Phosphides alkynes

The reaction of Ba[P(SiMe3)2]2(THF)2 with diphenylbutadiyne in toluene for 12 days induces a m-addition of the diyne to the phosphide, followed by a 1,3-silyl group shift and ring closure. The dinuclear complex 132 is then isolated in good yield.283 Its complex structure contains Ba-C a bonds (2.881(5), 2.899(5) A), side-on Ba-alkyne (3.003(6), 3.363(6) A) and arene interactions, and Ba-phospholide bonds (Ba-P = 3.487(2) A) (Figure 65). 

A mechanism that involves ytterbium phosphide species has been proposed, similarly to the foregoing intramolecular hydrophosphination. Generation of the phosphide species is supported by the formation of Ph2CDNHPh (after aqueous quench) upon treatment of the imine complex with Ph2PD (Scheme 15). Lanthanide phosphide is known to react with THF, forming a 4-diphenylphosphino-l-butoxyl species [21], which was indeed found as a side product in the catalytic hydrophosphination of disubstituted aliphatic alkynes run in THF, supporting further the ytterbium-phosphide intermediate (Scheme 16). 

The novel phospha-alkyne system (303) is formed in the reaction of lithium bis(trimethylsilyl)phosphide with 0,0 -diethyldithiocarbamate. C-chlorophosphaethyne, ClCsp, has been generated by the pyrolysis of trichloromethyldichlorophosphine over granulated zinc at 550°C, and characterised by infrared spectroscopy. A bimolecular proton transfer mechanism has been suggested for the base-promoted isomerism of alkynyl- and alkenyl-phosphines to the phospha-alkynes (304). The potential of phospha-alkynes as novel building blocks in heterocyclic chemistry has been reviewed. New examples of phospha-alkyne-derived... 

A few final comments should be made on the insertions of substrates containing C-C multiple bonds into the bonds between a transition metal and an electronegative heteroatom. First, insertions of olefins into related thiolate and phosphide complexes are as rare as insertions into alkoxo and amido complexes. Reactions of acrylonitrile into the metal-phosphorus bonds of palladium- and platinum-phosphido complexes to give products from formal insertions have been observed, and one example is showm in Equation 9.90. However, these reactions are more likely to occur by direct attack of the phosphorus on the electrophilic carbon of acrylonitrile than by migratory insertion. Second, the insertions of alkynes into metal-oxygen or metal-nitrogen covalent bonds are rare, even though the C-C ir-bond in an alkyne is weaker than the ir-bond in an alkene. 

The reaction of nickelocene with primary phosphines has allowed the preparation of the phosphido-bridged dimers 114 deprotonation and methylation of the phosphide moiety results in the formation of the methylated derivatives 115 (Scheme 31). Analogous reactions with 2-phosphinophenolates give Ni(2-phosphinophenolato)Cp complexes. Reaction of nickelocene with 1-norbornyl lithium and alkynes leads to NiCp(l-norbornyl)(77 -RC=CR) (R = Me, SiMcs, Ph, CH20Me, CH2NMc2, GH2OH). These complexes have been characterized by and NMR and mass spectroscopy. " ... 

The bridging phosphide group in bimetallic transition metal complexes appeared to participate in a transformation, rather than behave as an inert spectator ligand. This is particularly obvious in homobimetallic iron and cobalt systems.Mays et al. showed that the reactions of iron-cobalt phosphido-bridged complex 25 with both symmetrical and unsymmetrical alkynes gave five-membered ferracycle-containing compounds, such as 26, in which a CO and an alkyne were inserted regiospecifically into a Co-P bond in 25. Subsequent decarbonylation led to a set of four-membered ferracyclic species 27-30 in low yields. 

The transition metal-free addition of silylphosphines to styrenes, pyridines, and acrylates was promoted by a fluoride source (Scheme 4.17) [59]. The addition reaction occurred under extremely mild conditions and afforded moderate to excellent yields of the anti-Markovnikov addition prodnct. The reaction was proposed to proceed through initial formation of a phosphide anion that reacted with the alkenes through a phospha-Michael-type addition. The proton source for the generation of the final adduct was proposed to be adventitious moisture in the commercially available TBAF solution. While activated alkenes were quite amenable to this approach, unactivated alkenes were unresponsive. 2-Vmylpyridine was particularly reactive and was cleanly converted into the alkylphosphine (95%). While most of the substrates were terminal Michael acceptors, a number of internal alkenes as well as a tetrasubstituted alkene were converted into the alkylphosphines in moderate yields (Schane 4.18 and Example 4.17). The chemistry could be extended to terminal and internal alkynes, although a mixture of E- and Z-isomers were obtained with the EIZ> 1. Following this work, the authors were able take advantage of the need for another electrophile to complete the reaction and added an aldehyde to trap the intermediate carbanion [60]. This approach worked well and enabled the construction of gamma-hydroxyphosphonates in excellent yield (up to 88%). 

The transition metal-free addition of sodium phosphides to protected alkynols proceeds under mild conditions to selectively form the 1,1-addition products (Scheme 4.286) [73]. The alcohol was deprotonated prior to the addition of the anionic phosphorus reagent to ensure the selective addition to the alkyne. The lithium alkoxide was hydrolyzed after the P—C bond-forming reaction was obtained. The conditions were extremely mild, and moderate yields of the addition product were obtained. 

---