Abstract
The crystal structures of di-chlorido-palladium(II) complexes bearing 2-methyl- and 2-phenyl-8-(di-phenyl-phosphan-yl)quinoline, namely, di-chlorido-[8-(di-phenyl-phosphan-yl)-2-methyl-quinoline-κ2 N,P]palladium(II), [PdCl2(C22H18NP)] (1) and di-chlorido-[8-(di-phenyl-phosphan-yl)-2-phenyl-quinoline-κ2 N,P]palladium(II), [PdCl2(C27H20NP)] (2), were analyzed and compared to that of the 8-(di-phenyl-phosphan-yl)quinoline (PQH) analogue (3). In all three complexes, the phosphanyl-quinoline moiety acts as a bidentate P,N-donating chelate ligand. In the PQH complex (3), the PdII center has a typical planar coordination environment; however, both the methyl- and phenyl-substituted phosphanyl-quinoline (PQMe and PQPh, respectively) complexes (1) and (2) exhibit a considerable tetra-hedral distortion around the PdII center, as parameterized by the τ4 values of 0.1555 (4) and 0.1438 (4) for (1) and (2), respectively. The steric inter-action from the substituted group introduced at the 2-position of the quinoline ring enforces the cis-positioned Cl ligand to be displaced from the ideal coordination plane. Also, the ideally planar phosphanyl-quinoline five-membered chelate ring shows a large bending deformation by the displacement of the PdII center from the quinoline plane. In addition, in the phenyl-substituted complex (3), the coordinating quinolyl and the substituted phenyl rings are not co-planar to each other, having a dihedral angle of 33.08 (7)°. This twist conformation prohibits any inter-molecular π-π stacking inter-action between the quinoline planes, which is observed in the crystals of complexes (1) and (2).
Highlights
The crystal structures of dichloridopalladium(II) complexes bearing 2-methyland 2-phenyl-8-(diphenylphosphanyl)quinoline, namely, dichlorido[8-(diphenylphosphanyl)-2-methylquinoline-2N,P]palladium(II), [PdCl2(C22H18NP)] (1) and dichlorido[8-(diphenylphosphanyl)-2-phenylquinoline-2N,P]palladium(II), [PdCl2(C27H20NP)] (2), were analyzed and compared to that of the 8-(diphenylphosphanyl)quinoline (PQH) analogue (3)
The phosphanylquinoline moiety acts as a bidentate P,N-donating chelate ligand
The steric interaction from the substituted group introduced at the 2-position of the quinoline ring enforces the cis-positioned Cl ligand to be displaced from the ideal coordination plane
Summary
8-Quinolylphosphanes are competent ligands for various functional coordination compounds, because they consist of a strongly -donating phosphane donor group and a -conjugated quinoline moiety and form a stable planar fivemembered chelate ring on coordination to a metal center (Cai et al, 2018; Hopkins et al, 2019; Scattolin et al, 2017). The coordination plane (defined by the central Pd and four donor atoms) and the quinoline plane are almost co-planar, with their dihedral angle being 8.58 (3). The Pd1 atom is displaced by 0.755 (2) Afrom the chelating ligand plane (defined by P1, C8, C9 and N1), and the dihedral angle ’C between the plane [Pd1,P1,N1] and the quinoline plane. The PQPh complex (2) shows a more explicit distortion of the coordination environment on the quinolylphosphane ligand due to the 2-phenyl substitution group The Pd1 atom is displaced by 0.864 (2) Afrom the chelating ligand plane (defined by P1, C8, C9 and N1), and the dihedral angle. 3. Supramolecular features In the crystal structure, the molecular PQH complex (3) forms a dimer by an intermolecular – stacking interaction between the quinoline ring systems. There are no other obvious supramolecular features in the crystal structures of (1) and (2) (Figs. 5 and 6)
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