Pascual Royo

(C5Me5)SiMe3 as a mild and effective reagent for transfer of the C5Me5 ring: an improved route to monopentamethylcyclopentadienyl trihalides of the group 4 elements

Abstract The reaction between (C5Me5)SiMe3 and group 4 element tetrahalides MX4 (M  Ti, X  Cl, Br, I; M  Zr and Hf, X  Cl) gives the corresponding (η5-C5Me5)MX3 derivatives in nearly quantitative yields in a one-step procedure without the need for further purification.

Oxo and imido/imido exchange and C-H activation reactions based on pentamethylcylopentadienyl imido tantalum complexes

The authors acknowledge DGICYT (project PB97-0776) for financial support and J.S.N. acknowledges MEC for a fellowship.

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.

Chelated η5-cyclopentadienyl-η-ethyl complexes of molybdenum and tungsten; molecular structure of W(η5-C5H4CH2-η-CH2)(CO)3

Abstract Molybdenum and tungsten complexes M(η5-C5H4CH2-η-CH2)(CO)3 (M=Mo, W) containing the bidentate ethyl-functionalized cyclopentadienyl ligand C5H4CH2CH2 have been synthesized by the reaction of spiro[2.4]hepta-4,6-diene with M(CO)3L3 (M=Mo; L3=1,3,5-C6H3Me3; M=W; L=NCMe). Reaction of the more stable tungsten complex with C6H5ICl2 and HBF4 gave complexes of the type W(η5-C5H4CH2CH2Cl)(CO)3Cl, W(η5-C5H4CH2CH3)(CO)3Cl and W(η5-C5H4CH2CH3)(CO)3(FBF3), respectively. The crystal structure of the tungsten tricarbonyl complex W(η5-C5H4CH2-η-CH2)(CO)3 has been determined by X-ray crystal diffraction on a single crystal and shows a four-legged piano stool structure.

Monopentamethylcyclopentadienyltitanium(IV) halo-alkoxides, alkyl-alkoxides and acetylacetonates

Abstract Reactions of (C 5 Me 5 )TiCl 3 with lithium alkoxides in 1:1 or 1:2 molar ratio have given the halo-alkoxides (C 5 Me 5 )TiCl 3− n (OR) n ( n = 1, R = Me, SiPh 3 ; n = 2, R = SiPh 3 ) and (C 5 Me 5 )TiCl (O 2 R′)(R′ = C 6 H 4 , C 6 H 3 -4- t Bu). Protonolysis of (C 5 Me 5 TiMe 3 with HOSiPh 3 and Hacac gives (C 5 Me 5 )TiMe(OSiPh 3 ) 2 and (C 5 Me 5 )TiMe 2 (acac), and (C 5 Me 5 )TiCl 2 Me likewise gives (C 5 Me 5 )TiCl 2 (OC 6 H 3 -2.6-Me 2 ) and (C 5 Me 5 )TiCl 2 (acac). The crystal structure of (C 5 Me 5 )TiCl 2 (OC 6 H 3 -2,6-Me 2 ) has been determined and shows it to be monomeric, with a symmetry plane, a TiO distance of 1.785(2) A, and a TiOC angle of 162.3(2)°.

The hydrolysis of pentamethylcyclopentadienyltitanium trihalides and the formation of di-, tri-, and tetra-nuclear μ-oxo complexes. Crystal structure of [(C5Me5)TiBr(μ-O)]4CHCl3, which contains a Ti4O4 ring

Abstract Controlled hydrolysis of pentamethylcyclopentadienyltitanium trihalides Cp★TiX3 in toluene in the presence of NHEt2 leads to the isolation of compounds of the types [Cp★TiX2]2(μ-O) (X = Cl, Br, I), [Cp★TiX(μ-O)]n (X = Cl, n = 3; X = Br, n = 4] and finally [Cp★Ti]4(μ-O)6 depending upon the Ti/H2O stoichiometry. The crystal structure of [Cp★TiBr(μ-O)]4 has been determined: the compound crystallizes with one molecule of CHCl3 in the orthorhombic space group Pnca and contains a Ti4O4 ring of alternating Ti and O atoms. The four oxygen atoms lie in a plane, with the titanium atoms situated alternately ± 0.191(2) A above and below this plane.

Monocyclopentadienyl alkyl alkylidene niobium(V) and tantalum(V) complexes. X-ray crystal structure of Ta(η5-Cp′)(CH2SiMe3)2(CHSiMe3)

Abstract Reactions of monocyclopentadienyl complexes M(η5-Cp′)Cl4 with trimethylsilylmethyl lithium leads to the formation of alkylidene derivatives M(η5-Cp′)(CH2SiMe3)2(CHSiMe3), where M = Nb (1); Ta (2); Cp′= C5Me5 and M = Ta; Cp′ Me3Si(C5H4) (3), 1,3-(Me3Si)2(C5H3) (4). The new complexes were characterized by 1H and 13C NMR spectroscopy and the molecular structure of 2 was studied by X-ray diffraction methods.

Preparation and chemical behaviour of halodicyclopentadienyl-zirconium(III) and -hafnuim(III)

Abstract Reduction of (η 5 -C 5 H 5 ) 2 MCl 2 (M = Zr, Hf) with one equivalent of Na/Hg gives [(η 5 -C 5 H 5 M (μ-Cl)] 2 . The zirconium(III) complex is also obtained from reactions between LiCp and [ZrCl 3 L 2 ] 2 (L 2 = 2P-n-Bu 3 , dppe) or solutions of ZrCl 4 previously reduced with Na/Hg. These zirconium(III) and hafnium(III) complexes are oxidized by AgBF 4 or TlBF 4 to the cationic [(η 5 -C 5 H 5 M(μ-Cl)] 2 2+ complexes, which react with monodentate ligands to give [(η 5 -C 5 H 5 ) 2 MClL] + (L = OPPh 3 , NHPh 2 ) and with bidentate ligands to give dinuclear cationic derivatives [(η 5 -C 5 H 5 ) 2 MCl] 2 (μ-LL) 2+ (LL-dppe, 2,2′-bipyridine). Similar complexes can also be obtained from (η 5 -C 5 H 5 ) 2 MCl 2 by halide abstraction with a silver salt. Oxidation of zirconium(III) and hafnium(III) derivatives with halogens gives (η 5 -C 5 H 5 ) 2 MClX (X = Cl, Br) and [(η 5 -C 5 H 5 ) 2 ZrCl(OPPh 3 )]I 3 . Conductivity, magnetic susceptibility and IR and NMR data are discussed.

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.