Rearrangement of Tridentate [OSO]-Type Ligands and Migratory Insertion Reaction Mechanisms in Cyclopentadienyl Tantalum Complexes

Abstract

The mechanism of the isocyanide migratory insertion into the metal–carbon bond of monocylopentadienyltantalum dimethyl derivatives with [OSO]2– tridentate phenolate ligands has been investigated with DFT calculations. The presence of both a cyclopentadienyl and a tridentate ligand complicates a usually simple reaction, the migratory insertion reaction being coupled with a fac → mer rearrangement of the tridentate ligand. Two routes have been explored for the overall migratory insertion process, depending on the order of the fac → mer and insertion steps. Calculations show that the dissociative (first fac → mer rearrangement, then migratory insertion) and the associative (first migratory insertion, then fac → mer rearrangement) pathways are in principle competitive. However, electronic effects of the phenyl substituents can favor one of the pathways. The study also points out the influence of the donor atom, due to the inversion at the donor atom required in order to achieve the fac → mer interconversion.

Insertion Reactions in Ta–H and Ta–Me Bonds in Complexes Containing Tridentate κ3O,S,O-Type Ligands

“…An interesting feature of multidentate and alkoxide ligands is their ability to stabilize hydride complexes. , Moreover, mono- and dihydride complexes of niobium and tantalum with ancillary aryloxide ligands have been shown to take part as catalysts in the hydrogenation of unsaturated hydrocarbons. , With this idea in mind, we decided to synthesize the 2,2′-thiodiethanolate dihydride tantalum complex 3 and its homologue containing 2,2′-thiobis(6- tert -octylphenolate) 4 , which have not been described in our previous work . The synthesis was performed by reaction of the respective dichlorido complexes with 2 equiv of NaBHEt 3 (Scheme ).…”

“…In this molecule the tantalum atom is 0.528 Å out of the equatorial plane defined by O(1), O(2), Cl(1), and Cl(2). The Ta(1)–O(1) and Ta(1)–O(2) distances are 1.934(4) and 1.936(4) Å, respectively, and these values lie within the range found for other alkoxide and bis-alkoxide ,, chelate complexes. The Ta(1)–S(1) distance is 2.652(1) Å, which is long for a single bond but shorter than the sum of the van der Waals radii (3.80 Å) .…”

“…In recent years our research group has devoted significant attention to the relationship between the structural and electronic properties of multidentate ligands and the reactivity of the metallic center. A wide variety of homo- and heterofunctional multidentate ligands such as κ 3 O,O,O, κ 3 S,S,S, κ 3 S,O,S, and κ 3 O,S,O have been used to tune the reactivity of early transition metals such as tantalum (Figure ).…”

“…In fact, while the tbcp-containing derivatives reacted with isocyanides to give azatantalacyclopropane complexes, the tbop-containing complexes did not react . This observation could indicate a possible influence of the ring substituents on the electronic density on the tantalum center.…”

Vanadium, niobium and tantalum

“…The mechanism of migratory insertion of isocyanide into the metal-carbon bond of [Cp*Ta{k 3 -tbcp}Me 2 ] (tcbp = 2,2 0 -thiobis(4,6-dichlorophenolato) was examined computationally and was determined to be coupled with a facmer rearrangement of the tridentate ligand. 50 This journal is © The Royal Society of Chemistry 2013…”