1‐Hetero‐3,4‐diborolane und zwei neue Wege zu 1,2‐Diboretanen

Abstract

A, /i = 326.90(5) , Z = 4, V = 4599 A'; Vierkreisdiffrdktometer (Mo,,-Strahlung, (o-Scan), 291 3 beobdchtete Reflexe (I > 2q), Nichtwasserstoffatoine anisotrop, H-Atome (bis auf Methylgruppen) in gefundenen Lagen isotrop verfeinert. R = 0.041. Eine Verfeinerung in Cc zeigte starke Korrelation und konvergierte nicht [12]. 112) Weitere Einzelheiten ZLI den Kristdllstrukturuntersuchnngen konnen helm Fachinforniationszentrum Karlsruhe, Gesellschaft fur wissenschaftiichtechnische Information mbH, W-7514 Eggenstein-Leopoldshafen 2, unter Angdbe der Hinterlegungsnuminer CSD-56771, der Autoren uiid des Zeitschriftenzitdts angefordert werdcn.

Difluorenyl[2]borametallocenophanes of Group 4 Metals: Synthesis and Structure

“…In order to shed more light on this, NMR measurements at –50 °C were carried out. At low temperature, eight signals in the 1 H and twelve signals in the 13 C{ 1 H} NMR spectra were observed for the fluorenyl system, in agreement with NMR spectra previously recorded at room temperature for other bis(fluorenyl)[2]borametallocenophanes (M = Ca, Ba,10 Sn, Pb11). However, the corresponding alkali metal derivatives (Li, Na, K, Cs) show only six signals in their 13 C{ 1 H} NMR spectra at room temperature, which was explained by a less effective coordination of the fluorenyl ring to the metal center, thus allowing rotation of the fluorenyl rings around the B–C bond 10.…”

“…All metallation reactions have to be carried out in brown‐tinted glassware, as exposure of the reaction mixture to UV‐light induces a almost quantitative rearrangement reaction (Scheme ) as previously observed by Nöth and co‐workers,11 although isolated 3 as well as 4 and 5 seem to be stable against UV and visible light.…”

“…While a detailed mechanism of the rearrangement still remains unknown, it was suggested that the η 5 ‐M bond is broken upon exposure to UV light and a bond between the ipso ‐carbon atoms is formed with ring contraction. The resulting 1,2 diboretane then rearranges to the thermodynamically favoured 1,3‐diboretane 11. While 6 has been previously characterized in solution by multinuclear NMR spectroscopy, its structure in the crystal is now reported for the first time.…”

“…The 1,2‐bis(dimethylamino)‐1,2‐di‐η 1 ‐fluorenyldiborane(4) has been described previously by Nöth, along with the corresponding metallocenophanes of Li, Na, K, Cs, Ca, Ba,10 As, Sn and Pb 11…”

[2]Borametallocenophanes of Group 4 Metals: Synthesis and Structure

“…[12] This dynamic process was ascribed to the common property of amino-substituted diboranes(4) to avoid conformations in which the axes passing through the boron p z orbitals adopt a parallel orientation. [9,12,13] The Zr complex 8 was chosen as an representative example to study the dynamic behavior of the bis(cyclopentadienyl)complexes described here. As in the case of the aforementioned ansa-ferrocene, [12] 8 exhibits, at ambient temperature, signal patterns in the 1 H and 13 C NMR spectra corresponding to C 2v symmetry, giving evidence for a dynamic process that is fast compared to the NMR time scale.…”