INDO–MO Calculations and Proton Isotropic Shifts of Methyl-Substituted Pyridine Ligands in Ni(II) Complexes

Abstract

Relative p.m.r. isotropic shifts for the ligands in the complexes NiL,(NO,), (L = 4-picoline and 3,5-lutidine), NiL3(N03), (L = 3-picoline and 3,4-lutidine), and NiL,(NO,), (L = 2-picoline, 2,3-lutidine, 2,4-lutidine, and 2,5-lutidine) were determined in CDCI,. Proton hyperfine coupling constants for corresponding pyridine cations and analogous phenyl radicals were calculated by the INDO-MO method. Analysis of the p.m.r. shifts and subsequent correlation with the INDO data revealed that the spin transfer process between metal and ligand was dominated by a u-mechanism, as indicated by ring protons at the a-and B-positions. The y-ring proton and methyl protons at all positions indicated a n-mechanism was also operative through u-n spin polarization at the nitrogen atom. The INDO calculations based on spin densities of the hydrogen Is orbitals, however, predicted that all ring protons would be dominated by a u-mechanism, and that methyl protons at the a-and y-positions should manifest a n-mechanism. Both mechanisms should be operative for the 8-CH, protons, with 50-60% u-contribution in the pyridine cations and 30-50% u-contribution in the phenyl radicals. The pattern of spin polarization (i.e., negative at a-C and y-C, positive at P-C) is not altered by a small excess ofa or P spin in the n-system. However, the n-spin density ratios, especially at the a-and y-positions, areaffected, as is the magnitude of the n-spin densities on each carbon. A comparison of the observed isotropic shifts for the methyl protons and for the y-ring proton with the INDO calculated n-spin densities allows a determination of the spin delocalization in the ligand n-system. Les dCplacementsisotropiques relatifs p.m.r. pour les ligands dans les complexes NiL,(NO,), (L = picoline-4 et lutidine-3,5), NiL,(NO,), (L = picoline-3 et lutidine-3,4), et NiL,(NO,), (L = picoline-2,lutidine-2,3, lutidine-2,4 et lutidine-2,5), ont tte determines dans le CDCI,. Les constantes de couplage hyperfin du proton pour les cations pyridine correspondants et les radicaux analogues du phenyle, ont Cte calculees par la mtthode INDO-MO. L'analyse des deplacements p.m.r. et la correlation subsequente avec les donnees INDO, revhlent que le processus de transfert de spin entre le metal et le ligand est surtout un mecanisme-u, comme le montrent les protons du cycle en position a et P. Le proton y du cycle et les protons du methyle dans toutes les positions indiquent qu'un mecanisme-n est aussi effectif, par l'intermediaire d'une polarisation de spin u-n sur I'atome d'azote. Les calculs INDO, fondes sur les densites de spin dans les orbitales Is de I'hydroghne, laissent prevoir cependant que tous les protons du cycle seraient domines par un mkcanisme-u et que les protons du methyle sur les positions a et 7 manifesteraient un mecanisme de type n. Ces deux mecanismes seraient effectifs pour les protons du CH,-P, avec une contribution u de 50-60% dans les cations pyridine et 30-50% dans les radicaux phenyles. Le modele de la polarisation de spin (c'est-a-dire negative sur...

Studies on the proton and carbon-13 contact shifts for .sigma.-bonded molecules. Stereospecific electron spin transmission in cyclic and bicyclic amines

“…Piperidine (1), 4-methylpiperidine (2), 3-methylpiperidine (3), A-methylpiperidine (4), and quinuclidine (7) were obtained from commercial sources. 1,4-Dimethylpiperidine (5) and 1,3-dimethylpiperidine (6) were prepared by N-methylation of 2 and 3, respectively.12 1-Azaadamantane (8) was provided by Dr. W. N. Speckamp. 3,3,4-Trimethyl-2-chloro-l-azabicyclo[2.2.1]heptane (9) was provided by Professor P. G. Gassman.…”

“…/t^/ 'ch3 y a 1,4-Dimethylpiperidine (5) H Xch! l-Aza-7-chloromethylbicy clots,2.1 ¡octane (10) 6 In parts per million from Me4Si. c A relatively large downfield shift.…”

An investigation of the 1H nmr isotropic shifts for some methyl-substituted bipyridine complexes with Ni(II) and Co(II)

“…In this situation, the isotropic shift arises solely from the Fermi contact interaction, which is proportional to the hyperfine coupling constant resulting from electron spin delocalization on the proton, as shown in eq. [5].…”

“…The isotropic chemical shifts in the 'H nmr spectra of nickel(I1) complexes of pyridines and I some methyl-substituted pyridines have previously been studied in solution (1)(2)(3)(4)(5)(6)(7)(8). In a perfectly I octahedral crystal field, the ground term 3F of , Ni(I1) is split into two 3T excited states and one 3A2g ground level; this 3A2g level corresponds to an , isotropic magnetic susceptibility.…”

Nuclear magnetic resonance spectrometry

“…Theoretical (2113) and experimental studies of numerous paramagnetic amine adducts (2114-2125) of nickel(II) acetylacetonate, theory of contact and dipolar NMR shifts of Ni(II) complexes (2126), studies of pyridine and picoline ( ) complexes (2127,2128), diamagnetic and paramagnetic Ni(II) Schiff base and porphyrin compounds (2129)(2130)(2131)(2132)(2133)(2134)(2135)(2136)(2137)(2138)(2139)(2140)(2141)(2142)(2143), adducts of Ni(II) dithiophosphates (2144)(2145)(2146)(2147)(2148)(2149), Ni(II) nitrilocarboxylates (2150), calculations for the tris(o-phenanthroline)nickel(II) cation (2151), Ni(II) complexes with phosphine ligands (2152, 2153), nickelocene and nickelocenium cations (2154,2155), Ni(II) in aqueous solutions (2156)(2157)(2158)(2159), Ni(II) dionato (2160, 2161), flavoquinone (2162), triazine ligand (2163), and monohalo tridentate ligand (2164) complexes have been described, numerous studies of adducts of Co(II) ß-diketonates (2116, 2165-2172) have been reported, as have studies of ir-cyclopentadienylcobalt complexes (2173, 2174), borabenzene colbalt complexes (2175), Co(II) human carbonic anhydrase C (2176) and interactions of Co(II) with adenosine triphosphate (2177), acetonitrile (2178), thiourea and related ligands (2179), nonaqueous solvents (2180), aqueous solutions (2181)(2182)(2183), tetrafluoroborate anions (2184), and triethylenetetramine (2185), bis(salicylaldehydato)pyridazinecobalt(II) (2186), Co(II) porphyrin...…”