Reversible binding of Lewis bases to aluminum and gallium aryloxides

[摘要] The reaction of M(tBu)3 (M = Al, Ga) and hydroquinone in a non-coordinating solvent yields the metal aryloxide polymer, [{( tBu)2M}2(mu-OC6H4O)] n. The gallium aryloxide polymer reacts with pyridines, via both a solution and a solid/vapor reaction, to yield the yellow compound [(tBu) 2Ga(L)]2(mu-OC6H4O) [L = pyridine, 4-Mepy, and 3,5-Me2py] via cleavage of the Ga2O 2 dimeric core. The thermolysis in the solid state results in the loss of the Lewis base and the formation of [{(tBu)2Ga} 2(mu-OC6H4O)]n. The DeltaH‡ and DeltaS‡ for the solid/vapor reactions have been determined. The inter-conversion of polymer to the pyridine complexes, and the reverse reactions, have been followed by 13C CPMAS NMR spectroscopy, TG/DTA, SEM, EDX, and powder XRD. Insight into the solid state mechanism of this polycondensation polymerization reaction may be gained from the single crystal X-ray crystallographic packing diagrams of the pyridine complexes. The aluminum aryloxide polymer reacts with Lewis bases to yield the compound [(tBu)2Al)L)]2([mu-OC6H 4O) [L = py, 3,5-Me2py, and THF] via cleavage of the Al 2O2 dimeric core. Unlike their gallium-pyridine analogs, these compounds do not undergo a clean dissociation to [{(tBu) 2Al}2(mu-OC6H4O)]n in the solid state. But they react by a solid/vapor reaction with solid Lewis bases to form colorful polymers of [{(tBu)2Al} 2(mu-OC6H4O)(mu-L)]n, where L = pyrazine, 4,4-bipyridine, and 1,4-benzoquinone. The formation of these compounds has been comfirmed by 13C CPMAS, 27Al MAS, and solution 1H NMR. The reaction between [(tBu)2Al(mu-OPh)] 2 and 4,4-bipyridine in toluene or CH2Cl2 yields [(tBu)2Al(OPh)]2(mu-4,4-bipy). In CDCl 3, [(tBu)2Al(OPh)]2(mu-4,4-bipy) dissociates forming [(tBu)2Al(OPh)(mu-4,4-bipy)], [(tBu)2Al(mu-OPh)]2, and uncoordinated 4,4-bipyridine. Based on equilibrium data, we have found that for [( tBu)2Al(OPh)]2(mu-4,4-bipy) one aluminum center electronically ;;communicates;; to the second aluminum center by deactivating the nitrogen nine bonds away from the first aluminum center making one Al-N bond stronger than the other. The reaction of [Ga2(tBu)4(neol-H) 2] (neol-H2 = 2,2-dimethylpropane-1,3-diol) with TiCl 4, ZrCl4, or VCl4 in the presence of proton sponge [C10H6(NMe2)2] yields [( tBu)GaCl3][C10H6(NMe 2)2H]. The reaction of [Ga2(tBu) 4(neol-H)2] with M(NMe2)4 (M = Ti, Zr) yields [(tBu)2Ga(mu-NMe2)] 2 along with multiple transition metal containing products. The reaction of CpTi(NMe2)3 with [(tBu)2Ga(neol-H)] 2 yields [(tBu)2Ga(neol)2TiCp] and [(tBu)2Ga(mu-NMe2)]2.

[发布机构] Rice University