Bridge trans configuration

Hydrogenolysis of the acetylene-cumulenes 19 can be achieved by means of a partially poisoned palladium catalyst to yield the regular [22]porphyrin(2.2,2.2) 20 with cisjrans.cis,-trans configuration of the two-carbon bridges. 

A Pt(II)-bridged wire compound was prepared by Mayor et al. [18] by treating trans-bis(triphenylphosphane)platinum(II) chloride (63) with the alkyne 4 and Cul as catalyst (Scheme 10.20). The trans configuration of the product 64 was confirmed by X-ray crystallographic analysis. 

Bridged cations have been indicated as intermediates of the addition of bromine to dialkylacetylenes on the basis of the exclusive trans mode of the reactions. Bridged cations are in each case likely to be formed in the addition of sulphenyl derivatives to alkyl- as well as to arylacetylenes. The retention of trans configuration and the anchimeric assistance effects observed in SNl-type reactions of j8-arylthiovinyl sulphonates indicate that the bridged geometry is always favoured over a linear one. 

Planar chirality was finally combined with the achiral cis-2 addition pattern in a tethered Bingel type bis-adduct including a trans-configured ethene unit as planar chiral element in the macrocyclic bridge.118... 

The structure 1 proposed for silybin was supported from its mass spectmm, which showed fragment ions at/n/z 302 (H) and 180 (I), formed by RDA cleavage of the dioxane bridge of the molecule (Table 16). The trans configurations of H-2, H-3 and H-7", H-8" were resolved from their coupling constant values (/ = 11.3 and 7.9 Hz). Stmcture 1 assigned was finally confirmed by the synthesis of... 

The speciation and stabihty constants of the Cu(n), Ni(II), Zn(II) and VO(II) complexes of mimosine (9) were determined . The Cu(II) and VO(II) complexes adopt a coordination chemistry analogous to the those of maltol (discussed below). The Zn(II) complex of the deprotonated mimosine analogue 48 has a 1 2 distorted square-pyramidal structure with trans configuration and a water molecule at the apex (49) . Pb(II) forms a 1 2 complex with 48, which further interacts with one enolate of an adjacent Pb(II) center via Pb-0 bridges (2.64 A) to yield a dinuclear Pb complex (50). Vanadate (with a -1-5 oxidation state on V) forms with 48 the 1 1 [V02(48 )(0H)(H20)] and 1 2 [V02(48 )2] complex anions, as shown by potentiometry, cyclic voltammetry and NMR and EPR spectroscopies, with V NMR peaks at —502 and —476 ppm, respectively, similar to the maltol complexes (peaks at —509 and —496 ppm) discussed in the next section. 

Althougli the NMR spectrum has been interiireted (213) as indicative of a cis configuration [i.e., with the Cr(C ()) j moiety on the same side of the ring as the methylene bridge], a crystal analysis (34) has established the molecular structure (40) with a trans configuration. The metal atom is... 

Palladium forms complexes such as the dithio-oxalate ion, Pd(N2S2H)2, glyoximes, and phthalocyanine which are structurally similar to the compounds of Ni and Pt, and also numerous bridged compounds. Early X-ray studies established the planar trans configuration of (d) and (e) ... 

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