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Alkylidenes by α-H abstraction from metallacycles. Synthesis and characterization of alkylidene-bridged complexes of nickel

AuthorsBelderrain, Tomás R.; Gutiérrez, Enrique; Monge, M. Ángeles ; Nicasio, M. Carmen; Poveda, Manuel L.; Carmona, Ernesto
Issue Date1993
PublisherAmerican Chemical Society
CitationOrganometallics 12: 4431- 4442 (1993)
AbstractThe 16e- pseudoallylic complex Ni(η3-CH2C6H4-O-Me)Cl(PMe3) effects α-C-H abstraction from the benzoannelated nickelacycle Ni(CH2CMe2-o-C6H4)(PMe 3)2 (1) under very mild conditions, with formation of the tetrametallic species [Ni2(μ2-CHCMe2-o-C6H 4)(PMe3)2]2(μ-Cl)2 (2), in which two identical metal-metal-bonded bimetallic subunits are held together by chloride bridges. Each of these moieties incorporates a bifunctional organic fragment that possesses alkylidene and aryl termini that bridge the two metal atoms. Rupture of the (Ni2)2-(μ-Cl)2 bridges by PMe3 produces a binuclear nonsymmetric alkylidene, Ni2(μ2-CHCMe2-o-C6H 4)Cl(PMe3)3 (3), also exhibiting alkylidene and aryl bridges. A similar reaction of 2 with Me2PCH2CH2PMe2 (dmpe) furnishes the related, albeit cationic, alkylidene species [ÍÚ2(ì2-CHCMe2-o-C6H4) (dmpe)2]Cl (4). Interaction of the tetranuclear alkylidene 2 with NaCp produces the bimetallic product CpNi(μ2-CHCMe2-o-C6H4)Ni(PMe 3)2 (5). This complex can also be obtained by α-H abstraction from the methylene group of the metallacycle 1 by the 18-electron allyl derivative CpNi(η3-C3H5). The former reaction route also allows the synthesis of the analogous derivatives (C5H4R)Ni(η2-CHCMe2-o-C 6H4)Ni(PMe3)2 (R = Me (6), i-Pr (7)). Different kinds of μ-alkylidene compounds are furnished by the reaction of 2 and the poly(pyrazolyl)-borate salts K[HB(pz)3] (pz = pyrazolyl) and Tl[H2B(3-t-Bu-pz)2]. These new complexes have η2-bonded poly(pyrazolyl)borate ligands that bridge the two Ni atoms, i.e. Ni2(μ2-CHCMe2-o-C6H 4)[μ2-η1:η1-HB(pz) 3](PMe3)2 (8) and Ni2(μ2-CHCMe2-o-C6H 4)[μ2-η1:η1-H 2B(3-t-Bu-pz)2]-(PMe3)2 (9), respectively. Complexes 2 and 3 have been characterized by X-ray crystallography. Compound 2 crystallizes in the monoclinic space group P21/n with a = 9.815(4) Å, b = 10.550(4) Å, c = 19.669(7) Å, β= 104.39(3)°, and Z = 4. Crystals of 3 are orthorhombic, Pbca, with a = 17.152(4) Å, b = 18.431(3) Å, c = 32.577(5) Å, and Z = 16. Both display short metal-metal contacts (2.384(3) and 2.393(3) Å, respectively) suggestive of strong Ni-Ni bonding interactions. The alkylidene fragment symmetrically bridges the two Ni atoms in 2 and 3, but while in 2 the aryl bridges are also symmetric, in 3 one of the Ni-Caryl distances at 2.17(1) Å is perceivably longer than the other (1.99(2) Å). Compound 5 has also been characterized by X-ray crystallography. It crystallizes in the monoclinic space group P21/n, with unit cell constants a = 9.013(2) Å, b = 16.675(2) Å, c = 15.291(7) Å, β= 91.04(3)°, and Z = 4. © 1993 American Chemical Society.
Identifiersdoi: 10.1021/om00035a030
issn: 0276-7333
Appears in Collections:(IIQ) Artículos
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