Acetylene complexes alkyne addition

Instances in which cyclobutadiene complexes are the major products from the reactions of acetylene complexes with additional alkyne are uncommon. These generally have been found to be significant products with sterically hindered alkynes and with palladium and platinum metals. For example, phenyl tert-butyl acetylene was converted to the corresponding cyclobutadiene complex (one isomer) upon treatment with (PhCN)2 PdCl2 (Hos-okawa and Moritani, 1969) [Eq. (71)]. With sterically less demanding tolane,... 

As may be anticipated from the chemistry of the related iron complex, which has been extensively reviewed (108), the interaction of alkynes with both Ru3(CO)i2 and Os3(CO)j2 leads to a range of complexes involving addition of one or more acetylenic units to the cluster. 

Pyrrole and indole rings can also be constructed by intramolecular addition of nitrogen to a multiple bond activated by metal ion complexation. Thus, 1-aminomethyl-l-alkynyl carbinols (obtained by reduction of cyanohydrins of acetylenic ketones) are cyclized to pyrroles by palladium(II) salts. In this reaction the palladium(II)-complexed alkyne functions as the electrophile with aromatization involving elimination of palladium(II) and water (Scheme 42) (81TL4277). 

As delineated above, hydroarylation of electron-poor alkynes such as acetylene carboxylic acid ethyl ester 4 is best catalyzed by Au(I) complexes. In addition to the previously mentioned Ph3PAuCl/BF3-OEt2, several other Au(I)-complexes have been shown to be active catalysts, if activation by silver salts or Lewis acids is ensured [2, 4]. Remarkably, the Au(I)-precursor LAuCl can be prepared in situ by reacting AuCl with a phosphorus ligand. 

S.8.2.7.3. ri (7-Vinyl Complexes by Addition of Alkynes to Metal Hydrides The stereochemistry of the acetylene insertion into the M—H bond ... 

Recently Miyaura and co-workers have reported a trans-hydroboration of terminal alkynes using [Rh(COD)Cl]2[PCPr)3]4 or [Ir(COD)Cl]2[P( Pr)3]4 (eq 13). Mechanistic studies via deuteriumlabeling show that after the oxidative addition of the alkyne to the metal, the acetylenic deuterium undergoes migration to the S-carbon resulting in the formation of a vinylidene metal complex. Oxidative addition of borane to the metal complex and 1,2-... 

Linear Alkenes and Alkynes.— Addition of Bu NC to bishexafluorobut-2-yne complexes [M(X)(CF3C2CF3)2( -C6H5)] (M=Mo, X CFa M=W, X=C1) results in cyclization of the two acetylenes and Bu NC to give (1). Under certain conditions the intermediate (2) can be isolated which illustrates that the cyclization reaction probably requires prior co-ordination of the isocyanide to the metal. 

Nucleophilic attack by a carbanion on a rhodium-acetylene complex has been postulated in the reaction of tolane with MeMgBr in the presence of (Ph3P)3 RhBr (Michman and Balog, 1971). This interpretation is supported by the known formation of rhodium-alkyne complexes under these conditions (Muller and Segnitz, 1973) and by the predominant formation of trans-a-methyl-stilbene. Additional study of the scope of this reaction would seem worthwhile since recycling of the rhodium-containing by-product (Ph3P)3 RhOH, should be possible. 

The Pt(II)-acetylene complexes have been studied most thoroughly in this respect. Clark and his co-workers have considered the importance of the nature of the alkyne, the coordination geometry of the metal, ancillary ligands, etc., on the rate of M—R addition. In general, it appears that electron-deficient alkynes undergo addition more readily. Thus, it was observed that, whereas the diphenylacetylene complex (VIII) (R = Ph), is stable in refluxing benzene for two days, the corresponding perfluoro-2-butyne and acetylenedicarboxylate complexes (R = CF3, COjMe) are not isolable but... 

The interaction of isocyanides with acetylene complexes has been found to produce various organic and organometallic products differing in the number of alkyne and.isocyanide units incorporated. Cp(Ph3P)Co(PhC2Ph) reacts with two equivalents of isocyanide to form the diimino cobaltacycle (XVni) (Yamazaki et aU 1975). Further reaction of these complexes with additional isocyanide led to the novel cyclopentene derivatives (XIX). These... 

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. ... 

The intramolecular addition of the O-H bond to alkynes catalyzed by palladium complexes has been developed by K. Utimoto et al. (Eq. 6.59) [104]. An alkynyl alcohol can be converted to a cyclic alkenyl ether in the presence of a catalytic amount of [PdCl2(PhCN)2 or [PdCl2(MeCN)2] in ether or THE at room temperature. When the reaction was carried out in MeCN-H20 under reflux in the presence of a catalytic amount of PdCl2, hydration of the acetylenic alcohol occurred and the ketoalcohol was obtained in good yield instead. 

In a manner similar to OsH(OH)(CO)(P Pr3)2, the hydride-metallothiol complex OsH(SH)(CO)(P Pr3)2 adds Lewis bases that are not bulky such as CO and P(OMe)3 to give the corresponding six-coordinate hydride-metallothiol derivatives OsH(SH)(CO)L(P Pr3)2 (L = CO, P(OMe)3). OsH(OH)(CO)(PiPr3)2 and OsH(SH)(CO)(P Pr3 also show a similar behavior toward dimethyl acetylenedi-carboxylate. Treatment of OsH(SH)(CO)(P Pr3)2 with this alkyne affords 6sH SC(C02Me)CHC(OMe)6 (CO)P Pr3)2, which is the result of the tram addition of the S—H bond to the carbon-carbon triple bond of the alkyne. Phenyl-acetylene, in contrast to dimethyl acetylenedicarboxylate, reacts with OsH(SH) (CO)(P Pr3)2 by insertion of the carbon-carbon triple bond into the Os—H bond to give the unsaturated alkenyl-metallothiol derivative Os ( )-CH=CHPh (SH) (CO)(P Pr3 )2, the inorganic counterpart of the organic a, (3-unsaturated mercaptans (Scheme 46).92... 

DFT calculations confirmed the similarities with the alkyne/vinylidene transformation but have revealed that additional parameters were essential to achieve the isomerization [8, 20-23]. The hydride ligand on the 14-electron fragment RuHC1L2 opens up a pathway for the transformation similar to that obtained for the acetylene to vinylidene isomerization. However, thermodynamics is not in favor of the carbene isomer for unsubstituted olefins and the tautomerization is observed only when a re electron donor group is present on the alkene. Finally the nature of the X ligand on the RuHXL2+q (X = Cl, q=0 X = CO, q=l) 14-electron complex alters the relative energy of the various intermediates and enables to stop the reaction on route to carbene. 

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