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

Abstract

Analysis of previously reported [((Ph2PPr)PDI)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 [((Ph2PPr)PDI)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, (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoI. Successful isolation of the inner-sphere Mo(i) monoiodide complex, ((Ph2PPr)PDI)MoI, was achieved via reduction of [((Ph2PPr)PDI)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 ((Ph2PPr)PDI)MoI resulted in disproportionation to yield an equimolar quantity of (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoH and newly identified ((Ph2PPr)PDI)MoH2. Independent preparation of ((Ph2PPr)PDI)MoH2 was achieved by adding 2 equiv. NaEt3BH to [((Ph2PPr)PDI)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, ((Ph2PPr)PDI)MoH2 can be converted to (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoI upon iodomethane addition, while ((Ph2PPr)PDI)MoH2 is prepared from (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoI in the presence of excess NaEt3BH. Similarly, (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoI can be converted to (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoH with 1 equiv. of NaEt3BH, while the opposite transformation occurs following iodomethane addition to (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoH. Facile interconversion between [((Ph2PPr)PDI)MoI][I], (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoI, (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoH, and ((Ph2PPr)PDI)MoH2 is expected to guide future reactivity studies on this unique set of compounds.

Reaction of a Molybdenum Bis(dinitrogen) Complex with Carbon Dioxide: A Combined Experimental and Computational Investigation

“…One equivalent of I 2 was added to a THF solution of 1 , the reaction was heated to 100 °C under vacuum for 1 h, a freeze–pump–thaw cycle was performed, and the solution was heated to 100 °C under vacuum for an additional 1 h. Following work-up, a dark green solid identified as ( Ph2PPr DI)­MoI 2 ( 2 , Scheme ) was obtained. Alternatively, 2 can be prepared by adding Ph2PPr DI to (CO) 3 MoI 2 (H 3 CCN) 2 , and heating to 120 °C. This compound was found to exhibit broadened 1 H NMR resonances over a 150 ppm range and an ambient temperature magnetic susceptibility of 2.45 μ B , consistent with two unpaired electrons.…”

Hydrogen production from water using a bis(imino)pyridine molybdenum electrocatalyst

“…For this study, a onestep synthesis of 1 from Ph2PPr PDI 21 and (CH 3 CN) 2 (CO) 3 MoI 2 22 was utilized. 23 Heating an acetonitrile solution of 1 and styrene oxide at 60 1C in the presence of two equivalents of AgPF 6 produced a bright orange compound within hours. A singlet at 22.9 ppm and septet at À143.6 ppm in the 31 P NMR spectrum (Fig.…”

“…The coordination geometry of 3 is consistent with that of 2; however, 21 Therefore, the chelate bond lengths determined for 3 indicate considerable Mo-PDI p-backbonding rather than electron transfer to PDI, as reported for other Ph2PPr PDI Mo(II) complexes. 19,23 Formal Mo(II) oxo complexes are rare and the lone examples reported by Wieghardt and co-workers were found to have Mo-O distances between 1.754(4)-1.781(3) Å. 27 It is hypothesized that the reduced Mo-O bond order in 3 leads to increased oxo ligand nucleophilicity, 16 allowing for consecutive proton-coupled electron-transfer (PCET) processes to give ( Ph2PPr PDI)Mo I (OH) (4, Fig.…”