Alkyne Cyclotrimerisation, Acyclic Oligomerisation, and Hydrogenation Catalysed by a Titanium(IV) Phosphinoaryloxide Complex and its Redox Chemistry

The reaction of sodium 2,4‐di‐tert‐butyl‐6‐(diphenylphosphino)phenolate (1, NaOArP) with TiIVCl4(THF)2 in a 2:1 molar ratio yielded TiIV(OArP)2Cl2 (2). The reduction of 2 with magnesium gave the dimeric titanium(III) compound [TiIII(OArP)2Cl]2 (3). In the presence of magnesium, compound 2 was found to catalyse the cyclotrimerization, acyclic oligomerisation, and hydrogenation of terminal alkynes. The complexes were characterised by single‐crystal X‐ray diffraction, optical spectroscopy, elemental analysis, and NMR or EPR spectroscopy, respectively.