M−Cl/Si−Cl Preferential Reactivity in Chlorosilyl-Substituted Cyclopentadienyl Early Transition Metal Complexes in Reactions with Amines: Key to Understanding the Nature of the Final Product

Abstract

The reaction of [Ti(η 5 -C 5 Me 4 SiMe 2 Cl)Cl 3 ] (1) with 1 equiv of different ethylenediamines, NHR-(CH 2 ) 2 NR 0 R 00 , regiospecifically affords cyclopentadienyl-silyl-amido derivatives with constrainedgeometry, [Ti{η 5 -C 5 Me 4 SiMe 2 -κ-N(CH 2 ) 2 NR 0 R 00 }Cl 2 ] (R 0 =R 00 =H, 2a; R 0 =H, R 00 =Me, 2b; R 0 = R 00 =Me, 2c) or unstrained structure, [Ti{η 5 -C 5 Me 4 SiMe 2 NMe(CH 2 ) 2 -κ-NMe}Cl 2 ] (3). Treatment of 1 with 1.5 equiv of ethylenediamine gives a mixture of 2a and the transient complex [Ti{η 5 -C 5 Me 4 SiMe 2 NH(CH 2 ) 2 NH 2 }Cl 3 ] (4), which is transformed into 2a upon addition of a base. The reaction of 1 with N,N,N 0 -trimethylethylenediamine permits the synthesis and isolation of the complex [Ti{η 5 -C 5 Me 4 SiMe 2 NMe(CH 2 ) 2 NMe 2 }Cl 3 ] (5). Compound 1 reacts with 0.5 equiv of NH 2 (CH 2 ) 2 NH 2 to yield a mixture of 2a along with the tethered dinuclear cyclopentadienyl-silyl-amido compound [Ti{η 5 -C 5 Me 4 SiMe 2 -κ-N(CH 2 )-}Cl 2 ] 2 (6).Currently, there is a continuous and increasing interest in the chemistry of transition metal compounds bearing ancillary polydentate ligands. 1-5 Modification of the ligand environment at the metal centers has enabled the preparation of new generations of polymerization catalyst precursors with excellent performance. 6-14 Among the multidentate ligands most widely studied, a prominent class consists of bifunctional cyclopentadienyl ligands incorporating neutral or anionic appended donor substituents. [15][16][17][18] The relevance of this research area is inferred from the numerous reviews of derivatives of this type recently published. 1,3,16,17 This field has largely been stimulated by the remarkable success of the group 4 metal "constrained-geometry" complexes as alternative catalysts to the classical bis-(cyclopentadienyl) systems 19-22 (MCp 2 X 2 ) for R-olefin polymerization processes. 23,24 One of our ongoing research lines is focused on the development of a new, efficient, and versatile alternative strategy to prepare transition metal complexes containing a bifunctional cyclopentadienyl ligand, 25 based on protonolysis reactions of M-Cl and Si-Cl bonds from chlorosilylsubstituted cyclopentadienyl compounds, 26-28 in reactions with ‡Correspondence concerning the crystallography data should be addressed to this author.

Reactions of [Ti(η5-C5Me4SiMe2Cl)Cl3] with Diamines, a Suitable Approach to Prepare Mono- and Dinuclear Cyclopentadienyl-silyl-amido Titanium Complexes with Constrained and Unstrained Structures

“…The silicon and nitrogen chemical shifts of the resonances of the "CpSiMe 2 N" fragment provide a suitable tool to determine its coordination mode. 35,36 Thus, the spectroscopic behavior of 2 shows a unique upfield resonance (δ average ≈ À 17) in its 29 Si NMR spectrum and a downfield signal (δ average ≈ 350) in its 15 N NMR spectrum, confirming the suggested symmetry of these compounds with a constrained-geometry disposition in their metal-based molecular fragments. In contrast, the spectroscopic behavior of 4 shows two well-separated resonances at δ ≈ À6 and À17 in its 29 Si NMR spectrum, indicating that the two "CpSiMe 2 N" moieties occupy very different bonding environments.…”

“…32 As expected with a constrained-geometry disposition, compounds 2 and 3 show the typical upfield shifted resonance for the cyclopentadienyl ipso-carbon (δ < 110), with respect to the rest of the ring carbon atoms. 35,36 The 13 C NMR spectra of complexes 4 feature two clearly separated resonances for the cyclopentadienyl ipso-carbon (δ < 105 and >140), confirming the very different structural dispositions of both ends of the molecule. The silicon and nitrogen chemical shifts of the resonances of the "CpSiMe 2 N" fragment provide a suitable tool to determine its coordination mode.…”

Stereospecific Synthesis of Chiral Titanium Complexes Bearing a Bifunctionalized Cyclopentadienyl-Terpenoid Ligand Derived from α-Pinene

“…28,29 The synthesis of this new family of chiral compounds was achieved following the strategy described above, consisting of the protonolysis of Ti−Cl and/or Si−Cl bonds in monocyclopentadienyl complexes bearing a SiMe 2 Cl group on the Cp ring, such as [Ti(η 5 -C 5 H 4 SiMe 2 Cl)Cl 3 ] and [Ti{η 5 -C 5 H 3 (SiMe 3 )(SiMe 2 Cl)}Cl 3 ]. 30,31 Thereafter, reactions of the complexes [Ti(η 5 -C 5 H 4 SiMe 2 Cl)Cl 3 ] and [Ti{η 5 -C 5 H 3 (SiMe 3 )(SiMe 2 Cl)}Cl 3 ] with 1 equiv of the terpenoid preligand C 7 H 6 Me 3 (OH)-(NCH 2 CH 2 NH 2 ) in dichloromethane, at room temperature, and in the presence of 3 equiv of NEt 3 yielded the new constrained-geometry complexes [Ti{(η 5…”

“…The synthesis of this new family of chiral compounds was achieved following the strategy described above, consisting of the protonolysis of Ti–Cl and/or Si–Cl bonds in monocyclopentadienyl complexes bearing a SiMe 2 Cl group on the Cp ring, such as [Ti­(η 5 -C 5 H 4 SiMe 2 Cl)­Cl 3 ] and [Ti­{η 5 -C 5 H 3 (SiMe 3 )­(SiMe 2 Cl)}­Cl 3 ]. , …”

Suitable Approach to Prepare N‐Substituted Niobium Complexes – Study of the Factors Controlling the Process

“…In this field, one of our ongoing research lines is focused on the development of an alternative and efficient synthetic strategy for transition‐metal complexes bearing polydentate ligands consisting of a cyclopentadienyl ring that incorporates appended donor substituents , , . Such an approach is based on the protonolysis reactions of the Si–Cl and M–Cl bonds of the chlorosilyl‐substituted cyclopentadienyl compounds [M(η 5 ‐C 5 H 4 SiMe 2 Cl)Cl n ] (M = Ti, n = 3; M = Nb, n = 4) , …”