Enneacarbonyls

The syntheses of many Co3(CO)9X compounds from dicobalt octacarbonyl and XCCI3 have been optimized 347), and further reactions starting from 0(60)4 and XCCI3 360), or RCF —Co(CO)4 46) have been investigated in order to determine the mechanism of formation of the clusters. Methinyltricobalt enneacarbonyls are also formed from Co2(CO)g and such apical carbon precursors as acetylenes 140), dimethyl ketene 408), or carbyne chromium complexes (7 73). In several cases (7 72, 

A maximum of six CO groups are replaced by three S2C2(CF3)2 molecules in Co3(CO)gCX to give L3Co3(CO)3CX clusters for which no structure was suggested 232). 

Arenes replace three CO groups from one basal cobalt atom, as was shown from a crystal structure analysis 53, 137), and the arenes can replace one another 328). 

Of the cyclic olefins, norbornadiene replaces two CO groups from one Co to yield a labile complex 159, 160, 235), cyclooctatetraene replaces the axial CO ligands from all three cobalt atoms 53) and is itself replaced by other Lewis bases 330), and cyclopentadiene forms the unusual complex [95] with Co3(CO)gCMe 159,160). A few catalytic reactions were observed with methinyltricobalt enneacarbonyls including the dimerization of norbornadiene 160, 235) and the polymerization of functional olefins 312) with different Co3(CO)9CX. 

Considerable advances were made in the organic chemistry of the methinyltricobalt enneacarbonyls. It was shown that the C03C core can function as an electron donor as well as an electron acceptor 143), allowing electrophilic and nucleophilic attack at the apical carbon atom. Arenes and Co3(CO)9CHal form Co3(CO)9CAr 

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Methinyltricobait enneacarbonyl compounds preparation, structure and properties. G. Palyi, F. Piacenti and L. Marko, Inorg. Chim. Acta, Rev., 1970, 4,109-121 (94). 

Dellaca, R. J. Penfold, B. R. (1971) Structural studies of derivatives of methinyltricobaJt enneacarbonyls. IV. Crystal structure of hexacarbonoctacobalt tetracosacarbonyl, Cog-(CO)24C6, Inorg. Chem. 10,1269-1275. 

Klanberg, F., Askew, W. B. Guggenberger, L. J. (1968) Preparation and structure of Co3(CO)ioBH2N(C2H5)3, a new tricobalt enneacarbonyl carbon cluster, Inorg. Chem. 7, 2265-2271. 

Methinyitricobalt enneacarbonyl 13 compounds preparation, struc- (94) ture and properties... 

Density functional calculations have been carried out on the addition of H2 to [CH3(0)CCo(CO)3] as well as the product elimination step, in which AcH and HCo(CO)3 are formed.146 Mono-substituted derivatives of phenylmethinyltricobalt enneacarbonyls [PhCCo3 (CO)gL] (L = PPh3, AsPh3, SbPh3) (45) were used as hydroformylation catalysts.147... 

Pyrroles among other products are also formed from diiron enneacarbonyl or molybdenum carbonyl-induced decomposition of the Z-ketovinylazirine... 

A more complicated type of reaction leading to 2-styrylindoles is observed when 2-arylazirines are treated with the rhodium complexes,70 [(Ph3P)2 Rh(CO)Cl] or [Rh(CO)2Cl]2, or with dicobalt octacarbonyl71 (Scheme 42). In contrast, 2-arylazirines with molybdenum hexacarbonyl give pyrazines and dihydropyrazines, and with diiron enneacarbonyl give pyrroles (see Sections V,C,2 and IV,A,1, respectively). The use of relatively low molar ratios of 2-arylazirine to rhodium catalyst (2 1) causes the formation of 2,5-diarylpyrroles. 

Diarylthioketones are converted in good yields into orthometallated complexes by diiron enneacarbonyl.141 These in turn can be transformed oxidatively (Ce4+) or photochemically into isobenzothiophenes (see Section IV,C,2), or by reaction with mercuric trifluoroacetate into isobenzofurans (Scheme 78)142 the formation of methoxy esters is a competing process in... 

