| Abstract
| - Microwave spectra for 11 isotopomers of bis(η5-cyclopentadienyl)tungsten dihydride ((C5H5)2WH2)were recorded in the 5−14 GHz region using a Flygare−Balle-type pulsed beam spectrometer. Spectraarising from four tungsten isotopomers of both the (C5H5)2WH2 and (C5H5)2WHD species and three Wisotopomers for the (C5H5)2WD2 complex have been measured. The ∼250 b-type transition frequenciesassigned for these near-prolate asymmetric top molecules were accurately described (σfit = 2−4 kHz)using the rotational parameters A, B, and C and one centrifugal distortion constant, ΔJ. The small valueobtained for ΔJ indicates a fairly rigid structure. From a least-squares fit using the resulting 33 rotationalconstants to obtain the molecular structure, we were able to determine the W−H bond length, r(W−H)= 1.703(2) Å, the H−W−H bond angle, ∠(H−W−H) = 78.0(12)°, the W−Cp centroid distance, r(W−Cp) = 1.940(8) Å, the angle made by the Cp centroids with tungsten, ∠(Cp−W−Cp) = 155(2)°, and theaverage C−C bond length, r(C−C) = 1.429(8) Å. The hydrogen atom separation is r(H−H) = 2.14(2)Å, indicating that this is clearly a “classical dihydride” rather than an “η2-dihydrogen” complex. TheWH2 moiety parameters determined from Kraitchman's equations (r(W−H) = 1.682(2) Å, ∠(H−W−H) = 78.6(2), r(H−H) = 2.130(2) Å) agree well with the least-squares results. Furthermore, the reparameters obtained from DFT calculations agree well with the experimental r0 structural parameters.To our knowledge, this work marks the first microwave study of a bent-metallocene complex. The presentmeasurements were made with a pulsed-beam Fourier transform spectrometer employing a homodyne-type detection system, and this configuration is described. This homodyne system greatly simplifies themicrowave circuit, with no apparent loss in sensitivity.
- Gas-phase structural parameters of bis(η5-cyclopentadienyl)tungsten dihydride have been determined from the rotational spectra of 11 different isotopomers of the title complex. This is the first microwave study of a bent metallocene.
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