129125-06-0Relevant academic research and scientific papers
Acylation of pyridine rings mediated by group 4 metal aryl oxide compounds: High yield formation of α,α′-didubstituted-2,6-pyridinedimethoxide ligands
Zambrano, Cesar H.,McMullen, Anne K.,Kobriger, Lisa M.,Fanwick, Phillip E.,Rothwell, Ian P.
, p. 6565 - 6570 (2007/10/02)
The room-temperature carbonylation (typically 1000 psi) of solutions of the dialkyl compounds Zr(OAr′)2(R)2 (OAr′) = 2,6-di-tert-butylphenoxide; R = CH3, CH2Ph) in the presence of 1 equiv of a suitable pyridine leads to the formation of a series of α,α′-disubstituted-2,6-pyridinedimethoxide compounds (Ar′O)2Zr[OCH(R)-pyr-CH(R)O] [R = CH3 (1), CH2Ph (2); pyr = NC5H3, a; NC5H2-4-Ph, b; NC5H2-4-Me, c], Spectroscopic studies, 1H and 13C NMR, of the compounds show in all cases an approximately 50/50 mixture of the threo and meso diastereomers to be present in the initial reaction product mixture. Partial recrystallization of the zirconium benzyl product (2b) obtained by using 4-phenylpyridine yielded crystals of the pure threo diastereoisomer. A single-crystal X-ray diffraction of this product confirmed the stereochemistry and showed the five-coordinate zirconium metal center to be chelated by the tridentate pyridinedimethoxide ligand was well as the two 2,6-di-tert-butylphenoxide groups. Recrystallization of all the other derivatives yielded crystals containing both the threo and meso forms. In the presence of excess pyridine carbonylation of the compounds M(OAr′)2(CH3)2 (M = Zr, Hf) yields the six-coordinate adducts M(OAr′)2[OCH(R)NC5H3CH(R)O](C 5H5N) [M = Zr (3), Hf (4)]. The stoichiometry of the adducts was confirmed by a single-crystal X-ray diffraction analysis of the zirconium compound Zr(OAr′)2[OCH(CH3)C5H 3CH-(CH3)O](C5H5N) (3). In this case, the crystals were found to contain a 50/50 mixture of the threo and meso diastereomers, leading to a disorder involving the α-methyl groups. Hydrolysis of these compounds allows isolation of the corresponding α,α′-disubstituted pyridinedimethanol ligands in good yield. A mechanistic study of the carbonylation reaction employing a competition reaction between pyridine and pyridine-d5 showed the absence of a significant kinetic isotope effect. This and other studies are interpreted in terms of the reaction involving nucleophilic attack of intermediate metal-acyl groups at the 2- and 6-poshions of the pyridine rings. Crystal data for ZrO4NC55H65 (2b) at -135 °C: a = 12.933 (5), b = 14.088 (5), c = 14.336 (5) A?; α = 67.44 (3), β= (3), γ = 81.61 (3)°; Z = 2; dcalcd = 1.256 g cm-3 in space group P1?; for ZrO4N2C42H58 (3) at 22 °C: a = 10.599 (5), b = 18.153 (5), c = 11.155 (4) A?; β= 105.73 (4)°; Z = 2; dcalcd = 1.199 g cm-3 in space group P21.
