Picolinate complexes

A synthetic route for the two picoline complexes relies on the fact that when the base was added to m-Pt(DMSO)2Cl2, the trans-isomer is formed first. On standing, partial isomerization occurs to the cis-form, which can... 

On using Barton-oxidation procedures cyclohexane is oxidized by 1949, in the presence of FeCb and the Fe "-picolinate complex, to give cyclohexanone and cyclohexanol [166] whereas with FeCl2 1-chlorocyclohexane is the mayor product, with cyclohexanone and a small amount of cyclohexanol [167] (Scheme 12.47). 

Steric hindrance is well known to slow down the rates of ligand substitution reactions in square-planar metal complexes. An example for which steric hindrance controls the aquation rate is complex 9. The effect of 2-picoline on the rate of hydrolysis of CP trans to NH3 (cis to 2-picoline) is dramatic, being about 5 times as slow as the analogous CP ligand in the nonsterically hindered 3-picoline complex (Table I) (44). 

Information of the Gif system has been summarized,1055 1123 and new results, including new oxidants such as bis(trimethylsilyl) peroxide,1124 the synergistic oxidation of saturated hydrocarbons and H2S,1125 studies with the Fe3+-picolinate complex encapsulated within zeolites,1126 and the use of Udenfriend s system under Gif conditions1127 were disclosed. Gif-type oxidations were found to be moderately stereoselective.1128 Iron/zinc-containing species involved in Gif-type chemistry were synthesized, and their reactivity and catalytic behavior were studied.1129... 

The enthalpy and entropy of complex formation between Zn11 and picolinate and dipicolinate anions in aqueous solution have been determined by calorimetry and from formation constant data. The greater stability of the dipicolinate complex compared to the picolinate complex reflects an entropy effect, and Ais actually less favourable. These anions are well known to have a low basicity to H+ compared to their complexing ability to metals. In the present case, this probably reflects the coplanarity of the carboxylate anions and the pyridine ring, so that the oxygen atoms are in a favourable position to coordinate.800... 

Owing to their relevance in steroid chemistry Okamoto et al. investigated aerobic allylic hydroxylations of octahydronaphthalene derivatives such as lc in the presence of Fe(III) picolinate complexes Fe(PA)3H20 (Scheme 3.21) [108]. The combination of electrolysis and the Fe(PA)3-02-MeCN system suppressed epoxidation almost completely, leading exclusively to the oxidation products 2c and 3c, albeit with low yields. In contrast, when alkene lc was submitted to chemical oxidation using the... 

There is evidence from Raman studies that oxalate coordinates in a bidentate manner without elimination of a peroxo group [6], Possibly here, as for the picolinate complex, the question of the coordination could be more definitively answered by observation of 13C coordination-induced NMR chemical shifts. The x-ray structure for the oxalate complex shows that the two V0ox bond distances are very different. The VO distance to the equatorial oxalato oxygen is 2.060(4) A compared to 2.251(4) A to the apical oxygen [15], Similarly long distances are found in the picolinato complex (VOpic 2.290 A [16]) and other complexes [20], These distances are indicative of relatively weak bonds to the apical oxygens, and dissociation of that bond... 

Sakurai, H. and H. Yasui. 2003. Structure-activity relationship of insulinomimetic vanadyl-picolinate complexes in view of their clinical use. J. Trace Elem. Med. Biol. 16 269-280. 

Proton magnetic resonance spectroscopy was of no avail in the study of complex formation of Me2SnCl2 with pyridine in solution since insoluble species are formed with any ratio of reactants. An III spectrum of the Me2SnCl2-7-picoline complex contains (61) a strong singlet for cas(Sn—C), at 560 cm-1, and a broad Sn—Cl multiplet at 233 cm-1, suggesting the Ilia structure. The J( H—C—nl Sn) value of 102.0 Hz found for the solution in CHCh (145), and corrected for the possibility of dissociation, may confirm that the configuration is retained in solution. 

Chakov NE, Collins RA, Vincent JB. 1999. A re-investigation the electron spectra of chromium(III) picolinate complexes and high yield synthesis and characterization of Cr2(p-0H)2(pic)4-5H20 (Hpic=picolinate acid). Polyhedron 18 2891-2897. 

The metal-ligand stretching vibration should appear in the same frequency region if the metal is the same and the ligands are similar. For example, the v(Zn-N) (v stretching) of Zn(II) pyridine complexes are expected to be similar to those of Zn(II) a-picoline complexes. This method is applicable only when the metal-ligand vibration is known for one parent compound. 

Preparation. This chromium complex is usually prepared by the reaction of benzene with chromium hexacarbonyl under high pressure. Rausch has recently published a simple synthesis based on a patent procedure in which equi-volume amounts of benzene and 2-picoline are refluxed for an extended period under nitrogen. Carbon monoxide is evolved, and little sublimation of chromium hexacarbonyl occurs. Yields are 90-94% for reactions conducted for 96 hr. or more. The method is presumably successful because of formation of the 2-picoline complex (A), which reacts with benzene to form (1). 

Polymer-supported tetrabromooxomolybdate(V) was claimed to be a heterogeneous catalyst for alcohol oxidations with TBHP . However, it seems likely that molybdenum is leached from the surface and the observed catalysis may be, at least partially, homogeneous in nature. The same applies to Cr(III) and Ce(IV) catalysts supported on a perfluorinated sulfonic acid resin (Nafion K) which catalyze the oxidation of alcohols with TBHP . Similarly, vanadium-pillared montmorillonite clay (V-PILC) ° and a zeolite-encapsulated vanadium picolinate complex were shown to catalyze... 

The IR spectra of A1L + and A1L2, where HL = picolinic acid, were both consistent with picolinate complexation via the pyridine ring N and one car-boxylate O atoms." IR spectroscopy on the Al(III)-quinolinate system gave evidence for the presence of A1L+ and A1L2 species (quinolinic acid = H2L), with the quinolinate preferentially chelating to Al(III) using the pyridine ring N and a carboxylate O atoms." ... 

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