Ligands functional alkynyl

Recently, we reported the use of the bis(alkynyl)titanocene complex [(r/5-C5H4SiMe3)2Ti(C=CSiMe3)2] as a molecular tweezer that functions as a bi-dentate ligand by using the two alkynyl functions to coordinate to a single cop-... 

Despite the great success of the transmetalation process in the enantiose-lective arylation of ketones, its extension to allylation or alkynylation reactions failed, providing the corresponding tertiary alcohols with enantiomeric excesses never higher than 50% ee. On the other hand, more success has been found in the alkenylation of ketones. The process started with the hydrozirconation of terminal alkynes to give the corresponding alkenylzirconium intermediates, which were transmetalated by reaction, in this case, with various ketones in the presence of the HOCSAC ligand. This protocol tolerated the presence of other carbon-carbon multiple bonds on the alkyne, as well as different functionalities and achieved excellent results for alkyl ketones, a,(3-unsaturated ketones and even dialkylketones, as shown in Scheme 4.22. 

The selectivity of the hydrogen transfer is excellent When employing a catalyst with deuterium at the a-positions of the isopropoxide ligands (17), complete retention of the deuterium was observed. A computational study using the density functional theory comparing the six-membered transition state (as in Scheme 20.3, the direct transfer mechanism) with the hydride mechanism (Scheme 20.3, the hydride mechanism) supported the experimental results obtained [36]. A similar mechanism has been proposed for the MPV alkynylations [37] and cyanations [38]. 

Alkynyl(trimethyl)silanes, germanes, and stannanes produce alkynyl-(phenyl)-A3-iodanes via ligand exchange on iodine under similar conditions [36]. Stang and co-workers developed a useful procedure for the preparation of diverse /3-functionalized alkynyl-A3-iodanes, which involves a ligand exchange of cyano-A3-iodane 19 with alkynylstannanes [37]. 

An example that used this protocol the substrate of which contains a sensitive functionality is depicted in Scheme 45 [202]. 1,3-Diene monoepoxide is easily attacked by a palladium(O) complex to form the corresponding 7r-allylpalladium species. Thus such a process could be banished from the desired selective transformation as depicted in Scheme 46 by the employment of the alkynyltin reagent with an aid of triphenylarsine ligand [203]. Organotin protocol is also convenient for introduction of a small alkynyl moiety such as C2 or C3 or preparation of symmetrical diarylethynes (Scheme 47) [204]. Shirakawa et al. reported recently that iminophosphine 4 is much more effective ligand for palladium than tris(2-furyl)phosphine in this reaction (Scheme 48) [32,205]. 

Chen, Z.-N., Fan, Y, and Ni, J. (2008) Luminescent heteropolynuclear or multicomponent complexes with polypyridyl-functionalized alkynyl ligands. Dalton Transactions, 573. 

Li, X.-L., Shi, L.-X., Zhang, L.-Y, et al (2007) Syntheses, structures, and sensitized lanthanide luminescence by Pt- Ln (Ln = Eu, Nd, Yb) energy transfer for heteronuclear PtLn2 and R2Ln4 complexes with a terpyridyl-functionalized alkynyl ligand. Inorganic Chemistry, 46, 10892. 

---