Communication between Metal Centers in Tungsten ( 0 ) - Tungsten ( I 1 ) Complexes Bridged by 1 , 4 - Diisocyanobenzene : Is the Ligand . rr System Involved ?
نویسندگان
چکیده
The ability of the aromatic diisocyanide ligand 1,4-diisocyanobenzene to act as a mediator for charge polarization between W(0) and W(I1) centers was investigated. A series of bridged complexes were synthesized which contained W(0)-W(O), W(0)-W(II), and W(I1)-W(I1) metal centers, coupled by CNC6H4NC. C-N stretching vibrations for the W(0) ends of the molecules were actually at higher energies than those for the W(I1) ends. Infrared and multinuclear NMR studies indicated that the W(0)-W(I1) molecules were effectively unperturbed hybrids of the W(0)-W(0) and W(I1)-W(I1) molecules. In contrast, the MLCT band of the binuclear complexes is red-shifted 1221 cm-1 compared to that of the mononuclear complexes, indicating that the A system is involved in M-L-M bonding and should telegraph differences in charge from one metal center to the other through charge polarization across the ring. The apparent contradiction is resolved in the X-ray photoelectron spectra of the W(0)-W(I1) complexes, which exhibit nearly identical W(4f') chemical shifts for the two tungsten centers, indicating that the metals are in very similar electronic environments.
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