Versatile Production Of Novel Pnp Based Metal Complexes Applicable As Water Reduction Catalysts Showing Ch/M As Well As Ch/Pi Interactions

Several PNP-type ligands of the form bis(dianisylphosphanylmethyl)alkylamine, where alkyl is methyl, ethyl, isopropyl, and benzyl (1-4), have been coordinated to Co(II), Ni(II), Pd(II), and Pt(II) (5-26). This series of water reduction catalysts (WRC) has been characterized by single-crystal X-ray structure analysis, multinuclear and 2D NMR spectroscopy, mass spectrometry and a computational study. Intramolecular contact approaches show differences depending on hetero- or homoleptic complexes. Both solid state and solution structures indicate an enhancement of steric pressure for the latter. As a consequence CH/M as well as CH/pi interactions appear in the X-ray structures and H-1 NMR spectra. They can also be clearly identified by quantum mechanical calculations on a B3LYP level. Since these WRC contain proton relays due to the used PNP-ligands, they are prone to proton coupled electron transfer (PCET) during photocatalysis. The different steric pressure influences their reorganisation energy. Obviously, the observed intramolecular contact approaches should be regarded as a tool for the design of future WRC.