Manganese complexes acetylenes

The ease with which olefins form complexes with metals naturally led to investigation of acetylenes as ligands but until recent years only a few ill-defined, unstable acetylene complexes of copper and silver were known. Now complexes of acetylenes with metals of the chromium, manganese, iron, cobalt, nickel, and copper subgroups are known. These complexes fall naturally into two classes—those in which the structure of the acetylene is essentially retained and those in which the acetylene is changed into another ligand during complex formation. Complexes of the first class are discussed here and the second class is discussed in Section VI. 

Reversible adsorption and desorption of the acetylene is possible under suitable conditions. However, using the corresponding low molecular weight manganese complexes such as MeCpMn(CO)3 and CpMn(CO)3 (Cp = cyclopentadienyl ring), the acetylene complex could hardly be prepared due to instability of the acetylene complex. 

Manganese group metals form the acetylene complexes [Mncp(RCCR)(CO)2], which are analogous to olefin compounds, as well as [ReCl(RCCR)2] and [ReCl(RCCR)(PPh3)]. ... 

Ethylenic complexes analogous to these acetylene complexes, 8.1, are known and it seems a reasonable assumption that the acetylene-metal bond should resemble the ethylene-metal bond in these complexes. Thus the acetylene, which has two orthogonal / 3i-bonds, would use one filled / jr-bond to donate to the manganese and back-donation from the metal would take place mainly into the corresponding anti-bonding />jr -bond of the acetylene. A number of acetylene-platinum complexes are known in which again it may be assumed that the acetylene-metal bond is similar... 

Carbonyl insertions into metallocarbenes have previously been observed for several different metals, including iron48 (see Section VI,C) and manganese.49 Indeed, carbonyl insertions into chrominum and tungsten diphenyl-carbenes have been shown to be viable processes.50 Most importantly, Wulff has isolated51 an 774-vinylketenecobalt (I) complex from the reaction between a cobalt carbene and an acetylene, a transformation that necessitates such a carbonyl insertion (see Section V,B). 

The first metal-olefin complex was reported in 1827 by Zeise, but, until a few years ago, only palladium(II), platinum(Il), copper(I), silver(I), and mercury(II) were known to form such complexes (67, 188) and the nature of the bonding was not satisfactorily explained until 1951. However, recent work has shown that complexes of unsaturated hydrocarbons with metals of the vanadium, chromium, manganese, iron, and cobalt subgroups can be prepared when the metals are stabilized in a low-valent state by ligands such as carbon monoxide and the cyclopentadienyl anion. The wide variety of hydrocarbons which form complexes includes olefins, conjugated and nonconjugated polyolefins, cyclic polyolefins, and acetylenes. 

It is stated (116, 118) that manganese carbonyl gives a series of very stable complexes on treatment with acetylenes, but no details have been published. 

Metal cluster complexes containing vinylidene ligands have been considered as models of species present when olefins or alkynes are chemisorbed on metal surfaces (114). Vinylidene has been detected in reactions of ethylene or acetylene with Fe(100), Ni( 111), and Pt(l 11) surfaces (115), and was shown to be an intermediate by theoretical studies on a manganese surface (116). The facile cleavage of C-H bonds which occurs in these systems, together with hydrogen addition or abstraction, also occurs on metal clusters. Typical of the reactions considered is the hydrogen transfer reaction... 

It is perhaps first appropriate to consider how the coordination chemistry of lesser unsaturated derivatives evolved. In pioneering work by Coffield and his coworkers, it was demonstrated that reaction of acetylene with manganese pentacarbon-yl or methylmanganese tetracarbonyl under autoclave conditions led to production of the complex 174 (Scheme 28).248) The cyclopentadienyl unit in 174 is of course... 

Finally, it merits to be highlighted that, despite the relatively large number of phosphonioacetylide complexes reported to date, the reactivity of these species remains almost unexplored, the scarce data presently available preventing any conclusion on the chemical behavior of the coordinated R3P C C framework. Thus, while the Ph iP C—f unit remained unaltered after treatment of the manganese complex 76 with bromine, an unusual behavior for acetylenic compounds that confirms the heterocumulenic [MnBr(CO)4(=C=CPPh3)] character of this complex [75], the in situ formed nickel derivative [NiCl2(C=CP( -Bu)3 P(n-Bu)3 ] readily reacted with an excess of dichloroethyne to afford 87 (Fig. 16) through a classical [2-I-2-I-2] alkyne-cyclotrimerization process [86]. 

Manganese complexes (87) of dialkylarylphosphine sulphides have been prepared as dimers or monomers depending on the nature of the phosphorus substituents.39 The reactions of (87) with acetylene... 

A mixture of propylene oxide, (trimethylsilyl)manganese pentacarbonyl, and methyl acrylate in ether allowed to react for 24-96 h in a polypropylene syringe pressurized at 5 kbar intermediate siloxymanganese carbonyl complex (Y 82%), in acetonitrile irradiated (350 nm) at room temp, for 1-12 h, then hydrolyzed with water product (Y 53%). Acetylene derivs. furnished enones which were converted to cyclopent-2-enones. F.e. and stereoselectivity s. P. DeShong, D.R. Sidler, J. Org. Chem. 53, 4892-4 (1988). 

Olefins which undergo this reaction are 1-butene, 2-butene, isobutylene, a mixture of pentene isomers, diisobutylene, and tetrapropylene. Coffield et al. 82, 83) have shown that acetylene and manganese pentacarbonyl under 600 psi and at 150° C give l,2-(propenylene)cyclopentadienylmanganese tricarbonyl. The conditions of this synthesis are similar to those described by Reppe 84) for the reaction of acetylene with other metal carbonyls to form iT-bonded complexes. 

Ph2Mn reacts with an acetylene compound (Me-C=C-Me) and the cyclo-trimerized manganese complex is isolated by adding aqueous sodium tetra-phenylboron as shown in eq. (14.14) [28]. 

N. E. Kolobova, L. L. Ivanov, O. S. Zhvanko, V. F. Sizoi, and Yu. S. Nekrasov, Izv. Akad. Nauk SSSR, Ser. Khim., 1979, 2393. Syntheses of phosphorylide complexes of manganese. Complexes of type [Mn C(PPh3)CHC02MeKC0)2( j-C5H5)] prepared by addition of phosphine to acetylene adducts. 

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