Issue 24, 2016

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.

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

Supplementary files

Article information

Article type
Paper
Submitted
21 jan 2016
Accepted
13 apr 2016
First published
13 apr 2016

Dalton Trans., 2016,45, 10024-10033

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

R. Pal, B. R. Cherry, M. Flores, T. L. Groy and R. J. Trovitch, Dalton Trans., 2016, 45, 10024 DOI: 10.1039/C6DT00301J

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