Mn-7 readily forms hydrides upon activation. At room temperature the reaction of Mn-7 with KBHEt 3 in THF-d 8 gave rise to three new doublet resonances in 1 H NMR spectrum at -5.01, -5.65, and -6.77 ppm. with 2 J PH = 40.0, 48.0, and 88.0 Hz, respectively (Figures ). We attributed these peaks to the isomers of tricarbonyl Mn-H species 8, in total accounting for 97% of the activation products. The retention of three CO ligands upon the near-quantitative transformation of 7 during the activation step is confirmed by IR spectroscopy revealing three new bands at 1981, 1896, and 1876 cm -1 (Figure ). Since 8 is a tricarbonyl, monohydride complex featuring Mn-bound phosphine donor we conclude that activation of Mn-7 leads to the dissociation of the central N-donor group rendering it hemilabile (see section S8 in Supporting Information for the structural assignments based on the exhaustive expert-bias free configurational DFT analysis). This contrasts the case of nonmethylated analogue -Mn-5, 16j which dissociated the phosphine arm in a similar activation step.