Synthesis and spectroscopic and structural characterization of derivatives of the quasi-alkoxide ligand [OBMes2]- (Mes = 2,4,6-Me3C6H2)

Abstract

Treatment of Mes2BOH (1) with «-BuLi in hexane/ether affords a suspension of LiOBMes2, which can be crystallized from THF solution as the dimer [|Li(THF)OBMes2¡2] (2). Treatment of a slurry of anhydrous CoCl2 in THF with 2 equiv of 2 gives the complex [Co{OBMes2)2Li(THF)2Cl2Li(THF)2] (3) in good yield. The X-ray crystal structures of 1-3 are also reported. The structure of 1 is the first for a diorganoboronous acid, and it exists in the solid state as hydrogen-bonded tetramers. The lithium derivative 2 is the first structurally characterized example of a metal salt of a boronous acid, and it possesses a dimeric structure previously seen only with very bulky -OC(Z-Bu)3 and -OC6H2-2,6-i-Bu2-4-Me salts. The complex 3 has cobalt pseudotetrahedrally bound to two -OBMes2 and Cl" ligands, which also form bridges to two Li+ ions. Each Li+ is also pseudotetrahedrally coordinated, with two THF donors as the remaining ligands in each case. Crystallographic data with Mo Kce radiation ( = 0.71069 Á) at

An N‐Heterocyclic Boryloxy Ligand Isoelectronic with N‐Heterocyclic Imines: Access to an Acyclic Dioxysilylene and its Heavier Congeners

“…8 8 and 116.9(1)8 8 for [Dipp(Me 3 Si)N]-(X)Si, where X = (HCDippN) 2 Bo r( Me 3 Si)3 Si, respectively],[9a,c] consistent with the tenets of Bentsr ule.C omparison with [(HCDippN) 2 CN]( t Bu 3 SiO)Si, reveals av ery similar angle at Si [103.56(8)8 8], [6e] but significantly shorter Si-O distances in the case of 3 [1.6074(14) and 1.6052(14) vs. 1.643(1) ]. [6e] This difference presumably reflects the fact that in 3 there are two O-donor ligands,w hile in [(HCDippN) 2 CN]( t Bu 3 SiO)Si the dominant p-donor contribution comes from the more strongly electron-releasing NHI substituent.…”

“…[1] Among the most common are alkoxy (RO À ) ligands,w hich stand out in having only one pendant substituent, thereby giving them the potential to donate 2s + 4p electrons to ametal center-the maximum for any h 1 ligand system. [3] Applications in main-group chemistry are thus rare (limited primarily to groups 1, 2a nd 13 complexes), [3b-d] although very recently Sarazin and co-workers isolated monomeric species of the type (R 2 BO) 2 E( E = Sn, Pb,B a) by employing the bulky (Me 3 Si) 2 HC group to inhibit dimerization. [1b] This tendency towards aggregation is problematic for applications which involve low-coordinate metal centres,f or example ambiphilic main-group species (such as carbenes and their heavier group 14 analogues) of interest in smallmolecule activation chemistry.…”

“…[2] An approach used to counter this problem exploits aryloxy (ArO À )l igands featuring bulky ortho substituents, thereby extending steric protection towards the metal center. [3] Applications in main-group chemistry are thus rare (limited primarily to groups 1, 2a nd 13 complexes), [3b-d] although very recently Sarazin and co-workers isolated monomeric species of the type (R 2 BO) 2 E( E = Sn, Pb,B a) by employing the bulky (Me 3 Si) 2 HC group to inhibit dimerization. [1c-e] That said, further chemistry with these systems typically involves the ArO À unit acting as aleaving group (cf.…”

A sodium boroxide containing an unusual Na4O4 ladder core

“…A single example of a sodium boroxide salt has been reported [14], which forms the heterocubane structure in the solidstate. Further investigation of this area will require the development of new reagents for introducing the boroxide ligand, as it has already been noted that retention of the lithium halide biproduct can occur, illustrated in the mixed Co/Li [4], and Mg/Li complexes [6]. We report in this communication the formation of a new sodium salt of dimesityl borinic acid that was structurally characterized as containing an Na 4 O 4 -ladder motif.…”

“…To date, examples of main group (group 1 [3][4][5][6]; group 2 [6]; group 13 [3,7,8]) and transition metals (group 3 [9]; group 4 [10]; group 6 [2,11]; group 7 [12]; group 8 [12]; group 9 [4]; group 12 [6,8,13]) have been reported, although notable gaps exist within this series of compounds. By far the most dominant method for the introduction of boroxide ligands to metals is salt meththesis involving a group 1 metal derivative and, as such, several studies have been conducted on these compounds.…”