Tomás Cuenca

Transition metal complexes with functionalized silyl-substituted cyclopentadienyl and related ligands: synthesis and reactivity

Abstract Interest in modifying transition metal complexes using substituted cyclopentadienyl rings has been stimulated in the last years by their potential synthetic and catalytic applications in different processes. This review will feature mono- and dicyclopentadienyl-transition metal complexes containing silyl-cyclopentadienyl and related indenyl and fluorenyl ligands. All of these compounds contain silyl-substituted functionalities which are able to coordinate the metal center or used to introduce such a type of ligating moieties. The synthesis and chemical behaviour of these types of compounds are strongly emphasized. Compounds discussed are all those containing silicon-bound substituents which include: (a) hydrosilyl (Si–H); (b) halosilyl (Si–X); oxosilyl (Si–O); (c) amino– and amido–silyl (Si–N); (d) alkyl– and alkenyl–silyl (Si–C) and (d) boron–silyl (Si–B) compounds. A brief remark on their most significant structural characteristics is also included.

Synthetic and reactivity studies of mono- and dicyclopentadienyl titanium, zirconium and hafnium complexes with the chlorodimethylsilyl-cyclopentadienyl ligand. X-ray molecular structure of Hf{(η5-C5H4)SiMe2OSiMe2(η5-C5H4)}Cl2 and Zr(η5-1,3-tBu2C5H3)(η5-C5H4SiMe2-η-NtBu)Cl

Abstract Reaction of the disilylated cyclopentadiene C5H4(SiClMe2)(SiMe3) with HfCl4, in heptane, gave the monocyclopentadienyl complex Hf(η5-C5H4SiClMe2)Cl3 (1c). Addition of two equivalents of C5H5(SiClMe2) to a solution of MCl4, in toluene under reflux and in the presence of two equivalents of NEt3, afforded the dichloro derivatives M(η5-C5H4SiClMe2)2Cl2 [M=Ti (2a), Hf (2c)]. Compounds 2a and 2c react with a stoichiometric amount of water with selective hydrolysis of the SiCl bonds to give the tetramethyldisiloxane-bridged diciclopentadienyl complexes M{(η5-C5H4)SiMe2OSiMe2(η5-C5H4)}Cl2 [M=Ti (3a), Hf (3c)]. The reaction of the trichloro metal compounds M(η5-C5H4SiClMe2)Cl3 with Tl(1,3-tBu2C5H3), K(C5Me5) or Tl(C5H5) afforded the dichloro mixed dicyclopentadienyl MCp′(η5-C5H4SiClMe2)Cl2 derivatives [Cp′=1,3-tBu2C5H3, M=Ti (4a), Zr (4b), Hf (4c); Cp′=C5Me5, M=Zr (5b), Hf (5c); Cp′=C5H5, M=Hf (6c)]. The SiCl bond of the mixed dicyclopentadienyl complexes M(η5-1,3-tBu2C5H3)(η5-C5H4SiClMe2)Cl2, [M=Ti (4a), Zr (4b), Hf (4c)] reacts selectively with one equivalent of LiNHtBu in toluene at 50–60°C to give the amidosilyl(cyclopentadienyl) compounds M(η5-1,3-tBu2C5H3)(η5-C5H4SiMe2NHtBu)Cl2, [M=Ti (7a), Zr (7b), Hf (7c)]. The same reaction with two equivalents of the lithium amide gives the ansa-cyclopentadienylsilyl-amido compounds M(η5-1,3-tBu2C5H3)(η5-C5H4SiMe2-η-NtBu)Cl [M=Ti (8a), Zr (8b), Hf (8c)]. The X-ray molecular structure of Hf{(η5-C5H4)SiMe2OSiMe2(η5-C5H4)}Cl2 (3c) and Zr(η5-1,3-tBu2C5H3)(η5-C5H4SiMe2-η-NtBu)Cl (8b) have been determined by diffraction methods.Financial support for this research by DGICYT (Project PB97-0776) is gratefully acknowledged.

Dicyclopentadienyl-titanium and -zirconium complexes as catalysts for hydrogenation of olefins

We thank the Comision Interministerial de Ciencia y Tecnologia (Project PB89-0208) for financial support and Repsol Quimica for a Fellowship to J.C.F.

