Abstract Organyl-mercury hydridotris(3, 5-dimethylpyrazol-l-yl)borates have been prepared and characterized; solution data (1H, 13C and 199Hg NMR spectra) indicate that the R-HgQ compounds (R = alkyl, aryl, ferrocenyl; Q = [(3, 5-dimethylpyrazol-l-yl)3BH]−) are fluxional and are likely to contain two-coordinated mercury(II).