Polynuclear carbonyls substitution reactions

Some compounds and their reactions have been noted in Section 18-G-2. The homoleptic carbonyls are clusters such as M4(CO)i2 and M6(CO)i8. The hydride, HRh(CO)4, is very much less stable than HCo(CO)4 and has been made only under ca. 1400 atm pressure since it readily loses H2 to give clusters. Both Rh and Ir give anions [M(CO)4] and [M(CO)3]4 as R3NH+ salts as well as various cluster anions such as [Ir8(CO)22]2 and [Rh5(CO)i5] . Hydrido and other substituted polynuclear carbonyls are known. 

Substitution reactions on metal-carbonyl dimers (see Dinuclear Organometallic Cluster Complexes) and clusters see Polynuclear Organometallic Cluster Complexes) occur by replacement of a CO with an entering ligand ... 

Substitution reactions of polynuclear metal carbonyls with tertiary phosphines often induce the formation of bridging carbonyls. Provide an explanation. 

Substitution Reactions and Ouster Breakdown of Polynuclear Metal Carbonyls... 

Polynuclear Carbonyls.—It has been shown that substitution reactions of [Ru3(CO)ia] with Group Vb donors follow the rate law Arobs = Ati + AraiL], where L = PPha, AsPhg, P(OPh)3, P[(OCHa)3CEt], P(OEt)3, or PBu g, and that contrary to earlier reports the k term contributes significantly to the overall rate. A recent, more detailed analysis has now appeared. The nature of the reaction products varies considerably but the kinetic equation above is quite clear. The first-order path corresponds... 

The review of the literature of 1991 follows the sane format as last year, with some general review articles given in section 2. This chapter is further divided into sections for the metals of each periodic group with subdivisions, where necessary, to help the reader locate complexes of basic structural types. Substitution reactions of mononuclear metal carbonyls with group V and/or group VI donor ligands are fully discussed, but metal-metal bonded polynuclear metal carbonyls are only covered when reactions lead to products in which these bonds are cleaved. Carbonyl complexes which contain metal-metal bonds are fully reviewed in Chapter 9. 

Polynuclear Carbonyl Derivatives.-Variable temperature MAS n.m.r. methods have been used to probe the exchange processes occurring in solid homonuclear carbonyls containing 3 and 4 metal atoms.A quantitative investigation of the chemistry resulting from both continuous- and flash-photolysis of Ru3(C0)i2 has been carried out, and a new polymeric ruthenium carbonyl, Ru(C0)it n prepared from this precursor. The steric and electronic effects in associative substitution reactions of Iri (C0)i2 have also been examined. The combination of two OS3 units to yield an improved route to Ose raft-like clusters has been achieved, and a comprehensive analysis published on the different Mg cores of stacked Mg triangles in the [Mg C0)i8] "... 

Polynuclear complexes are produced by irradiation of substituted metal carbonyls in analogy to the reaction observed with simple metal carbonyls (see section El). In most cases either CO or another ligand attached to the mononuclear complex serve as bridging functions in the polynuclear products. 

Although polynuclear alkyne completes are often prepared by reaction of the alkyne with a suitable metal cluster fragment, heteropolynuclear complexes 69 (Scheme 4-38) have been obtained also by isolobal metal fragment substitution, as noted previously [26]. Higher-nuclearity alkyne complexes also can be produced by the addition of various metal carbonyl fragments to a lower-nuclearity alkyne complex [119], A novel entry to heterobi- (and tri-)metallic neutral p-propargyl complexes (e.g., Fe/Mo) via protonation of trinuclear p-Ti, T1 -o-propargyl derivatives 70 was recently described by Wojcicki and coworkers [120,121]. 

Silyl enol ethers and ketene silyl acetals add to aromatic nitro compounds in the presence of TASF(Me) to give intermediate dihydro aromatic nitronates which can be oxidized with bromine or 2,3-dichloro-5,6-dicyano-l,4-benzoquinone to give a-nitroaryl carbonyl compounds the latter are precursors for indoles and oxindoles. The reaction is widely applicable to alkyl-, halo-, and alkoxy-substituted aromatic nitro confounds, including heterocyclic and polynuclear derivatives (eq 7). 

Electron-transfer-catalyzed (ETC) nucleophilic substitution in polynuclear metal carbonyls promises to become a useful synthetic procedure for a wide variety of compounds. Scheme 6 shows the general reaction with a nucleophile L and Scheme 7 gives some mechanistic details (nonessential ligands omitted). For the ETC process to be efficient the radical-anion formation must be reversible, and the rate of electron transfer must be fast... 

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