Metal carbonyl anions cyanides

As noted above for reactions of [IPh2] salts with metal carbonyl anions, reactions do not always result in formation of new metal-carbon bonds. Thus, as shown in Scheme 38, [M(CN)(CO)5] reacts with 1(C = CR)Ph] in a manner consistent with nucleophilic attack by the nitrogen atom of the cyanide ligand. " Complex 67 (R = Ph) has been characterised by X-ray crystallography. For formation of the cyclobutenyl products 68 (M = Cr also characterised by X-ray... 

However, the cyanide ion does have the ability to stabilize metal ions in low formal oxidation states, and it presumably does this by accepting electron density into its n orbitals. The fact that cyano complexes of zerovalent metals are generally much less stable (in a practical as opposed to a well-defined thermodynamic or chemical sense) than similar metal carbonyls has often been taken to show the poor 7t-acidity of CN-, but it should be noted that the cyano compounds, e.g., [Ni(CN)4]4-, are anionic and might thus tend to be more reactive for this reason alone. In some instances cyano... 

It is apparent that if the Lewis base is charged rather than neutral, the substituted metal carbonyl will have the same charge as the Lewis base. In this manner certain anionic metal carbonyls can be synthesized by the displacement of carbonyl groups with anionic Lewis bases. Frequently used for this type of reaction are the halide ions and cyanide ion. Many of these reactions have been carried out on the relatively stable hexacarbonyls of chromium, molybdenum, and tungsten, their derivatives or other related... 

This observation parallels that of anionic binary transition metal cyanide complexes where the photodissociation of an electron i.s observed (Chapter 3). Photoinduced electron transfer reactions are also observed with binary metal carbonyl complexes... 

The phase-transfer catalysed reaction of nickel tetracarbonyl with sodium hydroxide under carbon monoxide produces the nickel carbonyl dianions, Ni,(CO) 2- and Ni6(CO)162, which convert allyl chloride into a mixture of but-3-enoic and but-2-enoic acids [18]. However, in view of the high toxicity of the volatile nickel tetracarbonyl, the use of the nickel cyanide as a precursor for the carbonyl complexes is preferred. Pretreatment of the cyanide with carbon monoxide under basic conditions is thought to produce the tricarbonylnickel cyanide anion [19], as the active metal catalyst. Reaction with allyl halides, in a manner analogous to that outlined for the preparation of the arylacetic acids, produces the butenoic acids (Table 8.7). 

Moreover, aryl-oxazoles, -imidazoles [17], or-thiazoles [18], anhydrides [19], and imides [20] are accessible via intramolecular Heck-type carbonylations. In addition to typical acid derivatives, aldehydes [21], ketones [22], aroyl cyanides, aroyl acetylenes, and their derivatives [23] could be synthesized via nucleophilic attack of the acyl metal complex with the corresponding hydrogen or carbon nucleophiles. Even anionic metal complexes like [Co(CO)4] can act as nucleophiles and lead to aroylcobalt complexes as products [24]. 

By way of example, we can focus on the cyano complexes. Palladium and platinum can form homoleptic complexes with two, four, or six cyanides, depending on the metal oxidation state zero, two, and four, respectively. Rhenium forms heptacyano complexes in its - -3 and -t-4 oxidation states but forms an octacyano complex in its -t-5 state. Molybdenum and tungsten also appear commonly in octacyano complexes for +4 and - -5 oxidation states, and heptacyano analogs for the - -2 and - -3 cases, with only one occurrence of [Mo(CN)6]" anions in two oxidation states (n = 3, 4). Similar situations can be found with phosphine or carbonyl complexes. For instance, the group... 

Reaction of ferrous chloride with cyanide ions in the presence of CO produces a mixture of cyano-carbonyl ions including T[Fe(CN)4(CO)2], /ra 3-[Fe(CN)4(CO)2] , and [Fe(CN)s(CO)] (Scheme H).63.70,7l OT-dicarbonyl compound was also prepared via the reaction of Fe(CO)4l2 with 4 equiv. of MCN (M = Na, K) in MeOH (Scheme Z) Treating [Fe(CN)3(CO)3] with NaCN also produced the m-derivative. As with the previous work reviewed in GOMC II (1982) and COMC (1995), alkylation of these anionic cyano complexes leads to isocyanide derivatives. Similarly, protonation leads to the formation of the bound isocyanic acid. Oxidation of the [Fe(CN)s(CO)] ion gives [Fe(CN)s(CO)]. Two-dimensional polymeric networks were obtained when [Na(DMF)2]2[7ra .f-Fe(GN)4(CO)2] was treated with divalent metal salts in agar gels (Equation (22)). ... 

When living poly(methyl methacrylate) (PMMA) prepared by group transfer polymerization (GTP) is used as a macroinitiator for the ROP of cyclic carbonates, a site transformation from the silyl ketene acetal (GTP-mechanism) to an alcoholate (anionic ROP-mechanism) with a metal-free counterion occurs (Scheme 12.5). The GTP of PMMA was initiated with l-methoxy-l-trimethylsilyloxy-2-methyl-l-propene (MTS) in combination with catalytic amounts of tetrabutyl ammonium cyanide in THF as solvent. Towards the end of the reaction, DTC is dissolved in the reaction mixture and lequiv. of fluoride anions (e.g. tris(dimethylamino) sulfonium difluorotrimethylsilicate TASF), with respect to the active species, is added. In this way, good yields of the respective block copolymers were obtained. A model experiment for this site transformation is the polymerization of DTC with MTS as the initiator and TASF as the desilylating agent. The fluoride anion promotes desilylation of the silyl ketene acetal with formation of an enolate, which reacts as a carbon-centered nucleophile with the carbonyl carbon of DTC, thereby... 

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