The synthesis and structural properties of [M(dippe)(η2-C4H4S)] complexes of Pd and Pt and comparison with their Ni analog

X-ray structural and NMR spectroscopic data for the ring-opened thiophene complexes [Pd(dippe)(T)] (2), and [Pt(dippe)(T)] (3) are now presented. The complex [Ni(dippe)(T)] (1), where T = (η2-C,S-C4H4S), was reported by our group, previously.The structural and bonding properties of complexes 2 and 3 were compared with those of complex 1. DFT calculations were carried out to rationalize their relative stabilities and structural properties. Compound 1 loses thiophene at ambient temperature in solution, while compound 2 decomposes rapidly in both acetone-d6 and THF-d8 with kobs = 7.15(9) × 10−5 and 7.7(3) × 10−5 s−1, respectively, to give products that varied by solvent. Complex 3 does not lose thiophene at temperatures below 100 °C. The ΔG0 values determined from DFT calculations are consistent with the observed stabilities of the complexes. The single crystal X-ray structures of all three complexes contain a disordered thienyl fragment in the asymmetric unit due to the interchange of the position of sulfur in the metal-inserted thiophenic ring. The thiophenic moiety is relatively flat in 1, 2 and 3, which is attributed to the open ligand environment at the M(dippe) fragment. All three complexes possess square-planar geometry around the metal center and have bond-length alternation among the thiophenic carbons, which indicates double bond localization. The calculated bond lengths are in good agreement with experimental data. Molecular orbital (MO) and natural bonding orbital (NBO) analyses were carried out to rationalize the results.

Graphical abstractThe reactions of the unsaturated metal fragments [M(dippe)] where M = Ni, Pd, or Pt with thiophene are described (dippe = bis-(diisopropylphosphino)ethane). DFT calculations are used to support the electronic and geometric features of the compounds.Figure optionsDownload full-size imageDownload as PowerPoint slide