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Issue 39, 2014
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Synthesis and reactivity of coordinatively unsaturated halocarbonyl molybdenum PNP pincer complexes

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Abstract

In the present study a series of six-coordinate neutral 16e halocarbonyl Mo(II) complexes of the type [Mo(PNPMe-iPr)(CO)X2] (X = I, Br, Cl), featuring the PNP pincer ligand N,N′-bis(diisopropylphosphino)-N,N′-dimethyl-2,6-diaminopyridine (PNPMe-iPr), were prepared and fully characterized. The synthesis of these complexes was accomplished by different methodologies depending on the halide ligands. For X = I and Br, [Mo(PNPMe-iPr)(CO)I2] and [Mo(PNPMe-iPr)(CO)Br2] were obtained by reacting [Mo(PNPMe-iPr)(CO)3] with stoichiometric amounts of I2 and Br2, respectively. In the case of X = Cl, [Mo(PNPMe-iPr)(CO)Cl2] was afforded by the reaction of [Mo(CO)4(μ-Cl)Cl]2 with 1 equiv. of PNPMe-iPr. The equivalent procedure also worked for X = Br. The modification of the 2,6-diaminopyridine scaffold by introducing NMe instead of NH spacers between the aromatic pyridine ring and the phosphine moieties changed the steric properties of the PNP-iPr ligand significantly. While in the present case exclusively neutral six-coordinate complexes of the type [Mo(PNPMe-iPr)(CO)X2] were obtained, with the parent PNP-iPr ligand, i.e. featuring NH spacers, cationic seven-coordinate complexes of the type [Mo(PNP-iPr)(CO)3X]X were afforded. Upon treatment of [Mo(PNPMe-iPr)(CO)X2] (X = Br, Cl) with Ag+ in CH3CN, the cationic complexes [Mo(PNPMe-iPr)(CO)(CH3CN)X]+ were formed. Halide abstraction from [Mo(PNPMe-iPr)(CO)Cl2] in THF–CH2Cl2 afforded [Mo(PNPMe-iPr)(CO)(THF)Cl]+. In keeping with the facile synthesis of monocationic complexes preliminary ESI-MS and DFT/B3LYP studies revealed that one halide ligand in complexes [Mo(PNPMe-iPr)(CO)X2] is labile forming cationic fragments [Mo(PNPMe-iPr)(CO)X]+ which react with molecular oxygen in parallel pathways to yield mono and dioxo Mo(IV) and Mo(VI) species. Structures of representative complexes were determined by X-ray single crystal analyses.

Graphical abstract: Synthesis and reactivity of coordinatively unsaturated halocarbonyl molybdenum PNP pincer complexes

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Publication details

The article was received on 26 Jun 2014, accepted on 08 Aug 2014 and first published on 08 Aug 2014


Article type: Paper
DOI: 10.1039/C4DT01932F
Author version available: Download Author version (PDF)
Citation: Dalton Trans., 2014,43, 14669-14679
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    Synthesis and reactivity of coordinatively unsaturated halocarbonyl molybdenum PNP pincer complexes

    S. R. M. M. de Aguiar, Ö. Öztopcu, B. Stöger, K. Mereiter, L. F. Veiros, E. Pittenauer, G. Allmaier and K. Kirchner, Dalton Trans., 2014, 43, 14669
    DOI: 10.1039/C4DT01932F

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