Double carbonylation, transition metal complexes

The answers to these questions and other questions about the cyanide and carbonyl transition-metal complexes can be derived from the idea that the cyanide and carbonyl groups form double bonds with the transition metal atom. 

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. 

In this section we will consider the interactions between transition metal complexes and carbon-oxygen double bonds, i.e. carbonyl groups. The transition metal functions as a reagent to deliver an alkylidene fragment and replace the oxygen atom. The process is analogous to a Wittig reaction (equation 17). ... 

In Table VII are recorded mean values for in a number of ethylene-metal carbonyl complexes and parent metal carbonyls as well as values for the double-bond infrared stretching frequency rc c the magnetic shielding parameter t for ethylene in those transition metal complexes for which data are available. Although with the metal carbonyl complexes, differences of geometry, oxidation state, etc., do not permit a correlation to be drawn between the absolute values of rco and for the various complexes, it is quite apparent from the tabulated data for the Mo, Mn, and Fe complexes that for a given metal. 

A cationic Sb(III) ligand is part of the tungsten complex [Cp(CO)2(Me3P)WSb(Me)-(Cl)Bu ]I, which was prepared from tr ns-Cp(CO)2(MeP)WSb(Cl)Bu and Mel in Et20 . The first transition metal complexes containing a metal-arsenic double bond were synthesized in 1983 . Transition metal substituted arsines of the type Cp(CO)3M—AsBu 2 (M = Mo, W) show increased Lewis basicity compared with triorganoarsines R3AS. From the above-mentioned complex one carbonyl is cleavable already at 60 °C (equation 35). 

Alkyl halides are usually considered to be less suitable for double carbonylation because of the possibility of the direct reaction of alkyl halides with nucleophiles and of instability of alkyl-transition metal complexes involved in the catalytic process. However, allylic halides were found amenable to double carbonylation promoted by zerovalent palladium complex. It is well known that allylic halides undergo ready oxidative addition with a Pd(0) species to produce Tj -allylpalladium halide complexes. Thus, it was reasoned that the double carbonylation process might be realized if CO insertion into the aUyl-palladium bond proceeds before attack of amine on the 17 -allylpaUadium halide takes place. On the basis of fundamental studies on the behavior of i7 -allylpalladium halide complexes with CO and secondary amines, double carbonylation processes of substituted aUyl halides to give a-keto amides in high yields have recently been achieved (Eqs. 15 and... 

H. DOUBLE CARBONYLATION REACTIONS PROMOTED BY OTHER TRANSITION METAL COMPLEXES... 

No unusual initiators, such as transition metal complexes or heterogeneous catalysts, are needed for perhaloacetaldehyde polymerizations, the polarization of the carbonyl group of the aldehyde monomer is well defined and does not cause the formation of head to head linkages in the polymer. The shorter carbon oxygen single bond (1.43 A) which is formed by ring opening of the carbonyl double bond (1.21 A) has a beneficial effect for the formation of a helical structure for the isotactic polymer and should, consequently, favor the formation of isotactic polymer. 

MA is capable of donating electrons from the olefin tt bond like other olefins. Besides transitory equilibrium species proposed as intermediates during various addition reactions of the olefin, the C—C double bond can function as a ligand. In so doing, it leads to a variety of transition-metal complexes. Weiss and Stark obtained bis-(maleic anhydride)nickel (O) as orange crystals when a benzene solution of MA and nickel carbonyl was heated. 

The surface of the silica may be dynamically coated with transition metals, and the selectivities observed can be attributed to the complexes between the metal ions and the analyte species [56], The use of silver-impregnated silica (adsorption of salts of transition metals on the silica surface) has been used for the analysis of saturated and unsaturated fatty acid methyl esters (FAME) and triacylglycerols (TAG) [57], The retention of the unsaturated FAME and TAG can be attributed to the stability of the complex that is formed between the K electrons of the carbon-carbon double bonds and the silver ions. The predominant interaction for saturated analytes is with the polar silanol groups. The secondary interactions are those of the silver ions with the unpaired electrons of the carbonyl oxygens of the analytes. The amount of silver adsorbed onto the silica and the pH (employment of acidic or basic modifiers) have been determined to have an effect on the retention and resolution of certain acidic and basic compounds and fatty acids [58]. 

Formula II shows one trans-double bond which is shared with the nickel atom. Furthermore, there are six carbon atoms which are in the state of an -hybridization. Each C atom shares one r-electron with the nickel. (The complex shows the correct molecular weight for NiCi2Hig, and there is no absorption in the infrared spectrum characteristic of double bonds.) This formulation has some relationship to structures which have been recently proposed by different authors (2, 4) for various allylic groups bonded to transition metal carbonyls. 

Indirect observation of transition metal chemical shifts via C was reported for the determination of 5( Fe) in a variety of ferrocenes and ferrocenyl carbenium ions, as well as in a natural myoglobin carbonyl complex and two synthetic model compounds. All measurements were made by selective double-resonance methods using either [ Fe]-labelled or... 

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