Synthesis, electrochemistry, geometric and electronic structure of oxo-molybdenum compounds involved in an oxygen atom transferring system

Abstract

The oxygen atom transfer reactivity of Tp( *)MoO(2)(SPh) (1) (where Tp( *)=hydrotris-(3,5-dimethylpyrazol-1-yl)borate) with trimethyl phosphine (PMe(3)) has been investigated. The reaction proceed through a diamagnetic phosphoryl intermediate complex, Tp( *)MoO(SPh)(OPMe(3)) (2), which has been isolated and characterized by IR, NMR, UV-visible spectroscopy, and mass spectrometry. The molecular structure of 2 has been determined by X-ray crystallography. The complex crystallizes in monoclinic (P2(1)/n) space group, a=19.81 (1)A, b=11.1 (4)A, c=18.416 (5)A, beta=121.2 (3) degrees , V=3463.8 (25)A(3) with Z=4. In acetonitrile, complex 2 exchanges its phosphoryl ligand with a solvent molecule resulting in Tp( *)MoO(SPh)(MeCN) (3), which has been isolated and also characterized spectroscopically and by X-ray crystallography. Compound 3 crystallizes in triclinic (P1 ) space group, a=10.159 (6)A, b=18.563 (5)A, c=7.986 (3)A, alpha=96.22 (3) degrees , beta=121.2 (3) degrees , gamma=84.64 (3) degrees , V=1452.4 (11)A(3) with Z=2. The electronic structures of the complexes have been investigated by density functional theory and the redox chemistry has been investigated by cyclic and differential pulse voltammetry. In acetonitrile, complex 2 spontaneously transforms to complex, 3 at a rate of 5.6x10(-4)s(-1).

Novel O,O′‐Donor Oxo‐MoIV Hydrotris(3‐isopropylpyrazolyl)borate Complexes Formed by Chelation of Potentially Hydrogen‐Bonding Phenolate Ligands on Reduction of Dioxo‐MoVI Complexes

“…A series of simulated voltammograms were produced, based on a proposed square scheme electrochemical mechanism, and these were found to closely match the experimental observations (see Supporting Information). [42] A similar observation was reported by Sengar and co-workers for the oxidation of Tp*MoO(SPh)(OPMe 3 ), [24] although the two peaks were not found to be affected by scan-rate.…”

Scorpionate Complexes as Models for Molybdenum Enzymes

“…A similar situation applies to the Tp* complexes although the energy minimum is shallower in these less hindered systems . The electronic structures of the complexes are strongly influenced by the strong field, terminal oxido ligand (along z ), which leads to a d xy ‐based highest occupied molecular orbital (HOMO) and “degenerate” d xz ‐ and d yz ‐based lowest unoccupied molecular orbitals (LUMOs) , , …”

“…1.69 Å), phosphoryl (Mo–O ca. 2.16 Å) and X ligands;, , , the structure of 12 and the close structural relationship of related species can be seen in Figures and , respectively. The Tp i Pr complexes exhibit O=Mo–O=P torsion angles in the range 47–59° and Mo–O–P angles in the range 130–147°.…”

“…Initially, the stability of these complexes was ascribed to the presence of the sterically bulky Tp i Pr ligand but it was soon discovered that Tp* stabilized related complexes, [Tp*MoOX(OPR 3 )] (X as above; R 3 = Me 3 . Et 3 , n Bu 3 , MePh 2 ) . Concurrent structural, spectroscopic, kinetic, and computational studies of both Tp x ligand systems have illuminated the OAT process, as described below.…”

Quantitation of the ligand effect in oxo-transfer reactions of dioxo-Mo(vi) trispyrazolyl borate complexes

“…In addition, all solutions were prepared under an argon atmosphere using standard Schlenk techniques and gas-tight syringes. The syntheses and characterization of 1 , 10 2–4 , 61 1c , 10 1f , 10 2a – 2c , 9, 11 4a 7, 8 , 5 , 10 6 , 9 8 7, 8 have been reported elsewhere. 5, 7–11, 14,62 Selected kinetic data (i.e., formation and solvolysis of 1a – 1g , 5, 18 and 4a 7, 8 ) and methodology for kinetic experiments 6, 18 have been reported.…”