Dinuclear molybdenum complexes derived from diphenols: electrochemical interactions and reduced species

The new diphenolato complexes [{Mo(NO){HB(dmpz)(3)}Cl}(2)Q] where dmpz = 3,5-dimethyl-pyrazolyl and Q = OC6H4(C6H4)(n)C6H4O (n = 1 or 2), OC6H4CR=CRC6H4O (R = H or Et), and OC6H4 CH=CHC6H4CH=CHC6H4O have been prepared and their electrochemical properties (cyclic and differential pulse voltammetry) compared with previously reported analogues where Q = OC6H4O, OC6H4EC6H4O (E = SO2, CO and S), OC6H4(CO)C6H4 C6H4(CO)C6H4O and 1,5- and 2,7-O2C10H6. The electrochemical interaction between the redox centres in the new complexes is very weak in contrast to that in the 1,4-benzenediolato and naphthalendiolato species. The EPR spectra of the reduced mixed-valence species [{Mo(NO){HB(dmpz)(3)}Cl}(2)Q](-) where Q = 1,3- and 1,4-OC6H4O and OC6H4EC6H4O shows that they are valence-trapped at room temperature, whereas those of the dianions [{Mo(NO){HB(dmpz)(3)}Cl}(2)Q](2-) where Q = 1,4-OC6H4O, OC6H4EC6H4O (E = CO or S) and OC6H4CH=CHC6H4CH=CHC6H4O shows that the unpaired spins on each molybdenum centre are strongly correlated (J, the spin exchange integral much greater than A(Mo), the metal-hyperfine coupling constant). The electrochemical properties and the comproportionation constants for the reaction [{Mo(NO){HB(dmpz)(3)} Cl}(2)Q]+ [{Mo(NO){HB(dmpz)(3)}Cl}(2)Q](2-)reversible arrow 2[{Mo(NO) {HB(dmpz)(3)}Cl}(2)Q](-) where are compared with related compounds containing benzenediamido and dianilido bridges. (C) 1997 Elsevier Science Ltd.