Olefin synthesis complexation

Problems of dilution and pH sensitivity have also been encountered in the synthesis of cts-[Pt(S-R2SO)(olefin)Cl2] complexes (85), where deoxygenation of the sulfoxide with concomitant oxidation of the metal center occurs at low pH. The reactions of [M(Ph2PCH2CH2PPh2)Cl2] (M = Pd, Pt) with one equivalent of silver perchlorate in the presence of Me2SO yield either the O-Me O complex or its deoxygenation product, depending upon reaction conditions. A sequence of reactions, Eq. (27), has been proposed (143). 

Recently, catalyst 50 (n > 4) was reported highly active and selective for olefin synthesis from alkyl halides with aqueous sodium or potassium hydroxide without the formation of by-product alcohols 172). The active catalyst structures were suggested to involve self-solvated polymeric alkoxides 173) 52 and/or complexed hydroxides 53. 

During their work on the arylation of aromatic compounds by substitution, Fujiwara, et al. observed biaryl formation when aromatic compounds were placed in the presence of olefin-palladium complexes and silver nitrate.80 Developing this reaction as a method for biphenyl synthesis, these authors showed that the more stable the olefin-palladium complex was, the lower the yield. Ethylene dichloropalladium proved to be the best choice, when used with silver nitrate. However, the reaction required stoichiometric amounts of both catalysts (Scheme 10.47). Benzene derivatives substituted by electron-donating or -withdrawing groups reacted as well, but a mixture of regioisomers was produced, except for nitrobenzene, which only gave m,m -dinitrobiphenyl. 

He received his Ph.D. in summer 1940 and firmly wished to stay in fundamental research. He was offered a post at St. Andrews University which he could not take up because of World War II. Instead he was assigned to a war problem at Cambridge involving the synthesis of the then unknown 1,3,5,7-tetranitro-naphthalene, which Sir Robert Robinson anticipated to be an exceptionally effective explosive. In 8 months he managed to make 100 g of the compound but was then dispatched to the Research Department of Woolwich Arsenal, at that time evacuated to the University College at Swansea. There he spent most of his time in the library where he eventually found R. N. Keller s review on olefin metal complexes [3]. He remembered that Mann had mentioned in his lectures that olefins were the only ligating species that did not possess a lone pair of electrons, which prompted him to work on their complexes as soon as he was free to do so. 

While a great number of tricarbonyl( -diene)iron complexes have been reported and their reactivity investigated, much less is known of the corresponding heterodiene complexes. In recent years, synthesis of several tricar-bonyl(heterodiene)iron systems involving r] coordination of the heterodiene unit has been achieved. Among the tetracarbonyl(/ -olefin)iron complexes prepared by Weiss was tetracarbonyl(cinnamaldehyde)iron, which converts on heating to the //-bonded tricarbonyl(cinnamaldehyde)iron. The preparation and synthetic utility of (benzylideneacetone)tricarbonyl iron, an analogous complex of an ar,/9-unsaturated ketone, are reported here. 

Warren continues to extend his phosphine oxide-based method of stereoselective olefin synthesis. The previously published method of acyl transfer followed by borohydride reduction to give selectively the threo-hydroxyalkylphosphine oxide intermediate has now been applied to more complex examples carrying other chiral centres.28 Optically active butyl(2-methoxyphenyOphosphine oxide (47) has been used to provide a chiral... 

Cyclization via intramolecular olefination of complex phosphonates remains the most important method of synthesis for complex natural macrocycles. Examples include syntheses of 20-membered macrolide antibiotic, aglycones of venturicidins A and B,108 oleandomycin (a 14-membered macrolide antibiotic), 109 the 19-membered macrocyclic antibiotic, anti-tumour agent (-t-)-hitachimycin,ll0 and the macrocyclic lactones (183).1H Cyclization of the phosphonate (184) under Masamune-Roush conditions has been used to synthesize the 28-membered macrolactam myxovirescin B.112... 

An interesting synthesis of isocoumarins uses the n-allyl nickel halides and n-olefin palladium complex, while another involves an aromatic nucleophilic substitution by the carbanion derived from acetone... 

The preparation of PtCl2(CH=CH—CN)2 from CH2=CH—CN and triethylammonium chloroplatinate(II) may illustrate a different method for the photochemical synthesis of olefin metal complexes 308>. 

