Synthesis organometallic

Phase-transfer catalysis can effectively promote the substitution of group 6 metal carbonyls by nitrogen, phosphorus, and arsenic ligands. Reaction of M(CO) [M = Cr, Mo, W] with a group 5 ligand and tetra-n-butylammonium iodide in benzene-sodium hydroxide (50%), at 25-80°C 

Ligand-Substitution Products Obtained from Equimolar Amounts of M(CO) and L in C H /50% NaOH 

Ligand (L) M Temperature (°C) Reaction time h) Products Yield (%) 

An investigation of the reaction of group 6 metal carbonyls with OH- in the absence of a Lewis base ligand indicates that oxygen exchange is a much more facile process than elimination of carbon dioxide from 53 (67). 

For the group 7B cations, M(CO)5L+ (M = Mn,Re), reaction with hydroxide ion in acetonitrile containing dibenzo-18-crown-6 results in acceleration of the rate of formation of the hydroxycarbonyl intermediate, and of the subsequent elimination of carbon dioxide to give the m-hydride 57 (62, 63). 

Hydration of a pendant alkene by coordinated hydroxide (top), displaying specificity in site of attack, with the five-membered chelate ring only formed, and stereospecific attack of a deprotonated amine nucleophile (bottom) at the alkene of a chelate maleate ion. 

It is notable that reaction does not occur between free maleate ion and free 1,2-ethanediamine, although it does occur (but only very slowly) with maleate diester and 1,2-ethanediamine. Acceleration of the reaction of the maleate resulting from coordination to a metal ion is significant, and lies in the range 106-1010. Accelerations of this size are common for reactions of coordinated nucleophiles. The observation of stereospecificity and large accelerations suggests that these types of reactions may be relevant to the modes of action of certain metalloenzymes, where reactions are very rapid, specific and stereoselective. Such reactions are met in Chapter 8. 

Compounds with metal-carbon bonds usually require specialized approaches to their synthesis that differ from those discussed above for traditional Werner-type coordination 

Metal carbonyls represent a key class of organometallic compounds, and are often a starting point for other chemistry. They tend to be monomers, dimers or small oligomers, such as Ni(CO)4 and Mn2(CO)io, the latter involving a formal metal-metal bond. Most metal carbonyls are made by reduction of simple salts or oxides in the presence of CO, or direct reaction of CO with finely-divided metals at elevated pressure. Examples appear in (6.43) and (6.44). 

The carbonyl ligands are able to be substituted by some other ligands, or else the coordination sphere can be expanded by addition reactions with other compounds. It is also straightforward to prepare compounds that incorporate carbonyl and other ligands such as 

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Olshavsky M A, Goldstein A N and Alivisatos A P 1990 Organometallic synthesis of GaAs orystallites exhibiting quantum oonfinement J. Am. Chem. Soc. 112 9438... 

R. B. King, Organometallic Synthesis, Academic Press, Inc., New York, 1968. 

Ionic liquids hold as much promise for inorganic and organometallic synthesis as they do for organic synthesis. Their lade of vapor pressure has already been exploited [13], as have their interesting solubility properties. The field can only be expected to accelerate from its slow beginnings. 

Much of the recent interest in insertion reactions undeniably stems from the emphasis placed on development of homogeneous catalysis as a rational discipline. One or more insertion is involved in such catalytic processes as the hydroformylation (31) or the polymerization of olefins 26, 75) and isocyanides 244). In addition, many insertion reactions have been successfully employed in organic and organometallic synthesis. The research in this general area has helped systematize a large body of previously unrelated facts and opened new areas of chemistry for investigation. Heck 114) and Lappert and Prokai 161) provide a comprehensive compilation and a systematic discussion of a wide variety of insertion reactions in two relatively recent (1965 and 1967) reviews. 

The authors wotrld like to thank Professor Dr. A. Salzer (RWTH Aachen, Germany) for cooperating with us in the field of organometallic synthesis of ruthenirrm complexes. 

The limitations on organometallic synthesis by thermal decarboxylation can arise from (i) a thermodynamic preference for the reverse reaction, (ii) mechanistic limitations, (iii) thermal instability of the target organometallics, and (iv) a preference for alternative decomposition paths. 

Radical initiated decarboxylation appears to have considerable scope in organometallic synthesis, especially where the incoming radical is part of a coordinated ligand. 

B. Comils, W. A Herrmann (Eds. ), Aqueous-Phase Organometallic Synthesis, Wiley-VCH, Weinheim 1998 2nd Ed. 2003,... 

The reactions appear to be similar to organometallic synthesis, where the reduction is performed by the metal instead of electricity. However, these reactions have been shown to be essentially different from the corresponding organometallic reactions. This method has valuable advantages. As the anode reaction is controlled, an undivided cell can be used, the reaction occurs in one-step, the conditions are quite simple, and so on. Sibille and Perichon et al. have found that the sacrificial zinc anode is quite effective for trifluoromethylation of aldehydes to form trifluoromethylated alcohols in almost quantitative yields (Eq. 6) [19]. The reaction proceeds via the reduction of Zinc(II) salts, followed by a chemical reaction between the reduced metal, CF3Br, and aldehyde. 

Electrocarboxylation is carried out when C02 is used as electrophile offering an interesting alternative to organometallic synthesis. A prerequisite of this type of electroreduction in industrial scale is electrolytic cells especially adapted to use aprotic solvents. These cells must fullfil the following requirements [148,149] ... 

More recently, Kira et al. have published a new route to the preparation of hydrido(trialkylsilyl)silyllithiums, such as (/-BuMe2Si)2SiHLi 160,298 which show promise as versatile starting materials in organometallic synthesis. 

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