SYNTHESIS, SPECTROSCOPIC STUDIES, AND STRUCTURE OF AN UNUSUAL DIRHENIUM COMPLEX WITH A BRIDGING HYDRIDE LIGAND
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The preparation and characterization of an unusual dirhenium hydrido-carbonyl compound is described. The product has been accessed by several methods, including the reaction of Re2Cl4(-dppm)2 with various carbonyl clusters in the presence of H2 and the direct combination of the starting material with an H2/CO gas mixture in refluxing toluene. Details of these and other syntheses are presented. Compound 1, Re2(-Cl)(-H)Cl2(CO)2(dppm)2, crystallizes in the tetragonal space group P41212 with unit cell dimensions a = 14.935 (2) ,b = 14.935 (2) , c = 25.804 (2) , V= 5755 (4) 3, and Z = 4. The structure was refined to least-squares residuals of R = 0.0304, Rw = 0.0368 and quality-of-fit 0.643. The molecules reside on crystallographic 2-fold axes, and the asymmetric unit is defined by half of a formula unit. The binuclear structure consists of two trans diphosphine ligands bisecting an equatorial plane that contains one bridging and two terminal chloride ligands on the same side of the molecule as well as two terminal carbonyl ligands. The bridging hydride ligand, although not located in the X-ray refinement, is postulated on the basis of detailed 1H NMR studies and is further substantiated by the diamagnetism of the compound. The -H resonance is quite unusual with a chemical shift of = +12.75 ppm in CD2Cl2. The presence of the -H ligand leads to the formulation of 1 as a molecule possessing an Re24+ core with an edge-sharing bioctahedral geometry. Both the Re-Re distance of 2.605 (1) and the electrochemistry of the new compound (Ep,c = +1.47, E1/2(ox) = +0.63, E1/2(red), = 0.73, and E1/2(red)2 = 1.44 V vs Ag/AgCl) are very similar to that which has been reported for other dirhenium M2L10 systems containing a mixture of chloride, phosphine, and carbonyl ligands. This point is discussed along with other pertinent structural data. In addition to an X-ray study, the new compound was characterized by elemental analysis, infrared spectroscopy, FAB mass spectrometry, 1H and 31P NMR spectroscopy, and cyclic voltammetry. 1990, American Chemical Society. All rights reserved.
