Thermodynamic Modulation of Dihydrogen Activation Through Rational Ligand Design in Ge<sup>II</sup>–Ni<sup>0</sup> Complexes
Philip M. Keil, Sophia Ezendu, Annika Schulz, Malte Kubisz, Tibor Szilvási, Terrance J. Hadlington
Abstract
High Resolution Image Download MS PowerPoint Slide A family of chelating aryl-functionalized germylene ligands has been developed and employed in the synthesis of their corresponding 16-electron Ni 0 complexes ( PhiP DippGeAr·Ni·IPr; PhiP Dipp = {[Ph 2 PCH 2 Si( i Pr) 2 ](Dipp)N} −; IPr = [{(H)CN(Dipp)} 2 C:]; Dipp = 2,6- i Pr 2 C 6 H 3 ). These complexes demonstrate the ability to cooperatively and reversibly activate dihydrogen at the germylene-nickel interface under mild conditions (1.5 atm H 2, 298 K). We show that the thermodynamics of the dihydrogen activation process can be modulated by tuning the electronic nature of the germylene ligands, with an increase in the electron-withdrawing character displaying more exergonic Δ G 298 values, as ascertained through NMR spectroscopic Van’t Hoff analyses for all systems. This is also shown to correlate with experimental 31 P NMR and UV/vis absorption data as well as with computationally derived parameters such as Ge–Ni bond order and Ni/Ge NPA charge, giving a thorough understanding of the modulating effect of ligand design on this reversible, cooperative bond activation reaction. Finally, the utility of this modulation was demonstrated in the catalytic dehydrocoupling of phenylsilane, whereby systems that disfavor dihydrogen activation are more efficient catalysts, aligning with H 2 -elimination being the rate-limiting step. A density functional theory analysis supports cooperative activation of the Si–H moiety in PhSiH 3 .