Phenylacetylene transition metal complexes

Some transition metal catalysts induce the living polymerization of various acetylenic compounds.68,69 Such polymerizations of phenylacetylene catalyzed by rhodium complexes are used in conjunction with a quantitative initiation and introduction of functional groups at the initiating chain end (Scheme 16).70 The catalyst is prepared from an [RhCl(nbd)]2/Ph2C=C(Ph)Li/PPh3 mixture and proceeds smoothly to give quantitatively the polymer 54 with a low polydispersity ratio. 

Well-controlled polymerization of substituted acetylenes was also reported. A tetracoordinate organorhodium complex induces the stereospecific living polymerization of phenylacetylene.600 The polymerization proceeds via a 2-1 -insertion mechanism to provide stereoregular poly(phenylacetylene) with m-transoidal backbone structure. Rh complexes were also used in the same process in supercritical C02601 and in the polymerization of terminal alkyl- and arylacetylenes.602 Single-component transition-metal catalysts based on Ni acetylides603 and Pd acet-ylides604 were used in the polymerization of p-diethynylbenzene. 

Preparation of Phosphines by Addition of P-H to Unsaturated Compounds. -This route has not received much attention over the past year. A stereoselective synthesis of tris(Z-styryl)phosphine is offered by the addition of phosphine to phenylacetylene in a superbasic system (HMPA-H20-K0H)." In a similar vein, the reaction of phosphine with styrene and a-methylstyrene in a superbasic medium (DMSO-KOH) provides a route to the primary phosphines, (2-phenylethyl)phosphine and (2-methyl-2-phenylethyl)phosphine, respectively. 7 Transition metal phosphine complexes have been shown to catalyse the a-hydroxylation, P-cyanoethylation, and P-alkoxycarbonylethylation of phosphine. 71 Addition of primary phosphines to acrylic esters has been used for the synthesis of the phosphines (80).7 A similar addition of diphenylphosphine to acrylic esters and amides has given a series of hydrophilic phosphines (81). 72 The bis(phosphorinanyl)ethane (82) is formed in the photochemical addition of l,2-bis(phosphino)ethane to 1,4-pentadiene. ... 

Calcium-based catalysts have also shown promise in hydrophosphination reactions (Scheme 4.299) [62]. Treatment of phenylacetylene with diphenylphosphine in the presence of a p-diketiminate-ligated calcium complex afforded an excellent yield of the vinylphosphine. Furthermore, the reaction was highly selective for the formation of the F-stereoisomer. This chemistry provided a transition metal-free route to the synthesis of these valuable targets. 

Metal salts or complexes have a role in promoting dehydration of nitro compounds. Thus, 5-phenylisoxazole has been obtained in low yield from the lithium salt of phenylacetylene with nitromethane in dioxan at room temperature [24]. The complex tetrakis(triphenylphosphane) platinum(O) on treatment with nitromethane leads to fulminatobis(triphenylphosphane)platinum(II), possibly via CT-nitromethyls [25-27]. Cerium and other metal nitrates have been claimed to promote condensation of nitro compounds with alkenes [28]. More examples of condensations caused by transition metal salts are reported in Section 8.2.4. 

It is noteworthy that all group -metal-based catalysts described above can only be used for primary amines, as opposite to most late transition metal-based systems. While the stoichiometric reaction of Ti(NMe2)4 with phenylacetylene was shown to produce some enamine hydroanunation product [196], a catalytic process was only facilitated using the tethered zirconium bis(ureate) complex 35 (29) [57]. 

Hydrophosphorylation of alkynes via external attack of //-phosphonate to an (alkyne)metal complex is a possible pathway, although the possibility has been concluded to be less likely as far as the nickel-catalyzed reaction is concerned [12]. However, such a process appears to proceed in early transition metal carbonyl-catalyzed reactiOTis [19]. For instance, refluxing a mixture of phenylacetylene, HP(0)(0Et)2, and Mo(CO)fi (10 mol%) affords the franr-addition product... 

It is also important to note that the hybrid calixphyrin-palladium and -rhodium complexes catalyze the Heck reaction (p-bromobenzaldehyde with n-butyl acrylate in A, A -dimethylacetamide at 100 °C) and hydrosilylations (acetophenone with Ph2SiH2 and of phenylacetylene with PhMe2SiH), respectively, with high efficiency. The present results demonstrate the potential utility of the phosphole-containing hybrid calixphyrins as highly promising hemilabile macrocyclic ligands for the construction of efficient transition-metal catalysts [160, 162]. 

---