Acid-Base Control of Hemilabile Proton-Responsive Protecting Devices in Dimolybdenum, Thiolate-Bridged Complexes

Dimolybdenum thiolate-bridged complexes
[Mo2Cp2(μ-SMe)2(μ-SCH2CH2E)]
(E = O (2) or NH (4)) with a proton-dependent
protecting device have been synthesized by reaction of [Mo2Cp2(μ-SMe)2(μ-Cl)2]
(1) with SCH2CH2EH. The reactivity
of the resultant quadruply bridged complexes with acid was investigated
in the absence and in the presence of a potential ligand (N2, MeCN, RNC). While the protonation of complexes 2 and 4 under N2 in dichloromethane produced only the
oxidized derivatives instead of the desired diazenido compound, ligand
binding was observed in MeCN or in the presence of RNC (R = t-Bu, Xyl). Whereas acetonitrile loss from [Mo2Cp2(μ-SMe)2(μ-SCH2CH2OH)­(MeCN)2]+ (8+) prevented the isolation and characterization
of this species, the t-BuNC analogue (6+) could be characterized by an X-ray crystal
structure. The electrochemistry of 2 and 2+ was investigated in CH2Cl2 and in MeCN, both in the absence and in the presence of acid.
While the addition of HBF4·Et2O to a dichloromethane
solution of 2 only produced 2+ (and presumably H2), 8+ was the major product of the protonation in
MeCN.