Stereorigid titanocene and zirconocene derivatives. Synthesis and crystal structure of the dialkyl complex [η5-η5-(C5H4)2Si(CH3)2]Ti[CH2Si(CH3)3]2

Abstract Reaction of M 2 ′[(η 5 -C 5 H 4 ) 2 Si(CH 3 ) 2 ] (M′ = Li, Na, K) with MCl 4 produced the known complexes [(η 5 -C 5 H 4 ) 2 Si(CH 3 ) 2 ]MCl 2 (M = Ti ( 1 ) and Zr ( 2 ). Along with the predominant product in each case a new titanium and zirconium compound is isolated. Treatment of the complexes 1 and 2 with LiCH 2 Si(CH 3 ) 3 gives the novel derivatives [(η 5 -C 5 H 4 ) 2 Si(CH 3 ) 2 ]M[CH 2 Si(CH 3 ) 3 ] 2 (M = Ti ( 4 ) and Zr ( 5 )) which have been characterized by NMR and mass spectrometry and in the case of 4 by an X-ray structural determination.

Fulvalene titanium and zirconium complexes: synthesis and NMR study of phosphanido-, alkyl-, and alkynyl-derivatives. X-ray crystal structures of [{Ti(η5−C5H5)(μ−PPH2)}2{μ−(η5−C5H4−η5−C5H4)}] and [{Zr(η5−C5H5)(μ−C≡CSiMe3)}2{μ−(η5−C5H4−η5−C5H4)}]

We gratefully acknowledge financial support from DGICYT (Project 92-0178-C) for this research. A.C. acknowledges MEC for a Fellowship.

Dicyclopentadienyl titanium and zirconium complexes with the double bridged bis(dimethylsilanodiyl) dicyclopentadienyl [(Me2Si)2(η5-C5 H3)2]2- ligand: X-ray molecular structure of [Ti{(SiMe2)2(η5-C5H3)2}Me2]

Financial support for this research by DGICYT (Project PB92-0178-C) is gratefully acknowledged. A,M. is grateful to Consejeria Educacion (CAM) for a fellowship.

Synthesis and characterization of ansa-dimethylsilylbiscyclopentadienyl titanium(II) complexes. Crystal structure of [Ti{Me2Si(C5H4)2}{CN(2,6-Me2C6H3)}2]

Abstract The titanium(II) adducts Ti[Me 2 Si(η 5 -C 5 H 4 ) 2 ]L 2 [L  CO ( 1 ), PMe 2 Ph ( 2 ), CNR (R = 2,6-Me 2 C 6 H 3 ) ( 3 ) have been made by the reduction of Ti[Me 2 Si(η 5 -C 5 H 4 ) 2 ]Cl 2 with HhCl 2 -activated magnesium in THF in the presence of the ligand L. Mixed titanocene adducts Ti[Me 2 Si(η 5 - C 5 H 4 ) 2 ]LL′ (L  CO; L′ PMe 2 Ph ( 4 ), CNR ( 5 )) can be prepared by the addition of ligands (PMe 2 Ph, CNR) to hexane solutions of Ti[Me 2 Si(η 5 -C 5 H 4 ) 2 )(CO) 2 exposed to sunlight. The crystal structure of 3 has been determined by X-ray diffraction; the phenyl groups of the isocyanide ligand are almost perpendicular to the reflection plane of the cyclopentadienyl groups.

Cyclopentadienyl–Silsesquioxane Titanium Complexes: Highly Active Catalysts for Epoxidation of Alkenes with Aqueous Hydrogen Peroxide

Titanium complexes bearing an unprecedented tridentate cyclopentadienyl-silsesquioxanate ligand provide a new class of efficient and selective catalysts for epoxidation of olefins with aqueous hydrogen peroxide under homogeneous conditions.

Synthesis and reactivity of new silyl substituted monocyclopentadienyl zirconium complexes. X-ray molecular structure of [Zr{η5-C5H4(SiMe2CH2Ph)}(CH2Ph)3]

We are grateful to the DGICYT (Project PB-92-0178-C) and University of Alcala for the financial support of this research.

Neutral and cationic di(tert-butyl) cyclopentadienyl titanium, zirconium and hafnium complexes. Dynamic NMR study of the ligand-free cations [M(1,3-tBu2-η5-C5H3)(η5-f5H5)(CH3)]+(M=Zr, Hf)

Financial support for this research by DGICYT (Project PB92-0178C) is gratefully acknowledged. J.I.A. acknowledges Repsol Petroleo S.A. for a fellowship. A.M. is grateful to Consejeria Educaci6n (CAM) for a fellowship.