Binuclear Mixed Ligand Carbonyls

Binuclear Mixed Ligand Carbonyls. Substitution in Co2(CO)6(alkyne) compounds follows the two-term rate law set out in the previous section, and proceeds by parallel dissociative and associative pathways.  

Substitution Replacement of Other Ligands in Mixed Carbonyls.— 

Displacement of arenes from W(CO)3(arene) by trimethyl phosphite, to give l,2,3-W(CO)a[P(OMe)3]3, is a second-order reaction. Reactivities are compared with those for chromium analogues, and for cycloheptatriene analogues. Rate trends cannot be entirely explained in terms of electronreleasing or -withdrawing effects of substituents on the electron density, 

In nucleophilic substitution reactions of metal carbonyls it is often difficult to decide whether the nucleophile attacks at the central metal or at a relatively positive site on one of the ligands. Such an example is afforded by reaction of hexamethylborazolechromium tricarbonyl (4) 

In a large number of carbonyls nucleophilic attack seems more likely at the carbonyl-carbon than at the metal. There is often good evidence from products for such attack at the ligand, and these examples are therefore discussed in a later section on reactions of co-ordinated ligands (p. 301). 

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A large fraction of the binuclear mixed chalcogen/carbonyl transition metal complexes of iron and manganese contain the M2E (CO)6 core with the butterfly-type structure (n = 2) or substructure (n — 3, see Section 1.10.3). As an example of a complex with thiolate ligands, the structure of [Fe2(SC3H7)2(CO)6] is shown in... 

The metal ions in mixed chalcogen/carbonyl complexes of manganese, iron and cobalt are often surrounded by five ligand donor functions (normally a E2(CO)3 donor set) in a sqnare-pyramidal fashion. A typical example is the binuclear complex [Fe2S2(CO)6, which contains a disulfide ligand shown in Fig. 

A third type of binuclear chalcogen/carbonyl complex is defined by three chalc-ogen atoms in bridging positions and six carbonyl ligands bonded terminally to the metal atoms. The general formula of these complexes is [Mn2(ER)3(CO)6] (E = g (6b,20,21] gg[6a,22] A mixed-metal derivative of formula [MnFe(SePh)3-... 

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