Bimetallic nickel-lutetium complexes: tuning the properties and catalytic hydrogenation activity of the Ni site by varying the Lu coordination environment.

ABSTRACT: We present three heterobimetallic complexes containing an isostructural nickel center and a lutetium ion in varying coordination environments. The bidentate ⁱPr₂PCH₂NHPh and nonadentate (ⁱPr₂PCH₂NHAr)₃tacn ligands were used to prepare the Lu metalloligands, Lu(ⁱPr₂PCH₂NPh)₃ (1) and Lu{(ⁱPr₂PCH₂NAr)₃tacn} (2), respectively. Reaction of Ni(COD)₂ (where COD is 1,5-cyclooctadiene) and 1 afforded NiLu(ⁱPr₂PCH₂NPh)₃ (3), with a Lu coordination number (CN) of 4 and a Ni-Lu distance, d(Ni-Lu), of 2.4644(2) Å. Complex 3 can further bind THF to form 3-THF, increasing both the Lu CN to 5 and d(Ni-Lu) to 2.5989(4) Å. On the other hand, incorporation of Ni(0) into 2 provides NiLu{(ⁱPr₂PCH₂NAr)₃tacn} (4), in which the Lu coordination environment is more saturated (CN = 6), and the d(Ni-Lu) is substantially elongated at 2.9771(5) Å. Cyclic voltammetry of the three Ni-Lu complexes shows an overall ?410 mV shift in the Ni(0/I) redox couple, suggesting tunability of the Ni electronics across the series. Computational studies reveal polarized bonding interactions between the Ni 3d _{z ²} (major) and the Lu 5d _{z ²} (minor) orbitals, where the percentage of Lu character increases in the order: 4 (6.0% Lu 5d _{z ²} ) < 3-THF (8.5%) < 3 (9.3%). All three Ni-Lu complexes bind H₂ at low temperatures (-30 to -80 °C) and are competent catalysts for styrene hydrogenation. Complex 3 outperforms 4 with a four-fold faster rate. Additionally, adding increasing THF equivalents to 3, which would favor build-up of 3-THF, decreases the rate. We propose that altering the coordination sphere of the Lu support can influence the resulting properties and catalytic activity of the active Ni(0) metal center.

SUBMITTER: Ramirez BL 

PROVIDER: S-EPMC6429466 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature