Reactivity of Cyclopentadienyl Molybdenum Compounds towards Formic Acid: Structural Characterization of CpMo(PMe₃)(CO)₂H, CpMo(PMe₃)₂(CO)H, [CpMo(μ-O)(μ-O₂CH)]₂, and [Cp*Mo(μ-O)(μ-O₂CH)]₂

Abstract

The molecular structures of CpMo(PMe)(CO)H and CpMo(PMe)(CO)H have been determined by X-ray diffraction, thereby revealing four-legged piano-stool structures in which the hydride ligand is trans to CO. However, in view of the different nature of the four basal ligands, the geometries of CpMo(PMe)(CO)H and CpMo(PMe)(CO)H deviate from that of an idealized four-legged piano stool, such that the two ligands that are orthogonal to the trans H-Mo-CO moiety are displaced towards the hydride ligand. While CpMo(PMe)(CO)H (Cp = Cp, Cp*; x = 1, 2, 3) are catalysts for the release of H from formic acid, the carbonyl derivatives, CpMo(CO)H, are also observed to form dinuclear formate compounds, namely, [CpMo(μ-O)(μ-OCH)]. The nature of the Mo···Mo interactions in [CpMo(μ-O)(μ-OCH)] and [Cp*Mo(μ-O)(μ-OCH)] have been addressed computationally. In this regard, the two highest occupied molecular orbitals of [CpMo(μ-O)(μ-OCH)] correspond to metal-based δ* (HOMO) and σ (HOMO-1) orbitals. The σδ* configuration thus corresponds to a formal direct Mo-Mo bond order of zero. The preferential occupation of the δ* orbital rather than the δ orbital is a consequence of the interaction of the latter orbital with p orbitals of the bridging oxo ligands. In essence, lone-pair donation from oxygen increases the electron count so that the molybdenum centers can achieve an 18-electron configuration without the existence of a Mo-Mo bond, whereas a Mo═Mo double bond is required in the absence of lone-pair donation.

Steric Switching From Photochemical to Thermal N2 Splitting: A Computational Analysis of the Isomerization Reaction {(Cp*)(Am)Mo}2(μ-η1:η1-N2) → {(Cp*)(Am)Mo}2(μ-N)2

“…The crystallographic Mo-Mo distances on the other hand are slightly shorter than twice Pauling's covalent bond radius for Mo (1.371 Å). At 2.676 and 2.648 Å, respectively, they are in the range of distances expected for a Mo-Mo single or double bond (Pauling and Kamb, 1986; Shin and Parkin, 1998; Neary and Parkin, 2017). Both diamond cores are to some extent asymmetric: the molybdenum ions in 1 dia have different bond lengths with the bridging nitrogen atoms (Mo 1 -N 1, 2 : 1.850 Å, Mo 2 -N 1, 2 : 1.964 Å), whereas each molybdenum in 2 dia has two different bond lengths with the nitrogen bridges (1.892, 1.927 Å) (Keane et al, 2015; Duman et al, 2016).…”

Zerovalent Nickel Compounds Supported by 1,2-Bis(diphenylphosphino)benzene: Synthesis, Structures, and Catalytic Properties

“…The decarboxylation of formic acid is of much current interest with respect to its ability to serve as a hydrogen storage material, and there is particular emphasis on the use of earth abundant nonprecious metals to catalyze the release of hydrogen. − In this regard, we previously demonstrated that Ni­(PMe 3 ) 4 is able to effect catalytic release of H 2 from formic acid at 80 °C. ,, We have now demonstrated that the heteroleptic variant, (dppbz)­Ni­(PMe 3 ) 2 , is also capable of such activity, with a turnover number of 10 over a period of ca. 16 h at 60 °C; however, the activity diminishes considerably after this period, and analysis of the reaction by 1 H NMR spectroscopy demonstrates that the reaction is accompanied by the formation of Ni­(dppbz) 2 and (dppbz)­Ni­(PMe 3 )­(CO).…”