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Strain imposed on square-planar Pt(II) complexes by bulky ligands like −Sn(tBu)3 and −CN(tBu) facilitate H2 activation due to minimal structural reorganization.
Experiments have indicated that bulky ligands are required for efficient H2 activation by Pt–Sn complexes. Herein, we unravel the mechanisms for a Pt–Sn complex, Pt(SntBu3)2(CNtBu)2 (1a), catalyzed reversible H2 activation. Among a number of Pt–Sn catalysts used to model H2 activation and H2/D2 exchange reactions, only 1a with large strain was found to be suitable because the addition of H2 to 1a requires lowest distortion energy, minimal structural changes, and smallest entropy of activation. The activity of this Pt–Sn complex was compared vis-à-vis its Pt–Ge and Pt–Si analogues, and we predicted that strained Pt–Ge complex can efficiently activate H2 reversibly. Direct dynamics calculations for the rate of reductive elimination of H2, HD, and D2 from Pt(SntBu3)(CNtBu)2H3 (4a) and Pt(SntBu3)(CNtBu)2HD2 (4a[2D]) shows that H/D atom tunneling contributes significantly, which leads to an enhanced kinetic isotope effect. Strain control is suggested as a design concept in H2 activation.
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