Metal carbonyl s. a. under

Recently, the thermally and photochemically induced one-electron transfers from the metal-carbonyl anions A[Mn(CO)5], A[Co(CO)4], and A[Re(CO)s] (A = Na and PPN) to fullerene have been studied. In the case of the thermal reactions of the Mn and Re anions, initial electron transfer to form Ceo and the corresponding 17e M(CO)s radical is followed by the competitive collapse to the metal dimer and formation of the tj -Ceo complexes A [Mn(CO)4(jj -Ceo)]. Under photochemical conditions, redissociation of the dimer results in exclusive formation of the jj -complexes, which are thought to be formed by nucleophilic displacement... 

Organometallic compounds (s. a. under individual metals. Group III element. . ., Group IV —. . ., Group V —. . ., Metal carbonyls. Metal complex compounds, organo-. Reagents, organometallic)... 

Dienes form very stable complexes with a variety of metal caibonyls, particularly Fe(CO)s, and the neutral V-diene metal carbonyl complexes are quite resistant to normal reactions of dienes (e.g. hydrogenation, Diels-Alder). However, they are subject to nucleophilic attack by a variety of nonstabilized carbanions. Treatment of -cyclohexadiene iron tricarbonyl with nonstabilized carbanions, followed by protonolysis of the resulting complex, produced isomeric mixtures of alkylated cyclohexenes (Scheme 15).24 With acyclic dienes, this alkylation was shown to be reversible, with kinetic alkylation occurring at an internal position of the complexed dienes but rearranging to the terminal position under thermodynamic conditions (Scheme 16).2S By trapping the kinetic product with an electrophile, overall carbo-... 

Both HRe(CO)s and H2Os(CO)4 can be oxidatively added to Os3(CO),, (NCMe) (126 -128). This leads to external attachment of the new metal carbonyl unit as in 64 (127), and a second HRe(CO)s molecule can be incorporated the same way (126). In both cases just one metal-metal bond has been formed in the first step. CO elimination from 64 introduces one more metal - metal bond, one possible result of which is rhomboidal 65 (126), whereas further CO elimination under H2 leads to full aggregation to tetrahedral 66 (127). All three steps of a M3 + M capping sequence have thereby been performed. A similar two-step sequence leads from Os6(CO)17(NCMe) and H2Os(CO)4 via H2Os7(CO)21 to H2Os7(CO)20 (128). 

The metal complex used was Ni(GO)4 under a carbon monoxide atmosphere in DMF at 50 °C for 3h. A suitable temperature was found to be in the range 70-90 °C and the optimum reaction time was 1-3 h. Under an inert nitrogen atmosphere the yield was reduced drastically since the CO atmosphere is essential for the reaction. The use of THF instead of dimethylformamide (DMF) led to a reduction of the yield. Similarly, when 0.1 equiv of Ni(CO)4 was used as a catalytic metal carbonylating agent, instead of 1 equiv, a low yield of the product was noted. The use of metal carbonyls such as Fe(CO)s, W(CO)s led to a negligible amount of diazetidinediones (Scheme 49). 

The first experiments which were carried out in the author s laboratory on organometallic phase-transfer catalysis were concerned with the reduction of nitrobenzenes (4) to anilines (5) by triiron dodecacarbonyl. Such a conversion was reported to occur in benzene containing methanol at reflux for 10-17 h, with the hydridoundecacarbonyltriferrate anion as the likely key intermediate (16). It was our expectation that the trinuclear iron hydride should be generated by phase-transfer catalysis and if so, effect reduction of nitro compounds (4) under exceedingly mild conditions. Indeed this was the case, as illustrated by the results shown in Table I (17). Not only is the reaction complete in 2 h or less using sodium hydroxide as the aqueous phase, benzene as the organic phase, and benzyltrieth-ylammonium chloride as the phase-transfer catalyst, but it occurs at room temperature and requires less metal carbonyl than when the reaction was... 

One of the most important metal carbonyl anions, as far as catalytic processes are concerned, is the cobalt tetracarbonyl anion, Co(CO)4. Prior to attempting phase-transfer catalysis using Co(CO)4" as a catalyst, it was imperative to establish that the anion is actually formed under these conditions. Therefore, model experiments in the author s laboratory involved the initial use of dicobalt octacarbonyl in a stoichiometric role. 

A high degree of stereoselectivity can be realized under chelation control, where an oxygen atom of an ether function (or more generally a Lewis base) in the a-, P- or possibly y-position of carbonyl compounds can serve as an anchor for the metal center of a Lewis acid. Since Cram s pioneering work on chelation control in Grignard-type addition to chiral alkoxy carbonyl substrates [30], a number of studies on related subjects have appeared [31], and related transition state structures have been calculated [32], Chelation control involves Cram s cyclic model and requires a Lewis acid bearing two coordination sites (usually transition metal-centered Lewis acids). 

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