Hydridoborates and hydridoborato metallates Part 26.Preparation and structures f dihydridoborates of lithium ad potassium

摘要

A series of alkali metal dihydrido borates has been prepared by three different routes. They were characterized by “B-spectroscopy and, in part, by IR spectroscopy. The following compounds were obtained: lithium dihydrido dimethyl borate lithium methyl trihydrido borate, 1 and 2, lithium and potassium dihydrido di-tert-butyl borate, 3 and 4, li*iium dihy dicyclopentyl borate, 5. lithium and potassium dihydrido 9-borata-bicyclo[3.3.01 nonane, 6a,b, potassium dihydrido bora hexane, 7, lithium dihydrido boratacycloheptane, 8, and lithium dihydrido-9-boratafluorene, 9. In the process of the formati I and 7 also Li(H3BMe) 2 and Li2(H3B—(CH,)5—BH~) are formed, most likely by a ligand redistribution process which is operative if bulky organyl groups are bound to the boron atom or if the boron atom is part of a ring system. In case entecholntc no H2U(OR)j- anions wwrc dvtectcd but for cphcdnno or dithiolato ligands the corresponding dihydrido bo4 complexes were readily detected by “B-NMR but the latter converted in THF solution into B(S2R’)2 anions. MO calcula show that the ligand redistribution for H,BX; ions into BH~ and BX~ becomes thermodynamically more favored increasing electronegativity of the substituent X. Characterization of the new hydrido borate species is usually unambiguous~~ 10 shows an anomalous temperature dependent behavior in THF solution which can be attributed to an equilibrium involvi Li(2H, 20), Li(2H, 30), and Li(30) structural units. This is supported by the X-ray structure of dimeric IOTHF and monoma 1OTHFTMEDA. While 93THF is monomeric and contains doubly bridging H2B groups ah other dihydrido diorganyl bore are dinuclear. The interaction between the alkali metal center and the boron bonded H atoms depends on number and size of d auxiliary ligands. Agostic’ Li~~H—C interactions play a role if ~-H atoms are present and when the alkali metal cation is. coordinatively saturated by the auxiliary ligand and the H(B) hydrogens. The mostsymmetric and so far unique arrangement found for [6a2THF], where all four H(B) hydrogens form Li” H~”Li bridges. Also lithium bis(dithiocatecholato)borate, 172 TEl is dimeric. Its Li centers are coordinated by four sulfur and two oxygen atoms. These atoms form a double heterocubane structu with two diametral edges missing.