Cyclic Hydroborate Complexes of Metallocenes. 1. Organodiborate Ring Transformations Promoted by Zirconocene and Hafnocene Dichlorides. Syntheses and Structures of Zirconocene and Hafnocene Boracyclopentane Derivatives

Abstract

The anion [H2B2(μ-H)(μ-C4H8)2]-, II, reacts with zirconocene dichloride and with hafnocene dichloride to form (η5-C5H5)2ZrCl{(μ-H)2BC4H8}, III, and (η5-C5H5)2HfCl{(μ-H)2BC4H8}, IV, complexes, which contain a boracyclopentane ring that is bound to the metal through hydrogen bridges. In these reactions, 0.5 mol of the transannular hydrogen-bridged 10-membered ring compound B2(μ-H)2(μ-C4H8)2 is also formed. A possible reaction pathway for the formation of these complexes is proposed on the basis of time-lapse 11B NMR spectroscopy. The methyl-substituted complex (η5-C5H5)2Zr(CH3){(μ-H)2BC4H8}, V, is prepared from the reaction of III with CH3Li. The molecular structure of III was reported earlier. The structures of IV and V are reported here. Crystal data for IV: space group P21/n (No. 14), a = 8.565(1) Å, b = 14.786(3) Å, c = 11.120(3) Å, β = 96.17(2)°, Z = 4. Crystal data for V: space group Pbca (No. 61), a = 8.436(1) Å, b = 16.343(2) Å, c = 20.827(2) Å, Z = 8.

Cyclic Hydroborate Complexes of Metallocenes III. Syntheses and Structures of Zirconocene Boracyclohexane Derivatives Cp2Zr(X){(μ-H)2BC5H10} (X = H, CH3, H2BC5H10)

“…The 11 B NMR spectrum of 4 consists of a triplet at δ = 24.57 ppm (t, J B - H = 40.2 Hz) which is consistent with the double hydrogen-bridged structure. The chemical shift occurs at about the same position as the neutral organodiborane {(μ-H)BC 5 H 10 } 2 , but the coupling constant is about 15 Hz less than occurs for the other compounds discussed here and in a previous report . In the 1 H NMR spectrum, two bridge hydrogens appear as a broad signal at δ = −2.82 ppm at ambient temperature and the signal from the other bridge hydrogens is believed to be overlapped with the signals of the boracyclohexane rings.…”

“…These products probably arise from competing reactions in which the methyllithium can displace terminal Cl or bridging H from Cp 2 ZrCl{(μ-H) 2 BC 5 H 10 }. Similar competing pathways in the reaction of methyllithium with Cp 2 ZrCl{(μ-H) 2 BC 4 H 8 } can account for the mixture of products formed …”

Cyclic Hydroborate Complexes of Metallocenes II: Reactivity of (μ-H)2(BC5H10)2 and Its Cyclic Derivative, [H2BC5H10]-; Synthesis of (η5-C5H5)2MCl(μ-H)2BC5H10 (M = Zr, Hf)

“…NMR spectra of 4 and 5 are similar. The 11 B NMR spectrum of 4 consists of a broad triplet at +13.6 ppm, similar to the spectrum of (η 5 -C 5 H 5 ) 2 MCl(μ-H) 2 BC 4 H 8 (M = Zr, Hf) . The coupling pattern is consistent with a boron atom bonded to two hydrogen atoms, and the coupling constant of J B - H = 53 Hz, is within the range expected for a bridging hydrogen interaction.…”

“…Anion 3 functions as a chelating agent in its reactions with zirconocene dichloride and hafnocene dichloride to produce (η 5 -C 5 H 5 ) 2 MCl(μ-H) 2 BC 5 H 10 (M = Zr, 4 , and Hf, 5 ) (reaction 7). The formation of 4 and 5 involves a simple metathesis reaction with the formation of KCl and a neutral transition metal−boron species. Interestingly, when the anion, [(μ-H) 2 B 2 H(μ-C 4 H 8 )] - , reacts with zirconocene dichloride and hafnocene dichloride, a ring transformation of the anion occurs and the boracyclopentane derivative (η 5 -C 5 H 5 ) 2 MCl(μ-H) 2 BC 4 H 8 (M = Zr, Hf) is formed …”

Zirconocene-Catalyzed Silylation of Alkenes with Chlorosilanes

“…[9] We report herein the first example of the transition metal catalyzed silylation of alkenes with chlorosilanes as well as silylsulfides, silylselenides, and silyltellurides. This reaction proceeds under mild conditions with a catalytic amount of a zirconocene complex [10] in the presence of a Grignard reagent to give alkenylsilanes and/or allylsilanes.…”