Protonation reactions of the oxo complex cis-[Mo2(η5-C5H5)2(O)(μ-PPh2)2(CO)]. Hydroxo and tetrafluoroborate derivatives

The dimolybdenum complex cis-[Mo2Cp2(O)(μ-PPh2)2(CO)] (1) reacted with either [H(OEt2)2](BAr′4), (Ar′ = 3,5-C6H3(CF3)2), or HBF4·OEt2 to give the corresponding hydroxo derivatives [Mo2Cp2(OH)(μ-PPh2)2(CO)]+, which at room temperature rearrange to the oxohydride isomers [Mo2Cp2(μ-H)(O)(μ-PPh2)2(CO)]+ via a protonation/deprotonation sequence involving the hydride-hydroxo complex [Mo2Cp2(μ-H)(OH)(μ-PPh2)2(CO)]2+ (Cp = η5-C5H5). All these cations were characterized spectroscopically in solution, but none of them could be isolated as a solid material. The reaction of 1 with 2 equiv of HBF4·OEt2 eventually led to the formation of the tetrafluoroborate complex [Mo2Cp2(κ2-F2BF2)(μ-PPh2)2(CO)](BF4) (Mo–Mo = 2.841(2) Å). The BF4− ligand in the latter complex was easily displaced by nitriles at room temperature to give the corresponding tris(nitrile) derivatives [Mo2Cp2(μ-PPh2)2(CO)(NCR)3](BF4)2 (R = Me, Ph), and by acetylacetone (acac-H), to give the acetylacetonate complex [Mo2Cp2(κ2-acac)(μ-PPh2)2(CO)](BF4) (2.831(2) Å).