Complex bases derivatives

Co(II), Ni(n), Cu(n), and Zn(II) complexes of Schiff bases derived from 4-aryl-2-aminothiazoles and salicylaldehyde have been prepared, and structure 276 (Scheme 170) was established by magnetic susceptibility measurements and by infrared, electronic, and mass spectra (512). 

Based on these observations [18,19,23], a variety of modified catalytic systems have been reported for the diastereoselective reductive carbon-carbon bond formation (Scheme 8). A complex 5 derived from Cp2TiCl2 and MgBr2 is proposed to be an efficient catalyst for the DL-diastereoselective pinacol coupling of aromatic aldehydes [24], Addition of a solution of benzalde-... 

Several silver(I) complexes of the macrocyclic Schiff base derived from the [2+2] condensation of terephthalaldehyde and 3-azapentane-1,5-diamine or A,A -bis(3-aminopropyl)methylamine have been described.509,510 The reaction of 2,ll-diaza-difluoro-m-[3,3]-cyclophane with 2,6-bis (bromomethyl)pyridine lead to the 3 + 3 addition product, which gives a complex with two silver... 

Ferrocene-containing sulfur ligands have been used in complex formation with zinc. 3-Ferro-cenyl-3-mercaptopropenale and l,l -bis(3-mercaptopropenale)ferrocene (112) form stable complexes as do their Schiff base derivatives with aniline or 1,2-ethylenediamine. The Fen/Fein redox couple shows only minor metal dependence, this is attributed to tetrahedral distortion.884... 

Pyridine derivatives with additional donor functions and sterically demanding substituents have been used with the intention of producing complexes of Cd (and of other metals) with low coordination number one of these ligands is the tridentate, planar-bonding 2,6-bis[(2,6-dimethyl-phenylimino)methyl] pyridine (pydim a Schiff base derived from 2,6-pyridine dialdehyde), which with Cd(BF4)2 and thiocyanate gives a dinuclear complex [(pydim)Cd(/x-NCS-S,N)]2(BF4)2 with N-dominated coordination sphere.191 As centrosymmetric Plijc, Z= 2), the complex has an antiparallel /x-1,3 NCS double bridge with Cd—N and Cd—S bonds (224.6 pm and 255.5 pm, respectively) the Cd—N(py) bond is clearly shorter than the Cd—N(imino) bonds (225.6 pm and 245.0 pm,... 

Dwivedi, B. K. et al., Indian J. Chem., 1987, 26A, 618-620 Twelve tris-complexes [Sn(C104)2.3L] between tin(II) perchlorate and Schifif bases derived from salicylaldehyde, anisaldehyde, or 2-hydroxy-l-naphthaldehyde and aromatic amines were investigated for thermal instability. 

Domination of the S-diastereomers for the dioxovanadium(V) Schiff base complexes being derivatives of aromatic orf/zo-hydroxyaldehydes or ketones and (S)-(+)-2-(aminomethyl)-pyrrolidine [35] was shown and the molar ratio of the diastereomers was determined by means of integration of the H signals.85... 

Fox et al.101-103 have studied the structure of Ni(II) complexes being derivatives of frans-l,2-diaminocyclohexane, using 1H NMR spectroscopy. Chemical shift differences (A<5) between di-Schiff base and its nickel (II) complexes observed for aromatic protons were attributed to the ring currents [40]. 

Szlyk et al.109 have studied the di-Schiff bases Zn(II) complexes, being derivatives of (7R/2R)-l,2-diaminocyclohexane and 5-bromo- or 5-chloro-salicylaldehydes by means of 1H and 13C NMR in CDCI3 and 13C CP MAS NMR spectra. 

Analysis of the 1H and 13C NMR spectra of the tin complexes, being derivatives of various di-Schiff bases, [46] has revealed the dependence of the position of tin centre on the type of linker between the two imine units and the metal coordination number.110... 

In Sn(II) complexes, the tin atom was located above the di-Schiff base coordination plane, while in Sn(IV) complexes, it was coplanar with the imine coordination framework. The position of the metal was supported by X-ray data. For the compounds studied, the 119Sn chemical shift values varied from 501.4 to —1015.9 ppm. Increase in the coordination number from Sn(II) to Sn(IV) led to an increase in the tin shielding. The differences of up to 3.0 ppm between 5119Sn values for the complexes, being derivatives of R,R and S,S 1,2-diaminocyclohexane, were observed. 

For the tin(II) complexes of the fluorinated Schiff bases derived from amino acids, [47] the 5119Sn chemical shifts in the range from -575 to 582 ppm suggested the four-coordinate square-planar geometry.111... 

Analysis of the 27A1 NMR spectra has confirmed the structure of the aluminium di-Schiff bases complexes being derivatives of trans-1,2-dia-minocyclohexane. The A1 chemical shift values of 6.57 and 39.48 ppm indicated the presence of dynamic equilibrium between five- and six-coordinated states in CDC13 solution. 

Charge. The small amount of charge distribution data for carbyne complexes (based on Mulliken population analyses) indicates that the metal-carbon bond is generally polarized Ms+—C5- and that the carbyne carbon is always more negative than adjacent carbonyl carbons (28,30). These conclusions are directly analogous to those derived for carbene complexes. 

In the course of our successful synthesis, we identified several limitations of our new method and associated strategy (1) the harsh conditions of the bicyclization reaction do not tolerate base-sensitive functionality such as vinyl halides (2) post-cyclization manipulations such as iododesilylation reactions are complicated by the sensitive/ reactive functionality of the products (a,p-unsaturated aldehyde, indoline, etc.) and (3) the incorporation of the required functionality into the Zincke aldehyde requires the synthesis of a complex tryptamine derivative, resulting in a lengthy, non-convergent route. In order to develop a concise route to strychnine, we would have to address each of these issues, and a straightforward solution to obviate all of these is described below. 

In contrast to the extensive studies on phosphine-phosphites, the corresponding phosphine-phosphinites are rarely exploited. Laschat introduced this design with a bicydic chiral skeleton derived from (lS)-(+)-camphorsulfonic acid [127]. The Rh-complex based on dimesitylphosphinite 154b was found to be the most reactive catalyst, and was used to produce methyl N-2-acetamidodnnamate, with 89% ee. 

It is interesting to note that these complexes are mixed-valent MnmMnIV complexes. Based on the relative structural data [the bond distances of the MnA atom are shorter than those of MnB], it has been concluded that in [Mn202(bipy)4]3+ one of the manganese ions is in the oxidation state IV [Mn(B)] and the other in the oxidation state III [Mn(A)]. Hence, the complex would have to be classified as a mixed-valent derivative with localized charge (Robin-Day Class I). Conversely, the two manganese sites are identical in [Mn202(phen)4]" +, from which one can infer that the charge is delocalized over the two centres (Robin-Day Class III). 

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