The dirhenium polyhydride complex [Re2H6(mu-mq)(2)(PPh(3))(4)](BF4)(2) (1), where mq represents the 2-mercaptoquinoline ligand, can be deprotonated in two steps to afford the diamagnetic complexes [Re2H5(mu-mq)(2)(PPh(3))(4)]BF4 (2) and Re2H4(mu-mq)(2)(PPh(3))(4) (3) through the use of the bases PMe(3) and DBU, respectively. The treatment of 2 and 3 with HBF4 . Et(2)O regenerates 1. The basic structure of the [Re-2(mu-mq)(2)(PPh(3))(4)] unit is retained throughout these deprotonations/protonations as demonstrated by H-1 and P-31{H-1} NMR spectroscopy. The neutral tetrahydrido complex 3 undergoes a two-electron oxidation when treated with the oxidants [(eta(5)-C5H5)(2)Fe]BF4 and [(eta(5)-C5H5)(2)-Fe]PF6 to afford the salts [Re2H4(mu-mq)(2)(PPh(3))(4)](BF4)(2) (4a) and [Re2H4(mu-mq)(2)(PPh(3))(4)](PF6)(2) (4b), respectively. The [Re2H4(mu-mq)(2)(PPh(3))(4)](2+)/(ReH4)-H-2(mu-mq)(2)(PPh(3))(4) couple has an E(1/2) value of -0.47 V vs Ag/AgCl as measured by the cyclic voltammetric technique on solutions of 3 and 4 in 0.1 M Bu(4)NPF(6)/CH2Cl2. The chemical reversibility of this process has been confirmed by the use of (eta(5)-C5H5)(2)Co to reduce 4a back to 3. An X-ray crystal structure on a salt of the [Re2H4(mu-mq)(2)(PPh(3))(4)](2+) cation, established that this complex is very similar structurally to 1 (see J. Ain. Chem. Sec., 1995, 117, 9715). Tne most important structural differences are (1) the different numbers of hydride ligands present and (2) the presence of a Re-Re single bond in 4a (the Re-Re distance is 3.000(1) Angstrom compared to 3.9034(8) Angstrom in [Re2H6(mu-mq)(2)(PPh(3))(4)](2+)). Crystal data for [Re2H4(mu-mq)(2)(PPh(3))(4)](ReO4)(1.18) (BF4)(0.82). 3CH(2)Cl(2) at 203 K : monoclinic space group P2(1)/n (No. 14) with a=14.716(4) Angstrom, b=43.908(13) Angstrom, c=14.860(3) Angstrom, beta=110.164(19)degrees, V=9013(4) Angstrom(3), Z=4. The structure was refined to R=0.071 (R(W)=0.159) for 14128 data (F-o(2) >2 sigma(F-o(2))).