Synthesis and Characterization of Titanium Complexes Containing Potentially Tridentate Amido‐cyclopentadienyl Ligands

Abstract

Two new titanium complexes of the general type Ti(q5:q1-function of the temperature, indicating the presence of a n C5H4SiMe,NCH,CH2X)C12 (X = NMe,, OMe), containing a equilibrium between the tri-and bidentate bonding mode tridentate ligand, were prepared by reaction of Ti(q5-C5H4Si-of the ligand. A single-crystal X-ray structural analysis of Me2C1)CI3 with the lithium amide Li(NHCH2CH2X) (X = Ti(q5 :q1-C,H4SiMe2NCH,CI-I,0Me)C12 revealed that the NMe2, OMe). The 'H-NMR chemical shifts for the protons methoxy function is not intramolecularly coordinated in the of the ethylene link were found to vary considerably as a solid state.Functionalized cyclopentadienyl liganddl] allow the synthesis of a wide variety of transition metal complexes with novel coordination spheres, which may be used in the control of the catalytic behavior of the metal center. In the context of designing new metallocene catalysts for olefin polymerization, amido-functionalized cyclopentadienyl ligands in particular have been of considerable recent interest[*]. Not only do they allow variation of the ring substituents and the nature of the bridge, which constitute common tools for the manipulation of Brintzinger-type ansa-metallocenes, but modification of the amido substit~ent[~] is also possible. In order to modulate the Lewis acidic group-4 metal center, we are studying potentially tridentate ligands by introducing an additional donor is significantly broadened at low temperatures. Despite the presumably higher Lewis acidity of the titanium center compared with that of the tetramethyl analog Ti(q5:q '-CSMe4SiMe2NCH2CH2NMe2)-Cl,['l, the dimethylamino group is apparently not more strongly coordinated [8]. On the other hand, a single-crystal structure analysis revealed that the additional donor site is unambiguously interacting with the titanium center, although considerable disorder in the CH2CH2NMe2 chain precluded an accurate solution of the Figure 1. ORTEP diagram of the molecular structure of Ti(q5:q1-C5H4SiMe2NCH2CH20Me)CI2. Thermal ellipsoids are drawn at the 50% probability level R Results and DiscussionPreviously we noted that the reaction of the dilithium derivatives Li2(C5H4SiMe2NCH2CH2X) (X = NMe2, OMe) with TiC14(THF)2, or with TiC13(THF)3 followed by oxidation, unexpectedly led to the formation of the stable C2-symmetric bis(1igand) complexes of the type Ti( q5:q'-CsH4SiMezNCH2CH2X)2[S,7a] rather than to the mono(1igand) complexes Ti(q5:q'-C5H4Si-Me2NCH2CH2X)CI2. In contrast, Ti($ :q1-C5H4SiMe2NCH2-CH2NMe2)C12 could be obtained as orange crystals in good yield by the reaction of the easily prepared Ti(q5-C5H4SiMe2CI)C13[6] with 1.33 equivalents of Li(NHCH2CH2NMe2) in toluene, followed by work-up of the reaction mixture by filtering off LiCl and the ammonium salt [NH3CH2CH2NHMe2]CI2. 'H-, I3C-NMR-spectroscopic as well as mass-spcctral and analytical data confirm the structure o f a mono(1igand) complex. However, the nature of the additional bonding site remains undefined. Variable temperature IH-NMR spectra show a fairty strong shif...

Synthesis, Structures, and Catalytic Reactions of Ring-Substituted Titanium(IV) Complexes

“…182 Royo 179 first introduced the synthesis of (η: 5 η 1 -C 5 H 4 SiMe 2 NCHMePh)TiCl 2 164 via route C also developed by his group, as an efficient synthetic route to CGC complexes from a suitable starting material (η 5 -C 5 H 4 SiMe 2 Cl)TiCl 3 . The reaction of (η 5 Okuda et al 165,169,181,184 also introduced a tridentate variation of the linked amidocyclopentadienyl ligand. They proposed that the two-electron donor functional groups X ) OMe and NMe 2 may act as labile ligands, thereby temporarily coordinating to the central metal during catalytic reactions and hence stabilizing the highly electrophilic centers.…”

Heterogeneous Constrained-Geometry Zirconium Catalysts

“…Constrained-geometry catalysts having the formula (η 5 -C 5 R 4 )SiR‘ 2 (η 1 -NR‘ ‘)MX 2 (M = Ti, Zr, Hf; X = Cl, Me, NR 2 ; R, R‘, R‘ ‘ = alkyl or aryl) are currently under intensive study and development − as a new generation of highly active and selective Ziegler−Natta-type catalysts − for the copolymerization of ethylene and α-olefins. The initial designs of ansa -monocyclopentadienylamido catalysts were introduced by Bercaw and co-workers, who developed scandium complexes for olefin polymerization catalysts. , Later Okuda 3 reported the synthesis of analogous titanium complexes, and soon afterward Dow and Exxon , detailed the synthesis and catalytic activities of group 4 constrained-geometry complexes in the patent literature.…”

Constrained geometry complexes of titanium (IV) and zirconium (IV) involving cyclopentadienyl fused to thiophene ring

“…The Ti(1)-N(1) distance (1.906(3) Å ) is consistent with a p-bonding contribution from an interaction between the nitrogen p p orbital and the appropriate vacant titanium d p orbital [36]. However, the magnitude of this interaction is controlled both by the constrained geometry of the molecule and by the electronic and steric properties of the amido substituent, as observed in other complexes of this type [Ti{(g 5 -C 5 R 4 )SiMe 2 (g 1 -NR)}Cl 2 ] [33,[37][38][39][40][41][42][43][44][45][46]. The Ti(1)-N(1) bond distance found in compound 2 is longer and therefore the p-bonding contribution is smaller than that found in unconstrained amido derivatives such as [Ti{(g 5 [51], and [Ti{(g 5 -C 9 H 7 )(g 1 -NMe 2 )}Cl 2 ] (1.864(4) Å ) [52].…”