A niobium pentafulvene ethylene complex: synthesis, properties and reaction pathways

Abstract

The π-η5:σ-η1 coordination mode of early transition metal pentafulvene ligands yields a strongly nucleophilic exocyclic carbon atom (Cexo). The substitution of the chlorido ligand of bis(η5:η1-(di-p-tolyl)pentafulvene)niobium chloride (1) by reaction...

Niobium Bis‐ and Mono(Pentafulvene) Complexes: E−H Bond Cleavage and Insertion Reactions (E=C, N, O)

“…Complex 4 crystallizes in the monoclinic space group P 2 1 / c , incorporating n ‐hexane into the system. All bonding parameters are similar to the reported ethyl variant [17] . The reaction with water is shown by the oxo ligand (Nb−O: 1.752(2) Å) and the C exo −C ispo single bonds (1.519(4) Å, 1.515(5) Å) [23] …”

“…We previously reported the ethyl substituted analogue of complex 4 , and other terminal oxo niobocene alkyl complexes are known [20–22] . The presented synthesis is superior to the synthesis of the ethyl complex which is a product of a carefully intercepted intermediate received in low yield [17] . In the 1 H NMR spectrum of 4 , the protonation of the exocyclic carbon atoms is clearly seen by a sharp singlet ( δ =5.78 ppm) next to the four multiplets of the Cp’ protons ( δ =4.61–5.65 ppm).…”

“…The isolated reaction of pentafulvene ligands is limited to two niobium examples. The double N−H bond splitting of 2,6‐xylidine at 1 yields an imido complex, and the interception of an instable bis(pentafulvene)niobium complex with water, protonating both C exo positions and receiving a terminal oxo complex [17] . In this study we exchanged the chlorido ligand at 1 for a comparatively more robust methyl group, expanding the scope of double E−H bond activation conducted by two pentafulvene ligands.…”

“…Employing a pentafulvene and the chlorido ligand, the formations of alkylidene complexes by an unprecedented nucleophilic attack onto a vinyl ligand and by a classic α‐C−H activation were reported [9,16] . Further, the β ‐C−H activation of an ethyl ligand yielded a niobium ethylene complex [17] . The reactivity of these mono(pentafulvene)niobium complexes was subsequently investigated, synthesizing imido, hydrazido and niobaaziridine complexes.…”

(Carbazol-9-ido-κN)dichlorido(η5:η1-2,3,4,5-tetramethylpentafulvene)tantalum(V)

“…The latter is dominated by group 4 complexes and their broad scope of consecutive reactions (Beckhaus, 2018). For group 5 derivatives, a bis(pentafulvene)niobium complex was synthesized (Manssen et al, 2018), and subsequently alkylidene (de Graaff et al, 2021), and ethylene pentafulvene complexes were investigated (de Graaff et al, 2022). For tantalum, a series of pentafulvene complexes has been prepared by C-H activation of a cyclopentadienyl methyl group, also known as 'tuck-in' complexes: from decamethyl tantalocene hydride by oxidative addition of one methyl C-H bond to the metal (Antonelli et al, 1993) and trapping by elemental sulfur (Brunner et al, 1996), as well as by rearrangement of a borataalkene tantalocene (Cook et al, 2002), or Cp*Ta[N( i Pr)C(NMe 2 )N( i Pr)]( 1 -NNMe 2 ) (Keane et al, 2013).…”