Borohydride ligands featuring multiple pendant donor functionalities have been prevalent in the chemical literature for many decades now. More recent times has seen their development into new families of so-called soft scorpionates, for example, those featuring sulfur based donors. Despite all of these developments, those ligands containing just one pendant group are rare. This article explores one ligand family based on the 2-mercaptopyridine heterocycle. The coordination chemistry of the monosubstituted ligand, [H 3 B(mp)] − (mp = 2-mercaptopyridyl), has been explored. Reaction of Na[BH 3 (mp)] with one equivalent of Cu (I) Cl in the presence of either triphenylphosphine or tricyclohexylphosphine co-ligands leads to the formation of [Cu{H 3 B(mp)}(PR 3 )] (R = Ph, 1; Cy, 2), respectively. Structural characterization confirms a κ 3 -S,H,H coordination mode for the borohydride-based ligand within 1 and 2, involving a dihydroborate bridging interaction (BH 2 Cu) with the copper centers.Inorganics 2019, 7, 93 2 of 11 differences when compared to Trofimenko's original scorpionates. The ligand was based on soft sulfur donor atoms [16], and perhaps more significantly, greater flexibility had been incorporated into the ligand by addition of the extra atom between the boron and the donor atom. It was this greater flexibility within the ligand structure that opened up the potential for activation at the boron bridgehead and formation of metal-borane (metallaboratrane) complexes [17][18][19][20][24][25][26][27], giving rise to reactivity not observed in the analogous polypyrazolylborate ligands [10][11][12][13][14][15][16].Inorganics 2019, 7, x FOR PEER REVIEW 2 of 11 differences when compared to Trofimenko's original scorpionates. The ligand was based on soft sulfur donor atoms [16], and perhaps more significantly, greater flexibility had been incorporated into the ligand by addition of the extra atom between the boron and the donor atom. It was this greater flexibility within the ligand structure that opened up the potential for activation at the boron bridgehead and formation of metal-borane (metallaboratrane) complexes [17][18][19][20][24][25][26][27], giving rise to reactivity not observed in the analogous polypyrazolylborate ligands [10][11][12][13][14][15][16].