Acetylenes with metal carbonyls

These compounds have been obtained indirectly by reactions of silylated acetylenes with metal carbonyls or olefin complexes. Thus, trimethylsilylphenylacetylene reacts with rj5-cyclopentadienylcobalt dicarbonyl, cobaltocene, or rjs-cyclopentadienyl-(l,3-cyclooctadiene) cobalt, in refluxing xylene, to give a mixture of cis- and trans-bis-(trimethylsilyl)cyclobutadiene complexes (R = Me, R = Ph) 68, 127, 137) ... 

Mass spectrometry has proved extremely useful in determining the composition of various polyferrocene products such as those formed by trimerization of ferrocenylacetylenes (180), reactions of ferrocenyl-acetylenes with metal carbonyls (175), oxidative coupling of ferrocenyl polyacetylenes (179), and lithiation of ferrocene (186). The 1,12-dimethyl-[l,l]ferrocenophane (XC) shows a very strong molecular ion and fragments [M—Me]+ [M—2 Me]+ and the doubly charged species M2+, [M —Me]2+, and [M —2 Me]2+ (197). 

Metalocycles are also formed by the reaction of acetylenes with metal carbonyls or with isonitrile complexes (3, 73, 99-102). Their formation may involve monohaptoacetylene intermediates. 

The reactions of acetylenes with metal carbonyls can be briefly mentioned at this point. Although a number of acetylene-transition metal complexes is known, in the vast majority of reactions involving metal carbonyls and acetylenes, the latter are converted into other ligands (often dienes) which in turn undergo complex formation. Reactions of this sort also often lead to new uncoordinated organic compounds and have been of distinct importance in organic synthesis. 

The reactions of acetylene with metal carbonyls can be grouped into two main classes (i) those in which no new C—C bonds are formed, and the acetylene is bonded to the metal atom(s) by /r-bonds, bent a bonds, or by a combination of p and a bonds, and (ii) those in which new C-C bonds are formed by combination of some of the CO with the acetylene to form a cyclic hydroxy-ligand or a lactone ring. 

Substituted cyclopentadienones react with iron carbonyls to form stable, diamagnetic 7r-co triplexes of the type [Fe(CO)3(cyclopentadienone)] (215). The proposed structure is shown in (XX). These complexes undergo reactions typical of metal carbonyls, e.g., displacement of carbon monoxide by tertiary phosphines, but the carbonyl group of the ligand does not show reactions characteristic of a keto-group. These complexes are also formed by interaction of acetylenes with iron carbonyls (see Section VI,C). Interaction of tetracyclone and Fe3(CO)i2 gives unstable complexes which contain the sandwich anion [Fe(tetracyclone)2]2 analogous to the anion (XXV) (215). 

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]. 

Acetylenes and olefins may react with metal carbonyls, metal halides, or other transition metal compounds to give cyclopentadienyl complexes [equations (9.44)-(9.46)]. 

A particular acetylene can afford various products depending on the conditions. Diphenylacetylene in the presence of water, acetic acid, and alcohol, affords 38% traw -PhCH C(Ph)COOH and 10% of its ethyl ester (5). Tolane can also be carbonylated in alkaline solutions (8) where a complex carbonylate, possibly Ni3(CO)8 , is the source of carbon monoxide. Under these conditions tetraphenylbutadiene is isolated in addition to ra x-PhCH=C(Ph)COOH. The carbonylation of diphenylacetylene in dioxane in the presence of absolute alcohol and concentrated hydrochloric acid affords l,2,3,4-tetraphenyl-2-cyclopentene-l-one (9). Finally, in inert solvents diphenylacetylene reacts with nickel carbonyl, forming both tetraphenylcyclopentadienone and a n complex, bis(tetra-phenylcyclopentadienone)-nickel (10) (see Section VI). Since cyclopenta-dienones are often formed by treating alkynes with metal carbonyls other than nickel carbonyl the carbonylation reaction with this carbonyl must be closely related. The only difference apparently arises from the presence of... 

