Gallane, adducts

Structural Trends within Alane and Gallane Adducts... 

Figure 42 Structures of the dimeric amine-gallane adduct 510 and the aminogallane 511.

Figure 51 Structures of the water-gallane adduct 762 and two gallium hydroxides 828 and 836.

Table 6.2 P-NMR resonances and coordination chemical shift values for phosphane chloro-gallane adducts...

The reaction between a Lewis acid R3M and a Lewis base ER3, usually resulting in the formation of a Lewis acid-base adduct R3M—ER3, is of fundamental interest in main group chemistry. Numerous experiments, in particular reactions of alane and gallane MH3 with amines and phosphines ER3, have been performed [14]. Several general coordination modes, as summarized in Fig. 2, have been identified by X-ray diffraction. 

In contrast to these trends observed for the stibine adducts, the H-NMR spectra of the bismuthine adducts R3M—BiR without exception show almost the same chemical shifts due to the organic groups as the starting trialkylalanes, -gallanes and -bismuthines, again indicating very weak acid-base interactions in solution. 

These particular properties of chloroalanes favor the formation of simple Lewis acid-base adducts, as was observed for the reaction of R2AICI with Sb(Tms)3 (R = Et, f-Bu). In contrast, reactions of the analogous gallanes and indanes yielded the desired heterocycles. The same tendencies were observed in reactions of R2MCI (M = Al, Ga, In R = Et, i-Bu) with P(Tms)3 and As(Tms)3. The gallane and indane react under formation of the expected M—E heterocycles [71], while the corresponding alanes yield the simple adducts... 

Group 13/15 compounds have a long-standing history in inorganic chemistry and have been known for almost two centuries. First reports on such compounds go back to 1809, when Gay Lussac synthesized F3B4—NH3,1 the historical prototype of a Lewis acid-base adduct, by reaction of BF3 and NH3. Since this initial study, numerous Lewis acid-base adducts of boranes, alanes, gallanes and indanes MX3, MF13 and MR3 (M = B, Al, Ga, In X = F, Cl, Br, I R = alkyl, aryl) of the type R3M <- ER 3 (E = N, P, As) (Type A) have been synthesized and... 

However, these trends, which cannot provide an absolute scale for Lewis acidity and basicity, do not necessarily allow predictions of what kind of adducts will be formed.18 Gallane GaH3 for instance forms more stable adducts with phosphines than with amines. Consequently, reactions between H3Ga-<— NMe3 and tertiary phosphines PR3 yield the corresponding phosphine adducts. In sharp contrast, A1H3 forms significantly more stable adducts with amines than phosphines.19... 

Selected Bonding Parameters [pm, ° TABLE VII ] of Borane, Gallane and Indane Stibine Adducts R3M - SbRj ... 

In contrast to these trends observed for borane-stibine adducts, the M-Sb bond lengths of alane-, gallane- and indane-stibine adducts are significantly elongated compared to the sum of the covalent radii (J>cov(AlSb) 266 J>cov(GaSb) 267 J>cov(InSb) 285 pm),48 as is expected for dative bonds. 

H3A1 NMe3,53 whose structure has been determined by X-ray diffraction.54 Since these initial studies, comparable reactions were observed for alanes, gallanes and indanes R3M (M = Al, Ga, In R = H, halogen) with amines and phosphines, yielding bis-amine, bis-phosphine and mixed amine/ phosphine adducts. Figure 13 presents the different coordination modes that have been observed so far. 

As already was observed for hypercoordinated adducts MX3(ER 3)2, no stibine and bismuthine adducts of low-valent alanes, gallanes or indanes have been prepared, to date. According to the lability of low-valent group 13 compounds toward disproportionation into M(III) and elemental M, stibines and bismuthines are expected to be too weak as Lewis bases, preventing them from the stabilization of such compounds. 

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