Carbonyl complexes of transition metals

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. 

When represented in this way the chemistry of carbonyl complexes of transition metals becomes easier to understand. Hydroformylation reactions and other carbonylations that are catalyzed by transition-metal complexes frequently involve hydride or alkyl transfers from the metal atom to the positive carbonyl carbon (Sections 16-9G, 31-3, and 31-4) ... 

Carbonyl complexes of transition metals in positive oxidation states... 

When propylene chemisorbs to form this symmetric allylic species, the double-bond frequency occurs at 1545 cm-1, a value 107 cm-1 lower than that found for gaseous propylene hence, by the usual criteria, the propylene is 7r-bonded to the surface. For such a surface ir-allyl there should be gross similarities to known ir-allyl complexes of transition metals. Data for allyl complexes of manganese carbonyls (SI) show that for the cr-allyl species the double-bond frequency occurs at about 1620 cm-1 formation of the x-allyl species causes a much larger double-bond frequency shift to 1505 cm-1. The shift observed for adsorbed propylene is far too large to involve a simple o--complex, but is somewhat less than that observed for transition metal r-allyls. Since simple -complexes show a correlation of bond strength to double-bond frequency shift, it seems reasonable to suppose that the smaller shift observed for surface x-allyls implies a weaker bonding than that found for transition metal complexes. 

The nucleophilic reaction of hydroxide with carbonyl ligands of transition metal complexes,... 

Boron-bonded p -borazine complexes of transition metals have been prepared by two different approaches (a) nucleophilic substitution of B,fi, fi"-trichloro-borazine with an anionic metal carbonyl reagent and (b) oxidative addition of a B-Br bond of 5,5, B"-tribromoborazine to a zerovalent group 10 complex (see examples in Scheme 9.2). 

A review of diene-iron carbonyl complexes has recently appeared (5) metal complexes of di- and oligoolefinic ligands have also been reviewed (6). A general review of olefin, acetylenic, and 7r-allylic complexes of transition metals is due to Guy and Shaw (7). 

The interests in homoleptic (see Homoleptic Compound) isocyanide ( isonitrile, see Isocyanide Ligands) complexes of transition metals have largely been associated with their similarities to metal carbonyls. The greater versatility of isocyanide ligands in comparison to CO makes isocyanide complexes potentially valuable reagents in synthetic chemistry and catalysis. The dication [V(CNBu )6] reported in 1980 remained the sole example of a homoleptic group 5 metal isocyanide until 1999, when the first binary... 

Carbene Complexes Carbonyl Complexes ofthe Transition Metals Cyanide Complexes of the Transition Metals Dinuclear Organometallic Cluster Complexes Electron Transfer in Coordination Compounds Electron Transfer Reactions Theory Electronic Structure of Organometallic Compounds Luminescence Nucleic Acid-Metal Ion Interactions Photochemistry of Transition Metal Complexes Photochemistry of Transition Metal Complexes Theory Polynuclear Organometallic Cluster Complexes. 

Sulphur- and phosphorus-bridged complexes of transition metals Lewis-base-metal carbonyl complexes... 

Despite the focus of this chapter on the most commonly utilized Lewis acids in organic synthesis, a much larger body of data regarding the structure of donor/acceptor complexes of transition metals with carbonyls exists. Although a comprehensive treatment of this subject is beyond the scope of the present discussion, it is nonetheless worthwhile to consider the structural features of some of these complexes briefly, since many demonstrate novel and unusual ways of interacting with the carbonyl group. ... 

For carbonylation reactions involving metal carbonyls as catalyst precursors, the best fit to requirements 1 and 2 apparently is given by 4d transition elements. It is known that when activation of CO is required, carbonyl complexes of 4d metals are better catalyst precursors than their 3d and 5d congeners. Pertinent to this point are the following experimental observations ... 

In Table 2 appear complexes of transition metals with acetylenic compounds. A study was made of the structure and interconversion of acetylene complexes with binuclear transition metals, where acetylene lies parallel or perpendicular to the metal-metal bond" . Carbonyl alkyne complexes with binuclear iron give good separations in reverse-phase HPLC 4... 

Most of these processes currently make use of homogeneous catalysts. These are usually soluble complexes of transition metals, e.g., Co, Rh, and Ru. For example, conversion of methanol into acetic acid requires catalysis by either Co carbonyl or Rh carbonyl complexes and co-catalysis by iodine. Under reaction conditions iodine is most likely present as HI and CH3I, the latter probably being the agent by which the catalytically active ion (Rh or Co) is alkylated " before a methyl migration to the co-ordinated CO takes place. 

Most of the reactions of PH3 with the carbonyls of the transition metals and with a variety of carbonyl derivatives can essentially be classified according to three main types of reactions (i) substitution of CO ligands, of other neutral Ti-acceptor ligands like, e.g. PR3, weak 0-, S-, N-donor ligands, and alkenes, or of anionic ligands, (ii) cleavage of metal-metal bonds, and (iii) oxidative addition. Only in a few cases combinations of two or three of these reaction types or completely different reactions are observed. Most reviews dealing with the chemistry of phosphanes, with complexes of transition metals, or with transition metal carbonyls and derivatives cover only some aspects of the coordination chemistry of PH3 see e.g. [1,4, 14, 16, 22, 24, 27 to 29]. 

The addition of HCN to olefins catalyzed by complexes of transition metals has been studied since about 1950. The first hydrocyanation by a homogeneous catalyst was reported by Arthur with cobalt carbonyl as catalyst. These reactions gave the branched nitrile as the predominant product. Nickel complexes of phosphites are more active catalysts for hydrocyanation, and these catalysts give the anti-Markovnikov product with terminal alkenes. The first nickel-catalyzed hydrocyanations were disclosed by Drinkard and by Brown and Rick. The development of this nickel-catalyzed chemistry into the commercially important addition to butadiene (Equation 16.3) was conducted at DuPont. Taylor and Swift referred to hydrocyanation of butadiene, and Drinkard exploited this chemistry for the synthesis of adiponitrile. The mechanism of ftiis process was pursued in depth by Tolman. As a result of this work, butadiene hydrocyanation was commercialized in 1971. The development of hydrocyanation is one of tfie early success stories in homogeneous catalysis. Significant improvements in catalysts have been made since that time, and many reviews have now been written on this subject. ... 

A very important class of organometallic compounds is complexes of transition metals with carbonyl (CO) ligands (see examples in Tables S3.13) [228-231]. The coordination number in these complexes is determined by the FAN mle, hence the stable complexes are tetrahedral Ni(CO)4 and Pd(CO)4, trigonal-bipyramidal [Mn(CO)5] andFe(CO)s, octahedral Cr(CO)e, Mo(CO)6 and W(CO)6. Formally CO is an inorganic ligand, the bond in it is shorter (1.128 A in the gas phase) than in CO2 (1.160 A) and is nearly triple (C O) in character. Usually CO coordinates with metal in a linear fashion which can be formally described by the valence-bond scheme M=C=0. However, metal carbonyls are typical k complexes in their... 

The substitution of CO in metal carbonyls by olefinic and acetylenic compounds is one of the chief methods for preparing tt complexes of transition metals. Unfortunately this procedure fails almost completely when applied to nickel carbonyl, and this may be one of the reasons why until recently no tt complexes of nickel with olefinic or acetylenic ligands were known. The reasons for this behavior of nickel carbonyl will become clearer, if both its electronic structure and the mechanism of the ligand exchange reactions are considered. 

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