Bis(acetylacetonate) Tungsten(IV) Complexes Containing a π-Basic Diazoalkane or Oxo Ligand

Tungsten­(IV) bis­(acetylacetonate) (acetylacetonate = acac) complexes were synthesized by incorporating either a diazoalkane or an oxo ligand into the coordination sphere of a tungsten­(II) reagent. The reaction of free diazoalkane (N2CRR′) with W­(CO)3(acac)2 leads to loss of two carbon monoxide ligands and coordination of the diazoalkane reagent through the terminal nitrogen to produce W­(CO)­(acac)2(N2CRR′). This monomer is best formulated as a tungsten­(IV) complex. A second example of converting a d4 tungsten carbonyl complex to a d2 product involves oxidation of W­(CO)­(acac)2(PhCN) with m-chloroperoxybenzoic acid (MCPBA) to replace the CO ligand with an oxygen atom. This increase in metal oxidation state causes rotation of the nitrile ligand by 90° relative to the two bidentate acac ligands. Electrophilic addition at the nitrogen of the π-bound nitrile ligand using methyl triflate (MeOTf) and subsequent nucleophilic addition at carbon with sodium trimethoxyborohydride, Na­[HB­(OMe)3], reduces the CN bond stereoselectively and produces the neutral imine complex W­(O)­(acac)2(PhHCNMe) with a diastereomeric ratio of 11:1.