The rhenium(VII) compound [ReO3{B(pz)(4))}] (1) is easily reduced by triphenylphosphine in tetrahydrofuran providing, in 60% yield, a very reactive oxo complex of Re that, on the basis of its reactivity, we tentatively formulate as "[ReO(mu-O){B(pz)(4)}](2)" (2). This air-stable compound is insoluble in tetrahydrofuran and water and slightly soluble in chloroform and dichloromethane and is a versatile material for the synthesis of monomeric compounds of Re(V) : [ReO{B(pz)(4)}Cl-2] (3), [ReO(L)(B(pz)(4)}] (L = OCH2CH2O (4), C6H4O2 (5)), [ReO{B(pz)(4))(OR)(2)] (R = Me (6), Et (7), Pr-i (8), Ph (9)), [ReO{B(pz)(4)}(SPh)(2)] (10), and [ReO(eta(2)-OCONPh){B(pz)(4)}] (11) Compounds 3-11 were characterized by elemental analyses, IR and H-1 NMR spectroscopies, and, in the case of compounds 9 and 10, X-ray crystallography. Compound 9 crystallizes in the triclinic space group P (1) over bar with cell parameters a = 9.611(4) Angstrom, b = 11.808(3) Angstrom, 12.400(5) Angstrom, alpha = 88.69(2)degrees, beta = 69.61(3)degrees, gamma = 74.01(3)degrees, V = 1264(1) Angstrom(3), Z = 2, and R = 0.031, R(w) = 0.037 for 5226 reflections (F-0 > 3 sigma(F-0)); compound 10 also crystallizes in the triclinic space group P (1) over bar with cell parameters a = 10.563(3) Angstrom, b = 11.768(2) Angstrom, c = 12.149(3) Angstrom, alpha = 94.10(2)degrees, beta = 100.50(2)degrees, gamma = 92.44(2)degrees, V = 1479(1) Angstrom(3), Z = 2, and R = 0.043, R(w) = 0.051 for 4721 reflections (F-0 > 3 sigma(F-0)). For all the compounds the characterization includes laser desorption and electron impact Fourier transform ion cyclotron resonance mass spectrometry. For complex 2 variable-temperature H-1 NMR studies are also described.