Carbonylative dimerization

Nonhomolytic cleavage pathways in the photochemistry of metal-metal bonded carbonyl dimers. A, E. Stiegman and D. R. Tyler, Acc. Chem. Res , 1984,17, 61-66 (36). 

Dihydro-lH-l,2-azaboroles derive from cyclopentadiene by the isoelectronic replacement of a C=C group by a BN moiety ". The neutral rings react in xs boiling Fe(CO)j without any other solvent to form red-brown iron-dihydro-1,2-azaborolyldi-carbonyl dimers as their cis and transisomers in 56% yield, or with CojfCOg in petroleum ether at 60-80°C to the half-sandwich complex (dihydro-1,2-azaborolyl)Co(CO)2 (40%). The CO group can easily be substituted by olefins ... 

Under some conditions carbonyl dimers can give rise to noninsertion products ... 

Metals can be inserted into metal-metal bonds during electrochemical oxidation reactions. The compounds Hg[M(CO),]2 (M = Mn or Re), Hg[Mo(CO)3Cp-T7 ]2 and Hg(Fe(CO)2Cp-i7 ]2 are formed during electrolysis of the carbonyl dimers in dimethoxyethanc with Hg electrodes . The electrolytic syntheses of Zn and Cd derivatives ... 

The carboxytelomerization, a variant to the usual telomerization, is the carbonylation-dimerization of butadiene, carbon monoxide and alcohols. 

Similar acetylene addition reactions take place with bis-cydopentadienylnickel carbonyl dimer (93). Changing from carbonyl to cyanide ligands seems to allow the formation of a true vinyl derivative. Thus, potassium pentacyanocobaltate, which may react as a dimer with a cobalt-cobalt bond (20), reacts with acetylene to give the adduct XV (31). The product was thought to be the trans isomer, but the data were not conclusive. 

All manipulations are performed under argon or dry nitrogen using standard Schlenk and glovebox techniques. Phosphines (Strem), cyclopentadienylirondi-carbonyl dimer, and tetrafluoroboric acid (Aldrich) are commercial samples used as received. 

Matrix isolation studies usually permit spectroscopic observation of the species M(CO), M(CO)2,. M(CO) , the coordinatively saturated molecule. In some early studies, species thought to be simple unsaturated carbonyls were in fact carbonyls of metal clusters Mx(CO) a very low concentration of metal in the matrix (e.g., I mol in 104 mol noble gas) has to be used to prevent clustering. All the partially coordinated carbonyls are only matrix species, that is, they only exist when completely isolated from other molecules of their own kind or from CO. The coordinately saturated carbonyls are of more interest in the context of this review. The following new molecules have been reported Au(CO)2 (84a) Ag(CO)3, Cu2(CO)6 (46, 87) Pd(CO)4 (22), Pt(CO)4 (69) Rh2(CO)g, Ir2(CO)g (37) M(CO)6[M = Pr, Nd, Gd, Ho, Yb (100), Ta (24), U (117)]. The Cu, Pd, Pt, Rh, and Ir carbonyls can be obtained by condensing the metal vapors with pure CO at 40 K and then pumping off excess CO to leave a film of the carbonyl. The Cu, Pd, and Pt carbonyls decompose under vacuum temperatures above -100°C, and the Rh and Ir carbonyls dimerize with loss of CO to give M4(CO)12 above -60°C. The gold and silver carbonyls are not stable outside matrix isolation conditions. Unfortunately, the literature is presently unclear about the stability of the Ta and lanthanide hexacarbonyls outside a matrix. 

Cyclopentadienylnickel carbonyl dimer is also known to react with acetylenes to form bridged complexes. With bis(trimethylsilyl)acetylene and with l,4-bis(trimethylsilyl)butadiyne it reacts to give organosilyl acetylene complexes 63) [Eqs. (47) and (48)]. The silylated butadiyne... 

A. Cleavage of Radical Anions of Diiron Carbonyl Dimers... 

Lower yields of Na3[Mn(CO)4] were obtained from the direct reduction of Mn2(CO)10 in Na-HMPA, because the neutral dimer underwent slow disproportionation in this medium to form [Mn(HMPA)Jt][Mn(CO)5]2, in contrast to Re2(CO)10, which showed no tendency to react with HMPA at room temperature. Of all neutral binary carbonyl dimers known, Re2(CO)10 appears to be the most resistant toward Lewis base-promoted disproportionation reactions. The slightly lower yields of Na3[Re(CO)4], compared to those of Na3[Mn(CO)4], may have arisen from the fact that Re2(CO)10 does not cleanly reduce to [Re(CO)5] in HMPA or other solvents (22). It should... 

Homonuclear carbonyl dimers, palladium complexes, 8, 206 Homonuclear element-element bonds, addition to C-C multiple bonds boron-boron bonds, 10, 727 chalcogen-chalcogen additions, 10, 752 germanium-germanium bonds, 10, 747 phosphorus-phosphorus bonds, 10, 751 silicon—silicon bonds, 10, 734 tin—tin bonds, 10, 748... 

Mixed donor tridentate [NPS] ligated derivatives, chromium(III) complexes, 5, 370 Mixed iridium carbonyl dimers, preparation, 7, 289 Mixed isonitrile acetylides, liquid crystals, 12, 281 Mixed isonitrile phenyl complexes, liquid crystals, 12, 282 Mixed ligand triangular Pt carbonyl clusters, characteristics, 8, 411... 

Metal carbonyl dimers have proved to be useful reagents for the synthesis of mixed-metal clusters. This is particularly true for Fe and Co clusters since Fe2(CO) and Co2(CO)8 are readily available starting materials. The prediction of the reaction products is usually fruitless. However, examination of the available data indicates that the initial dimeric unit is preserved in approximately half of the reactions. Typical examples are illustrated in Eqs. (4-6) (102), (7) (28), and (8-10) (121). 

Several examples of the use of hexamethyldistannoxane as a Me3Sn group transfer agent are reported. Thus the dimetallic carbonyl dimers of Mo, Mn, Fe, Co, and Ni react with Me3SnOSnMe3 [and also with tris(trimethylstannyl)amine, N(SnMe3)3] to form metal-carbonyl derivatives containing tin complexes (equation 118)277. 

The related three-coordinate complexes Mo[ CpRMo(CO)3)2Pb(thf)] were obtained as green crystalline solids in fairly good yield. Changing the reaction solvent from THF to a hydrocarbon resulted in the formation of an unusual bridging carbonyl dimeric Mo-lead complex (Cp Mo(CO)3)PbCp Mo(CO)2(/z-CO) 2, HS4 517. 

C. E. Housecroft, Metal-Metal Bonded Carbonyl Dimers and Clusters (Oxford University Press, Oxford-New York-Tokyo, 1996, pp. 22 and 23). 

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