Reactivity of the Four-Membered Heterometallacycles CH(3,5-Me2Pz)2(CO)3WSnAr3 (Pz = Pyrazol-1-yl) with P(OR)3: Unexpected P−O/C Exchange Reactions in Phosphite

Reactions of CH(3,5-Me2Pz)2(CO)3WSnAr3 (Pz = pyrazol-1-yl; Ar = phenyl, p-tolyl) with P(OR)3 (R = methyl, isopropyl) under solvent-free conditions give the decarbonylated complexes CH(3,5-Me2Pz)2(CO)2(P(OR)3)WSnAr3. However, treatment of CH(3,5-Me2Pz)2(CO)3WSnAr3 with P(OMe)3 at elevated temperature results in unexpected P−O/C exchange reactions with the cleavage of the W−C bond to give the novel reductive elimination product (MeO)2PCH(3,5-Me2Pz)2W(CO)3. Furthermore, even at low temperature, the reaction of CH(3,5-Me2Pz)2(CO)3WSnAr3 with P(OAr)3 only yields the similar reductive elimination products (ArO)2PCH(3,5-Me2Pz)2W(CO)3. In these novel tungsten(0) complexes, the newly formed diaryl or dialkyl bis(3,5-dimethylpyrazol-1-yl)methylphosphonite acts as a neutral tridentate κ3[N,N,P] chelating ligand.