Pentacarbonyl metallate

The 1,3-dipolar cycloadditions are a powerful kind of reaction for the preparation of functionalised five-membered heterocycles [42]. In the field of Fischer carbene complexes, the a,/ -unsaturated derivatives have been scarcely used in cyclo additions with 1,3-dipoles in contrast with other types of cyclo additions [43]. These complexes have low energy LUMOs, due to the electron-acceptor character of the pentacarbonyl metal fragment, and hence, they react with electron-rich dipoles with high energy HOMOs. 

It has been demonstrated that group 6 Fischer-type metal carbene complexes can in principle undergo carbene transfer reactions in the presence of suitable transition metals [122]. It was therefore interesting to test the compatibility of ruthenium-based metathesis catalysts and electrophilic metal carbene functionalities. A series of examples of the formation of oxacyclic carbene complexes by metathesis (e.g., 128, 129, Scheme 26) was published by Dotz et al. [123]. These include substrates where double bonds conjugated to the pentacarbonyl metal moiety participate in the metathesis reaction. Evidence is... 

A little later, we were able to obtain the pentacarbonyl metalates -II) Na2[Mo II(CO)5] and Na2[W-u(CO)5] in low yields (17). The yields were low due to the predominance of further reduction to the sparingly soluble, mononuclear tetracarbonyl metalates -IV) and formation of Na2C202 ... 

REACTIONS OF THE PENTACARBONYL METALATES(-II) AND THE DECACARBONYL DIMETALATES(-I) OF CHROMIUM, MOLYBDENUM, AND TUNGSTEN... 

With the preparation of Na[Cr(CO)5CN], we not only obtained the first anionic hexacoordinated, pentacarbonyl metalate(O) of Group VIB, but also initiated the extremely extensive chemistry of the [M(CO)sX]- anions. 

Scheme 9.1 Preparation of the methylmanganese and -rhenium complexes 2a,b from the pentacarbonyl metallates la,b and their conversion into the acyl metal derivatives 3 (L = CO, PR3, NH2R) via migratory insertion of a carbonyl ligand into the M—CH3 bond (a M = Mn b M = Re)...

CKM was adequate (53). Apparently, this conclusion concurs with that of Johnson et al. (77), but conflicts with that of Braterraan et al. (26). However, assuming the CKM holds, a vibronic contribution to the intensities (29) and the same characteristic dipole moment derivative for the two modes, Darensbourg and Brown (53) calculated the two characteristic moment derivatives for the symmetric and asymmetric modes and obtained again physically reasonable values of the angle a for a range of pentacarbonyl metal complexes. 

In summary, from the considerable study that has been made of pentacarbonyl metal complexes, there is some doubt about the adequacy of the CKM for the calculation of both relative and absolute intensities (26, 53). Measured intensities obtained from different laboratories lead to differing results (2, 53,136). Evidence suggests that individual carbonyl bond dipole moments exist (85, 123) and that solvent effects could cause the coexistence of characteristic dipole moment derivatives for the various modes (Section V). In any case, the existence of the latter has, independent of solvent... 

Absolute Integrated Intensities of Pentacarbonyl Metal Derivatives... 

The isostructural pentacarbonyl metallates Mn(CO)5 and Re(CO)5" form a series of thermally or photochemically unstable charge-transfer salts with N-methylpyridinium cations. For example, A-methylacridinium reacts with penta-carbonylrhenate immediately upon mixing in acetonitrile to form the (A-methyl-9-acridanyl)pentacarbonylrhenium(I) adduct in 90 % yield [126] (Eq. 46). 

A stu on the reaction of metal caihon with naked enolates to produce metallocarbene-enolates and alkyl-carbonylmetallates has been released" and the preparation of metal formates via die oxidation of metal carbonyl halides is also noted and the steiic and electronic tuning of Michael Additian reactions induced by pentacarbonyl metal fiagments has been studied. ... 

CFg-PFa and iron pentacarbonyl. Metallic nickel (formed by decarboxylation of nickel oxalate) has been shown to react directly at 60 °C with several fluorophosphines, including CFs-PF and (CF8)2PF, to give the corresponding zerovalent nickel complexes, e.g. Ni(CFj PF2)4 analogous complexes of zerovalent platinum, e.g. Pt[(CF3)jPF]4 (which can also be obtained from potassium tetrachloroplatinite and fluorobistrifluoromethylphosphine ), have been prepared from platinum(n) chloride and PFj, CFj-PFj, and (CF3)2PF at 60°C. = ... 

Fischer carbene complexes have proven to be useful in a number of selective syntheses, although the major drawback of these systems is the need for a stoichiometric amount of metal. One way to circiunvent this problem is to employ polymer-boimd complexes that can be recycled. Barluenga et aL [34] prepared polymer-bound Fischer timgsten carbene complexes from the corresponding pentacarbonyl metal compounds The reactivity and reusabihty of the polymer-supported complexes was exemplified by a cyclopropana-tion reaction (Scheme 9). Carbene 11 was heated with methyl acrylate in dichloroethane, and after cooling, saturation with CO, filtration and washing, the polymer 12 could be re-converted to a carbene and recycled. The product of the reaction was a mixture of cyclopropane 13 and C - H inser-... 

Wagner H, Baumgartner J, Marschner C (2005) Silyl-, germyl-, and stannyl-substituted group 6 pentacarbonyl metalates. Organometallics 24 4649... 

The straightforward access to O-glycosidic metal carbenes relies on the nucleophilic addition of an unprotected sugar alcohol to the electrophilic carbene carbon. In order to overcome problems arising from the inherent steric bulk of protected sugar nucleophiles the electrophilicity of metal oxycarbenes can be enhanced by 0-acylation. Acyloxycarbene complexes are temperature-sensitive intermediates but readily accessible from tetramethylammonium [acyl(pentacarbonyl)]metalates... 

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