Carbonyl with bridging

The tendency to form carbonyls with bridging CO groups decreases with increase in atomic size of the metal. This trend is observed in groups as well as in series of the... 

M ,(CO) Metal carbonyl clusters with bridging CO groups M-C(0) M... 

So far, only reactions in which the internal nucleophile is tethered to the nitrogen atom of the A -acyliminium ion have been discussed, however, cyclizations with nucleophiles attached to other positions are also possible. If the nucleophile is connected to the carbon atom adjacent to the carbonyl group, bridged azabicycloalkane derivatives are obtained in high yield by using the more reactive allyl- or propargylsilanes. 

While essentially all the metal carbonyl complexes for group 4B contain terminal CO ligands, only recently have some bonafide doubly bridging carbonyl complexes been reported. However, these complexes are hetero-nuclear, since the carbonyl ligand bridges a zirconium atom with the metal center of a late transition metal. 

The cluster anion, [Os3Ir(CO)i3], was prepared in 50% yield by reaction of Os3(CO)i2 with [Ir(CO)4]. The single-crystal X-ray structure analysis shows it to consist of a tetrahedral metal core with one of the 13 carbonyl ligands bridging. The catalytic activity for carbonylation of... 

The structures of the derivatives have been inferred from their infrared spectra the carbonyls Fe2M(CO)12 (M = Ru, Os) are similar to Fe3(CO)I2 with bridging carbonyl groups between the iron centers, while the carbonyls FeM2(CO)12 have the Ru3(CO)12 structure (235-237). 

Pd7(CO)7(PMe3)7] has been isolated from the reaction of (23) with CO.115 This cluster has a monocapped octahedral structure with one phosphine attached to each Pd atom. Four of the carbonyl ligands bridge the octahedral faces, while the other carbonyls edge bridge (Pd—Pd 2.79(2) A). 

Cotton has discussed this phenomenon extensively (37). For complementary sets of more than two carbonyl bridges, the equilibration is also probably concerted. All of the carbonyls in Rh4(CO)u appear magnetically equivalent at room temperature, with bridge terminal interconversion occurring via the formation of an unbridged species whose structure is analogous to Ir4(CO)12 (39). 

It is also relevant to record that several iron-carbonyl complexes with bridging, and in one case terminal, aryltellurol ligands have been prepared by reaction of Fe(CO)5, Fe(CO)12 or [ji-CpFe(CO)2]2 with diaryl ditellurides and which, together with complexes containing other transition metal carbonyls, e.g, ruthenium, osmium and manganese, provide a substantial number of interesting compounds.2... 

Numerous dinucleating macrocyclic and macrobicyclic ligands have been synthesized, in particular by the versatile amine + carbonyl — imine reaction they form dinuclear metal complexes as well as cascade complexes with bridging groups [2.58-2.63, 3.24-3.27, 4.1-4.4], for instance in dicobalt complexes that are oxygen carriers [3.26]. 

Again, the structure of 8 resembles that of 5, but with bridging hydride in place of the bridging carbonyl (17). 

Attempts have been made to mimic proposed steps in catalysis at a platinum metal surface using well-characterized binuclear platinum complexes. A series of such complexes, stabilized by bridging bis(diphenyl-phosphino)methane ligands, has been prepared and structurally characterized. Included are diplati-num(I) complexes with Pt-Pt bonds, complexes with bridging hydride, carbonyl or methylene groups, and binuclear methylplatinum complexes. Reactions of these complexes have been studied and new binuclear oxidative addition and reductive elimination reactions, and a new catalyst for the water gas shift reaction have been discovered. 

Chromium-based reagent systems, for pinacol coupling, 11, 63 Chromium carbenes, in ene-yne metathesis, 11, 272 Chromium carbonyl compounds with bridging hydrides, 5, 206 computational studies and spectroscopy, 5, 203 experimentally determined structures, 5, 204 nitro and nitroso compounds, 5, 205 silatropic migrations, 5, 249 with very weakly bonded ligands, 5, 205 Chromium carbonyl hydrides, preparation and characteristics,... 

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