Propargyl complexes with metal propargyls

A new preparative method for allylic indium(m) reagents via a reductive transmetallation of 7r-allylpalladium(n) or 7T-allylnickel(n) complexes with indium(i) salts is reported. This method enables the use of a wide variety of allylic compounds, such as allylic chlorides, acetates, and even allylic alcohols, in combination with Pd or Ni catalysts.43-50 7r-Allylpalladium(ii) resulting from the addition of arylpalladium(n) to allene is also transformed by metallic indium to the corresponding allylindium.51-54 Similarly, propargylindium(m) can be prepared from the corresponding propargyl alcohol derivatives.55-58... 

The formation of 1,5-diyne complexes as side-products in some reactions of cations 92 with metal alkyls [41] and the facile, regioselective reduction of a propargylic chloride complex by Zn/HOAc, used in the synthesis of the insect pheromone 5-(Z)-tetradecenyl acetate [221], provided early evidence for the intermediacy of (propargyl)Co2(CO)5 mdicals. In a similar vein, the binuclear molybdenum-complexed propargyl cations react with Na/Hg to produce... 

The jt-allyl ligand bonded to cationic Pd(II) center tends to undergo nucleophilic substitution by organic nucleophiles from the opposite side of the metal center (Chapter 8). Attack of Pd(0) or Pt(0) complex in this fashion causes inversion of stereochemistry of the complex repetition of the reactions results in epimerization. The allyl ligand transfer between Pd centers takes place much faster than that from Pd to Pt. Isomerization between the Pt(II) complexes with a propargyl ligand and that with an allenyl ligand is catalyzed by Pd(0) complex (Eq. 5.58) [200,201]. 

The ophcally active Pd complex with a chiral allenyl ligand undergoes epimer-izahon in the presence of a catalytic amount of Pd(0) complex. This reaction does not involve the isomerization to the propargyl complex, but takes place via a dinuclear intermediate as depicted in Scheme 5.39. The -allenyl ligand in the dinuclear palladium intermediate may racemize via a vinyl-vinyidene intermediate. This type of reaction is prohahly involved in a kinetic resolution of racemic propargyl alcohols promoted hy chiral transihon metal complex [203]. The intermolecular allyl ligand transfer from Pd to Ee complexes occurs under... 

Reactions of reagents 1 and 2 with metal-complexed aromatic, propargylic and dienylic aldehydes provides homoallylic alcohol products with improved selectivity compared to their uncomplexed counterparts. The reaction of benzaldehyde chromium tricarbonyl complex 14 with (R,R)-1 followed by oxidative decomplexation provided ( -15 in 90% yield and 83% ee. The (JE)-crotylboration of 14 with (R,R)-2 provided 16 in 90% yield and 92% ee. Reaction of aldehyde 14 with (. -crotylboronate 3, however, provided adduct 17 in only 41% ee. 

This transformation is catalyzed by metal-hydride complexes such as RuHCl(CO)(PPh3)3 as shown in the cycloisomerization of 17 into 18 (Eq. 3) [12], but can also be promoted by in situ generated metal-hydride species resulting from the interaction of non-hydridic complexes with acidic coreagent. This is illustrated by the cycloisomerization of aUyl propargyl ethers 19 into dienes 20 in the presence of catalytic amounts of RuCp Cl(COD) in acetic acid (Eq. 4) [13]. 

Fc3Pd) jU4-vinylidene complex with a butterfly metal array has been reported. " Formation of //-allenylidene complexes 50 from propargyl alcohols with Fe3(CO)i2 may involve a dehydration process/ ... 

Umani-Ronchi adapted the Furstner protocol to achieve the first catalytic, enantioselective variant of this reaction. The chiral chromium salen complex was prepared from the in situ reduction of the anhydrous CrCb to CrCl2 with an excess of manganese metal, followed by complexation with the salen ligand 8 in the presence of catalytic triethylamine." Then the addition of allylic chloride (9) to aldehydes 10 to give the allylic alcohols 11 in moderate yields and in up to 95% ee. The same groups employed the same conditions for the addition of 2-butenyl bromides to aldehydes to achieve up to 83 17 syn/anti of allylic alcohol products and for the addition of 1,3-dichloropropene to aromatic aldehydes to obtain the syn chlorohydrin adduct in modest yield which were further converted to optically active vinyl epoxides. The [Cr(salen)]-catalyzed addition of propargyl halides to aromatic aldehydes allowed the synthesis of enantiomerically enriched homopropargyl alcohols in moderate yields with up to 56% ee. ... 

Molybdenum imido alkylidene complexes have been prepared that contain bulky carboxylate ligands such as triphenylacetate [35]. Such species are isola-ble, perhaps in part because the carboxylate is bound to the metal in an r 2 fashion and the steric bulk prevents a carboxylate from bridging between metals. If carboxylates are counted as chelating three electron donors, and the linear imido ligand forms a pseudo triple bond to the metal, then bis(r 2-carboxylate) species are formally 18 electron complexes. They are poor catalysts for the metathesis of ordinary olefins, because the metal is electronically saturated unless one of the carboxylates slips to an ri1 coordination mode. However, they do react with terminal acetylenes of the propargylic type (see below). 

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