Amido complexes of (cyclopentadienyl)dichlorotitanium(IV): titanium-nitrogen multiple-bond character

Abstract

Reaction of (RCsH4)TiClj (la, R = H; lb, R = CH3) with Li(NH(t-Bu)} in THF affords (RCsH4)TiC12{NH(r-Bu)) (2a, R = H; 2b, R = CH3) in 80-90% isolated yields. The moisture-sensitive red-orangecompoundscan becrystallized from CHzClJhexane mixtures. The X-ray structures for the two compounds were determined and found to be similar. Multiple-bond character in the Ti-N bond is suggested by short Ti-N distances, 1.879 (3) A (2a) and 1.871 (5) A (2b). Data were collected on an Enraf-Nonius CAD-4 diffractometer (X(Mo Ka) = 0.710 73 A) in the -28 mode to a maximum 28 of 52'. Crystal data for 2a: C~H I S C~~N T~, M r = 256.03, monoclinic, P21/m, a = 6.149 (1) A, b = 10.888 (3) A, c = 9.004 (3) A, / 3 = 100.44 (2)O, V = 593 A3, Dcald = 1.43 g ~m -~, Z = 2. A total of 1352 reflections were collected, of which 1239 were unique, and 836 reflections with Fo2 > 3.0u(F0)2 were used in the refinement, which gave R = 0.036 and R, = 0.045. Crystal data for 2b: C I O H I~C~Z N T~, M, = 270.06, monoclinic, P21/c, o = 6.198 (2) A, b = 11.660 (2) A, c = 17.748 (4) A, 6 = 98.73 (2)', V = 1268 A3, Dcald = 1.41 g cm-3,Z = 4. A total of 2865 reflections were collected, of which 2620 were unique, and 990 reflections with F2> ~.OU(F,)~ were used in the refinement, which gave R = 0.048 and R, = 0.051. A variable-temperature NMR study was conducted to further explore the r-character of the Ti-N bond.

Derivatisation of boryl substituted titanium half-sandwich complexes – Molecular structures of [Ti{(η5-C5H4)B(NiPr2)N(H)tBu}Cl2(NMe2)] and [{TiCl2(μ-{OB(NHMe2)-η5-C5H4})}2-μ-O]

“…Overall, the structure resembles very much those of previously reported related compounds [(g 5 -C 5 R 4 R 0 )TiCl 2 (NHtBu)] (R, R 0 = H, Me) [15,16], [(g 5 -C 5 R 5 )TiCl 2 (NiPr 2 )] (R = H, Me) [17], and [(g 5 -C 5 H 5 )TiCl 2 {N(SiMe 3 ) 2 }] [18].…”

“…Hydrogen atoms are omitted for clarity. Table 1 Selected bond distances (Å ) and angles (°) for complex 10 (1) 108.66 (19) Ti (1) (1) 1.605 (3) distances in boron-bridged constrained geometry titanium dichloride complexes 1a (1.989 and 1.995 Å , respectively, for two crystallographically independent molecules) and 2 (1.992 Å ) [11b], but comparable to those in [(g 5 -C 5 H 5 )-TiCl 2 (NHtBu)] (2.032 Å ) [15] and [(g 5 -C 5 H 5 )TiCl 2 (NiPr 2 )] (2.035 Å ) [17]. The relative disposition of the bulky boryl substituent on the C 5 ring and the NMe 2 group as the sterically most demanding g 1 -substituent on titanium can be described by the N(3)-Ti-Cp(centroid)-B torsion of 38.0°a nd is most likely enforced by crystal packing forces.…”

“…The trigonal planar geometry of the N(3) atom on titanium (sum of angles of respective substituents 359.9°) and the short N(3)-Ti distance of 1.867(2) Å indicate significant p-interaction despite the observation of only one resonance in the 1 H NMR spectrum at ambient temperature for the NMe 2 group (vide supra). However, variable temperature NMR investigations on related complexes [(g 5 -C 5 H 5 )-TiCl 2 (NMe 2 )] and [(g 5 -C 5 H 5 )TiCl 2 (NHtBu)] indicated virtually free rotation about the Ti-N vector in solution that is facilitated by two orthogonal sets of p-acceptor orbitals on titanium [15]. The NMe 2 moiety adopts a virtually orthogonal position with respect to the C 5 ring plane (torsion angle between respective planes: 86.8°) and is bent away from the C 5 ring as is illustrated by the angles Ti-N(3)-C (17) and Ti-N(3)-C(16) of 140.64 (18)°and 108.66(19)°, respectively.…”

“…Ti (1) (1) 110.77 (15) boron-bridged CGCs 1a (1.602(6) and 1.605(6) Å for two crystallographically independent molecules, respectively) and 2 (1.595 (5) (1) (maximum p-interaction in a Ti-O bond corresponds to angles of 180°with regard to the two substituents on oxygen [19a]). This assumption is further supported by the relative short Ti (1) (1) angle resemble very much the corresponding values found in the C 3 -bridged cyclopentadienyl alkoxy complex [Ti{g 5 :g 1 -(C 5 Me 4 )(CH 2 ) 3 O}Cl 2 ] [20].…”

Monocyclopentadienyl Phenoxido–Amino and Phenoxido–Amido Titanium Complexes: Synthesis, Characterisation, and Reactivity of Asymmetric Metal Centre Derivatives

“…The C-C distances within the cyclopentadienyl ring, Ti-Cg(centroid) distance and Ti-Cl bond length are within the range for monocyclopentadienyl and dicyclopentadienyl titanium complexes. [31,33] …”