Understanding the solution and solid-state structures of Pd and Pt PSiP pincer-supported hydrides
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Date
2015-11-19
Journal Title
Journal ISSN
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Publisher
American Chemical Society
Abstract
The PSiP pincer-supported complex (CyPSiP)PdH [CyPSiP = Si(Me)(2-PCy2-C6H4)2] has been implicated as a crucial intermediate in carboxylation of both allenes and boranes. At this stage, however, there is uncertainty regarding the exact structure of (CyPSiP)PdH, especially in solution. Previously, both a Pd(II) structure with a terminal Pd hydride and a Pd(0) structure featuring an η2-silane have been proposed. In this contribution, a range of techniques were used to establish that (CyPSiP)PdH and the related Pt species, (CyPSiP)PtH, are true M(II) hydrides in both the solid state and solution. The single-crystal X-ray structures of (CyPSiP)MH (M = Pd and Pt) and the related species (iPrPSiP)PdH [iPrPSiP = Si(Me)(2-PiPr2-C6H4)2] are in agreement with the presence of a terminal metal hydride, and the exact geometry of (CyPSiP)PtH was confirmed using neutron diffraction. The 1H and 29Si{1H}NMR chemical shifts of (CyPSiP)MH (M = Pd and Pt) are consistent with a structure containing a terminal hydride, especially when compared to the chemical shifts of related pincer-supported complexes. In fact, in this work, two general trends relating to the 1H NMR chemical shifts of group 10 pincer-supported terminal hydrides were elucidated: (i) the hydride shift moves downfield from Ni to Pd to Pt and (ii) the hydride shift moves downfield with more trans-influencing pincer central donors. DFT calculations indicate that structures containing a M(II) hydride are lower in energy than the corresponding η2-silane isomers. Furthermore, the calculated NMR chemical shifts of the M(II) hydrides using a relativistic four-component methodology incorporating all significant scalar and spin-orbit corrections are consistent with those observed experimentally. Finally, in situ X-ray absorption spectroscopy (XAS) was used to provide further support that (CyPSiP)MH exist as M(II) hydrides in solution. © 2015 American Chemical Society.
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Keywords
Hydrides, Palladium, Platinum, Silicon, Solutions, Anions, Ligands, Crystal structure, Temperature range
Citation
Suh, H.-W., Balcells, D., Edwards, A. J., Guard, L. M., Hazari, N., Mader, E. A., Mercado, B. Q., & Repisky, M. (2015). Understanding the solution and solid-state structures of Pd and Pt PSiP pincer-supported hydrides. Inorganic Chemistry, 54(23), 11411–11422. doi:10.1021/acs.inorgchem.5b02073