title: Understanding the Solution and Solid-State Structures of Pd and Pt PSiP Pincer-Supported Hydrides.
abstract: The PSiP pincer-supported complex ((Cy)PSiP)PdH [(Cy)PSiP = 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 ((Cy)PSiP)PdH, especially in solution. Previously, both a Pd(II) structure with a terminal Pd hydride and a Pd(0) structure featuring an η(2)-silane have been proposed. In this contribution, a range of techniques were used to establish that ((Cy)PSiP)PdH and the related Pt species, ((Cy)PSiP)PtH, are true M(II) hydrides in both the solid state and solution. The single-crystal X-ray structures of ((Cy)PSiP)MH (M = Pd and Pt) and the related species ((iPr)PSiP)PdH [(iPr)PSiP = Si(Me)(2-P(i)Pr2-C6H4)2] are in agreement with the presence of a terminal metal hydride, and the exact geometry of ((Cy)PSiP)PtH was confirmed using neutron diffraction. The (1)H and (29)Si{(1)H}NMR chemical shifts of ((Cy)PSiP)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 (1)H 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 η(2)-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 ((Cy)PSiP)MH exist as M(II) hydrides in solution.
authors.affiliation: The Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: Hee-Won
authors.initials: HW
authors.lastname: Suh
authors.affiliation: Centre for Theoretical and Computational Chemistry (CTCC), Department of Chemistry, University of Oslo , P.O. Box 1033, Blindern, 0315 Oslo, Norway.
authors.forename: David
authors.initials: D
authors.lastname: Balcells
authors.affiliation: Bragg Institute, Australian Nuclear Science and Technology Organization, New Illawarra Road, Lucas Heights, NSW 2234, Australia.
authors.forename: Alison J
authors.initials: AJ
authors.lastname: Edwards
authors.affiliation: The Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: Louise M
authors.initials: LM
authors.lastname: Guard
authors.affiliation: The Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: Nilay
authors.initials: N
authors.lastname: Hazari
authors.affiliation: The Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Mader
authors.affiliation: The Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: Brandon Q
authors.initials: BQ
authors.lastname: Mercado
authors.affiliation: Centre for Theoretical and Computational Chemistry (CTCC), University of Tromsø-The Arctic University of Norway , N-9037 Tromsø, Norway.
authors.forename: Michal
authors.initials: M
authors.lastname: Repisky