Synthesis, Structure, and Optical Properties of Pt(II) and Pd(II) Complexes with Oxazolyl- and Pyridyl-Functionalized DPPM-Type Ligands: A Combined Experimental and Theoretical Study

Abstract

New square-planar complexes [Pt(1(-H))2] (2a) [1(-H) = (oxazolin-2-yl)bis(diphenylphosphino)methanide] and [Pd(1(-H))2] (2b), of general formula [M{(Ph2P)2C---C---NCH2CH2O}2] (M = Pt, 2a; M = Pd, 2b), result from deprotonation of 2-{bis(diphenylphosphino)methyl}oxazoline (1) at the PCHP site. The new, functionalized dppm-type ligand 4-{bis(diphenylphosphino)methyl}pyridine, (Ph2P)2CH(4-C5H4N) (4), was prepared by double lithiation and phosphorylation of 4-picoline. In the presence of NEt3, the reactions of 2 equiv of 4 with [PtCl2(NCPh)2] and [Pd(acac)2] (acac = acetylacetonate) afforded [Pt(4(-H))2] (5a) [4(-H) = bis(diphenylphosphino)(pyridin-4-yl)methanide] and [Pd(4(-H))2] (5b), of general formula [M{(Ph2P)2C(4-C5H4N)}2] (M = Pt, 5a; M = Pd, 5b), respectively. In the absence of base, the reactions of 2 equiv of 4 with [PtCl2(NCPh)2] and [PdCl2(NCPh)2] afforded (5a·2HCl) (6a) and (5b·2HCl) (6b), respectively, in which the PCHP proton of 4 has migrated from carbon to nitrogen to give a pyridinium derivative of general formula [M{(Ph2P)2C(4-C5H4NH)}2]Cl2 (M = Pt, 6a; M = Pd, 6b). The complexes 3a, 5a·2MeOH, and 6b·4CH2Cl2 have been structurally characterized by X-ray diffraction. The absorption/emission properties of the Pt(II) complexes 2a and 5a and the Pd(II) complexes 2b and 5b have been investigated by UV-vis spectroscopy and theoretical analysis based on density functional theory. The UV-vis absorption spectra of the neutral complexes recorded in dilute N,N'-dimethylformamide solutions are dominated by intense spin-allowed intraligand transitions in the region below 350 nm. The complexes exhibit charge-transfer bands between 350 and 500 nm. The experimental and theoretical absorption spectra agree qualitatively and point to two low-lying ligand-to-metal charge transfer states that contribute to the bands observed between 350 and 500 nm. The complexes are emissive in frozen solutions at 77 K, in the pure solid state, and when doped into films of poly(methyl methacrylate) but are nonemissive in solution. A red shift is observed when Pt(II) is replaced by Pd(II).

Reactivity of 4‐Pyridyltellurolate with Pd(II)/Pt(II) Complexes

“…The mononuclear structure of [Pt{(Ph 2 P) 2 C(4‐TeC 5 H 4 N)} 2 ] 4 (Figure , Table ) is similar to the one reported recently for [Pt{(Ph 2 P) 2 C(2‐TeC 5 H 4 N)} 2 ] and [Pt{(Ph 2 P) 2 C(4‐C 5 H 4 N)} 2 ] . A distorted square planar Pt(II) is chelated by four phosphorus atoms of the deprotonated dppm ligand.…”

“…The chelating bite angle P1–Pt1–P2 (69°) and the angle P1–Pt1–P2 i (111°) are largely deviated from the ideal right angle and all other structural features closely match with the above reported complexes except the two Pt−P (2.40 and 2.27 Å) and P−C distances (1.70 and 1.79 Å) are dissimilar. However both the P−C (C6) bond distances are shorter than the usual P−C single bonds due to the delocalization of the double bond over P2−C6−P1 bonds . Also the length of Te1−C6 is shortened and the sum of the angles of three coplanar bonds around C6 atom is 359.5°, indicating a sp 2 hybridization of the carbon atom.…”

Computational Protocol to Calculate the Phosphorescence Energy of Pt(II) Complexes: Is the Lowest Triplet Excited State Always Involved in Emission? A Comprehensive Benchmark Study

“…Their photophysical properties have been the scope of multiple investigations. [28][29][30][31] Square-planar Pt(II) complexes often possess very complex and rich photochemical properties, 32,33 such as anti-kasha emission but also dual photoluminescence. [34][35][36][37] These complex photochemical scenarios make difficult the development of computational protocols enabling the calculation of the phosphorescence energy of a given arbitrary Pt(II) complex without prior information on its measured photophysical properties.…”

“…The calculation of accurate phosphorescence energies has been proven difficult for Pt­(II) complexes. , Many pseudo-square-planar Pt­(II) complexes displaying various cyclometalating and ancillary ligands have been synthesized and characterized in the literature. Their photophysical properties have been the scope of multiple investigations. − Square-planar Pt­(II) complexes often possess very complex and rich photochemical properties, , such as anti-kasha emission and dual photoluminescence. − These complex photochemical scenarios make it difficult to develop computational protocols enabling the calculation of the phosphorescence energy of a given arbitrary Pt­(II) complex without prior information on its measured photophysical properties. Thus, in this contribution, we first aim at benchmarking state-of-the-art methods for the phosphorescence energies of Pt­(II) complexes and second to devise strategies to systematically assess whether the lowest triplet excited-state minimum is involved in the emission processes or not.…”

A Computational Protocol to Calculate the Phosphorescence Energy of Pt (II) Complexes: Is the lowest triplet excited state always involved in emission? A Comprehensive Benchmark Study

“…Their photophysical properties have been the scope of multiple investigations. [28][29][30][31] Square-planar Pt(II) complexes often possess very complex and rich photochemical properties, 32,33 such as anti-kasha emission but also dual photoluminescence. [34][35][36][37] These complex photochemical scenarios make difficult the development of computational protocols enabling the calculation of the phosphorescence energy of a given arbitrary Pt(II) complex without prior information on its measured photophysical properties.…”