The compounds trans,trans-[ReO2(py)(4)][ReO2{H2B(pz*)(2)}(2)] (pz* = pz (1), 3,5-Me(2)pz (2)) have been prepared by reacting trans-[ReO2(py)(4)]Cl with the corresponding dihydrobis(pyrazolyl)borate. Compounds 1 and 2 react with electrophilic substrates, such as ClXMe3 (X = Si, Sn), leading to the neutral monoxo derivatives [ReO(OSiMe3){H2B(pz*)(2)}(2)] (pz* = pz (3), 3,5-Me(2)pz (4)) and [ReO(OSnMe3){H2B(pz)(2)}(2)] (5) and regenerating trans-[ReO2(py)(4)]Cl. Compounds 1 and 3 crystallize from dicbloromethane/n-hexane as yellow crystals, with one molecule of solvated CH2Cl2 in the case of 1. Crystallographic data: 1, triclinic space group P (1) over bar, a = 9.419(1) Angstrom, b = 9.584(1) Angstrom, c = 12.652(1) Angstrom, alpha = 89.03(1)degrees, beta = 82.41(1)degrees, gamma = 72.75(1)degrees, V = 1080.9(2) Angstrom(3), Z = 2; 3, monoclinic space group P2(1)/n, a = 10.785(2) Angstrom, b = 17.680(2) Angstrom, c = 11.971(2) Angstrom, beta = 98.67(1)degrees, V = 2256.5(6) Angstrom(3), Z = 4.