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Titolo:
Hydridoborates and hydridoborato metallates - Part 26. Preparation and structures of dihydridoborates of lithium and potassium
Autore:
Knizek, J; Noth, H;
Indirizzi:
Univ Munich, Dept Chem, D-81377 Munich, Germany Univ Munich Munich Germany D-81377 h, Dept Chem, D-81377 Munich, Germany
Titolo Testata:
JOURNAL OF ORGANOMETALLIC CHEMISTRY
, volume: 614, anno: 2000,
pagine: 168 - 187
SICI:
0022-328X(200012)614:<168:HAHM-P>2.0.ZU;2-C
Fonte:
ISI
Lingua:
ENG
Soggetto:
CYCLIC HYDROBORATE COMPLEXES; DIETHYL-ETHER SOLVATE; ADDITION-COMPOUNDS; CHEMISTRY; HYDROGEN; SODIUM; BORON; DIALKYLBOROHYDRIDES; METALLOCENES; BOROHYDRIDE;
Keywords:
hydridoborates and hydridoborato metallates; dihydridoborates; lithium; potassium;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
37
Recensione:
Indirizzi per estratti:
Indirizzo: Noth, H Univ Munich, Dept Chem, Butenandtstr 5-13,Haus D, D-81377 Munich, Germany Univ Munich Butenandtstr 5-13,Haus D Munich Germany D-81377 rmany
Citazione:
J. Knizek e H. Noth, "Hydridoborates and hydridoborato metallates - Part 26. Preparation and structures of dihydridoborates of lithium and potassium", J ORGMET CH, 614, 2000, pp. 168-187

Abstract

A series of alkali metal dihydrido berates has been prepared by three different routes. They were characterized by B-11-NMR spectroscopy and, in part, by IR spectroscopy. The following compounds were obtained: lithium dihydrido dimethyl berate and lithium methyl trihydrido berate, 1 and 2, lithium and potassium dihydrido di-tert-butyl berate, 3 and 4, lithium dihydrido dicyclopentyl berate, 5, lithium and potassium dihydrido 9-borata-bicyclo[3.3.0] nonane, 6a,b, potassium dihydrido boratacyclohexane, 7, lithium dihydrido boratacycloheptane, 8, and lithium dihydrido-9-boratafluorene, 9. In theprocess of the formation of 1 and 7 also Li(H3BMe) 2 and Li-2(H3B-(CH2)(5)-BH3) are formed, most likely by a ligand redistribution process which is not operative if bulky organyl groups are bound to the boron atom or if the boron atom is part of a ring system. In case of catecholate no H2B(OR)(2)(-) anions were detected but for ephedrino or dithiolato ligands the corresponding dihydrido berate complexes were readily detected by B-11-NMR but the latter converted in THF solution into B(S2R')(2) anions. MO calculations show that the ligand redistribution for H2BX2- ions into BH4- and BX4- becomes thermodynamically more favored with increasing electronegativity of the substituent X. Characterization of the new hydride berate species is usuallyunambiguous, but 10 shows an anomalous temperature dependent behavior in THF solution which can be attributed to an equilibrium involving Li(2H, 2O),Li(2H, 3O), and Li(3O) structural units. This is supported by the X-ray structure of dimeric 10(. )THF and monomeric 10(. )THF(. )TMEDA. While 9(.)3THF is monomeric and contains doubly bridging H2B groups all other dihydrido diorganyl berates are dinuclear. The interaction between the alkali metal center and the boron bonded H atoms depends on number and size of the auxiliary ligands. 'Agostic' Li . . .H-C interactions play a role if P-H atoms are present and when the alkali metal cation is not coordinatively saturated bythe auxiliary ligand and the H(B) hydrogens. The most symmetric and so farunique arrangement is found for [6a . 2THF](2) where all four H(B) hydrogens form Li . . .H . . . Li bridges. Also lithium bis(dithiocatecholato)berate, 17(.)2 THF is dimeric. Its Li centers are coordinated by four sulfur and two oxygen atoms. These atoms form a double heterocubane structure with two diametral edges missing. (C) 2000 Elsevier Science B.V. All rights reserved.

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Documento generato il 20/09/20 alle ore 04:35:24