Pyridin-Borabenzol und Pyridin-2-Boranaphthalin als Liganden von Metallen der Chromgruppe / Pyridine-borabenzene and Pyridine-2-boranaphthaline as Ligands of Group 6 A Metals

Abstract

<jats:p>Pyridine-borabenzene (1) and pyridine-2-boranaphthalene (2) can be coordinated to group 6A metals M to form compounds of the type (OC)<jats:sub>3</jats:sub>M·1 and (OC)<jats:sub>3</jats:sub>M·2, respectively. X-ray structure determinations prove the ligands to be η<jats:sup>6</jats:sup>-bonded to the metal via the boron-containing six-membered ring.</jats:p>

Half-Sandwich Complexes of an Extremely Electron-Donating, Redox-Active η6-Diborabenzene Ligand

“…In order to quantify the electron-donating properties of ligand 1 , we measured IR absorption spectra of compounds 2 – 4 to obtain the stretching frequencies of the carbonyl ligands. The results are summarized in Table alongside those of [(C 6 H 6 )­Cr­(CO) 3 ] and Schmid’s pyridine-borabenzene complex . It is immediately clear that the diborabenzene complexes exhibit a large shift of the bands to lower energy.…”

“…The results are summarised in Table 2 alongside those of [(C 6 H 6 )Cr(CO) 3 ] 28 and Schmid's pyridine-borabenzene complex. 15 It is immediately clear that the diborabenzene complexes exhibit a large shift of the bands to lower energy. The A 1 and E carbonyl stretching frequencies of Cr complex 2 are 107 cm -1 and 130 cm -1 lower, respectively, than those of the parent benzene complex.…”

“…13 The expected strong donor ability of borabenzenes as ligands for transition metals was first observed experimentally by Schmid and co-workers with the preparation of Group 6 M(CO) 3 complexes of pyridine-borabenzene and pyridine-2- boranaphthalene, in which the CO stretching frequencies are markedly lower than in arene analogues. 15 The group of Fu (and later others) developed a general synthetic protocol for such borabenzene-base adducts, 14,16,17 and showed that their coordination to Cr(CO) 3 dramatically increases the rate of nucleophilic aromatic substitution at boron. 18 It follows that incorporation of further boron atoms into the arene ring (with associated Lewis base donors) should produce an even more strongly electron-donating ligand.…”

Complexes of the (Tetramethylcyclobutadiene)cobalt Fragment with Boratabenzene Ligands and an Unprecedented Formation of a Borabenzene Complex − Structures of (C4Me4)Co(3,5-Me2C5H3BSnMe3) with an Sn−B Bond and of the Dinuclear Complex [(C4Me4)Co(3,5-Me2C5H3B)]2O

“…Those that have been synthesised are in all cases tricarbonyl compounds of group‐6 metals,7c,8 such as e.g. Cr(CO) 3 (C 5 H 5 BNC 5 H 5 ) and its homologues of Mo and W 8c…”

Nucleophilic Aromatic Substitution Reactions of Borabenzene-Trimethylphosphine: A Versatile Route to 1-Substituted Boratabenzenes

“…Although borabenzene complexes ( 1 ) are one of the simplest families of heterocycles, very little is known about their chemistry . As part of a program directed toward the development of applications of borabenzenes in organic synthesis, we have initiated studies of their fundamental reactivity.…”