Influence of η1‐Acetylide Ligands on the Spin State and Catalytic Activity of Iron(II) PNP Pincer Complexes

• Published in: European journal of inorganic chemistry 2024-12, Vol.27 (35), p.n/a
• Main Authors: Eder, Wolfgang, Stöger, Berthold, Kirchner, Karl, Gorgas, Nikolaus
• Format: Article
• Language: English
• Subjects: Acetylide ligands; Alkyne dimerization; Alkynes; Catalytic activity; Dimerization; Field strength; Homogeneous catalysis; Iron; Ligands; Lithium; Spin states
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.202400490

Here, we report the preparation, structures and reactivity of iron(II) PNP pincer complexes bearing one, two or three η1‐acetylide ligands bound to the metal center. The described complexes are accessible through the reaction of either one, two or ≥3 equivalent of LiCCR (R=SiMe3, Ph) with the dibromide complex [Fe(PNP)Br2] (1). Through increasing the number of η1‐acetylides the overall ligand field strength can be modulated resulting in S=2, S=1 and S=0 spin states for mono‐, bis‐ and tris‐acetylated complexes, respectively. These findings are supported by DFT calculations on the spin state spitting in these complexes and appear to affect their binding affinity towards additional co‐ligands. The Fe(II) mono‐, bis‐ and tris‐acetylides were tested as catalyst in the catalytic dimerization of terminal alkynes. These test reactions revealed that only the bis‐acetylated complexes are catalytically competent while mono‐acetylated species are inactive. The tris‐acetylated complexes were found to be off‐cycle intermediates in the presence of lithium acetylides. Here we describe iron(ii) pincer complexes bearing one, two or even three η1‐acetylide ligands bound to the metal center. The overall ligand field strength changes across the series and affects the spin states, reactivity and catalytic activity of these complexes.