Darstellung carboxylatsubstituierter Rhenium-Gold-Metallatetrahedrane Re2(AuPPh3)2(μ-PCy2)(CO)7(η1-OC(R)O) (R = H,Me, CF3, Ph, 3,4-(OMe)2C6H3) |
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Authors: | H.-J. Haupt,H. Egold,R. Siefert,U. Flö rke |
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Abstract: | Synthesis of Carboxylate Substituted Rhenium Gold Metallatetrahedranes Re2(AuPPh3)2(μ-PCy2)(CO)7(η1-OC(R)O) (R = H, Me, CF3, Ph, 3,4-(OMe)2C6H3) The reaction of the in situ prepared salt Li[Re2(μ-H)(μ-PCy2)(CO)7(ax-C(Ph)O)] ( 2 ) with 1,5 equivalents of monocarboxylic acid RCOOH (R = H ( 4 a ), Me ( 4 b ), CF3 ( 4 c ), Ph ( 4 d ), 3,4-(OMe)2C6H3 ( 4 e ) in tetrahydrofruan (THF) solution at 60 °C gives within 4 h under release of benzaldehyde (PhCHO) the η1-carboxylate substituted dirhenium salt Li[Re2(μ-H)(μ-PCy2)(CO)7(η1-OC(R)O)] (R = H ( 4 a ), Me ( 4 b ), CF3 ( 4 c ), Ph ( 4 d ), 3,4-(OMe)2C6H3 ( 4 e )) in almost quantitative yield. The lower the pKa value of the respective carboxylic acid the faster the reaction proceeds. It was only in the case of CF3COOH possible to prove the formation of the hydroxycarbene complex Re2(μ-H)(μ-PCy2)(CO)7(=C(Ph)OH) ( 5 ) prior to elimination of PhCHO. The new compounds 4 a–4 e were only characterized by 31P NMR and ν(CO) IR spectroscopy as they are only stable in solution. They are converted with two equivalents of BF4AuPPh3 at 0 °C in a so-called cluster expansion reaction into the heterometallic metallatetrahedrane complexes Re2(AuPPh3)2(μ-PCy2)(CO)7(η1-OC(R)O) (R = H ( 7 a ), Me ( 7 b ), CF3 ( 7 c ), Ph ( 7 d ), 3,4-(OMe)2C6H3 ( 7 e )) (yield 47–71% ). The expected precursor complexes of 7 a–7 e Li[Re2(AuPPh3)(μ-PCy2)(CO)7(η1-OC(R)O] ( 8 ) were not detected by NMR and IR spectroscopy in the course of the reaction. Their existence was retrosynthetically proved by the reaction of 7 b with an excess of the chelating base TBD (1,5,7-Triazabicyclo[4.4.0]dec-5-en) forming [(TBD)xAuPPh3][Re2(AuPPh3)(μ-PCy2)(CO)7(η1-OC(Me)O] ( 8 b ) in solution. The η1-bound carboxylate ligand in 7 a–7 e can photochemically be converted into a μ-bound ligand in Re2(AuPPh3)2(μ-PCy2)(μ-OC(R)O)(CO)6 (R = H ( 9 a ), Me ( 9 b ), CF3 ( 9 c ), Ph ( 9 d ), 3.4-(MeO)2C6H3 ( 9 e )) under release of one equivalent CO. All isolated cluster complexes were characterized and identified by the following analytical methods: elementary analysis, NMR (1H, 31P) spectroscopy, ν(CO) IR spectroscopy and in the case of 7 d and 9 b by X-ray structure analysis. |
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Keywords: | Rhenium carbonyl carboxylate complex rhenium gold metallatetrahedran cluster complex rhenium acylanion hydroxycarbene complex |
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