A Molecular Rotor Possessing an H–M–H “Spoke” on a P–M–P “Axle”: A Platinum(II) <i>trans</i>-Dihydride Spins Rapidly Even at 75 K

A new class of low-barrier molecular rotors, metal trans-dihydrides, is suggested here. To test whether rapid rotation can be achieved, the known complex trans-H2Pt­(PtBu3)2 was experimentally studied by 2H and 195Pt solid-state NMR spectroscopy (powder pattern changes with temperature) and computationally modeled as a tBu3P–Pt–PtBu3 stator with a spinning H–Pt–H rotator. Whereas the related chloro-hydride complex, trans-H­(Cl)­Pt­(PtBu3)2, does not show rotational behavior at room temperature, the dihydride trans-H2Pt­(PtBu3)2 rotates fast on the NMR time scale, even at low temperatures down to at least 75 K. The highest barrier to rotation is estimated to be ∼3 kcal mol–1, for the roughly 3 Å long rotator in trans-H2Pt­(PtBu3)2.