Cyclometalated Complexes of Palladium(II) and Platinum(II):  cis-Configured Homoleptic and Heteroleptic Compounds with Aromatic C⌒N Ligands

Abstract

The palladium(II) and platinum(II) bis-homoleptic complexes M(C&arcraise;N)(2), where C&arcraise;N is benzo[h]quinoline (H-bhq), 2-phenylpyridine (H-phpy), 2-(2'-benzothienyl)pyridine (H-bthpy), 2-(2'-thienyl)quinoline (H-thq), and 2-(2'-thienyl)pyridine (H-thpy), were prepared by metal exchange of the lithiated ligands C&arcraise;N with M(Et(2)S)(2)Cl(2). The palladium(II) bis-heteroleptic complexes, Pd(C&arcraise;N)(C'&arcraise;N'), were synthesized from Pd(C&arcraise;N)(2) bis-homoleptic complexes, which were converted by HCl into the dichloro-bridged compounds [Pd(C&arcraise;N)Cl](2). By addition of Et(2)S, the Pd(C&arcraise;N)(Et(2)S)Cl complexes were formed, which were allowed to react with Li(C'&arcraise;N'), yielding M(C&arcraise;N)(C'&arcraise;N') compounds. An alternative way for obtaining the bis-heteroleptic molecules is by ligand exchange, according to the equilibrium M(C&arcraise;N)(2) + M(C'&arcraise;N')(2) = 2M(C&arcraise;N)(C'&arcraise;N'). The crystal structures of Pt(bhq)(2) (1) and Pt(thq)(2) (3) present an important distortion of the square planar (SP-4) geometry toward a two-bladed helix. Bis-homoleptic and some bis-heteroleptic complexes of palladium(II) have also been synthesized. In both cases, the steric interactions between the two ligands cause again a helical distortion rather than yielding trans compounds. For cis-bis(benzo[h]quinoline)platinum(II) (1), in the crystal (monoclinic, space group P2(1)/n, a = 13.728(3) Å, b = 6.9537(15) Å, c = 19.701(5) Å, beta = 106.17(2) degrees, Z = 4, rho(calcd) = 2.028 g.cm(-)(3); diffractometer measurements, block-matrix least-squares refinement, R = 0.043, R(w) = 0.047) the average Pt-N and Pt-C distances are 2.151(6) and 1.988(7) Å, respectively. One benzo[h]quinoline ligand is significantly less planar than the other. For cis-bis[2-(2'-thienyl)quinoline]platinum(II) (3), in the crystal (trigonal, space group P3(2)21, a = b = 9.373(1) Å, c = 20.152(3) Å, Z = 3, rho(calcd) = 2.022 g.cm(-)(3); diffractometer measurements, full-matrix least-squares refinement, R = 0.010, R(w) = 0.010) the molecule has C(2) symmetry and is chiral. The Pt-N and Pt-C bond lengths are 2.156(2) and 1.984(3) Å, respectively. The quinoline moitey is not planar but bent about the fused bond by 6.8 degrees. The thiophene moiety is inclined to the best plane through the quinoline moiety by 24.4 degrees.

Biscyclometalated platinum complexes with thiophene ligands

“…4c has no methylene spacer between the metallacycle and the dangling phenyl group, unlike many of our earlier reported structures. However, bond lengths and angles are in the expected range for analogous compounds [23,45,46]. In all cases, the stereochemistry at the C]N is necessarily trans.…”

“…The complexes with two such ligands are much more inert than the complexes with only one C ˇ N ligand, as can be observed from their lack of reactivity in refluxing toluene and they are also relatively unreactive for several days at room temperature in common solvents. The biscyclometalated compounds reported here are formed as a straightforward manner as a direct result of oxidative addition of the appropriate CeH bond followed by a subsequent reductive elimination of methane and are more easily prepared and purified than the previously reported thienylpyridine complexes, which do not have an imine functionality, were orthometalated at the 3-position of the thiophene ring, and required lithiation of the ligands to activate them in order to obtain the bismetalated products [46]. Therefore our synthesis allows for a direct reaction and eliminates the need of extra halogenation/lithiation steps.…”

“…The compound consists of a square planar platinum (II) center bonded to one cyclometalated 4a ligand, a methyl group, and a dimethylsulfide ligand. Bond lengths and angles are in the expected range for analogous compounds [23,45,46]. Suitable crystals of [Pt((C 4 H 2 S)CH]N(C 6 H 5 )) 2 ], 4c, were grown by slow evaporation of acetone.…”

Pure Red Phosphorescent Organic Light-Emitting Diodes Made of Iridium(III) Complex with Thiophene-Quinoline Ligand

“…[1][2][3][4] By using triplet emitters with heavy metal cores and various organic ligands, strong spin-orbital coupling leads to enhanced mixing of singlets and triplets, which in turn, induces efficient intersystem crossing to overcome the internal quantum yield. [5][6][7][8] Many phosphorescent materials containing various heavy metals such as Ru(II), 9 10 Rh(III), [11][12][13][14] Re(I), 15 Ir(III), 16 and Pt(II,IV) [17][18][19][20] have been extensively developed to demonstrate red, green, and blue electrophosphorescent emission. In particular, cyclometalated iridium(III) complexes show strong electrophosphorescent emission with a high quantum efficiency.…”

Synthesis, characterization, photophysics and electrophosphorescent applications of phosphorescent platinum cyclometalated complexes with 9-arylcarbazole moieties

“…Among them, Pt(II) complexes incorporating pyridine ligands such as bipyridine [11][12][13][14][15][16][17][18][19][20][21][22][23] and terpyridine [24] derivatives have attracted a great deal of interest as luminescent dyes for OLED applications since they often exhibit high phosphorescence quantum yields. On the other hand, several cyclometalated homo-or heteroleptic Pt(II) complexes based on 2-phenylpyridine (ppy) and analogues have been reported in the literature [25][26][27].…”