Metal tetrahydroborates and tetrahydroborato metalates. 30 [1] solvates of alcoholato-, phenolato-, and bis(trimethylsilyl)amido-magnesium tetrahydroborates XMgBH4(L-n)

摘要

A series of alcoholato and phenolato magnesium tetrahydroborates have been prepared as solvates (RO)Mg(BH4)(OEt2) by 1:1 reactions of ROH (R = Me, Et, iPr, tBu, CH2CMe3, Et-2(tBu)C, Ph3C, Ph, 2,4,6-Me3C6H2, (2,6-iPr)(2)C6H3, (2,6-tBu(2))C6H3, 2-(iPrO)C6H4, 2,6-(MeO)(2)C6H3) with diethyl ether solutions of EtMg(BH4). Displacement of diethyl ether by thf, dme, and di-glyme produced various solvates (RO)Mg(BH4)(L)(n) (L = thf, dme, diglyme, n = 1, 2, 3). Most of these compounds are centrosymmetric dimers with a central Mg2O2 four membered ring. Irrespective of the composition, the B-11 NMR signals are 1:4:6:4:1 quintets showing that the hydrogen atoms of the BH4 groups are magnetically equivalent. The molecular structure of eight compounds [(RO)Mg(BH4)(OEt2)](2) (R = iPr, tBu, tBuCH(2), Et3C, Me3Si), [(PhO)Mg(BH4)(thf)(2)](2), (2,6-tBu(2)C(6)H(3)O)Mg(BH4)(thf)(2), (2,6-tBu(2)C(6)H(3)O)-Mg(BH4)(thf)(dme)) have been determined. Typical for all compounds are hexacoordinated Mg atoms. The mononuclear complexes feature bidentate BH4 groups while dinuclear species show di- or tridentate BH4 groups depending on the number of coordinated O atoms.Mononuclear species are obtained only for compounds with bulky R groups, e. g. 2,6-(tBu(2))(C6H3O)Mg(BH4)(thf)(2) with tridentate BH4 groups. This compound has a linear O-C-Mg unit. In Me2SO the compound [(2-iPrO)C6H4O]Mg(BH4)(OEt2) underwent ligand exchange to produce [(2-iPrO)C6H4O](2)Mg(OSMe2)](2).Reaction of EtMgBH4 with a stoichiometric amount (1: 1) of (Me3-Si)(2)NH gives [((Me3Si)(2)N)-Mg(BH4)(OEt2)](2), 46 with a tridentate BH4 group. Its diethyl ether molecule can be replaced by thf, dme and diglyme. Amongst these solvates the compound [(Me3Si)(2)N]Mg(BH4)(diglyme) is mononuclear and its structure shows a bidentate BH4 group. Compound 46 on repeated crystallization from diethyl ether is transformed into [(Me3SiO)Mg(BH4)(OEt2)](2-)No compound with a BH4 group bonded to two Mg atoms has so far been found.