Bis(η⁵:η¹‐pentafulvene)niobium(V) Complexes: Efficient Synthons for Niobium Carbene and Imido Derivatives

Abstract

Transition-metal carbene complexes and their reactivities are akey topic of chemistry.They are an integral part of researches in catalysis,organic synthesis,coordination chemistry,a nd numerous other areas.I nt his context, we report the synthesis of al ow-valent bis(h 5 :h 1 -(di-p-tolyl)-pentafulvene)niobium chloride.O wing to the p-h 5 :s-h 1 coordination mode of the pentafulvenes and the resulting high nucleophilic character of the exocyclic carbon atom of the ligand, the bis(h 5 :h 1 -pentafulvene)niobium complex is able to achieve the umpolung of ac oordinated vinyl unit and the resulting formation of the first h 5 :h 1 cyclic niobium Schrock carbene complex. This new synthetic route is,incomparison to classical a-hydrogen elimination reactions or thermolysis of diazo compounds,c ompletely unprecedented. The reactivity of the cyclic carbene function and the remaining fulvene ligand is demonstrated by double NÀHb ond activation of primary amines to niobium imido 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).…”

Vanadium Pentafulvene Complexes: Synthon for Unprecedented VanadoceneIIIDerivatives

“…Prior to this work, vanadium pentafulvene complexes with a π‐η 5 :σ‐η 1 .coordiantion mode were unknown (Scheme 1, iv ). For tantalum, a series of tuck‐in complexes have been prepared (e. g. Ta , Scheme 2), [19,26] and for niobium, the synthesis of bis(η 5 :η 1 ‐di‐ para ‐tolylpentafulvene)niobium chloride ( Nb ) was followed by consecutive work on derived pentafulvene complexes [20,27] . In that course, the broadly examined chemistry of group 4 pentafulvene complexes (e. g. Ti1 ) was transferred to niobium [28] …”

“…Middle: Key structural parameters of pentafulvene complexes. Bottom: Selected examples of pentafulvene complexes of tantalum, [19] niobium, [20] titanium [21] and chromium [22] …”