Metallocycles nickel

A3-Pyrroline formation with carbonyl insertion also occurs during the reaction of /V-sulfinylarylamines with diphenylcyclopropenone in the presence of nickel carbonyl (Scheme 36).64 Phenyl isocyanate does not give a pyrroline product under these reaction conditions, hence the SO-CO exchange probably occurs within an intermediate metallocycle. The reaction... 

The formation of l,3,4-triarylpyrroline-2,5-diones from the reaction of diphenylcyclopropenone and N-sulfinylarylamines with nickel carbonyl has been described earlier (see Scheme 36 in Section IV,A,2).64 In contrast with this result, 2,4,5-triphenyl-3-isothiazolone 1-oxide is produced in this type of process using iron pentacarbonyl, and the analogous cyclohexyl derivative is formed in a nickel carbonyl-mediated reaction (Scheme 115).64 It is probable that metallocyclic species (cf. 93) are intermediates in these transformations. 

Ni(cod)2] in the presence of the diphosphines Ph2P(CH2) PPh2 (n = 1-4) catalyzes the reaction of 1-hexyne with C02 to give the lactone (125) in addition to products not containing C02 (equation 155).586 The best results regarding the phosphorus ligands were obtained with n=4. The reaction was believed to proceed via a metallocycle formed by dimerization of the 1-hexyne at a nickel(0)-phosphine complex (equation 156). 

The complex obtained on the basis of thiocarbazone of 2-furylaldehyde has the structure containing a five-member metallocycle [821]. Two five-member and one six-member metal-cycles are formed in the nickel complex shown by 466 [822],... 

Other metallocycles assembled from two ligand molecules and two metal atoms have been reported by Harding et aV Bimetallic [2+2] macrocycles from the bis(bipyridyl) derivatives 3-7 and nickel(II), copper(I), silver(I), zinc(II) and cad-mium(II) have been reported. Products of this type may have either chiral, helical... 

Likewise, the phosphorus-31 coordination chemical shift (JdP reori/coord) of the chelate-phosphorus reflects fhe properties of fhe intact steering hgand which are transmitted by the nickel into fhe metallocycle. The intact yhde -dependent chemical shift behavior is mirrored in fhe activity profile of fhe catalyst system [12]. 

The ease of interaction of Ni(0) complexes with organic substrates has been shown to depend upon both the ligands on nickel and the solvent. The presence of a,a-bipyridyl with the Ni(0) complex and the alkyne led to the isolation of a nickelacyclopropene, an observation in accord with the recently proposed metallocyclic pathway for the Ni(0)-cata-lyzed trimerization of alkynes. Allylic and benzylic ethers and epoxides have been observed to undergo oxidative insertion of Ni(0) into their C-0 bonds with solvent (TMEDA > THE > Et O > CeHe) and ligand (EtsP > PhsP a,a-bipy > COD) effects consistent with an electron-transfer attack by Ni(0). With such sulfur heterocycles as dibenzothiophene, phenoxathiin, phenothiazine, and thian-threne, a 1 1 admixture of (COD)2Ni with a,a-bipyridyl gave as the principal product the desulfurized, ring-contracted cyclic product. 

This result can be explained by the fact that nickel(II) complexes with 14-membered macrocyclic ligands with alternating 6-5-6-S metallocycles are more stable than their 15-membered 6-S-6-6 analogues [289]. However, if there are... 

To explain the preceding results, the authors proposed the mechanism depicted in Scheme 4.15. First, both the enoate and alkyne substrates coordinate to the Ni(0) catalyst, which bears the chiral N-heterocyclic carbene ligand. Next, the enantioselectivity-determining step of the process is the oxidative cyclisation, giving metallocyclic intermediate E. Then, cyclisation and subsequent (3-alkoxide elimination releases the enone. Transmetallation with BEtj, followed by p-hydride elimination, gives a nickel hydride. Reductive elimination then closes the catalytic cycle. 

Books have been published on cyclic polyolefin complexes and metal vapour synthesis, while a review on metal vapour cryochemistry also contains information relevant to the latter. Reviews have also been published on organometallic derivatives of alkenes and ketenes, cationic Rh diolefin complexes, and nucleophilic addition to cationic hydrocarbon complexes. More personalized reviews have appeared by Maitlis on Pd -acetylene chemistry, by Jonas and Kruger on alkali-metal-transition-metal w-complexes, and by Werner on bridged allyl and cyclopentadienyl complexes. Articles by Wilke on homogeneous catalysis, by Vollhardt on metal-mediated approaches to steroid synthesis, by Schrock > on organotantalum chemistry, and by Grubbs on nickel metallocycles also contain material of relevance to r-complexes. 

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