Structural diversity of halocarbonyl molybdenum and tungsten PNP pincer complexes through ligand modifications

Sara R.M.M. De Aguiar, Berthold Stöger, Ernst Pittenauer, Günter Allmaier, Luis F. Veiros, Karl Kirchner

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Abstract

This work presents a comparative study of a series of halocarbonyl Mo(ii) and W(ii) complexes of the types [M(PNP)(CO)3X]X and [M(PNP)(CO)2X2] (M = Mo, W; X = I, Br), featuring PNP pincer ligands based on a 2,6-diaminopyridine scaffold. The complexes were prepared and fully characterized. The syntheses of these complexes were accomplished by treatment of [M(PNP)(CO)3] with stoichiometric amounts of I2 and Br2, respectively. The modification of the 2,6-diaminopyridine scaffold by introducing NMe and NPh instead of NH spacers with concomitant modification of the phosphine moieties changed the steric and electronic properties of the PNP ligand significantly. While in the case of NH linkers exclusively cationic seven-coordinate complexes of the type [M(PNP)(CO)3X]+ were obtained with NMe and NPh spacers neutral seven-coordinate complexes of the type [M(PNP)(CO)2X2] were afforded. In the case of the latter, when the reaction is performed in the presence of CO also [M(PNP)(CO)3X]+ complexes are formed which slowly lose CO to give [M(PNP)(CO)2X2]. The halocarbonyl tungsten chemistry parallels that of molybdenum. The only exception is molybdenum in conjunction with the PNPMe-iPr ligand, where the coordinatively unsaturated complex [Mo(PNPMe-iPr)(CO)X2] is formed. DFT mechanistic studies reveal that the seven-coordinate complexes should be the thermodynamic as well as the kinetic products. Since [Mo(PNPMe-iPr)(CO)X2] is the observed product it suggests that the reaction follows an alternative path. Structures of representative complexes were determined by X-ray single crystal analyses.

Original languageEnglish
Pages (from-to)13834-13845
Number of pages12
JournalDalton Transactions
Volume45
Issue number35
DOIs
Publication statusPublished - 20 Jul 2016

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

De Aguiar, S. R. M. M., Stöger, B., Pittenauer, E., Allmaier, G., Veiros, L. F., & Kirchner, K. (2016). Structural diversity of halocarbonyl molybdenum and tungsten PNP pincer complexes through ligand modifications. Dalton Transactions, 45(35), 13834-13845. https://doi.org/10.1039/c6dt02251k