Syntheses and Structures of Zirconium Tetranuclear Polyhydrides

Abstract

Compound Cp*ZrCl(BH4)2, 1, was isolated from a reaction of Cp*ZrCl3 with two equivalents of Cp*Zr(BH4)3. The tetranuclear Zr(IV) polyhydride [(μ2-H)(μ3-H)(Cp*ZrCl)]4, 2, was prepared by the reaction of 1 with excess N(C2H5)3, whereas the related Zr(IV) polyhydrides [(μ2-H)3(μ2-η2-BH4){Cp*Zr(BH4)}2]2, 3, and [(μ2-H)3(μ2-H){Cp*Zr(BH4)}2]2, 4, were isolated from the reaction of Cp*Zr(BH4)3 with excess N(C2H5)3. Compound 4 can be also prepared from the reaction of Cp*Zr(BH4)3 with excess N(CH3)3. Single-crystal X-ray structures of 1, 2, 3, and 4 were determined. In compound 1 two tetrahydroborate ligands coordinate to a zirconium atom in a tridentate bonding mode. Compounds 2, 3, and 4 are tetranuclear polyhydrides. Compound 2 features a butterfly arrangement of zirconium atoms surrounded by eight bridging hydrides. Each triangular face is capped by a μ3-bridging hydride, and the other four hydrides are μ2-bridging to the zirconium atoms in the perimeter. Compounds 3 and 4 are rectangular planar polyhydrides where the adjacent Zr atoms in 3 are linked by a bridging tetrahydroborate ligand and three μ2-bridging hydrides, and the adjacent Zr atoms in 4 are linked by a μ2-bridging hydride and three μ2-bridging hydrides. The proton NMR spectrum and the solid-state structure of 4·(toluene) suggested that the tetramer dissociates to [Cp*Zr(BH4)H(μ-H)]2 in solution.

Trinuclear Zirconium Polyhydride ({Cp*Zr(BH3CH3)}(μ-H)2{Cp*Zr(BH3CH3)}(μ-H){Cp*Zr(BH3CH3)})(μ-κ2C,H:κ1C:κ2C,H-CHBH3) and Its Derivatives: Compounds Containing a Pentacoordinated Carbon Atom

“…In general, these hypercarbon complexes were prepared from the reaction of an organometallic precursor with Lewis acids, including electrophilic metal-containing reagents and nonmetal Lewis acids . In continuing efforts toward the study of the chemistry of hydroborate complexes, we found that the pentacoordinated carbon-containing complex ({Cp*Zr(BH 3 CH 3 )}­(μ-H) 2 ­{Cp*Zr(BH 3 CH 3 )}(μ-H)­{Cp*Zr(BH 3 CH 3 )})­(μ-κ 2 C,H :κ 1 C :κ 2 C,H -CHBH 3 ), 1 , can be prepared from the reaction of Cp*Zr(BH 3 CH 3 ) 3 with excess trimethylamine. The reactions of hydroborate complexes with amine Lewis bases always result in metal hydride species. , To our knowledge, the formation of a hypercarbon complex though C–H activation initiated by an amine Lewis base is unprecedented.…”

“…In continuing efforts toward the study of the chemistry of hydroborate complexes, we found that the pentacoordinated carbon-containing complex ({Cp*Zr(BH 3 CH 3 )}­(μ-H) 2 ­{Cp*Zr(BH 3 CH 3 )}(μ-H)­{Cp*Zr(BH 3 CH 3 )})­(μ-κ 2 C,H :κ 1 C :κ 2 C,H -CHBH 3 ), 1 , can be prepared from the reaction of Cp*Zr(BH 3 CH 3 ) 3 with excess trimethylamine. The reactions of hydroborate complexes with amine Lewis bases always result in metal hydride species. , To our knowledge, the formation of a hypercarbon complex though C–H activation initiated by an amine Lewis base is unprecedented. The reactivity of 1 was further investigated, and the results show the robust framework of this hypercarbon.…”

“…The Zr–C(1) bond distances fall into the range 2.311(2)–2.391(2) Å and are within the sum of the Zr–C covalent bond radii . The C(1)–B(1) bond distance is 1.587(3) Å, which is comparable to distances found in the three terminal [BH 3 CH 3 ] − ligands (1.575(4)–1.596(4) Å) and to distances found in other methyltrihydroborate complexes. , The hydrogen atom (H(1D)) attached to C(1) is located and refined isotropically with a C(1)–H(1D) distance of 0.88(3) Å. The three bridging hydrides connect the adjacent Zr atoms in a single and double hydride-bridged fashion with corresponding Zr···Zr distances of 3.2928(4) and 3.1194(3) Å, respectively.…”

Tetranuclear Zirconium and Hafnium Polyhydride Complexes Composed of the “CpMH2” Units

“…In 1982, Wolczanski and Bercaw reported the first mono-Cp-coordinated zirconium hydride complex, [{Cp*Zr(BH 4 )H(μ-H)} 2 ], in combination with a tetrahydroborate unit. Since then, several analogous mono-Cp-coordinated group 4 metal hydride complexes, such as [{Cp*Zr(BH 4 )} 2 (μ-η 2 -BH 4 )(μ-H) 3 ] 2 , [{Cp*Zr(BH 4 )} 2 (μ-H)(μ-H) 3 ] 2 , , [(Cp*MCl)(μ-H)(μ 3 -H)] 4 (M = Zr, Hf), , and [(Cp*Hf) 4 (μ-C 6 H 8 )(μ-H) 6 ], have been reported. However, group 4 metal hydride complexes composed of only the “CpMH n ” unit without a third component have not yet been reported.…”

Titanium, zirconium, hafnium

“…84 Two interesting titanium silsesquioxane frameworks have been synthesised as models for Ti-containing active sites on the surface of silica ], which has a tripodal Ti site, these have weaker catalytic ability for the epoxidation of cyclohexene with tert-butyl hydroperoxide. 85 86 A zirconium salicyloxazoline complex, [Cp*LZr(NMe 2 ) 2 ] (L=k 2 -salicyloxazoline), catalyses the cyclohydroamination of primary aminoalkenes; the reaction is first order in catalyst but zero order in substrate, with a rate increased by steric bulk of the catalyst. A mechanism involving a reactive imide is invoked.…”