Rhodium complexes acetylene

Similar reactions have been carried out on acetylene. Aldehydes add to alkynes in the presence of a rhodium catalyst to give conjugated ketones. In a cyclic version of the addition of aldehydes, 4-pentenal was converted to cyclopen-tanone with a rhodium-complex catalyst. In the presence of a palladium catalyst, a tosylamide group added to an alkene unit to generate A-tosylpyrrolidine derivatives. ... 

In contrast to the reaction of an i72-CS2-rhodium complex with dimethyl acetylenedicarboxylate which gives rise to a metallocycle,186 the iron complexes 103 are converted by activated acetylenes into air-sensitive carbene complexes 104. Decomposition of the latter in air provides an unusual synthetic route to substituted tetrathiofulvene derivatives (Scheme 121).187... 

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. 

In less-coordinating solvents such as dichloromethane or benzene, most of the cationic rhodium catalysts [Rh(nbd)(PR3)n]+A (19) are less effective as alkyne hydrogenation catalysts [21, 27]. However, in such solvents, a few related cationic and neutral rhodium complexes can efficiently hydrogenate 1-alkynes to the corresponding alkene [27-29]. A kinetic study revealed that a different mechanism operates in dichloromethane, since the rate law for the hydrogenation of phenyl acetylene by [Rh(nbd)(PPh3)2]+BF4 is given by r=k[catalyst][alkyne][pH2]2 [29]. 

A moderate pressure (>5 atm.) of CO in the reaction system leads to the selective formation of 29, while alkynes undergo rhodium-catalyzed hydrosilylation with a hydrosilane to afford vinylsilanes in the absence of CO. The presence of the rhodium complex is crucial for the smooth progression of siiyiformyiation, regardless of the presence of mononuclear or polynuclear complexes. This generalization is supported by the studies of many others [15]. The most important feature of this reaction is the excellent regioselectivity, which favors the formylation of the internal sp-carbon of the acetylenic bond of terminal... 

We have explored two types of carbon-carbon bond forming reactions operated under almost neutral conditions. Both reactions are initiated by the formation of an H-Rh-Si species through oxidative addition of a hydrosilane to a low-valence rhodium complex. Aldol-type three-component couphngs are followed by the insertion of an a,yS-unsatu-rated carbonyl compound into a Rh-H bond, whereas silylformylation is accomplished by the insertion of an acetylenic moiety into a Rh-Si bond. 

A bimetaUic rhodium complex has also been employed for the cyclotrimerization of (trifluoromethyl)acetylene 45 at room temperature to afford 1,3,5-trifluoromethyl-benzene 46 in good yield (Eq. 13) [32]. 

Similar reactions have been carried out on acetylene.563 In a cyclic version of the addition of aldehydes, 4-pentenal was converted to cyclopentanone with a rhodium-complex catalyst.564... 

In 2001, Van den Hoven and Alper reported the unexpected 2(Z)-6(ft)-47/-[l,4]-thiazepin-5-one 215, as the major product, from the reaction of acetylenic thiazole 214 with carbon monoxide and hydrogen in presence of a zwitterionic rhodium complex and triphenyl phosphite. After optimization of the reaction condition, the pressure, and the temperature, up to 90% yield is achieved with good selectivity for thiazepine 215 over thiazole side products 216-218 (Scheme 38) <2001 JA1017>. 

For the intermolecular hydroacylation of olefins and acetylenes, ruthenium complexes - as well as rhodium complexes - are effective [60-64]. In 1980, Miller reported the first example of an intermolecular hydroacylation of aldehydes with olefins to give ketones, during their studies of the mechanism of the rhodium-catalyzed intramolecular cydization of 4-pentenal using ethylene-saturated chloroform as the solvent [60]. A similar example of the hydroacylation of aldehydes with olefins using ruthenium catalyst is shown in Eq. 9.43. When the reaction of propionaldehyde with ethylene was conducted in the presence of RuCl2(PPh3)3 as the catalyst without... 

