Interconvertible Cationic and Neutral Pyridinylimidazole η³-Allylpalladium Complexes. Structural Assignment by ¹H, ¹³C, and ¹⁵N NMR and X-ray Diffraction

Abstract

Interconvertible cationic pyridinylimidazole η 3-allylpalladium complex 2 and neutral pyridinylimidazolyl η 3-allylpalladium complex 3 were synthesized and their structures analyzed by 1H, 13C, and 15N NMR and X-ray diffraction. Cationic 2 and neutral 3 can be changed into each other by deprotonation and protonation.

Palladium complexes containing ligands with hydrogen-bonding functionalities. Reactivity and catalytic studies with CO and olefins

“…The Pd-N and Pd-C distances (see Fig. 4) are very similar to those observed in other g 3 -allyl-pyridyl-and g 3 -allyl-pyridyl-imino-palladium(II) complexes [45][46][47]. The N,N 0 chelate ring has an envelope conformation with the palladium atom lying 0.14 Å out of the plane of the remaining atoms, which are coplanar to within 0.003 Å .…”

Isomerization Behavior in the (π-Allyl)palladium(II) Complexes with N21,N22-Bridged Porphyrin Ligands

“…Table exhibits selected distances, angles, and dihedral angles between least-squares planes for cis- 3a ‘. The Pd−N (2.106−2.118 Å) and Pd−C (2.085-2.147 Å) bond lengths as well as the N3−Pd-N4 (83.4°) and C59−Pd−C61 (68.7°) bite angles are similar to those of the (π-allyl)palladium complex of 2,2‘-bipyridine. − The four coordinating atoms (N3, N4, C59, C61) of Pd constitute a square-planar coordination plane with the deviation of each atom being less than 0.06 Å from the mean plane. The allyl central carbon C60 deviates by 0.65 Å from the mean plane, while the Pd atom is displaced by 0.03 Å in the opposite direction.…”

15N NMR coordination shifts in Pd(II), Pt(II), Au(III), Co(III), Rh(III), Ir(III), Pd(IV), and Pt(IV) complexes with pyridine, 2,2′-bipyridine, 1,10-phenanthroline, quinoline, isoquinoline, 2,2′-biquinoline, 2,2′:6′, 2′-terpyridine and their alkyl or aryl

“…[15,16] www.interscience.wiley.com/journal/mrc [23] In the same species, the | 15N coord | parameters for nitrogens of the monodentate L ligands (py, 2-phenyl-py, 7,8-benzoquinoline) are again within the range typical for their trans position to N (ca 61-80 ppm). [15,16] An analogous ca 35 ppm difference between py nitrogens trans to N and trans to CH 3 [11,12] and a relatively high structural similarity of this ligand to the earlier mentioned 2-(3 -methyl-5 -pyrazolyl)-py (δ 15N lig = −84.9 ppm [9] ), one can evaluate | 15N coord | as ca 50-60 ppm. The influence of Cl atoms in the trans position is generally slightly smaller than that caused by N. This is evident for some dichloride complexes described by Pazderski et [7,14,19] Another species fitting to this scheme is the diazide complex trans-[Pd(py) 2 www.interscience.wiley.com/journal/mrc Axial 4-tert-butyl-py −161.4 [25] −92.6 g 1 J 15N -103Rh = 17.9 Hz Equatorial 4-tert-butyl-py (trans to CH 2 C 6 H 5 )…”

“…[6] c Versus free 2-(3 -methyl-5 -pyrazolyl)-py in CD 2 Cl 2 + CD 3 OD 1 : 1: δ 15N lig = −84.9 ppm (+273.2 ppm with respect to NH 4 NO 3 in DMSO-d 6 ). [9] d Recalculated with respect to nitromethane, from original values for these 2-(2 -imidazolyl)-py and 3-methyl-2-(2 -imidazolyl)-py complexes (primarily referenced to NH 4 NO 3 in DMSO-d 6 ), being +221.3, +221.8 ppm [11] and +222.7, +217.7 ppm, [12] respectively, by subtracting 358.1 ppm relative shift. [6] [ 15] n Versus free py in CD 2 Cl 2 : δ 15N lig = −65.3 ppm (our data); originally some 15 N coordination shifts were determined by Milani et al versus free py in CDCl 3 .…”

“…coord | values for [Pd(2-(3 -methyl-5 -pyrazolyl)-py)(CH 2 CHCH 2 )] + and [Pd(2-(3 -methyl-5 -pyrazolate)-py)(CH 2 CHCH 2 )] (47.9 ppm vs 54.5 ppm), [10] [12] www.interscience.wiley.com/journal/mrc [7] ca −136 b [7] cis-[Pt(py) 2 Cl 4 ] DMF−d7,303 K −173.0 [7] −109.0 c [7] [Pt(bpy) Cl 4 ] DMSO−d 6 , 303 K −172.1 [7] −99.5 d [7] [Pt(phen) Cl 4 ] DMSO−d 6 , 303 K −174.4 [7] −105.1 e [7] a Versus free py in DMSO-d 6 : δ 15N lig = −63.1 ppm (our data). b Versus free py averaged for CDCl 3 , CD 2 Summing up, for a large set of Pd(II) coordination compounds, the trans effect of auxiliary ligands on the | 15N coord | parameters increases in the order of donor atoms C Cl < N; however, it is weakened by a possible lability of Pd-N bonds; on the other hand, it is nearly independent of the slight variations in the azine ring structure or of the presence of electric charge.…”