Metal-ligand charge transfer mechanism

Brinkley et al. demonstrated89 a simple to use, easy to interpret, low cost, and environmentally friendly colorimetric detector of the chemical warfare agent - mustard gas (HD, l,l-thiobis(2-chloroethane)). An optically transparent xerogel encapsulating Cu(II) acetate was fabricated to detect HD analogues and can serve as the optical sensor based on metal-ligand charge-transfer mechanism. 

Acac = acetyacetonate BArf = tetra(3,5-bis(trifluorome-thyl)phenyl)borate anion bridge = 1,3-diisocyanopropane COD = cycloocta-1,5-diene COE = cyclooctene DFT = Density Functional Theory dimen = 2,1,8-diisocyanoment-hane DMAD = dimethylacetylene dicarboxylate DMSO = dimethylsulfoxide dpmp = bis(diphenylphosphinomethyl) phenylphosphine DPPB = l,4-bis(diphenylphosphino)but-ane DPPE = l,2-bis(diphenylphosphino)ethane DPPM = bis(diphenylphosphino)methane en= 1,2-diaminoethane hfac = hexafluoroacetylacetonate HFB = hexafluorobut-2-yne HOTf = trifluoromethanesulfonic acid (triflic acid) MLCT = Metal Ligand Charge Transfer MO/MM = Molecular Orbital/Molecular Mechanics NBD = bicyclo[2. 2.1]heptadiene OTf = trifluoromethanesulfonate (triflate) ion OTs = p-toluenesulfonate (tosylate) ion /j-anis = /7-MeOC6H4 pip = piperidine pn = 1,2-diaminopropane PPN+ = bis(triphenylphosphine)iminium cation p-to = p-MeCeUt pz = pyrazolate QM/MM = Quantum Mechan-ics/Molecular Mechanics TFB = tetrafluorobenzobarrelene TM4 = 2,5-diisocyano-2,5-dimethyIhexane tn = 1,3-diami-nopropane. 

The reaction mechanism was proposed to involve electron transfer from the d-7i metal to ligand charge transfer excited state (MLCT transition) to the chlorinated solvent,... 

Copper-catalyzed [2 + 2] photocycloadditions are related to the latter reactions. These transformations have been extensively studied, frequently in the context of application to organic synthesis [21], When irradiated in the presence of copper(I) triflate, norbomene 12 was effidently transformed into its dimer 13 (Scheme 5.3, reaction 4) [22]. Although complexes such as III are involved in the reaction mechanism [22, 23], it is unclear whether MLCT (metal to ligand charge transfer) or LMCT (ligand to metal charge transfer) excitation induces the transformation. 

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