Palladium chloride and metallic palladium are useful for carbonylating olefinic and acetylenic compounds. Further, palladium is active for decarbonylation of aldehydes and acyl halides. Homogeneous decarbonylation of aldehydes and acyl halides and carbonylation of alkyl halides were carried out smoothly using rhodium complexes. An acyl-rhodium complex, thought to be an intermediate in decarbonylation, was isolated by the oxidative addition of acyl halide to chlorotris(triphenylphosphine)rhodium. The mechanisms of these carbonylation and decarbonylation reactions are discussed. 

Joo et al. utilized the highly water-soluble rhodium complex [RhCl(CO)(TPPTS)2] for the polymerization of terminal alkynes (phenylacetylene and (4-methylphe-nyl)acetylene for the structure of TPPTS cf. Section 7.2.2.3) [150]. This catalyst selectively produces cis-transoid polymers at room temperature in homogeneous solution in water/methanol mixtures, as well as in biphasic mixtures of water and chloro-... 

Acetylenic ketones of type (1) are decarbonylated to give the coupled product (2) when heated for many hours with the rhodium complex in benzene or xylene solution. In contrast with decarbonylation of aldehydes, an equivalent of the rhodium complex is required.12... 

A mechanism is proposed to accommodate the observed stereoselectivity. The mechanism includes a first silicon shift to an acetylenic bond and a carbene-type zwit-terionic rhodium complex (7) as the key intermediate, which undergoes isomerization from a higher energy form (Z-complex, 6) to a lower energy form ( -complex, 8) followed by reductive elimination to cis-isomer (3) as the kinetic product. 

Tributyltin hydride adds to terminal acetylenes in the presence of triethylborane to give mixtures of E)- and (Z)- alkenes, in which the tin atom is attached to C(l), e.g. equation 40215,216 reverse regiochemistry is observed in the reaction of tributylstannane with terminal acetylenes in the presence of rhodium complexes, e.g. [RhCl (1,5-cyclooctadiene)]2, to yield exclusively the adducts 297. ... 

Table 12-3. Same characteristics of rhodium complexes attached to phosphynated CSSDVB (2% DVB) and their activities in butadiene and acetylene hydrogenation. ...

It is tempting to speculate that only for the dinuclear complexes of iridium is there initial formation of a dihydrido-complex, which subsequently reacts with an alkene to form an alkyl intermediate, or with an alkyne to form an alkenyl intermediate. If such is the case, the activity of dinuclear rhodium complexes must depend on initial formation of an alkyne or alkene complex, which would then react with hydrogen. There exists some evidence for such a scheme. The successive hydrogenation of alkynes and alkenes " suggests that activation of an alkene is inhibited by an alkyne, probably by preferential coordination of the latter. Further, complexes (VII, X = H) or (IX) do not alone react with hydrogen, but do so after reaction with an alkyne (acetylene or phenylactylene). ... 

In 1996, Garcia et al. reported cyclotrimerization of (trifluoromethyl)acetylene 390a using a bimetallic rhodium complex at room temperature to afford l,3,5-/ra (trifluoromethyl) benzene 391 in high yield (Scheme 2-33). Recently, Tanaka et al. reported a chemoselective and regioselective intermolecular cross-cyclotrimerization of two different alkynes using a cationic Rh complex as catalyst (Scheme 2-34). ° ... 

Ferrocene was the first organometallic guest incorporated and numerous spectroscopic and electrochemical studies have been performed on ferrocene, substituted ferrocene, and related metallocene (e.g. cobaltocene) inclusion complexes (444-469]. Half-sandwich cyclopentadienyl- and benzene-metal carbonyl complexes have also been studied quite extensively [470-479] as have // -allyl metal (palladium) complexes [480], diene metal (rhodium) complexes [481-484], acetylene cobalt carbonyl cluster complexes [485], and complexes with metal carbonyls, e.g. Fe(CO)5, Mn2(CO)io, and CoNO(CO)3 [485a]. 

---