Low‐Valent Titanium–Pentafulvene Complexes — Formation of Dinuclear Titanium–Nitrogen Complexes

Abstract

Sodium amalgam reduction of [(η5‐C5Me5)TiCl3] (1) in the presence of the pentafulvenes {C5H4=CR2, R: p‐tol (2), p‐FPh (3), CR2: adamantyl (4)} under nitrogen smoothly produces dark green or dark blue dinuclear low‐valent titanium complexes [{(η5‐C5Me5)Ti(η6‐C5H4=CR2)}2(μ2,η1,η1‐N2)] {R: p‐tol (6), p‐FPh (7), CR2: adamantyl (8)}, characterized by a bridging end‐on coordinated dinitrogen ligand, in high yield. In the same way, the nitrogen‐free, low‐coordinated complex [(η5‐C5Me5)Ti(η6‐C9H6=C(p‐tol)2)] (10) is obtained by using the more sterically demanding benzofulvene C9H6=C(p‐tol)2 (5) instead of 2–4. The solid‐state structures of the dinitrogen compounds reveal weakly activated end‐on bound N2 ligands with identical N–N distances of 1.160(3) Å (6) and 1.160(5) Å (8). The dinitrogen complexes 6, 7 and 8 show diamagnetic behaviour, which allowed a complete NMR spectroscopic characterization. So a correlation between the situation in solution, measured by NMR, and in the solid state (X‐ray diffraction) becomes possible and shows a congruent picture. A broad range of reactions can be imagined concerning the easily replaceable dinitrogen ligand as well as the known reactivity of fulvene ligands in complexes of early transition metals. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Crystal structure of (η 5-pentamethylcyclopentadienyl)titanium(III)dichloride (THF), C14H23Cl2OTi

“…2.3 Å [9]. The distance between titanium and the center of the vemembered ring (2.004 Å) is one of the shortest, found so far, compared to other Cp*Ti-complexes (Cp*TiCl 3 , 2.021 Å [10]; Cp* 2 TiH, 2.03 Å [11]; Cp*Ti(η 5 :η 1 -benzofulvene) 2.006 Å [12]). …”

Crystal structure of an isomeric bis[(η 5:η 1-6,6-di-p-tolylpentafulvene)(η 5-pentamethylcyclopentadienyl)titanium(III)]-μ 2,η 1:η 1-dinitrogen complex, C60H66N2Ti2

“…Besides many early transition metal complexes which are capable to activate and bind molecular nitrogen [5][6][7][8][9], our group reported the easy and smooth formation of dinuclear nitrogen-bridged low-valent titanium complexes [1]. These complexes appear to serve as synthons for di erent titanocenes, due to the weakly activated and displaceable dinitrogen.…”

“…The isomeric compound B crystallizes in the triclinic space group P¯ . Unlike the starting material A [1], the inversion center is located in the middle of the N 2 ligand, causing the two pentamethylcyclopentadienyl ligands to be on opposite sides. The N-N bond length of 1.151(2) Å is also slightly shorter as in A (1.160(3) Å), while the bond angle of Ti-N-N with 175.83(14)°is greater (171.0(2)°, 169.1(2)°).…”

Spectroscopic Comparison of Dinuclear Ti+ and Ti2+ μ‐η1:η1 Dinitrogen Complexes with Cp*/Pentafulvene and Amine/Amide Ligation: Moderate versus Strong Activation of N2

“…[6] Moderately activated dinitrogen complexes are generally found for titanocene-based systems with N-N bond lengths in the range of 1.15-1.20 Å. [7][8][9][10][11][12] Strong activation, on the other hand, is observed for titanium complexes with ligand sets that are different from cyclopentadienyl, exhibiting N-N bond lengths of 1.25-1.30 Å. [13][14][15] A collection of N-N bond lengths of different dinitrogen complexes is given in Table 1.…”