(tert‐Butoxy)aluminium and ‐gallium Hydrides

Abstract

The crystal structures obtained by X-ray methods of (tertbutoxy)alane and -gallane (tBuOMH2) are isotypic and are composed of discrete centrosymmetric dimers. The dimers !rise from almost symmetrical Al-0-A1 [1.810(3), 1.815 (3) A] and Ga-0-Ga [1.902(9), 1.908(9) A] bridges forming a central rhombohedra1 four membered M202 cycle [ 0 -A l -0 81.0(2)', 0 -G a -0 ?8.6(5)'] with the metallic atoms in a distorted tetrahedral environment. When one of the hydride ligands on the metals is further substituted by tert-butoxy, Very recently the synthesis and crystal structure determination of bis(tert-buty1)methoxyalane (tBu2HC-0-AlH2) and the corresponding gallane were described['? We have independently studied quite similar compounds. Our intention has been to "bridge" the structural gap between AlH3r21 and AI(O~BU), [~] with the missing mixed compounds, e.g. tBuOAlH, and (tBuO),AlH, and to examine the homologous gallium compounds. We were interested in the structures of these compounds because we had used them in CVD processes [4]. A profound synthetic work on the aluminium compounds has already been published in 1968 by Noth and Suchyf51, and some predictions of structures were made on the basis of IR spectroscopy and molecular weight determinations.The synthesis of the compounds tBuOMH, and (tBuO),MH (M = Al, Ga) was achieved by alcoholysis of diethyl ether solutions of alane and gallanef51 [equation (l)].The correct stoichiometry of the reaction is important for obtaining the desired products and the yields have been very satisfactory. The products were isolated by sublimation and crystallization. tBuOAIHz and tBuOGaHz show very simple NMR spectra in solution: in the 'H-NMR spectrum, the tert-butyl group exhibits a singlet, and in the 13C-NMR spectrum two lines for the pnmary and quaternary carbon atoms are detected. The 'H and I3C-NMR spectra of (tBuO),AlH and (tBuO),GaH are much more complex. In each case two sets of two signals of equal intensity were found that can be attributed to four chemically different tert-butyl groups. In the aluminium denvative, the ratio of the sets of signals is approximately 45:55, whereas it is 33:66 in the case of gallium derivative. We tentatively ascribed the four signals in the 'H-NMR spectra to a mixture of cis and trans isomers [cis and trans refer to the position of the hydrides with respect to the M202 central ring (see structure below)]. The trans isomer presumably leads to higher intensities. The chemical shifts of the signals change with the temperature of the formation of (tBuO),AlH and (tBu0) the NMR probe, but no changes of the intensities or a coalescence phenomenon have been All four compounds are dimeric in benzene, as found by cryoscopy.The data for the X-ray structure determination on single crystals of tBuOMH, and (tBuO),MH (M = Al, Ga) have been assembled in Table 1; the most important bond lengths and angles are summarized in Table 2t7]. As a result of the structure analyses, the molecule tBuOAIHz (tBuOGaH, is isotypic) has been depicted in Figure 1, and the mol...

Oxidative Addition Reactions of Element–Hydrogen Bonds with Different Polarities to a Gallium(I) Compound

“…Compared to other gallium hydrides, this covers the whole known shift range. [21,22,30,[34][35][36][37] The trend in the series of compounds 2-6 shows a shift to lower frequencies with increasing electronegativity of X. Consequently, 2, with the electropositive tin atom connected to gallium, has the most deshielded Ga À H. Formally, the gallium atom has reversed polarity.…”

Metal centered molecules and their application in chemistry and physics

“…When we did the X-ray diffraction studies on single crystals of the molecules [(tBuOAlH 2 )] 2 and [(tBuO) 2 AlH] 2 we realized that H. Nöth and coworkers had prepared one of these compounds several years before [46]. From our structural studies we could conclude that the dimers have a Al 2 O 2 four-membered cycle in common [47]. We also prepared the deuterated compound [tBuOAlD 2 ] 2 .…”

β‐Diketiminate Gallium Amides: Useful Synthons in Gallium Chemistry

“…It is noteworthy that compound 8 is the first gallium compound containing two terminal ethoxy groups. Up to now, only [{(Me 3 Si) 3 Si}(EtO)Ga(µ-OEt)] 2 , [22] [(tBuO)HGa(µ-OtBu)] 2 , [23] Ga(OtBu) 3 NHMe 2 , [24] Ga[(µ-OiPr) 2 Ga(OiPr) 2 ] 3 , [24] Ga[OCH(CF 3 ) 2 ] 3 (4-Me 2 Npy) (py = pyridine), [25] Ga[OCMe 2 CF 3 ] 3 (4-Me 2 Npy), [25] and [Ga(µ-OCMe 2 Et)(OCMe 2 Et) 2 ] 2 [24] have been reported to contain at least one terminal alkoxide group. The only other compounds containing nonbridging Ga-O(alkyl) bonds are stabilized against oligomerization by the presence of donor groups that fill vacant coordination sites of the gallium atom and can lead to an increase in the coordination number for gallium to 5 or 6.…”