STEREOCHEMICALLY NONRIGID ORGANOMETALLIC MOLECULES .19. (1,2,3-TRIHAPTO - 4,5,6,7-TETRAHAPTOCYCLOHEPTATRIENYL)-[(PENTAHAPTOCYCLOPENTADIENYL) DICARBONYLMOLYBDENUM]-[TRICARBONYLIRON] . PREPARATION STRUCTURE AND TEMPERATURE-DEPENDENT PROTON MAGNETIC RESONANCE SPECTRUM

A compound containing both the C5H5)(CO)2Mo and Fe(CO)3 groups bound to a cycloheptatrienyl ring, C7H7, has been prepared by photochemical reaction of (C7H7)(C5H5)Mo(CO)2 withFe(CO)5 and/or Fe2(CO)9. This red crystalline compound, (C5H5)(CO)2Mo(C7H7)Fe(CO)3, appears to have a structure in which the (C5H5)-(CO)2Mo group lies over one face of the C7H7 ring and interacts wth a sequence of three carbon atoms (a π-allyl-type complex) of the C7H7 ring, while the Fe(CO)3 lies over the other face and interacts with a butadiene-like sequence of four carbon atoms. The molecule is fluxional and gives a pmr spectrum consistent with this structure only at temperatures below about –50˚. Above this temperature the complex pattern of resonances due to the C7H7 ring collapses, and at room temperature and above these seven protons give only a single resonance. The Arrhenius activation energy for the rearrangement (in 4:1 CDC13/CD2C6D5) is 13 ± 1 kcal/mol. The low-temperature spectrum collapses unsymmetrically and detailed analysis, including comparison with computer-simulated spectra, permits us to exclude all rearrangement pathways except 1,2 shifts or a mixture of 1,2 and 1,3 shifts. © 1969, American Chemical Society. All rights reserved.