Issue 39, 2014

Synthesis and reactivity of coordinatively unsaturated halocarbonyl molybdenum PNP pincer complexes

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

Supplementary files

Article information

Article type
Paper
Submitted
26 Jun 2014
Accepted
08 Aug 2014
First published
08 Aug 2014

Dalton Trans., 2014,43, 14669-14679

Author version available

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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