Complex xvii

The reaction rate of enyne 107j having a terminal alkyne is very slow, and the starting material is recovered [Eq. (6.80)]. ° Presumably, the terminal alkene of the product 108j should further react with ruthenium carbene complex Ih to form XVII, whose ruthenium carbene should be coordinated by the olefin in the pyrrolidine ring. Thus, the catalytic activity of Ih should be decreased. If complex XVII reacts with ethylene, 108j and methylidene ruthenium carbene complex Ih should be regenerated. On the basis of this idea, the reaction was carried out under ethylene... 

Catalyst XV promoted the cyclooctene ROMP with an extremely low catalyst loading (30 000 1) reaching a TOF of 9200 min (Table 8.3, entries 1,2) but its activity decreased at a ratio 100000 1. The catalyst containing P Pr3 XVI showed excellent activity whereas, as expected, complex XVII with the poor electron donor and less bulky phosphine PPh3 showed low activity. 

If cycloalkene-yne 65 having an o -alkynyl substituent at an olefinic position in a cycloalkene is treated with a ruthenium catalyst, what kinds of products are produced. In this reaction, ruthenium mono-substituted carbene complex XVII is anticipated to be formed from a highly strained ruthenacyclobutane intermediate. If it then reacts with ethylene, triene 67 should be formed, but if XVII reacts with an alkene part intramolecularly, bicyclic compound 66 should be formed via ruthenacyclobutane (Scheme 23). 

It is interesting that Complex XVI has a bridging chloride and terminal hydride ligands, whereas Complex XVII has bridging hydride and terminal chloride ligands. Complex XVII can be reversibly deprotonated to give the diplatinum(I) complex (II) (12, 13). 

Alkylation then yields the trans alkene shown other alkynes can give rise to cis products. It seems likely that the metal-alkene complex (XVII) is similar to intermediates believed to occur in various catalytic processes involving nickel-bipyridyl complexes. 

Using the more bulky l-t-butyl-3,4-dimethylphosphole and the same iron carbonyl, the main product was complex XVII analogous to Braye s complex XIV. Thus the more bulky the P-substituent on the phosphole ring, the more likely the formation of the metal-metal bond. 

Note that the same cr,7T-binuclear complex (XVII) may be obtained through a one-step synthesis from (XV) or through an independent synthesis from... 

Another mechanism for the reaction of (7r-C5H5)2Ni with triphenyl-phosphine in halogen-containing solvents has been advanced by Ustynyuk 225). In his opinion nucleophilic PPhj attack at the nickel and formation of the a-cyclopentadicnyl complex (XVII) in a transition state take place. 

Attempts were made to isolate complex (XVII). However, only indirect proof of its formation could be obtained 227). 

From the observation that was retained in the carbonyl group during the thermal decomposition of t-butyl o-(2,2-diphenylvinyl) perbenzoate, it was concluded that neighboring group participation occurred at the peroxide oxygen of the perester °. The rate acceleration and the observation that the activation parameters fall into the range expected for the loss of rotational freedom of three bonds led Fisher and Martin to suggest the activated complex (XVII) for the decomposition of /-butyl 8-(phenylthio)per-I-naphthoate (XVIII). Presumably,... 

By adding 1 mole of an organic phosphine per mole nickel in XIII, the catalytic activity is further increased. This phosphine-modified complex, XVI, reacts at —40°C. with only 1 mole of carbon monoxide to yield an inactive complex XVII. In the phosphine-modified complex XVI, there is accordingly one free coordination position. Catalytic activity disappears also an adding a second mole of a phosphine (XVIII). 

Complexes XVII are labile, in particular in halogenated solvents, and must be prepared at —10 to — 40°C . Butadiene, isoprene, cyclohexadiene, etc., may be used. In contrast, the niobium hydride XVIH reacts smoothly with butadiene to give XK ... 

Hucho, R Randall, D.D. Roche, T.E. Burgett, M.W. Pelley, J.W. Reed, L.J. a-Keto acid dehydrogenase complexes. XVII. Kinetic and regulatory properties of pyruvate dehydrogenase kinase and pyruvate dehydrogenase phosphatase from bovine kidney and heart. Arch. Biochem. Biophys., 151, 328-340 (1972)... 

The chelation of metal ions has been discussed by Clark and Geissman (1949). They suggest that several sites might be concerned in chelation. In quercetin, for instance, sites A and B can both be considered as competent to form chelate complexes (XVII). Site C is perhaps even more likely to be involved. 

To test for the intermediacy of free carbenes in the decomposition of metal-carbene complexes, the thermolysis of the 2-oxacyclopentylidene complex XVII was studied (Anderson and Casey, 1975). 2-Oxacyclopentylidene has been generated by pyrolysis of the sodium salt of butyrolactone tosylhy-drazone and shown to rearrange to give both dihydrofuran and cyclobutanone (Agosta and Foster, 1972). The thermolysis of XVII in decalin at 180° for 15... 

Mohr and Laguna reported in 2007 the ability of water-soluble Au-phosphine complexes XVII-XVIII to promote hydration of phenylacetylene in water (Scheme 16.29). Using 0.1 mol% of the gold complex, and 10 mol% of H2SO4 as additive, they obtained moderate conversions to the hydrated product. Although the obtained conversions were lower than the ones... 

The central catalytic cycle is characterized by the use of the pincer complex XVII. The authors supposed that the boronate group is transferred from diboronate XIII to catalyst XVn, affording the jj -boronato complex XVIII. The boronato group substitutes the activated hydroxyl group in XV to give allyl boronic acid XVI and boric acid. Importantly, this step ensures that the waste product of the reaction is non-toxic boric acid. 

Nesmeyanov and co-workers (1971) have found that thermolysis of tolane complex (XVII) gives diphenylindenone as the major product. Formation of this product was suggested to occur through a complexed benzyne intermediate. Attempted preparation of the corresponding lead complex gave only the indenone derivative in 58% yield. 

---