Organic transition metal carbonyls

It has generally been concluded that the photoinitiation of polymerization by the transition metal carbonyls/ halide system may occur by three routes (1) electron transfer to an organic halide with rupture of C—Cl bond, (2) electron transfer to a strong-attracting monomer such as C2F4, probably with scission of-bond, and (3) halogen atom transfer from monomer molecule or solvent to a photoexcited metal carbonyl species. Of these, (1) is the most frequently encountered. 

Three approaches have been tested, as already described above for inorganic supports. The first attempts concern the direct reaction of transition metal carbonyls with unmodified organic polymers like poly-2-vinyl-pyridine.61 62 However, this kind of anchoring is restricted to only a few complexes. Various polymers have been functionalized with donor groups 63-72 ligand displacement reactions using these afforded the corresponding immobilized complexes. Finally, tests with modified complexes and unmodified polymers are scarce because of the low stability of these complexes under the conditions of reactions. 

Azidorhodium complexes are of considerable structural interest, but limited applicability can be expected from the unusual triazole synthesis illustrated in Scheme 125.190 It is also difficult to envisage synthetic utility from reactions in which organic azides are decomposed by transition metal carbonyls. Thus 2-arylbenzotriazoles are formed in such reactions on... 

High pressure infrared (HP IR) spectroscopy has now been used for over 30 years for the study of homogeneous transition metal catalysed processes. The technique is particularly useful for reactions involving carbon monoxide, for which transition metal carbonyl complexes are key intermediates in the catalytic mechanisms. Such complexes have one or more strong r(CO) absorptions, the frequencies and relative intensities of which provide information about the geometry and electronic character of the metal center. As well as probing the metal species, HP IR spectroscopy can also be used to monitor the depletion and formation of organic reactants and products if they have appropriate IR absorptions. 

Carbon-13 chemical shifts of transition metal carbonyls [471, 473] decrease as one proceeds down a given group of the periodic table, as demonstrated for the triad Cr(CO)6, Mo(CO)e, and W(CO)e in Table 4.71. Substitution of CO by cyclopentadienide and other organic ligands deshields the carbonyl carbon nuclei. This is exemplified by iron pentacarbonyl (211 ppm) in comparison to cyclopentadienylirondicarbonyl-dimer, which displays one avaraged carbonyl signal ( 240 ppm) at room temperature [488] due to rapid cis-trans isomerization and intramolecular bridged-terminal carbonyl interconversion ... 

Cyclopropylcarbene complexes of the type L M=C(XR )R2 (X = O, S R1 = alkyl, aryl R2 = cyclopropyl) having a stabilizing heteroalkyl (XR1) group on the electrophilic carbene ligand (Scheme 3) have found widespread application in organic synthesis. These so-called Fischer carbene complexes are best known via their group 6 transition metal carbonyl complexes (CO)5M=(OR )R2(M = Cr, Mo, W)132. Much less abundant are the Schrock-type cyclopropylcarbene complexes L M=CR R2 where no heteroatom is bound to the carbene carbon atom133. 

This section highlights some of the significant features of chromium(O) carbonyls and of the chemistry of this oxidation state. Further information can be found in the articles Carbonyl Complexes of the Transition Metals and Organic Synthesis using Transition Metal Carbonyl Complexes, and in the review literature. ... 

Many transition metal carbonyl complexes have been prepared, often inadvertently, by allowing a metal halide or polyhalometallate to react with a ligand in an organic solvent with carbon-oxygen bonds. Indeed, carbonyl abstraction is an important synthetic route to tran5 -[MCl(CO)(PPh3)2] (M = Rh, Ir) or [OsHX(CO)(ZPh3)3] (X = Cl, Br Z = P, As) and related osmium(II) complexes. 

The carbonyl complexes of iridium have perhaps not been as extensively studied as those of some other metals (see Carbonyl Complexes of the Transition Metals Carbonylation Processes by Homogeneous Catalysis, and Organic Synthesis using Transition Metal Carbonyl Complexes). Nevertheless some interesting findings in this area both in terms of stmeture and reactivity have been reported. 

Certain classical coordination complexes (see Coordination Complexes) of iron (e.g. Prussian blue) will be dealt with in other articles (see Iron Inorganic Coordination Chemistry and Cyanide Complexes of the Transition Metals), as will much of the chemistries of iron carbonyls (see Metal Carbonyls) and iron hydrides (see Hydrides) (see Carbonyl Complexes of the Transition Metals Transition Metal Carbonyls Infrared Spectra, and Hydride Complexes of the Transition Metals). The use of organoiron complexes as catalysts (see Catalysis) in organic transformations will be mentioned but will primarily be covered elsewhere (see Asymmetric Synthesis by Homogeneous Catalysis, and Organic Synthesis using Transition Metal Carbonyl Complexes). 

Organic Synthesis using Transition Metal Carbonyl Complexes... 

Synthetically important reactions employing transition metal carbonyl complexes see Carbonyl Complexes of the Transition Metals) have been extensively developed and applied in total synthesis of complex organic molecules. Stoichiometric amounts of metal carbonyl complexes are usually employed, but the often significant increase in complexity going from starting material to product and the... 

ORGANIC SYNTHESIS USING TRANSITION METAL CARBONYL COMPLEXES... 

ORGANIC SYNTHESIS USING TRANSITION METaL CARBONYL COMPLEXES 13... 

---