DEPROTONATION OF RE2(MU-H)(MU-PPH2)(CO)8 FOR SYNTHESIS OF MIXED RHENIUM-GOLD CLUSTERS WITH RE2AUN CORES (N = 1-3)

The dirhenium complex Re2(μ-H)(μ-PPh2)(CO)8 (1) is deprotonated with NaOEt (or 1,8-diazabicyclo[5.4.0]undec-7-ene, DBU) to give the anion [(μ-PPh2)(CO)8Re2]− (2−), which was isolated as tetraethylammonium salt [C8H20N][2], The exchange of the isolobal fragment ÀuPPh3 for H in 1 (via 2−) generates [(μ-PPh2(CO)8Re2AuPPh3] (3). The treatment of 1 in THF solution with lithium organyls RLi (R = Me, n-Bu, Ph) gives products of two types: first, [(μ-C(R)O)(μ-PPh2)(CO)6Re2(AuPPh3)2] (R = Ph (4), Me (5), n-Bu (6)) and, second, [(μ-PPh2)(CO)6Re2(AuPPh3)3] (7). Complex 1 was also reacted with diphenylacetylene to give [(μ-σ:η2)2-CPh=CHPh)(μ-PPh2)(CO)7Re2] (8). 31P NMR data have been measured for the newly synthesized compounds. The molecular structures of [C8H20N][2], 3, 4, 7, and 8 have been determined from X-ray data collected on an automated diffractometer with monochromatized Mo Kα radiation. Compounds 3, 7, and 8 crystallize in the triclinic space group P1 with Z = 2, while 2 and 4 crystallize in the monoclinic space groups C2/c with Z = 8 and P21/n with Z = 4, respectively. For 2, a = 18.007 (3) Å, b = 17.165 (3) Å, c = 21.368 (5) Å, and β = 109.36 (1)°; for 3, a = 14.918 (7) Å, b = 15.456 (4) Å, c = 9.229 (4) Å, α = 93.12 (1)°, ß = 97.10 (1)°, and γ = 83.27 (1)°; for 4, a = 24.434 (4) Å, b = 10.284 (2) Å, c = 24.618 (4) Å, and β = 113.75 (1)°; for 7, a = 13.676 (5) Å, b = 13.817 (4) Å, c = 21.723 (7) Å, α = 71.26 (1)°, β = 87.05 (1)°, and γ = 82.37 (1)°; and for 8, a = 9.436 (2) Å, b = 11.774 (3) Å, c = 14.353 (4) Å, α = 95.91 (2)°, β = 99.57 (2)°, and γ = 95.71 (2)°. The molecular structure of the diamagnetic anion 2− as the [NEt4+] salt contains an Re2(μ-P) ring with four cis-terminal carbonyl ligands at each Re atom of an idealized C2v symmetry. The Re–Re bond length is 3.062 (2) Å with bond angle Re–P–Re = 78.6 (1)β. The addition of the sterically demanding [AuPPh3+] cation to 2− leads to a planar four-membered AuPRe2 ring in 3. The Re-Re bond of 3.225 (2) Å is elongated and the angle Re–P–Re = 83.8 (3)° enlarged compared to those of [C8H20N] [2]. The average Au-Re single-bond length is 2.787 (2) Å. The molecular structure of 4 shows an Re2Au2 metallatetrahedron core in which the Re-Re bond is bridged through the acylic C(Ph)O group (Re-C = 2.17 (3) Å, C–O = 1.24 (4) Å). The Re–Re bond length is 3.122 (2) Å, and the other metal–metal distances are 2.734 (2) Å (Au–Au) and 2.901 (2) Å (average Au–Re). These values are consistent with metal–metal single bonds. The molecular structure of 7 contains a trigonal-bipyramidal Re2Au3 core. The Re-Re bond length of 2.914 (3) Å, of double-bond character, is shorter than that of 4, whereas the average Au–Au bond length of 2.829 (2) Å is elongated; the average Au–Re bond length is 2.830 (2) Å. The molecular structure of 8, which results from a release of one CO ligand from 1 and a hydride transfer to coordinated diphenylacetylene, contains the vinylic μ-σ:η2-CPh=CHPh ligand (C=C = 1.394 (16) Å) bridging an Re-Re bond, Re–Re = 2.998 (1) Å. In the isoelectronic series of compounds 1–3 in which the H+ in 1 is substituted by the isolobal fragment [PPh3Au+] via the anion 2; the Re2 core becomes more electron-rich, which facilitates the anodic one-electron transfer as measured by cyclic voltammetry; i.e., Ep,a1 decreases from 1508 mV in 1 to 1132 mV in [C8H20N] [2] to 241 mV in 3. The same is observed for the Re2 core in the exchange of an electron-poor phenyl acyl against an electron-rich diisopropylamino acyl group in the isoelectronic compounds of the type [(μ-C(R)O)(μ-PPh2)- (CO)6Re2(AuPPh3)2] (R = Ph, Ef = 682 mV; R = N(i-Pr2), Ef = 576 mV). For 7 the Ef values of the reversible one-electron-transfer processes are 289 and 752 mV. © 1990, American Chemical Society. All rights reserved.