Diaryl thioketones are converted by diiron enneacarbonyl into products of orthometallation.141 Oxidative or photochemically induced deligation of these complexes provides an unusual and valuable synthetic entry into compounds in the uncommon isobenzothiophene category142,151 (Scheme 84). Moreover, the photochemical procedure provides the novel complex, (tetracyanoethylene)tetracarbonyl iron. The orthometallated complexes (68) can also be used to prepare isobenzofurans (see Section IV,B,5). 

Diiron enneacarbonyl, 50, 2J Diketones, from diazoketones and organoboranes, 53/ 82 3-DIKETONES FROM METHYL ALKYL KETONES 3-n-BUTYL-2,4-PENTANEDIONE, 51, 90 2,6-Dimethoxybenzaldehyde, by reduction of 2,6-dime thoxy-benzonitrile with Raney nickel alloy in formic acid,... 

The synthesis of metal-coordinated 1-azirines and the reactions of azirines induced by metals have opened a new area in the chemistry of this small ring heterocycle. Many of the reactions encountered bear resemblance to previously discussed thermally and photo-chemically induced reactions of 1-azirines. The reaction of a series of diiron enneacarbonyls in benzene results in coupling and insertion to give diimine complexes and ureadiiron complexes as well as pyrroles and ketones (76CC191). A mechanism for the formation of these products which involves initial 1,3-bond cleavage and generation of a nitrene-iron carbonyl complex as an intermediate was proposed. 

Diiron nonacarbonyl is available from Alpha Inorganics, Inc., or Strem Chemicals, Inc. The submitters made the complex through photolysis of iron pentacarbonyl by the method of King.4 Procedures for preparation are also given by E. H. Braye and W. Hubei, Inorg. Syn., 8, 178 (1966), in which the name diiron enneacarbonyl is used. 

The already voluminous review literature on clusters will be considered as a basis for this review. The topics treated so far are clusters in general (109, 241) and in connection with metal-metal bonding (30, 338, 380), special types of clusters like those with TT-acceptor ligands (231), hydrides (233), carbonyls (85, 86) or methinyl tricobalt enneacarbonyls (313, 317) properties of clusters like structures (56, 316), fluxionality (110), mass spectra (226), vibrational spectra (365), and redox behavior (292). Clusters have been treated in the context of metal carbonyls (3, 4), metal sulfur complexes (2, 381), and in relation to coordination polyhedra (297). Reviews... 

With more and more clusters becoming available, the synthetic chemistry of clusters turns more to the use of clusters as starting materials. Thus, there is an extensive literature on CO substitutions in metal carbonyl clusters and on the organic chemistry of methinyltricobalt enneacarbonyls. Reactions of this type are dealt with in part in Chapter 2.5. and in detail in Chapter 3. 

Cobalt offers many possibilities of cluster-core-geometry, but the chemistry of cobalt clusters is limited, again due to the weakness of first row metal-metal bonds and their susceptibihty to nucleophilic cleavage. Only in case of the methinyl tricobalt enneacarbonyls has a singular chemistry been developed, and therefore these compounds will be treated under a separate heading. 

All other trinuclear cobalt clusters contain triply-bridging ligands. Most of these belong to the structural type 91, which is similar to the methinyl tricobalt enneacarbonyls. Structure 91 is realized with X = S or Se 368) (see [27] in Chapter 2.3.),... 

Iron enneacarbonyl reacts smoothly with 1,1-dimethylsilacyclobutane to insert into the ring Si—C bond with complete regiospecificity (76JCS(D)910). The ferrosilacyclopentane (54) is thermally stable but reacts with HCl, and can also be prepared from 3-chIoropropyI-dimethylchlorosilane and Fe(CO)42. Carbonyl anions will substitute at silicon if this atom bears chlorine, and platinum will insert into the Si—H bond (Scheme 79) (72CC445, 78JOM( 144)317). 

Thiobenzophenone can also serve as a C3S intermediate in the synthesis of some benzo[c]thiophenes. The carbon source in this case is carbon monoxide. Reaction of various thiobenzophenones with diiron enneacarbonyl in benzene at room temperature produced a complex, Ar2CSFe2(CO)6, which could be oxidized to form 2-hydroxy-5-aryl-benzo[c]thiophenes (226e) in 60-80% yield (73JA4905). 

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