Cooperative Reactions of Pentafulvene Niobium Complexes: Formation of Alkylidene, Imido, Hydrazido, and Niobaaziridine Complexes

Abstract

The substitution of the chlorido ligand of bis(η 5 :η 1 -(di-p-tolyl)-pentafulvene)niobium chloride by reaction with (trimethylsilyl)methyllithium is followed by α-C−H bond activation. Because of the π-η 5 :σ-η 1 coordination mode, the exocyclic carbon atom of the pentafulvene ligand is strongly nucleophilic and therefore protonated, and the niobium alkylidene species (3) is isolated. The formed complex 3 shows cooperating reactions of the remaining pentafulvene and the alkylidene ligand in activating different E−H bonds. Under mild conditions, terminal imido complexes (4) and a hydrazido complex (5) are obtained by double N−H bond splitting. By the reaction of 3 with Nmethylaniline, a niobaaziridine ( 6) is formed via simultaneous N−H and C−H bond activation. By deuterium labeling, the N−H bond can be assigned to the pentafulvene moiety and the C−H bond to the alkylidene carbon center.

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

“…For the related pentafulvene-induced α-C-H bond activation recently reported, the reaction is slow enough to monitor the intermediate by NMR spectroscopy. 32 In the present case, this was unsuccessful. Instead, the postulated intermediate could be trapped with water, yielding the terminal niobocene oxo alkyl complex 3 (Scheme 3).…”

“…The determined 15 N chemical shift of the niobaaziridine nitrogen atom (δ = 119 ppm), found by coupling to the hydride and the methylene protons, is close to the shift found for a related known niobaaziridine complex (hydride formally exchanged for neosilyl: δ = 129 ppm). 32 The niobocene(III) alkyl and niobium(III) trisamido stabilization by oxidative β-C-H addition to the metal center was shown to be reversible by the addition of a suitable substrate. 7,10,12 In the case of niobaaziridine hydride 5, an equilibrium would explain why crystallization or precipitation of 5 fails.…”

“…31 Recently reported, bis(η 5 :η 1 -(di- p -tolyl)pentafulvene)niobium chloride ( 1 ) is capable of selectively activating a σ-organyl α-C–H bond to generate an alkylidene complex. 32 Here, we present the synthesis of a niobium ethylene complex, formed by β-C–H activation of an introduced ethyl ligand using a pentafulvene ligand as a proton acceptor. The formation, properties and reactivity of this niobium pentafulvene ethylene complex are discussed and possible mechanistic pathways are studied via deuterium labeling and synthesis of a postulated intermediate.…”

(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).…”

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

“…And indeed, the bis(pentafulvene)niobium complex 1 and its additional chlorido ligand is an interesting crossover of the bis‐ and mono(pentafulvene) complexes of group 4 metals [1] . 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] .…”