A convenient synthesis, chemical characterization and reactivity of [Re(CO)3(H2O)3]Br: the crystal and molecular structure of [Re(CO)3(CH3CN)2Br]

The useful synthetic precursor [Re(CO)3(H2O)3]Br (1) may be prepared in nearly quantitative yield by refluxing [Re(CO)5]Br in H2O for 24 h. Upon concentrating the solution, compound 1 is isolated as a microcrystalline light green powder, which is soluble in water and polar organic solvents. Recrystallization from methanol affords [Re(CO)3(MeOH)2Br] (2), while recrystallization from acetonitrile provides the crystalline [Re(CO)3(CH3CN)2Br] (3). The lability of the aqua ligands of 1 is also manifested upon recrystallization from ethyl acetate/hexane, which yields [Re(CO)3(OH)]4 · 4H2O (4 · 4H2O). The reaction chemistry of 1 with dipyridylamine has been compared to that of the conventional starting material [NEt4]2[Re(CO)3Br3] and shown to produce a monophasic compound, free of contamination with NEt4Br. Crystal data: C7H6BrN2O3Re (3): orthorhombic Pnma, a = 6.2289(3) Å, b = 13.1323(7) Å, c = 13.1700(7) Å, V = 1077.3(1) Å3, Dcalc = 2.665 g/cm3. C3H3O5Re (4 · 4H2O): tetragonal I-4, a = 11.5964(3) Å, c = 8.8764(4) Å, V = 1193.67(7) Å3, Dcalc = 3.397 g/cm3.