Adding to the Family of Copper Complexes Featuring Borohydride Ligands Based on 2-Mercaptopyridyl Units

Abstract

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].

Synthesis and Chemistry of Dihydridoborate Group 7 Metal Complexes with Varied N,E-Chelated Ligands (E = O, NH, or S)

“…2-mercaptopyridine, 2-amino-5-mercapto-1,3,4-thiadiazole, 2-hydroxypyridine, 2-aminopyridine, 2,6-diaminopyridine, [NaBH 4 ], [Mn 2 (CO) 10 ], [Re 2 (CO) 10 ], and phenyl acetylene were purchased commercially (Sigma-Aldrich) and utilized as they were given. Following the procedures outlined in the literature, compounds like Na­[(H 3 B)­mp], Na­[(H 3 B)­amt], and the external reference for 11 B NMR, [Bu 4 N]­[B 3 H 8 ], were synthesized. Silica gel TLC plates (250 μm aluminum supported) were used for thin layer chromatography.…”

“…As shown in Figure 7a, the HOMO−2 of complex 8 shows the π-bonding as they were given. Following the procedures outlined in the literature, compounds like Na[(H 3 B)mp], 33 Na[(H 3 B)amt], 21 25 mmol) and NaBH 4 (0.402 g, 10.63 mmol) were taken in a Schlenk tube that had been flame-dried and were dissolved in 30 mL of THF/ EtOAc mixture and refluxed for 12 h. Following the removal of the solvent, the sample was rinsed with hot toluene (40 mL) and was then vacuum-dried to provide Na[(H 2 B)bap] as a white solid. Yield: ∼74% (1.74 g).…”