Synthesis and Characterization of Hydrido Carbonyl Molybdenum and Tungsten PNP Pincer Complexes

Abstract

In the present study the Mo(0) and W(0) complexes [M(PNP)(CO)3] as well as seven-coordinate cationic hydridocarbonyl Mo(II) and W(II) complexes of the type [M(PNP)(CO)3H]+, featuring PNP pincer ligands based on 2,6-diaminopyridine, have been prepared and fully characterized. The synthesis of Mo(0) complexes [Mo(PNP)(CO)3] was accomplished by treatment of [Mo(CO)3(CH3CN)3] with the respective PNP ligands. The analogous W(0) complexes were prepared by reduction of the bromocarbonyl complexes [W(PNP)(CO)3Br]+ with NaHg. These intermediates were obtained from the known dinuclear complex [W(CO)4(μ-Br)Br]2, prepared in situ from W(CO)6 and stoichiometric amounts of Br2. Addition of HBF4 to [M(PNP)(CO)3] resulted in clean protonation at the molybdenum and tungsten centers to generate the Mo(II) and W(II) hydride complexes [M(PNP)(CO)3H]+. The protonation is fully reversible, and upon addition of NEt3 as base the Mo(0) and W(0) complexes [M(PNP)(CO)3] are regenerated quantitatively. All heptacoordinate complexes exhibit fluxional behavior in solution. The mechanism of the dynamic process of the hydrido carbonyl complexes was investigated by means of DFT calculations, revealing that it occurs in a single step. The structures of representative complexes were determined by X-ray single-crystal analyses.

Nickel‐Molybdenum and Nickel‐Tungsten Dithiolates: Hybrid Models for Hydrogenases and Hydrodesulfurization

“…Stable examples of heptacoordinate carbonyl hydrides of Mo II and W II are known, [14,15] and complexes 7 and 9 were examined here. , respectively (decarbonylated fragments are common ESI products).…”

“…The mean energy of the four ν CO bands (2006 cm -1 ) for [9H]BF 4 is 118 cm -1 greater than that of 9, a similar change (119 cm -1 ) having been obtained for the protonation of a related (PNP)W 0 (CO) 3 complex. [14] Returning to the analogy with iron tricarbonyls, the hydrido in [(dppe)Pt(pdt)HFe(CO) 3 cores often results in more symmetric, bona fide μ-hydrido species. [16] Hydride [9H] + exhibits an irreversible reduction at -1.28 V associated with the formation of H 2 and 9, the latter evidenced by the appearance of the 9 0/+ wave at -0.25 V. Figure 5).…”

Synthesis and reactivity of coordinatively unsaturated halocarbonyl molybdenum PNP pincer complexes

“…This was shown recently in the course of the synthesis of a series of Mo(II) PNP halocarbonyl complexes of the types [Mo(PNP)-(CO) 3 X] + (X = I, Br, Cl) (I) and [Mo(PNP)(CO) 2 X 2 ] (X = I, Br, Cl, F) (II) as illustrated in Chart 1. [8][9][10] Complexes based on the parent PNP ligands bearing NH moieties form cationic heptacoordinated monohalo species with three CO ligands (complexes I) with both PPh 2 and PiPr 2 moieties, whereas the PNP ligands bearing NMe moieties lead to formation of neutral dihalo species that are either hepta-coordinate and feature two CO ligands (with PPh 2 substituents, complexes II) or hexacoordinate and feature only one CO ligand (with PiPr 2 substituents, complexes III). On the other hand, the formation of the hydridocarbonyl complexes of the type [Mo(PNP)(CO) 3 H] + (X = I, Br, Cl) was independent of the nature of the amine linker.…”

A new class of PN3-pincer ligands for metal–ligand cooperative catalysis

“…For instance, the reactions with Br 2 or I 2 and the PN 3 P-Mo complexes in CH 2 Cl 2 were able to give the products Mo5 and Mo6. Interestingly, the mono(acetonitrile) complex Mo7 was obtained when the reaction was performed in acetonitrile [68,84] (Scheme 18). Notably, these results represent the first seven-coordinate molybdenum pincer complexes reported.…”