Stepwise Synthesis of the Functionalized Metallatetrahedron Re₂(AuPPh₃)₂(μ-PCy₂)(CO)₇X (X = Cl, Br, I)

In THF solution the dirhenium complex Re2(μ-H)(μ-PCy2)(CO)8 (1) reacts with an equimolar amount of LiPh at −100 °C to afford after warming up to room temperature within 1 h the salt Li[Re2(μ-H)(μ-PCy2)(C(Ph)O)(CO)7] (Li[2]). Through cation exchange of Li+ against PPh4+, Li[2] gives the airstable solid PPh4[2] in 86% yield. The selectivity of the LiPh attack at one of the four axial carbonyls in 1 was proved by the chiral shift reagent Eu(hfac)3 which was dissolved in a CDCl3 solution of PPh4[2]. The 1H and 31P NMR spectra show the diastereomeric resolution of the respective peaks in an integral ratio of 1:1 e.g. Δδ(μ-P) 0.43. The anion [2-] generates with 2 equiv of XAuPPh3 (X = Cl, Br, I) in THF at room temperature within 15 min under release of the leaving group PhCHO the yellow cluster complexes Re2(AuPPh3)2(μ-PCy2)(CO)7X (4a−c). Their precursor complex anions [Re2(μ-AuPPh3)(μ-PCy2)(CO)7X]- (3a−c) are obtained from 1 and an equimolar amount of XAuPPh3 or from the deauration by treatment of 4a (X = Cl) with 1 equiv of LiPh via a transmetalation reaction. Such anions are isolable as salts, N(PPh3)2[3a−c]. All new cluster complexes are identified by means of 1H NMR, 31P NMR and ν(CO) IR spectroscopic measurements, Li[2] and 4a (X = Cl) additionally by means of X-ray single-crystal structure analyses. Li[2] crystallizes triclinic, space group P1̄, Z = 2, a = 10.536(2) Å, b = 11.433(2) Å, c = 19.125(3) Å, α = 98.01(1)°, β = 89.94(1)°, and γ = 112.22(1)°; 4a crystallizes monoclinic, space group P21/c, with Z = 4, a = 18.615(5) Å, b = 13.606(2) Å, c = 24.223(6) Å, and β = 105.14(2)°. The molecular structure of Li[2] shows a μ-H-, μ-P-bridged Re−Re bond of 3.1667(7) Å, the one of 4a a tetrahedrally shaped Re2Au2 core with a μ-P-bridged Re−Re edge of 3.2680(10) Å.