Loading...
2 results
Search Results
Now showing 1 - 2 of 2
- Syntheses and properties of hydride–cyanamide and derived hydrogen-cyanamide complexes of molybdenum(IV). Crystal structure of [MoH2(NCNH2)2(Ph2PCH2CH2PPh2)2][BF4]2Publication . Martins, Luisa; Alegria, Elisabete; Hughes, David L.; Fraústo Da Silva, João; Pombeiro, ArmandoThe first hydride–cyanamide (or –cyanoguanidine) complexes of molybdenum, [MoH2(NCR)2(dppe)2][BF4]2 (R = NH2 1a, NMe2 1b, NEt2 1c or NC(NH2)2 1d; dppe = Ph2PCH2CH2PPh2), have been prepared by treatment of [MoH4(dppe)2] in THF with the appropriate cyanamide (or cyanoguanidine) in the presence of HBF4. Reaction of 1a with a base leads to the bis(hydrogen-cyanamide) [or bis(hydrogen-cyananoimide)] complex trans-[Mo(NCNH)2(dppe)2][BF4]2 2 or to the bis(cyanoimide) complex trans-[Mo(NCN)2(dppe)2] 3, via basecatalysed or base-promoted dehydrogenation, whereas cathodically-induced dehydrogenation appears to form [MoH2(NCNH)(NCNH2)(dppe)2] 4. The spectroscopic properties of the complexes are also reported along with their electrochemical behaviours and the molecular structure of 1a as established by X-ray crystallography which indicates the presence of the NCNH2 ligands involved in two hydrogen bonds connecting the ions in dimeric units.
- Cyclohexane oxidation with dioxygen catalyzed by supported pyrazole rhenium complexesPublication . Mishra, Gopal S.; Alegria, Elisabete; Martins, Luisa; Fraústo Da Silva, João; Pombeiro, ArmandoThe pyrazole complexes [ReCl2{N2C(O)Ph}(Hpz)(PPh3)2] 2 (Hpz = pyrazole), [ReCl2{N2C(O)Ph}(Hpz)2(PPh3)] 3 and [ReClF{N2C(O)Ph}(Hpz)2(PPh3)] 4, and their precursor [ReOCl3(PPh3)2] 1, immobilized on 3-aminopropyl functionalized silica, catalyze the cyclohexane oxidation with dioxygen, to cyclohexanol and cyclohexanone (the main product), in the absence of solvent and additives and under relatively mild conditions. Complex 4, whose synthesis and characterization are reported herein for the first time, provides the best activity (ca. 16% overall conversion towards the ketone and alcohol, at the O2 pressure of 19 atm, at 150 °C, 8 h reaction time). The reaction is further promoted by pyrazinecarboxylic acid. TGA analysis shows that the supported complexes are stable up to ca. 200 °C. The use of radical traps supports the involvement of a free-radical mechanism via carbon- and oxygen-centred radicals. The effects of various factors were studied towards the optimization of the processes. Complex 4 also catalyzes the oxidation of other cycloalkanes to the corresponding cycloalkanols and cycloalkanones.