Molybdenum(0) tricarbonyl and tetracarbonyl complexes with a cationic pyrazolylpyridine ligand: synthesis, crystal structures and catalytic performance in olefin epoxidation

authors	Nogueira, LS; Neves, P; Gomes, AC; Lavrador, P; Cunha-Silva, L; Valente, AA; Goncalves, IS; Pillinger, M
nationality	International
journal	RSC ADVANCES
keywords	CARBONYL-COMPLEXES; HYDROGEN-PEROXIDE; DERIVATIVES; TUNGSTEN; REACTIVITY; MO; 1,10-PHENANTHROLINE; OCTAMOLYBDATE; PRECURSORS; REDUCTION
abstract	The synthesis of molybdenum(0) tricarbonyl and tetracarbonyl complexes of the form [Mo(CO)(3)(ptapzpy)Br] (1) and cis-[Mo(CO)(4)(ptapzpy)]Br (2) is reported, where ptapzpy = 2-(1-propyltrimethylammonium-3-pyrazolyl)pyridine. Preparation of these derivatives was accomplished either through thermal replacement of CO in Mo(CO)(6) (for 1) or substitution under milder conditions of piperidine ligands in the precursor cis-[Mo(CO)(4)(pip)(2)] (for 2). The crystal structures of the ligand [ptapzpy] Br and complexes 1 and 2 were determined. Thermal treatment of 2 at 125-150 degrees C leads to mono decarbonylation and formation of 1. On the other hand, oxidative decarbonylation of 1 and 2 by reaction with tert-butylhydroperoxide (TBHP, 10 equiv.) gives a molybdenum oxide hybrid material formulated as [Mo3O9([ptapzpy]Br)(2)]center dot nH(2)O (3), which was characterised by FT-IR and Raman spectroscopy, thermogravimetric analysis, and C-13{H-1} CP MAS NMR spectroscopy. Compounds 1-3 were effective (pre)catalysts for the epoxidation of cis-cyclooctene at 55 degrees C with aqueous H2O2 or TBHP (slightly better results were obtained with the former). The characterisation of the Mo-containing solids isolated after the catalytic reaction showed that poorly soluble beta-octamolybdate salts, (L)(x)[Mo8O26], were formed from 1-3 with TBHP and from 1 with H2O2, while soluble oxoperoxo species were formed from 3 with H2O2. These findings helped to explain the different catalytic performances obtained.
publisher	ROYAL SOC CHEMISTRY
issn	2046-2069
year published	2018
volume	8
issue	29
beginning page	16294
ending page	16302
digital object identifier (doi)	10.1039/c8ra01687a
web of science category	Chemistry, Multidisciplinary
subject category	Chemistry
unique article identifier	WOS:000431814200052