| Abstract
| - The tropylium salt (2-hydroxy-3,5-dimethylphenyl)cycloheptatrienylium tetrafluoroborate (3) has been synthesizedin three steps from THP-protected 2,4-dimethylphenol and tropylium tetrafluoroborate, (C7H7)BF4. In CH2Cl2 solution,the unexpected formation of tricyclic 2,4-dimethylbenzo[b]cyclohepta[d]furanylium tetrafluoroborate (5) has beenobserved, which must have formed from 3 by loss of H2. 5 was characterized by an X-ray crystal structuredetermination and could independently be synthesized by treatment of 3 with NaHCO3 to give 2,4-dimethylbenzo[b]cyclohepta[d]furan (4) followed by acidification with HBF4·Et2O. The arene transfer reaction of 3 with [(η-p-xylene)Mo(CO)3] furnished the cycloheptatrienyl complex [(HOC6H2Me2-η7-C7H6)Mo(CO)3]BF4 (6), which could beconverted into the chiral chelate complexes (9a, R = Ph; 9b, R = c-C6H11; 9c,i-Pr) by subsequent treatment with NaI, PR3, and NaH. The linked cycloheptatienyl−phenolate ligand in 9a couldbe protonated at the coordinated oxygen atom employing HBF4·Et2O to yield (10). In 10, the appended phenol group is coordinated in a hemilabile fashion, which allowed the introductionof 2,6-dimethylphenyl isocyanide and CO and formation of complexes [(HOC6H2Me2-η7-C7H6)Mo(CO)(PPh3)L]BF4(11, L = XyNC; 12, L = CO). On thermal reaction of [(HOC6H2Me2-η7-C7H6)Mo(CO)2I] (7) with dppe, the additionof the diphosphine was observed together with the simultaneous formation of the molydenum−oxygen bond toyield (13), in which the cycloheptatrienyl ring has reduced its hapticity fromseven to three. The pseudooctahedral complex 13 exhibits an interesting fluxional behavior in solution, which hasbeen studied by means of variable-temperature 31P and 1H NMR spectroscopy. A η3 → η7 hapticity reversioncould be achieved by UV irradiation of a solution of 13 in THF to give the electron-rich complex (14). 14 was readily oxidized with ferrocenium hexafluorophosphate, and the resulting paramagneticmonocationic complex 15 has been studied by means of ESR spectroscopy and X-ray diffraction. In addition, theX-ray crystal structures of complexes 9a, 10·2CH2Cl2, 12, and 13 are reported.
- The concept of donor functionalization is introduced to cycloheptatrienyl−transition metal chemistry, and a series of monophosphine complexes with linked cycloheptatrienyl−phenolate ligands of the type (R = Ph, c-C6H11, i-Pr) have been prepared. For R = Ph, protonation at the phenolate oxygen atom leads to the formation of a cationic complex, in which the appended phenol is coordinated in a hemilabile fashion and allows the introduction of CO and isocyanide ligands. In addition, the synthesis and reactivity of the electron-rich diphosphine complexes is reported.
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