463 niobium additions, 10, 427 osmium additions, 10, 445 palladium additions, 10, 468 rhodium additions, 10, 455 ruthenium additions, 10, 444 Sc and Y additions, 10, 405 tantalum additions, 10, 429 titanium additions, 10, 421 vanadium additions, 10, 426 zirconium additions, 10, 424 Carbon-oxygen bond formation via alkyne hydration, 10, 678 for aryl and alkenyl ethers, 10, 650 via cobalt-mediated propargylic etherification, 10, 665 Cu-mediated, with borons, 9, 219 cycloetherification, 10, 673 etherification, 10, 669, 10, 685 via hydro- and alkylative alkoxylation, 10, 683 via inter- andd intramolecular hydroalkoxylation, 10, 672 via metal vinylidenes, 10, 676 via SnI and S Z processes, 10, 684 via transition metal rc-arene complexes, 10, 685 via transition metal-mediated etherification, overview,... 

Another route to heteroatom stabilized carbenes involves first the interaction of a terminal alkyne with an iridium complex to yield an iridium vinylidene compound. The vinylidene complex then reacts with nucleophiles, typically alcohols, to form oxa stabilized carbene complexes. O Connor extended this strategy to form a carbene ligand on the same iridium center as a metallacycle (76) and was also able to... 

The basicity at the 3-carbon is illustrated by the reactions in Equations 13.26 and 13.27. Reaction of the octahedral rhenium vinylidene in Equation 13.26 with HBF generates the cationic carbyne complex from addition of a proton to the basic 3-carbon. Because low-valent metals are often basic, addition of a proton to the vinylidene 3-carbon is likely to occur by a multi-step process initiated by protonation of the metal center. This initial protonation at the metal center would then be followed by migration of the proton to the 3-carbon. The reaction of acid with the iridium vinylidene in Equation 13.27 illustrates this mechanism. In this case, protonation first generates an iridium-hydride complex. The hydride in this complex tlien migrates to the p-carbon to generate an alkylidyne complex. ... 

The iridium dimer tIr2l2(CO)(jt-CO)(dppm)2l reacted with ethyne to afford363 [Ir2l2(CO)( i-HCX HKdppm)2] in which the alkyne was parallel to the Ir-Ir vector. The compound underwent a transformation in solution at ambient temperature to afford the vinylidene compound [Ii2l2(00)(fi-CXIH2)(dppm)2]. A mechanism for the reaction was proposed. 

The chemistry and reactivity of iridium vinylidene complexes has progressed during the last decade. Particularly, Werner and co-workers have continued studying unsaturated carbenes of rhodium and iridium and have developed an original route to prepare iridium disubstituted vinylidene complexes, /ra 3-[IrCl(C=CRR)(PPry2] (R = Me, Ph 561), which are accessible in moderate yield by using vinyl chlorides and sodium (see Scheme 79). " Analogous compounds with SbPr 3 were also described. 

The reactivity of the (vinylidene)iridium(l) complexes /ra ir-[IrCl(C=CR R )(PPr 3)2] toward both Grignard reagents and organolithium compounds has been investigated. The hydrocarbyl vinylidenes /ra 3-[IrR(C=CR R )(PPr 3)2] (R = Me, Ph, C=CPh 562), which straightforwardly form upon treatment with the organolithium reagents, react in the... 

Neutral and cationic square planar (SP) iridium vinylidenes were prepared by the reaction of the octahedral hydridoiridium(iii) complex [IrHCl /t (C ,P)-CH2OCH2CH2PPr 2 K (T,0)-Pr 2PCH2CH2OMe ] 566 with terminal... 

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