Dirhenium Polyhydrides Containing Bridging 2-Mercaptoquinoline Ligands

The dirhenium polyhydride complex [Re 2 H 6 (μ-mq) 2 (PPh 3 ) 4 ](BF 4 ) 2 ( 1 ), where mq represents the 2-mercaptoquinoline ligand, can be deprotonated in two steps to afford the diamagnetic complexes [Re 2 H 5 (μ-mq) 2 (PPh 3 ) 4 ]BF 4 ( 2 ) and Re 2 H 4 (μ-mq) 2 (PPh 3 ) 4 ( 3 ) through the use of the bases PMe 3 and DBU, respectively. The treatment of 2 and 3 with HBF 4 ·Et 2 O regenerates 1 . The basic structure of the [Re 2 (μ-mq) 2 (PPh 3 ) 4 ] unit is retained throughout these deprotonations/protonations as demonstrated by 1 H and 31 P{ 1 H} NMR spectroscopy. The neutral tetrahydrido complex 3 undergoes a two-electron oxidation when treated with the oxidants [(η 5 -C 5 H 5 ) 2 Fe]BF 4 and [(η 5 -C 5 H 5 ) 2 Fe]PF 6 to afford the salts [Re 2 H 4 (μ-mq) 2 (PPh 3 ) 4 ](BF 4 ) 2 ( 4a ) and [Re 2 H 4 (μ-mq) 2 (PPh 3 ) 4 ](PF 6 ) 2 ( 4b ), respectively. The [Re 2 H 4 (μ-mq) 2 (PPh 3 ) 4 ] 2+ /Re 2 H 4 (μ-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 /CH 2 Cl 2 . The chemical reversibility of this process has been confirmed by the use of (η 5 -C 5 H 5 ) 2 Co to reduce 4a back to 3 . An X-ray crystal structure on a salt of the [Re 2 H 4 (μ-mq) 2 (PPh 3 ) 4 ] 2+ cation, established that this complex is very similar structurally to 1 (see J. Am. Chem. Soc., 1995, 117, 9715). The most important structural differences are (1) the different numbers of hydrido ligands present and (2) the presence of a Re−Re single bond in 4a (the Re−Re distance is 3.000(1) Å compared to 3.9034(8) Å in [Re 2 H 6 (μ-mq) 2 (PPh 3 ) 4 ] 2+ ). Crystal data for [Re 2 H 4 (μ-mq) 2 (PPh 3 ) 4 ](ReO 4 ) 1.18 (BF 4 ) 0.82 ·3CH 2 Cl 2 at 203 K: monoclinic space group P 2 1 / n (No. 14) with a = 14.716(4) Å, b = 43.908(13) Å, c = 14.860(3) Å, β = 110.164(19)°, V = 9013(4) Å 3, Z = 4. The structure was refined to R = 0.071 ( R w = 0.159) for 14128 data ( F o 2 > 2σ( F o 2 )).