Reactivity Studies of a Bis(π-η⁵:σ-η¹-benzofulvene)titanium Complex Including Simultaneous N–H and C(sp²)–H Activation of Dibenzylamine

Abstract

The improved multigram synthesis of the bis(π-η 5 :σ-η 1 -benzofulvene)titanium complex 1 is reported. On the basis of this, the follow-up chemistry of complex 1 was investigated and selective mono or double insertion reactions with ketones and nitriles into the polarized Ti−C q,exo bond(s) were found to diastereoselectively yield complexes 2−5. Compound 1 reacts with molecular hydrogen to afford the formal H 2 addition products 6a−c of the benzofulvene ligand precursor. The reactions of 1 with selected secondary Nmethylamines yield the titanium bisamides 7a and 7b in which both former benzofulvene C q,exo atoms are protonated. Finally, treatment of 1 with equimolar amounts of dibenzylamine selectively yields the titanaazapentacycle 8. Complex 8 is the result of an unprecedented and simultaneous N−H and C(sp 2 )−H (in position γ to the nitrogen atom) activation reaction. Single-crystal X-ray diffraction analyses of the key complexes reveal that the indenyl ligands in 2, 4a, and 5 consistently show the η 5 coordination mode. The one exception is complex 8, in which one indenyl ligand shows signs for a haptotropic shift to η 3 .

Synthesis and Characterization of Zr and Hf Triazenido Complexes with Rare κ1N-Coordination Built Directly in the Coordination Sphere of the Metal

“…Nitrogen-based ligands are well-known and versatile ligands in homogeneous catalysis − and organometallic chemistry in the form of amido ligands, − imido ligands − and various metallacycles. ,− Organic azides and triazenes (Figure , top) are common, electron rich N 3 -building blocks, which have broad applications in organic chemistry, − while nitrogen rich complexes are of general interest due to their various applications. − The triazenido anion is a multifaceted nitrogen containing ligand in coordination chemistry due to its different coordination modes and is capable of acting not only as a 4-electron donor, but also as a 2-electron donating ligand. Therefore, the triazenido anion can bind as a monodentate, − chelating − and bridging ligand ,, to one or two metal centers (Figure , bottom) …”

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

“…The NMR spectroscopic investigations show the formation of an insertion product with retained C 1 symmetry, with eight signals for the eight Cp protons (δ = 5.21-6.14 ppm). Like in 8, the insertion is shown in the 13 C NMR spectrum by the significant high field shift of the quaternary C exo compared to the pentafulvene C exo of 3 (δ = 64.30 (9) 68.14 (8), 107.98 (3) ppm). The incorporation of the isocyanate is shown in the 1 H NMR spectrum by the prominent singlet of its methyl groups (δ = 2.39 ppm).…”

“…The double reduction of pentafulvenes coordinating to a low‐valent early transition metal and the thereby achieved η 5 : η 1 coordination mode yields an inversed reaction behavior compared to classic organic pentafulvene reactivity (Scheme 1). [1,2] This well‐understood group 4 chemistry shows numerous examples of element‐H bond activations, [3–5] and insertions of multiple bond containing substrates [6–8] . In these cases, the exocyclic carbon atom (C exo ) acts as a nucleophile compared to its electrophilic character in the free pentafulvene [2] .…”

“…[1,2] This well-understood group 4 chemistry shows numerous examples of element-H bond activations, [3][4][5] and insertions of multiple bond containing substrates. [6][7][8] In these cases, the exocyclic carbon atom (C exo ) acts as a nucleophile compared to its electrophilic character in the free pentafulvene. [2] On top of this charge inversion, the η 5 :η 1 coordination to a metal center yields a frustrated geometry.…”