Pentacarbonyl-metal complexes

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... 

Condensation of vinyl chloride with formaldehyde and HCl (Prins reaction) yields 3,3-dichloro-l-propanol [83682-72-8] and 2,3-dichloro-l-propanol [616-23-9]. The 1,1-addition of chloroform [67-66-3] as well as the addition of other polyhalogen compounds to vinyl chloride are cataly2ed by transition-metal complexes (58). In the presence of iron pentacarbonyl [13463-40-6] both bromoform [75-25-2] CHBr, and iodoform [75-47-8] CHl, add to vinyl chloride (59,60). Other useful products of vinyl chloride addition reactions include 2,2-di luoro-4-chloro-l,3-dioxolane [162970-83-4] (61), 2-chloro-l-propanol [78-89-7] (62), 2-chloropropionaldehyde [683-50-1] (63), 4-nitrophenyl-p,p-dichloroethyl ketone [31689-13-1] (64), and p,p-dichloroethyl phenyl sulfone [3123-10-2] (65). 

CN > NO2 > NH3 > H2O, F > Cl . Exceptions do occur. Photochemical Ligand dissociation is useful in the synthesis of multinuclear metal complexes such as diiron nonacarbonyl [15321-51 from iron pentacarbonyl [13463-40-6]... 

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. 

The reaction of ethyl 2,2-diethoxyacrylate with alkynylalkoxycarbene complexes affords 6-ethoxy-2H-2-pyranylidene metal complexes [92] (Scheme 48). The mechanism that explains this process is initiated by a [2+2] cycloaddition reaction (see Sect. 2.3), followed by a cyclobutene ring opening to generate a tetracarbonylcarbene complex. This complex can be isolated and on standing for one day at room temperature renders the final 6-ethoxy-2Ff-pyranylidene pentacarbonyl complex. This last transformation requires the formal transfer of one carbonyl group and one proton from the diethoxy methylene moiety to the metal and to the C3 2H-pyranylidene ring, respectively, with concomitant cyclisation. Further studies on this unusual transformation have been extensively performed by Moreto et al. [93]. 

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... 

This paper reviews the recent studies in the field of radical reactions of organobromine compounds. A special attention is paid to the use of metal-complex systems based on iron pentacarbonyl as catalysts this makes it possible to perform the initiation and chain transfer reactions selectively at C-Br bond. 

Of course, commercially available transition metal complexes are stable at room temperature because they have achieved an 18-electron noble gas-like electronic configuration. Thus, molecules like iron pentacarbonyl [Fe(CO)s], ferrocene [Fe(C5H5)2], as well as piano-stool complexes such as C5H5Co(CO)2 are chemically quite inert. In order to study bimolecular reactions, it is necessary to first prepare unsaturated complexes. For studies using molecular beams, one approach is through photolysis of a stable volatile precursor in a supersonic nozzle. 

In spite of the fact that silver(i) X-heterocyclic carbene complexes were widely employed as carbene-transfer reagents for the synthesis of other transition metal carbene complexes, their synthesis could also be achieved by the reaction of silver salts with relatively more labile carbene metal complexes, albeit rare. Complexes 71a-71c were reported to be synthesized from the reaction of the corresponding pentacarbonyl(carbene)chromium(i) complexes with silver(i) hexafluorophosphate in CDC13 under inert atmosphere (Scheme 17).117... 

Historically, vinylidene complexes of zero-valent pentacarbonyl Group 6 metals appeared as a fleeting intermediate for the preparation of Fischer-type carbene complexes. Probably the first example of the formation of such a pentacarbonyl vinylidene complex of a Group 6 metal was proposed in 1974 by Fischer et al, who examined the reaction of pentacarbonyl[hydroxy(methyl)carbene] chromium 1 with dicyclohexylcarbodiimide(DCC) [3]. Thus, treatment of 1 with DCC in CH2CI2 at —20°C rt gave a novel azetidinylidene complex 2 in 47% yield. As a possible... 

Utilization of Pentacarbonyl Vinylidene Complexes of Croup 6 Metals for Synthetic Reactions... 

Utilization of Pentacarbonyl Vinyiidene Complexes of Group 6 Metals for Synthetic Reactions 165... 

The pentaphenylborole dianion was incorporated as a ligand in transition metal complexes with platinum and cobalt as well as with iron, nickel and manganese. An interesting formation of such a complex from 1-phenyl-4,5-dihydroborepin (53) was performed in boiling mesity-lene in the presence of iron pentacarbonyl. Six-membered borinate complexes were also found in the reaction mixture (77AG43). 

Interaction of metals with cyclopropenylidene to form stable complexes has been widely studied340 in the last two decades since the first reported synthesis of pentacarbonyl(2,3-diphenylcyclopropenylidene)chromium (see belowy4. Two groups of cyclopropenylidene metal derivatives may be distinguished neutral cyclopropenylidene complexes represented by two resonance forms, and the cationic cyclopropenylium transition metal complexes of groups 6 (Cr, Mo, W), 7 (Mn), 8 (Fe) and 10 (Pd, Pt), whereas the latter cationic cr-complexes are derived from both main group metals (Li, Mg) and group 10 (Pd, Pt) transition metals. 

Pentaalkynylferrocenes, preparation, 6, 190 Pentaarylantimonys, in C-C bond formation, 9, 430 Pentaarylcyclopentadienyl compounds, with iron, 6, 159 Pentacarbaboranes, metal complexes, 3, 230-233 Pentacarbonyl(3-aminoallenylidene)chromium complexes, preparation, 5, 270... 

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)...

Phosphinidenes (R-P), short-lived, reactive intermediates that are isoelec-tronic with nitrenes and carbenes, are accessible by fragmentation of phos-phiranes, phosphol-3-enes, triazaphospholenes, and oxazaphospholenes and can be characterized by trapping reactions. The metal-complexed species [R-P-M, e.g., M = W(CO)5] are more stable (but also not isolable) and react more selectively. As a model example we describe the transformation of (3,4-dimethyl-l-phenylphosphole)(pentacarbonyl)tungsten 4 with dimethyl acetylenedicarboxylate to the 7-phosphanorbomadiene derivative 5.11 The (phosphinidene)(pentacarbonyl)tungsten complex 6 is generated from the latter by a [4+ 1]-cycloreversion and trapped with diphenylacetylene via a [2+1]-cycloaddition to furnish the triphenyl-2-phosphirene complex 7 (Scheme l).12... 

This route probably involves carbonyl insertion into a metal-carbene bond. Closely related compounds can also be prepared from M(CO)g (M = Cr, W)-a-lithiated sulfides-[Et3 0][Bp4] or by treatment of pentacarbonyl(thio)metal complexes,... 

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