Isolation of a bis(imino)pyridine molybdenum(i) iodide complex through controlled reduction and interconversion of its reaction products

Abstract

Analysis of previously reported [(^Ph2PPrPDI)MoI][I] by cyclic voltammetry revealed a reversible wave at −1.20 V vs. Fc^+/0, corresponding to the Mo(II)/Mo(I) redox couple. Reduction of [(^Ph2PPrPDI)MoI][I] using stoichiometric K/naphthalene resulted in ligand deprotonation rather than reduction to yield a Mo(II) monoiodide complex featuring a Mo–C bond to the α-position of one imine substituent, (κ⁶-P,N,N,N,C,P-^Ph2PPrPDI)MoI. Successful isolation of the inner-sphere Mo(I) monoiodide complex, (^Ph2PPrPDI)MoI, was achieved via reduction of [(^Ph2PPrPDI)MoI][I] with equimolar Na/naphthalene. This complex was found to have a near octahedral coordination geometry by single crystal X-ray diffraction and electron paramagnetic resonance (EPR) spectroscopy revealed an unpaired Mo-based electron which is highly delocalized onto the PDI chelate core. Attempts to prepare a Mo(I) monohydride complex upon adding NaEt₃BH to (^Ph2PPrPDI)MoI resulted in disproportionation to yield an equimolar quantity of (κ⁶-P,N,N,N,C,P-^Ph2PPrPDI)MoH and newly identified (^Ph2PPrPDI)MoH₂. Independent preparation of (^Ph2PPrPDI)MoH₂ was achieved by adding 2 equiv. NaEt₃BH to [(^Ph2PPrPDI)MoI][I] and a minimum hydride resonance T₁ of 176 ms suggests that the Mo-bound H atoms are best described as classical hydrides. Interestingly, (^Ph2PPrPDI)MoH₂ can be converted to (κ⁶-P,N,N,N,C,P-^Ph2PPrPDI)MoI upon iodomethane addition, while (^Ph2PPrPDI)MoH₂ is prepared from (κ⁶-P,N,N,N,C,P-^Ph2PPrPDI)MoI in the presence of excess NaEt₃BH. Similarly, (κ⁶-P,N,N,N,C,P-^Ph2PPrPDI)MoI can be converted to (κ⁶-P,N,N,N,C,P-^Ph2PPrPDI)MoH with 1 equiv. of NaEt₃BH, while the opposite transformation occurs following iodomethane addition to (κ⁶-P,N,N,N,C,P-^Ph2PPrPDI)MoH. Facile interconversion between [(^Ph2PPrPDI)MoI][I], (κ⁶-P,N,N,N,C,P-^Ph2PPrPDI)MoI, (κ⁶-P,N,N,N,C,P-^Ph2PPrPDI)MoH, and (^Ph2PPrPDI)MoH₂ is expected to guide future reactivity studies on this unique set of compounds.