Polynuclear carbonyls

Carbonyl polynuclear carbonyl species containing bridging carbonyl ligands in addition to the... 

Soon after the synthesis of mononuclear transition metal carbonyls, polynuclear metal carbonyls featuring bridging carbonyls, such as Fc2(CO)9 and Co2(CO)g, were obtained and cyclopentadienyl anirni containing complexes like [(Cp)Fe (CO)2l2 followed. The first example, Fe2(CO)9, features three identical bridging carbonyls and six terminal carbonyls in a high-symmetiy (D3 ) strucmre that facilitated theoretical treatment and was extensively studied [16—22], though its X-ray stmcture was obtained quite late [4, 23]. These studies examined two fundamental questions (1) what is the electronic nature of Fe-C(0)-Fe three-center bridge and (2) what role does the metal—metal interaction play in the complex, as the short distance between two irons and the 18-e mle imply a metal-metal bond ... 

Drnuclear carbonyls Polynuclear carbonyls P2-bridging carbonyls Ps-bridging carbonyls Carbonyl hydrides... 

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. 

The cross-conjugated system of two a,P-unsaturated carbonyl groups of both 1,2- and 1,4-quinones occurs in many polynuclear hydrocarbons, eg, 1,2-naphthoquinone [524-42-5] (8) and 1,4-naphthalenedione [130-15-4] (1,4-naphthoquinone) (9) (see Fig. 1). The carbonyl groups may be located in different rings, but occupy positions corresponding to the 1,2- or 1,4-orientation of monocyclic quinones, eg, in naphthalenes such as 2,6-naphthoquinone... 

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. 

Polynuclear Carbonyls. Several stmctures consist of dinuclear metal carbonyls as shown in stmctures (4)—(6). The metal atoms in Mn2(CO) Q, as also for technetium and rhenium, are held together by a metal—metal bond and the compound contains 10 terminal CO ligands, five coordinated to each atom. The CO ligands of Mn2(00) 0 adopt a staggered configuration as illustrated in stmcture... 

Synthesis of Heteronuclear and Polynuclear Metal Carbonyls. Heteronuclear metal carbonyls are usually synthesized either by metathesis (27) or addition (28,40). 

The most important fragmentation reactions of sulfur diimides occur with polynuclear metal carbonyls, e.g., M3(CO)i2 (M = Fe, in... 

Encapsulated H atom detected and located in octahedral polynuclear carbonyls such as [HRu6(CO)i8l and [HCo6(CO)i5l following A. Simon s characterization of interstitial H in HNbeln. 

Ni(CO)4] is readily oxidized by air and can be reduced by alkali metals in liquid ammonia or thf to yield a series of polynuclear carbonylate anion... 

Sulfur Compounds. All crude oils contain sulfur in one of several forms including elemental sulfur, hydrogen sulfide, carbonyl sulfide (COS), and in aliphatic and aromatic compounds. The amount of sulfur-containing compounds increases progressively with an increase in the boiling point of the fraction. A majority of these compounds have one sulfur atom per molecule, but certain aromatic and polynuclear aromatic molecules found in low concentrations in crude oil contain two and even three sulfur atoms. Identification of the individual sulfur compounds in the heavy fractions poses a considerable challenge to the analytical chemist. 

A possible mechanism for the reactions of electrophiles with polynuclear transition metal carbonyls and related complexes. A. R. Manning, Coord. Chem. Rev., 1983, 51, 41-67 (41). 

Metal-metal bonds and covalent atomic radii of transition metals in their n-complexes and polynuclear carbonyls. B. P. Biryukov and Y. T. Struchkov, Russ. Chem. Rev. (Engl. Transl.), 1970, 39,... 

A metal cluster can be considered as a polynuclear compound which contains at least one metal-metal bond. A better definition of cluster catalysis is a reaction in which at least one site of the cluster molecule is mechanistically necessary. Theoretically, homogeneous clusters should be capable of multiple-site catalysis. Many heterogeneous catalytic reactions require multiple-site catalysis and for these reasons discrete molecular metal clusters are often proposed as models of metal surfaces in the processes of chemisorption and catalysis. The use of carbonyl clusters as catalysts for hydrogenation reactions has been the subject of a number of papers, an important question actually being whether the cluster itself is the species responsible for the hydrogenation. Often the cluster is recovered from the catalytic reaction, or is the only species spectroscopically observed under catalytic conditions. These data have been taken as evidence for cluster catalysis. 

In this section, we outline a number of studies by various workers in which matrix isolation experiments have contributed to the understanding of some photochemical pathways and where the objective was to relate the experiments to room-temperature photochemistry. We then consider briefly some current problems involving dinuclear and polynuclear carbonyls. 

A further point of interest is their ready interconversion in solution, which we have studied by variable temperature n.m.r. measurements (8). Reaction of [(n-C5H5)(0C)2W =CR] with polynuclear metal carbonyl species is likely to afford many new heteronuclear cluster compounds containing tungsten. 

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