Catalytically active nanosized Pd9Te4 (telluropalladinite) and PdTe (kotulskite) alloys: first precursor-architecture controlled synthesis using palladium complexes of organotellurium compounds as single source precursors

Abstract

Several intermetallic binary phases of Pd-Te including Pd₃Te₂, PdTe, PdTe₂, Pd₉Te₄, Pd₃Te, Pd₂Te, Pd₂₀Te₇, Pd₈Te₃, Pd₇Te₂, Pd₇Te₃, Pd₄Te and Pd₁₇Te₄ are known, and negligible work (except few studies on PdTe) has been done on exploring applications of such phases and their fabrication at nanoscale. Hence, Pd(ii) complexes Pd(L1)Cl₂ and Pd(L2-H)Cl (L1): Ph-Te-CH₂-CH₂-NH₂ and L2: HO-2-C₆H₄-CH[double bond, length as m-dash]N-CH₂CH₂-Te-Ph were synthesized. Under similar thermolytic conditions, complex Pd(L1)Cl₂ with bidentate coordination mode of ligand provided nanostructures of Pd₉Te₄ (telluropalladinite) whereas Pd(L2-H)Cl with tridentate coordination mode of ligand yielded PdTe (kotulskite). Bimetallic alloy nanostructures possess high catalytic potential for Suzuki coupling of aryl chlorides, and reduction of 4-nitrophenol. They are also recyclable upto six reaction cycles in Suzuki coupling.

Fig. 1. ORTEP diagram of complex 1 with 50% thermal ellipsoids. Selected bond lengths (Å): Te–Pd: 2.5057(6), Te–C_aryl: 2.118(6), Te–C_alkyl: 2.149(6), Pd–Cl: 2.3142(16), Pd–Cl; Pd–N: 2.063(5). Selected bond angles (°): Cl–Pd–Te: 88.82(4), Cl–Pd–Cl: 94.42(6), N–Pd–Te: 88.21(13), N–Pd–Cl: 88.54(14).

Fig. 2. ORTEP diagram of complex 2 with 50% thermal ellipsoids. Selected bond lengths (Å): Te–Pd: 2.5002(4), Te–C: 2.120(4), Pd–Cl: 2.3271(11), Pd–O: 2.007(3), Pd–N: 2.017(4). Selected bond angles (°): Cl–Pd–Te: 86.74(3), O–Pd–Cl: 88.98(9), N–Pd–Te: 90.94(10), N–Pd–O: 93.18(13).

Scheme 1. Strategy for syntheses and catalytic reactions.

Fig. 3. TGA curves of (a) complex 1 (b) complex 2.

Fig. 4. FTIR spectra of (a) Pd₉Te₄ (b) PdTe nanostructures.

Fig. 5. PXRD spectra of (a) Pd₉Te₄ (b) PdTe nanostructures.

Fig. 6. SEM-EDS spectra of (a) Pd₉Te₄ (b) PdTe nanostructures.

Fig. 7. HRTEM images of nanostructures of Pd₉Te₄ (a and c) and PdTe (b and d).

Fig. 8. DLS analysis of (a) Pd₉Te₄ and (b) PdTe nanostructures.

Fig. 9. XPS spectra of (a) Pd₉Te₄ and (b) PdTe nanostructures.

Fig. 10. N₂ adsorption–desorption isotherm of Pd₉Te₄ and PdTe nanostructures.

Fig. 11. (a) Reduction of 4-nitrophenol (b) plot of ln(C_t/C₀) versus time: determination of rate constant.

Fig. 12. Recyclability plot of catalytic use of Pd₉Te₄ alloy nanoparticles in the Suzuki coupling of 4-chlorobenzaldehyde and phenylboronic acid.