Ghromium trichloride tri(tetrahydrofuranate) stirred under Ng into tetra-hydrofuran, treated dropwise at —20° with ethylmagnesium bromide in tetra-hydrofuran, the resulting clear triethglchromium soln. treated at —20° with 2-butyne, and allowed to stand 3 days at room temp. hexamethylbenzene. Y 60% based on chromium compound.—These condensations are considered to proceed via acetylenic yr-complexes of chromium and are useful as a general synthetic method. F. e. s. W. Herwig, W. Metlesics, and H. Zeiss, Am. Soc. 81, 6203 (1959) with metal carbonyl compounds, particularly [Go(GO)4]2Hg, s. W. Hiibel and G. Hoogzand, B. 93, 103 (1960). 

Although stoichiometric ethynylation of carbonyl compounds with metal acetyUdes was known as early as 1899 (9), Reppe s contribution was the development of catalytic ethynylation. Heavy metal acetyUdes, particularly cuprous acetyUde, were found to cataly2e the addition of acetylene to aldehydes. Although ethynylation of many aldehydes has been described (10), only formaldehyde has been catalyticaHy ethynylated on a commercial scale. Copper acetjlide is not effective as catalyst for ethynylation of ketones. For these, and for higher aldehydes, alkaline promoters have been used. 

This observation may well explain the considerable difference between metal-olefin and metal-acetylene chemistry observed for the trinuclear metal carbonyl compounds of this group. As with iron, ruthenium and osmium have an extensive and rich chemistry, with acetylenic complexes involving in many instances polymerization reactions, and, as noted above for both ruthenium and osmium trinuclear carbonyl derivatives, olefin addition normally occurs with interaction at one olefin center. The main metal-ligand framework is often the same for both acetylene and olefin adducts, and differs in that, for the olefin complexes, two metal-hydrogen bonds are formed by transfer of hydrogen from the olefin. The steric requirements of these two edgebridging hydrogen atoms appear to be considerable and may reduce the tendency for the addition of the second olefin molecule to the metal cluster unit and hence restrict the equivalent chemistry to that observed for the acetylene derivatives. 

In the Favorski reaction [8], etbyne is coupled with a carbonyl compound in the presence of powdered alkali hydroxide suspended in an organic solvent, in which the acetylene has good solubility. Some acetylenic carbinols, derived from ketones, can be obtained in high yields by introducing acetylene at atmospheric pressure. The active intermediate possibly is a metal acetylide formed in low concentration. 

In the metal carbonyl catalysts, the use of a catalytic amount of Ph2CCl2 enables the omission of CGI4. For example, the polymerization of phenylacetylene with W(CO)6 in the presence of Ph2GGl2 in toluene upon photoirradiation proceeds homogeneously to give a polymer with of ca. 2 x 127,128 MW polymers > 10 ) are attainable from sterically bulky aromatic and aliphatic acetylenes. It is also effective to use a catalytic amount of Lewis acids instead of GGI4 in the M(GO)6-based catalysts (M = W, Mo). ... 

Several cyclopentadienyl(alkyl)metal carbonyl derivatives have reacted with acetylenes. In some examples, insertion reactions may also be involved, although the mechanisms have not been investigated. Cyclopentadienyl(methyl)iron dicarbonyl with diphenylacetylene gave a 10% yield of cyclopen tadienyltetra-phenylcyclopentadienyliron 71). 

This review deals with metal-hydrocarbon complexes under the following headings (1) the nature of the metal-olefin and -acetylene bond (2) olefin complexes (3) acetylene complexes (4) rr-allylic complexes and (5) complexes in which the ligand is not the original olefin or acetylene, but a molecule produced from it during complex formation. ir-Cyclopentadienyl complexes, formed by reaction of cyclopentadiene or its derivatives with metal salts or carbonyls (78, 217), are not discussed in this review, neither are complexes derived from aromatic systems, e.g., benzene, the cyclo-pentadienyl anion, and the cycloheptatrienyl cation (74, 78, 217), and from acetylides (169, 170), which have been reviewed elsewhere. 

Very few such compounds are known. Three general procedures can be used for their preparation (a) addition of the olefin to a transition metal compound (b) replacement of carbon monoxide in metal carbonyls and (c) migration of organosilicon groups from metal to ligand in some reactions of silylmetal compounds with acetylenes. 

---