A dynamic frequency shift (DFS) in the 1 H NMR resonance of the HD unit of the deuterium-labeled dihydrogen complex [Ru(D)(η 2 -HD)(P 3 P 3 i Pr )][BPh 4 ] [P 3 P 3 i Pr = P(CH 2 CH 2 CH 2 P i Pr 2 ) 3 ] has been observed and analyzed. To the best of our knowledge, this is the first demonstration of the DFS for a H−D pair. The observed DFS of the center line relative to the outside lines in the H−D triplet is large, up to ∼11 Hz, because of the short H−D distance encountered in dihydrogen complexes. Analysis of the DFS as a function of the temperature, combined with density-functional-theory-calculated or least-squares-fitted electric-fieldgradient (EFG) parameters, suggests an H−D bond length of 0.92−0.94 Å. A DFS was also observed in trans-[Fe(η 2 -HD)(H)(dppe) 2 ] + , suggesting the DFS will be commonplace in dihydrogen complexes if appropriate conditions are employed for its observation. Possible applications of the DFS as a probe of the bond lengths, EFGs, and molecular motion, particularly in inorganic systems, are discussed.