resumo
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.
palavras-chave
CARBONYL-COMPLEXES; HYDROGEN-PEROXIDE; DERIVATIVES; TUNGSTEN; REACTIVITY; MO; 1,10-PHENANTHROLINE; OCTAMOLYBDATE; PRECURSORS; REDUCTION
categoria
Chemistry
autores
Nogueira, LS; Neves, P; Gomes, AC; Lavrador, P; Cunha-Silva, L; Valente, AA; Goncalves, IS; Pillinger, M
nossos autores
Ana Catarina Costa Gomes Alves
Investigador Auxiliar
Anabela Tavares Aguiar Valente
Investigador Principal
Isabel Maria de Sousa Gonçalves
Professor associado
Lucie Solange Nogueira
Estudante de doutoramento
Martyn Pillinger
Investigador Principal
Patrícia dos Santos Neves
Investigador Auxiliar
Pedro Lavrador
Estudante de doutoramentoGrupos
G1 - Materiais Porosos e Nanossistemas
G4 - Materiais Renováveis e Economia Circular
G5 - Materiais Biomiméticos, Biológicos e Vivos
agradecimentos
This work was developed in the scope of the projects (Associate Laboratories) CICECO-Aveiro Institute of Materials-POCI-01-0145-FEDER-007679 [FCT (Fundacao para a Ciencia e a Tecnologia) ref. UID/CTM/50011/2013] and REQUIMTE-LAQV-POCI-01-0145-FEDER-007265 (FCT ref. UID/QUI/50006/2013), financed by national funds through the FCT/MEC and when applicable co-financed by FEDER (Fundo Europeu de Desenvolvimento Regional) under the PT2020 Partnership Agreement. The FCT and the European Union are acknowledged for a PhD grant to L. N. (PD/BD/109666/2015), and post-doctoral grants to P. N. (SFRH/BPD/110530/2015), A. C. G. (SFRH/BPD/108541/2015) and L. C-S. (SFRH/BPD/111899/2015), co-funded by MCTES and the European Social Fund through the program POPH of QREN.