Cationic RhI Complexes of Azulenes and Their Catalytic Activity on the Formation of Heptalene-1,2-dicarboxylates from Dimethyl Acetylenedicarboxylate and Azulenes |
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Authors: | Andreas Johannes Rippert Anthony Linden Hans-Jürgen Hansen |
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Abstract: | Rh1(η5-azulene)(cod)]+BF complexes 3a–g (cod = (Z,Z)-cycloocta-1,5-diene) have been synthesized by reaction of Rh1(cod)]+BF in THF with the corresponding azulenes 1a–g (Table 1). The structure of Rh1(cod)(η5-guaiazulene)]+BF ( 3a ) has been determined by X-ray diffraction analysis (Fig. 1 and 2). The Rh-atom is oriented above the five-membered ring of the azulene with almost equal Rh? C distances to all five C-atoms of the ring. The (Z,Z)-cycloocta-1,5-diene ring occurs in two enantiomorphic distorted (C2v → C2) tub conformations in the crystals (Fig. 3). In CDCl3 solution, the cod ligand in the complexes 3 shows a dynamic behavior on the 1H-NMR time scale which is best explained by rotation of the cod ligand relative to the azulene ligands around an imaginary cod? Rh? azulene axis. The new complexes 3 catalyze the formation of heptalene-1,2-dicarboxylates 2 from dimethyl acetylenedicarboxylate (ADM) and the corresponding azulenes 1 just as effectively as RuH2(PPh3)4] and the analogous RhH(PPh3)4] complex in MeCN solution (Table 3). On grounds of simplicity, 3 can be generated in situ, when RhCl(cod)]2 is applied as catalyst (Table 3). |
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