Stereochemical nonrigidity in heterobimetallic complexes containing the bent metallocene-thiolate fragment
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The physical properties and reactions of Cp2Ti(S-p-C6H4X)2 (1) and Cp2Ti(μ-S-p-C6H4X)2Mo(CO)4 (2) (X = Cl, H, CH3, OCH3) complexes as well as the mechanism of the Cp site equilibration process in bimetallic complexes were investigated. Cyclic voltammographs recorded in CH2Cl2 showed two reversible waves for Ti(IV) ⥩ Ti(III) and Mo(0) Mo(I) processes in 2 and one reversible wave for Ti(IV) ⥩ Ti(III) in 1. Positions of these waves varied uniformly with the Hammett σ parameter of the X substituent. Variable-temperature 1H NMR studies provided values for ΔG* of the Cp equilibration process which are ca. 30 kJ/mol smaller than ΔG* for Cp2Ti(S-p-C6H4X)2 displacement from 2 by CO. This indicates that the fluxional process in 2 does not occur through a ligand dissociation process and argues for a mechanism of pyramidal inversion on sulfur. The X-ray structure for Cp2Ti(μ-S-p-C6H4Cl)2Mo(CO)4 (2a) is reported. Complex 2a crystallizes in the monoclinic space group P21/n, with a = 12.396 (7) Å, b= 16.78 (2) Å, c = 12.838 (9) Å, β = 94.29 (5)°, Z = 4, and V = 2662 (3) Å3. The Ti atom is in pseudotetrahedral coordination environment whereas the Mo is octahedrally coordinated. The S1-Ti-S2 and S1-Mo-S2 angles are obtuse (100.8 (1) and 97.6 (1)°, respectively) and Ti-S-Mo angles are acute (80.8 (1)°) in the planar Ti-S2-Mo ring, supportive of metal-metal interactions implied by spectroscopic and electrochemical data. The phenyl groups are in an anti arrangement with respect to the Ti-S2-Mo plane. © 1992, American Chemical Society. All rights reserved.
author list (cited authors)
Darensbourg, M. Y., Pala, M., Houliston, S. A., Kidwell, K. P., Spencer, D., Chojnacki, S. S., & Reibenspies, J. H.