Polynuclear carbonyl complexes

Organometallic Compounds. The predominant oxidation states of indium in organometalUcs are +1 and +3. Iridium forms mononuclear and polynuclear carbonyl complexes including [IrCl(P(C3H3)3)2(CO)2] [14871-41-1], [Ir2014(00)2] [12703-90-1], [Ir4(CO)22] [18827-81 -1], and the conducting, polymeric [IrCl(CO)3] [32594-40-4]. Isonitnle and carbene complexes are also known. 

Structure. The CO molecule coordinates in the ways shown diagrammaticaHy in Figure 1. Terminal carbonyls are the most common. Bridging carbonyls are common in most polynuclear metal carbonyls. As depicted, metal—metal bonds also play an important role in polynuclear metal carbonyls. The metal atoms in carbonyl complexes show a strong tendency to use ak their valence orbitals in forming bonds. These include the n + 1)5 and the n + l)p orbitals. As a result, use of the 18-electron rule is successflil in predicting the stmcture of most metal carbonyls. 

Many of the mononuclear metal carbonyls have been the object of detailed and precise calorimetric measurement by Wilkinson10 and Skinner6 and their respective groups. Measurements on the more complex, polynuclear carbonyls have been made almost exclusively by microcalorimetry4 9, with the notable exception of Good s work12 on Mn2(CO)10. The results of these measurements are collected in Table 1. 

The electrochemistry of polynuclear carbonyl complexes has been reviewed... 

Ojima has reported that a number of mono- and polynuclear rhodium carbonyl complexes catalyze the cyclization/... 

Eliminations from Os(CO)4RR occur by dinuclear mechanisms only if either R or R is H. A hydride on one metal is necessary to interact with a vacant coordination site on the other in the dinuclear transition state. With Os(CO)4H2, the vacant site is created by dissociation of CO. With Os(CO)4-(H)CH the vacant site is created by a facile rate-determining isomerization which we suggest is to an acetyl hydride. The unique instability of hydridoalkyl carbonyls thus is explained. The synthesis and properties of Os(CO)4(H)C2H and various polynuclear ethyl osmium derivatives show that (3-hydrogens have no significant effect on these elimination mechanisms. Dinuclear hydridoalkyls are excellent starting points for the synthesis of more complex polynuclear alkyls. 

In this chapter we have examined examples of polynuclear metal carbonyl complexes as well as simple metal carbonyl hydrides. Consider now the polynuclear carbonyl hydride complex, H,Os,(CO)i2- Rationalize the formulation of this species. From your application of the 18-electron rule, what can you say about the structure of this molecule1 How is it similar to or different from the complex Os COln shown in Figure 5.9 (See Churchill M. R. Wasserman, H. J. Iticrg, Chen. 1980, 19, 2391-2395.)... 

These complexes ure chemically like polynuclear metal carbonyl complexes (class I) but are included here instead of in Chapter 15 because they do not possess metal-carbon bonds. A rich chemistry has been developed in which alkoxides Func-... 

Polyelectronic atom, 20-43 Polyhalide ions, 839-843 Polyhalogen cations, 848 Polymers, and phosphazene polymers, 773-775 Polynuclear carbonyl complexes, 633-639... 

Earlier in this chapter, the polynuclear carbonyl complex Os4tCO),ft sens referred to as an analogue of cydubutane. It should now be dear that the connection between... 

In other variations ketones are produced. The acyliron monoanion may be alkylated again with another alkyl halide to form a transient acyl-alkyl iron intermediate, which rapidly decomposes into ketone and the polynuclear iron carbonyl complex. This reaction is limited, however, because only very reactive alkylating agents such as methyl, allyl, and benzyl halides will react with the weakly nucleophilic acyliron monoanions ... 

Trends and Implications of P-31 NMR Parameters. With X-ray structural data now available in our laboratory for a large number of bi-and polynuclear iron-group carbonyl complexes with phosphido bridges, we have attempted to correlate structural changes with P-31 NMR chemical shifts and coupling constants in an effort to establish... 

Binuclear and polynuclear carbonyl complexes were among the first compounds containing M-M bonds to be prepared early in the present century, but it was not until the crystal structure determination of Mn2(CO)i0, i.e. (CO)5Mn—Mn(CO)5, in 1957 that such bonds were authenticated in carbonyls. The study of polynuclear carbonyl complexes has been a major growth area of chemistry since then. Clusters containing more than 50 M atoms have been characterised. Some examples are illustrated in Fig. 8.8. 

The 18-electron rule can be applied - with some adjustments - to the structures and stoichiometries of polynuclear carbonyl complexes. To illustrate the principles, let us go back to the simple case of Mn2(CO)10. We found that the Mn atom was one electron short of 18 and that formation of the Mn-Mn bond - giving each Mn atom a share in an extra electron - would make up the deficit. In the general case of an M cluster, we can say that N, the number of two-centre, electron-pair M-M bonds, is given by ... 

Heterometallic metallomesogens, liquid crystals, 12, 223—224 Heterometallic polynuclear platinum carbonyl complexes heterodinuclear clusters, 8, 415 triangular clusters, 8, 417... 

My co-worker J. Sedlmeier then held the view that the amine-containing iron carbonyl complexes were also ionic compounds (VII, 14, 21). Hence the compound Fe2(CO)4(en)3 (en= 1,2-ethylenediamine) was formulated as [Fe(en)3]2+[Fe(CO)4]2. Systematic investigations revealed that reactions of the iron carbonyls with other nitrogen and oxygen donors likewise involved valency disproportionation of the metal with concomitant formation of mono- and polynuclear carbonylferrates, viz., [Fe(CO)4]2, [Fe2(CO)8]2-, [Fe3(CO)n]2-. R. Werner (VII, 15, 17, 19, 20) even discovered and characterized compounds containing the tetranuclear anion [Fe4(CO)13]2, the first being that from pyridine and iron carbonyl, viz.,... 

Formation of polynuclear compounds with chalcogen atoms as bridging ligands between metal atoms is a characteristic feature of chalcogen metal carbonyl complexes. Such polynuclear complexes, in which often an additional metal-metal bond is assumed so as to account for the diamagnetism, have become known in increasing numbers because of the work of various research groups, and it is neither possible nor is it within the scope of this article to review this subject here. Only a few of our own results will be mentioned herein. 

Only metals in carbonyl complexes are in the zero-valent state and can be polynuclear. 

It may be noted that other reactions can occur with polynuclear carbonyl complexes, such as oxidative fragmentation [17, 61, 66], This is observed when [HRu3(CO)io(0-A1=)] is transformed into [Ru(CO)2 (0-A1h)2] at 473 K (Fig. 6), leading to an oxidation of Ru[Pg.176]

In the last three decades of the twentieth century, following Walter Hieber s retirement, four aspects of the research on mono- and polynuclear metal carbonyl complexes found particular attention. These were the preparation of highly reduced carbonyl metallate anions, the generation of stable metal carbonyl cations, the matrix isolation of uncharged metal carbonyls obeying or not the 18-electron rule and, last but not least, the giant metal carbonyl clusters. 

The 13C NMR spectrum, however, comprises a single resonance (204 ppm), indicating that the three isomers interconvert very rapidly (k 103 s 1). This is a very common phenomenon in bi- and polynuclear (cluster) carbonyl complexes. 

Polynuclear Rhodium Carbonyl Complexes and Their Relationships to Mononuclear and Binuclear Rhodium Carbonyl Complexes1... 

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