Thus, the silene reaction with ketones represents a formal analogy of the Wittig olefin synthesis. Silanone is believed to be formed, since its trimer and other oligomers are isolated from the final product mixtures. Thermal reactions of the known stable 2-siloxetanes are quite complex, but at least in some cases the expected olefin is formed110,244. 

M. Orchin University of Cincinnati) Some very recent work done in our laboratory by Lawrence Kirch strongly suggests that an olefin-hydrocarbonyl complex is the important intermediate in the oxo synthesis. This new evidence was made possible by the experimental technique of quenching the hot, pressured autoclave in dry ice and releasing the gases below — 50°. The results of this work (1) show that (a) dicobalt octacarbonyl is rapidly converted to cobalt hydrocarbonyl (6) the hydrocarbonyl is rapidly complexed by olefin (c) when the olefin is consumed by normal oxo reaction, the cobalt again appears as the hydrocarbonyl (d) the extent of conversion of dicobalt octacarbonyl to cobalt hydrocarbonyl is dependent on the hydrogen partial pressure. 

Compounds Ni(olefin)2 have significant application in catalysis. Olefin-carbonyl complexes of the type [Ni(CO)j, (olefin) ] are not known. Their existence as unstable intermediate compounds in many reactions results from catalytic properties of tetracarbonylnickel in olefin oligomerization processes, oxo synthesis, olefin isomerization, etc. 

Indenylidene complexes have also made their mark in ruthenium olefin metathesis complexes. First noticed by Nolan and coworkers [48] and Furstner et al. [49], these complexes were developed by Nolan and coworkers [50,51] to afford the very stable second-generation complexes 14 (with NHC ligands). More recently, Schrodi and coworkers [52] and Bruneau and coworkers [53,54] presented chelated indenylidene complexes 15 and 16 (Figure 11.5). The relatively fecile methodology for their synthesis and their increased stability certainly makes the indenylidene complexes another well-studied family in the rutheniiun olefin metathesis catalyst field. 

The role of palladium in organic synthesis continues to be explored and exploited. Enol stannanes are monoalkylated by allylic acetates in the presence of tetrakis(triphenylphosphine)palladium, Enol stannanes give higher selectivity for monoalkylation than enolate ions or silyl enol ethers. High regioselec-tivity is observed for alkylation at the less substituted end of the allyl moiety. Olefins, after complexation to palladium(ll), alkylate enolate anions. The organopalladium product may be converted into saturated ketones, or into enones by /3-elimination, or acylated with carbon monoxide (Scheme... 

In fact, Wacker type oxidations (largely applied for aldehyde synthesis, acetoxylation reactions) can be considered as an intra or, more probably according to the recent literature, as an out-of-sphere nucleophilic attack on a palladium-olefin 7r-complex. 

As is apparent from the preceding discussion, a full understanding of the observed diastereoselectivity in dihydroxylation reactions of acyclic allylic alcohols remains elusive. Thus, the use of any one model is insufficient, and a careful analysis of the steric and electronic particulars of a given substrate must be conducted. Nevertheless, an impressive number of diastereoselec-tive dihydroxylations of acyclic olefins in complex molecule synthesis attest to the central role of this transformation [42, 43], Selected examples of stereodivergent dihydroxylations reported by Danishefsky are showcased in Schemes 9.36 and 9.37 [201]. Dihydroxylation of ( )- and (Z)-unsaturated esters 287 and 290, respectively, thus proceeded with excellent diastereoselectivity. Danishefsky has proposed a transition state model based on the ground state conformations of the starting materials as determined by X-ray analysis. The dihydroxylations were thus postulated to occur from the sterically less hindered faces of the olefins, as depicted in 288 and 291. Diol 292 was subsequently converted into N-acetylneuraminic acid (293). 

Nickel(O) forms a n-complex with three butadiene molecules at low temperature. This complex rearranges spontaneously at 0 °C to afford a bisallylic system, from which a large number of interesting olefins can be obtained. The scheme given below and the example of the synthesis of the odorous compound muscone (R. Baker, 1972, 1974 A.P. Kozikowski, 1976) indicate the variability of such rearrangements (P. Heimbach, 1970). Nowadays many rather complicated cycloolefins are synthesized on a large scale by such reactions and should be kept in mind as possible starting materials, e.g. after ozonolysis. 

---