SYNTHESIS OF CARBOXYLATE SUBSTITUTED RHENIUM GOLD METALLATETRAHEDRANES RE-2(AUPPH3)(2)(MU-PCY2)(CO)(7)(ETA(1)-OC(R)O) (R = H, ME, CF3, PH, 3,4-(OME)(2)C6H3)

The reaction of the in situ prepared salt Li[Re-2(mu-H)(mu-PCy2)(CO)(7 )(ax-C(Ph)O)] (2) with 1,5 equivalents of monocarboxylic acid RCOOH (R = H (4a), Me (4b), CF3 (4c), Ph (4d), 3,4-(OMe)(2)C6H3 (4e) in tetrah ydrofruan (THF) solution at 60 degrees C gives within 4 h under releas e of benzaldehyde (PhCHO) the eta(1)-carboxylate substituted di-rheniu m salt Li[Re-2(mu-H)(mu-PCy2)(CO)(7)(eta(1)-OC(R)O)] (R = H (4a) Me (4 b) CF3 (4c) Ph (4d), 3,4-(OMe)(2)C6H3 (4e)) in almost quantitative yie ld. The lower the pK(a) value of the respective carboxylic acid the fa ster the reaction proceeds. It was only in the case of CF3COOH possibl e to prove the formation of the hydroxycarbene complex Re-2(mu-H)(mu-P Cy2)(CO)(7)(=C(Ph)OH) (5) prior to elimination of PhCHO. The new compo unds 4a-4e were only characterized by P-31 NMR and nu(CO) IR spectrosc opy as they are only stable in solution. They are converted with two e quivalents of BF4AuPPh3 at 0 degrees C in a so-called cluster expansio n reaction into the heterometallic metallatetrahedrane complexes Re-2( Aupph(3))(2)(mu-pCy(2))(CO)(7)(eta(1)-OC(R)O) (R=H (7a), Me (7b), CF3 (7c), Ph (7d), 3,4-(OMe)(2)C6H3 (7e)) (yield 47-71%). The expected pre cursor complexes of 7a-7e Li[Re-2(AuPPh3)(mu-PCy2) (CO)(7)(eta(1)-OC(R )O] (8) were not detected by NMR and LR spectroscopy in the course of the reaction. Their existence was retrosynthetically proved by the rea ction of 7b with an excess of the chelating base TBD (1,5,7-Triazabicy clo [4.4.0]dec-5-en) forming [(TBD)(x)AuPPh3][Re-2(AuPPh3)(mu-PCy2) (C O)(7)(eta(1)-OC(Me)O] (8b) in solution. The eta(1)-bound carboxylate l igand in 7a-7e can photochemically be converted into a mu-bound ligand in Re-2(AuPPh3)(2)(mu-PCy2)(mu-OC(R)O)(CO)(6) (R = H (9a), Me (9b), C F3 (9c), Ph (9d), 3.4-(MeO)(2)C6H3 (9e)) under release of one equivale nt CO. All isolated cluster complexes were characterized and identifie d by the following analytical methods: elementary analysis, NMR (H-1, P-31) spectroscopy, nu(CO) LR spectroscopy and in the case of 7d and 9 b by X-ray structure analysis.