Reaction of 4-(2,2-dimethylhydrazino)dimethylhydrazone-3(Z)-penten-2-one with BrRe(CO)5 and fac-BrRe(CO)3(THF)2: Synthesis, structural characterization, and DFT examination of the β-diketimine-substituted compound fac-BrRe(CO)3[(Me2NNCMe)2CH2

Abstract

Thermolysis of BrRe(CO)5 with 4-(2,2-dimethylhydrazino)dimethylhydrazone-3(Z)-penten-2-one in toluene at 70 °C furnishes the new β-diketimine-substituted complex fac-BrRe(CO)3[(Me2NNCMe)2CH2] (1) in 50–70% isolated yield. Product 1 is also obtained in comparable yield when the same reactants are irradiated at 366 nm at room temperature in fluid solution. Treatment of the parent ligand with the “lightly stabilized” rhenium compound fac-BrRe(CO)3(THF)2 affords 1 as the sole observable rhenium product. Complex 1 has been characterized in solution by IR and 1H NMR spectroscopy, and the molecular structure has been determined by single-crystal X-ray diffraction analysis. The solid-state structure confirms that the ancillary nitrogen ligand in 1 coordinates to the rhenium center as a chelating β-diketimine moiety, making this the first structurally characterized example of a β-diketimine derivative containing the parent ligand. Complex 1 has been examined by DFT analysis, and the ground-state structure computed for 1 is in agreement with the X-ray diffraction structure. Treatment of 1 with the phosphines Ph2PH and 1,2-(Z)-Ph2PCHCHPPh2 (dppen) leads to loss of the β-diketimine ligand and formation of fac-BrRe(CO)3(Ph2PH)2 (2) and fac-BrRe(CO)3(dppen) (3), respectively. Both of these products have been isolated, and the X-ray diffraction structure of the Ph2PH-substituted derivative determined. The relative energies of the different tautomeric forms of the 4-(2,2-dimethylhydrazino)dimethylhydrazone-3(Z)-penten-2-one ligand and 4-(2,2-dimethylhydrazino)-3(Z)-penten-2-one, the precursor to the parent ligand, have been investigated by DFT analyses. The most stable tautomer for each compound contains a six-membered ring and exhibits an intramolecular N–H bond to the imine and keto moiety, respectively.