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
dataset
posted on 2014-12-15, 00:00 authored by Shuanming Zhang, Roberto Pattacini, Pierre Braunstein, Luisa De Cola, Edward Plummer, Matteo Mauro, Christophe Gourlaouen, Chantal DanielNew
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).
