Modulation of quantum mechanical exchange couplings in transition metal hydrides through hydrogen bonding

Addition of various proton donors (methanol, indole, phenol, p-I-phenol, p-CF3-phenol and hexafluoroisopropanol) to solutions of Cp*RuH3(PCy3) (1) in d(8)-toluene leads to an increase of the quantum mechanical exchange couplings J(ab) between the hydride sites of 1 and to changes of the hydride chemical shifts, e.g. at 193 K the exchange couplings of 1 in d(8)-toluene vary from 74 Hz in the absence of additives to 249 Hz in the presence of 3 equiv. of (CF3)(2)CHOH. Exchange couplings and hydride chemical shifts are non-linear functions of the number of hydrogen bond donor equivalents (R). The effect is reversed when pyridine is added and does not occur with tetrahydrofuran as solvent. These observations provide evidence for the formation of hydrogen bonded associates between 1 and the proton donors added. Linear correlations are observed between the exchange couplings and the hydride chemical shifts of hydrogen bonded complexes indicating that these parameters can be used as sensors of the hydrogen bond strength and geometry.