Transition metal carbonyls, early

Application of small metal particles has attracted the attention of the scientists for a long time. As early as in the seventies Turkevich already prepared mono-dispersed gold particles [19], and later, using molecular transition metal carbonyl clusters [20], the importance of small nanoparticles increased considerably. One of the crucial points is whether turnover frequency measured for a given catalytic reaction increases or decreases as the particle size is diminished. 

B. Syntheses and Charecterizations of [Nb(CO)B]3 and [Ta(CO)J3 Thermal Instability and Shock Sensitivity of Unsolvated Alkali Metal Salts of Early Transition Metal Carbonyls... 

Although the related unsolvated Na2[Cr(CO)5] (4) does not normally explode or decompose at room temperature under an inert atmosphere, we have observed that a finely divided black powder, similar in appearance to the aforementioned one, rapidly formed when small amounts of air were inadvertently introduced into an evacuated flask of unsolvated Na2[Cr(CO)5], Under these conditions, the latter violently exploded, due to thermolysis of the pyrophoric product. Interestingly, unsolvated Na-[(C5H5)Ti(CO)4.] has also been observed to easily explode at room temperature on mild impact under an argon atmosphere. Thus, unsolvated alkali metal salts of all early transition metal carbonyl anions must be regarded as potentially explosive or shock-sensitive substances and manipulated carefully and handled with considerable care and respect. 

Consequently, in the early work with hydridosilicon derivatives, diethyl ether was normally used in the case of very volatile products, dimethyl ether offered some practical advantages. It was tacitly assumed that a polar solvent was essential in order to dissolve, at least partly, the transition-metal carbonyl derivative. More recently, however, it has become clear that alkanes, although nonpolar, provide a very suitable reaction medium, and can be used in cases where ethers, for example, are inimical to the products (8, 32, 306, 310). The hydrocarbon, besides acting as a diluent for the silicon halide, seems to assist the separation of alkali halide from the surface of the reacting transition-metal carbonyl salt. 

Redaction of (5) with alkali metal forms the green clnster anion Co6(CO)i5 , which can be further rednced to the red dianion Co6(CO)i4, and isolated as a potassinm salt. The latter clnster anion is an early example of the expanding family of highly rednced transition metal carbonyls, for example Na3Co(CO)3, where np to two CO gronps are replaced by two electrons each. Co6(CO)is is also the mainprodnct from valence disproportionation of Co2(CO)g in ethanol. Oxidation (or acidification) of the clnster anions gives Co6(CO)i6. 

Since power ultrasound is capable of generating extremely high pressures and temperatures within microbubbles in a liquid medium the possibility arises that sonochemistry might replace conventional (and expensive) high pressure reactors. Power ultrasound has been found to dramatically reduce the temperatures and pressures required for the preparation of early transition metal carbonyl anions from the direct reaction of the corresponding metal chlorides with carbon monoxide (Scheme 10.6) [18]. In this particular case the yield of V(CO)6 (35%) can be obtained at 4.4 atmos pressure and 10°C whereas conventional methodology requires 200 atmos and 160°C. 

Suslick has made an extensive study of the sonochemistry of Fe(CO)5 which he has used as a probe to explore the chemical effects of high intensity ultrasound. Suslick and Johnson [280] have also shown that sonication greatly facilitates the preparation of early transition metal carbonyl anions. Hence, sonication of vanadium trichloride and sodium sand in THF solution gave a 35 % yield of NaV(CO)g under 4.4 atmospheres of carbon monoxide at 10 °(i. The equivalent thermal reaction requires the reaction to be caried out at 160 °C under 200 atmospheres of carbon monoxide. That is, the temperatures and pressures produced by cavitation are comparable to the bomb conditions normally required for the preparation of these compounds [281]. Suslick s review [3] presents further evidence in support of this original observation however, no further details of this work have appeared to date. 

Arduengo and Herrmann described the coordination of NHCs to a series of transition metal carbonyls in the early 1990s e.g. [Ni(CO)4] [M(CO)g], M = Cr, Mo, W [Fe(CO)5]). In each case, a carbonyl ligand was readily displaced to yield the corresponding [(NHC)M(CO)J species (1-5) (Scheme 2.1). The reactions of various neutral ligands with [Ni(CO)4] form the basis of the TEP, which has been used to compare the net electron-donating ability of different phosphines and NHCs. ... 

Hydrophosphorylation of alkynes via external attack of //-phosphonate to an (alkyne)metal complex is a possible pathway, although the possibility has been concluded to be less likely as far as the nickel-catalyzed reaction is concerned [12]. However, such a process appears to proceed in early transition metal carbonyl-catalyzed reactiOTis [19]. For instance, refluxing a mixture of phenylacetylene, HP(0)(0Et)2, and Mo(CO)fi (10 mol%) affords the franr-addition product... 

Low Pressure Syntheses. The majority of metal carbonyls are synthesized under high pressures of CO. Early preparations of carbonyls were made under superpressures of 1 GPa (ca 10,000 atm). Numerous reports have appeared in the Hterature concerning low pressure syntheses of metal carbonyls, but the reactions have been restricted primarily to the carbonyls of the transition metals of Groups 8—10 (VIII). A procedure for preparing Mn2(CO)2Q, however, from commercially available methylcyclopentadienyknanganese tricarbonyl [12108-13-3] and atmospheric pressures of CO has been reported (117). The carbonyls of mthenium (118,119), rhodium (120,121), and iridium (122,123) have been synthesized in good yields employing low pressure techniques. In all three cases, very low or even atmospheric pressures of CO effect carbonylation. Examples of successful low pressure syntheses are... 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

Low valent transition metal centers preferentially coordinate to the phosphorus in diazaphospholes. Accordingly, P-coordinated complexes of [l,2,3]diazapho-spholes with Cr, W, Fe, and Mn carbonyls were obtained as early as 1980 [1, 2,4], Later, Kraaijkamp et al. observed [108] both P- or -coordination modes in complexes of [l,2,3]diazaphospholes with MX2(PEt3) (M = Pt, Pd X = C1, Br). Methanolysis of these complexes led to the diazaphosphole ring opening and formation of five membered metallacyclic P,/V-chelates (103), incorporating P-bonded phosphonite and /V-coordinated hydrazone functionalities (Scheme 32) [109],... 

Spectroscopists also saw the potential of reacting ligands with transition metal under matrix isolation conditions. Photolysis of metal carbonyls in organic (383 or inert gas matrices (39) had already been done, but atoms offered the possibility of step-wise addition of ligands. DeKock (40), Turner (41 ), and Moskovits and Ozin (42) made early contributions, but the work of the last two became dominant (32). By 1972, there were the two distinct branches in transition metal atom chemistry, the preparative and matrix spectroscopic studies. 

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