Mixed carbonyls

Ma.nufa.cture. Nickel carbonyl can be prepared by the direct combination of carbon monoxide and metallic nickel (77). The presence of sulfur, the surface area, and the surface activity of the nickel affect the formation of nickel carbonyl (78). The thermodynamics of formation and reaction are documented (79). Two commercial processes are used for large-scale production (80). An atmospheric method, whereby carbon monoxide is passed over nickel sulfide and freshly reduced nickel metal, is used in the United Kingdom to produce pure nickel carbonyl (81). The second method, used in Canada, involves high pressure CO in the formation of iron and nickel carbonyls the two are separated by distillation (81). Very high pressure CO is required for the formation of cobalt carbonyl and a method has been described where the mixed carbonyls are scmbbed with ammonia or an amine and the cobalt is extracted as the ammine carbonyl (82). A discontinued commercial process in the United States involved the reaction of carbon monoxide with nickel sulfate solution. 

Apart from Ru(CO)5 and other carbonyls, there are mixed carbonyl-phosphine species and a few simple phosphine complexes like Ru(PF3)5 and Ru[P(OMe)3]5 [61a]. 

Lnsymmetrical ptnacols, e.g. (19) can be made by reductive coupling of the mixed carbonyl precurHorH, but the yields are poor as the two dimers are also formed,... 

Nitro sulfides are conveniently prepared by simply mixing carbonyl compounds, nitroal-kanes, and thiols in the presence of triethylamine.2 P-Nitro sulfide, which is used for synthesis of rf-biotin, is prepared by this procedure (Eq. 4.2).3... 

Because Ni(CO)4 is volatile (b.p. 43 °C) and cobalt will not react under these conditions, this process afforded a method for separating Ni from Co by the process now known as the Mond process. Although there are many complexes known that contain both carbonyl and other ligands (mixed carbonyl complexes), the number containing only a metal and carbonyl ligands is small. They are known as binary metal carbonyls, and they are listed in Table 21.1. The structures of most of these compounds are shown later in Figures 21.1 through 21.3. 

In this case, the product is the fac isomer, in which all NH3 ligands are trans to the CO molecules. Ammonia does not form ty bonds to metals because it has no orbitals of suitable energy to accept electron density. Thus, the back donation from Cr in Cr(NH3)3(CO)3 goes to only three CO molecules, and the bond order is reduced even more than it is in Cr(CO)s, where back donation occurs equally to six CO molecules. There is, of course, an increase in Cr-C bond order and stretching frequency in Cr(NH3)3(CO)3 compared to Cr(CO)s. Based on the study of many mixed carbonyl complexes, it is possible to compare the ability of various ligands to accept back donation. When this is done, it is found that the ability to accept back donation decreases in the order... 

Metal carbonyls undergo reactions with a great many compounds to produce mixed carbonyl complexes. A large number of these reactions involve the replacement of one or more carbonyl groups by a substitution reaction. Such reactions have also been studied kinetically in some cases. 

We have restricted the discussion in the section primarily to mixed carbonyl, carbonyl-hydride, or phosphine-substituted cluster compounds. On the basis of electronegativity, there should be an enhance-... 

For mixed carbonyl adducts, from other groups, redox condensation reactions have been employed to considerable effect. Thus for osmium-cobalt, a range of derivatives has been prepared (241, 248, 249) by reactions of the types ... 

Mixed Carbonyl-Cyclopentadienyl and Carbonyl-Arene Metal Complexes.142... 

The mixed carbonyls, FeM3(CO)i3H2 (M = Ru1S8,2S2, Os197 ) have been prepared in low yields as shown in Eqs. (38) and (39) ... 

We have already mentioned in Eq. (7) the synthesis of Co2Rh2(CO)12. A general method of synthesis consists of the precipitation of the mixed carbonyls from an aqueous solution ... 

The first mixed carbonyl, the anion [FeCo3(CO)i2]-, was obtained using the redox condensation shown in Eq. (63)52. ... 

Structural models, which are synthesized to imitate features of the proposed structure of the active site. These may be used to demonstrate the chemical conditions, which allow such structures to exist, to investigate their chemical properties and to give a better understanding of the spectroscopic characteristics of the native proteins. Examples of these include the mixed carbonyl/cyano complexes of iron, used to verify the infrared spectra to the hydrogenases (Fig 7.4) (Lai et al. 1998) and the nickel-thiolate complexes which have low redox potentials like the hydrogenases (Franolic et al. 1992). 

Different mixed carbonyl cluster precursors of Ru and Pt having phenyl-containing tin Hgands have recently been proposed for the preparation of Ru PtySnz nanoparticles on mesoporous sihca support These systems show high performance for the production of cyclododecene and 1,4-cyclohexanedimethanol by selective hydrogenation reactions [117]. 

Only more recent investigations of organic isocyanide complexes of chromium are in this section, because general synthetic methods for metal isocyanide complexes, including mixed carbonyl isocyanides, and the nature of the metal-isocyanide bond are discussed in Sections... 

Few complexes containing only nilrosyl ligands are well characterized, bui many mixed carbonyl-nitrosyl complexes tire known 41 They may be formed readily by replacement of carbon monoxide with nitric oxide ... 

Only a limited number of cyano and isocyano complexes and mixed carbonyl, nitrosyl and phosphine cyano complexes of nickel(O) have been described so far.16... 

K4Ni(CN)4 is a yellow solid which is extremely sensitive to oxygen and moisture. It can be prepared by reducing K2Ni(CN)4 in liquid NH3 with an excess of potassium17 and decomposes in water with H2 evolution. CN ions can be easily replaced by ligands with greater jt acceptor properties such as CO, NO and phosphines. Mixed carbonyl and nitrosyl cyano complexes have been prepared by direct reactions (equations 1 and 2).18,19... 

A fairly large number of mixed carbonyl phosphine and arsine complexes have been reported so far. They are generally prepared by displacement of CO from Ni(CO)4. Owing to the high stability of Ni(CO)4, when it is reacted with phosphines and arsines at room temperature and atmospheric pressure, only a partial displacement of CO usually occurs. Most of the mixed phosphine (or arsine) carbonyl compounds have the general formula [Ni(CO) (PR3)4 ] (n = 3, 2) and [Ni(CO)2(L—L)] (L—L is a diphosphine or diarsine). These complexes are colourless or yellow-orange solids or liquids. Many of them are thermally stable but decompose in air. The most relevant mixed carbonyl complexes with common phosphines are reported in Table 4. 

Some of the mixed carbonyl phosphine complexes have been found to be efficient catalysts of oligomerization of alkanes. 

Table 4 Mixed Carbonyl Phosphine and Arsine Complexes...

In cocondensation experiments of nickel atoms in various CO/N2 matrices, mixed carbonyl-dinitrogen species Ni(CO)x(N2)4 x (jc = 1-3) were observed.243 The Ni(CO)3(N2)244 245 species was also generated by the UV photolysis of Ni(CO)4 in N2-doped liquid Kr, and the decay kinetics were studied.246 The Ni—N2 dissociation energy was estimated to be about 42kJmor1. 

X-Ray powder photographs showed that the chloride and bromide complexes were isomorphous. The i.r. spectrum has been interpreted in terms of both chloro bridges (2)11 and mixed carbonyl-chloro bridges (3).12 Both [PdCl(CO)] and [PdBr(CO)]... 

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