Zinc Bis (Amide) Compounds Evaluated as Designed Precursors for Site-Selective P-type Doping of ZnSe
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117 Mat. Res. Soc. Symp. Proc. Vol. 415 0 1996 Materials Research Society
synthesis was completed by addition of one equivalent of triethylchlorosilane (eq. 2). The deprotonation of the alkyl-trialkylsilylamine was accomplished with n-butyl lithium (eq. 3). Synthesis of the compounds with the general formula Zn[N(R)(R')] 2 is completed by a salt elimination reaction between one equivalent of zinc dichloride and two equivalents of the alkali metal alkyl-trialkylsilylamide (eq. 4). > LiN(H)R + BuH H 2NR + n-BuLi -----
(1)
> HN(R)(Si(CH 2 CH 3)3) + LiCl LiN(H)R + ClSi(CH 2 CH 3)3-----
(2)
> LiN(R)(Si(CH2 CH 3)3) + BuH HN(R)(Si(CH 2 CH 3)3) + n-BuLi -----
(3)
> Zn[N(R)(Si(CH 2CH 3)312 + 2 LiCl (4) 2 LiN(R)(Si(CH 2CH 3)3 ) + ZnCI2 ----R = n-Pr, i-Pr, n-Bu, i-Bu, s-Bu, t-Bu, c-Hex, Ph To increase the electronic stabilization while probing the effect of symmetry on vapor pressure, unsymmetrical bis(trialkylsilyl)amide ligands were synthesized. Primary trialkylsilylamines were formed by addition of excess ammonia to a stirred solution of trialkylsilylchloride (eq 5). Further reaction of the generated primary trialkylsilylamines with one equivalent of n-butyl lithium at -78 C produced the alkali metal trialkylsilylamides (eq 6) which were reacted with one equivalent of a different zinc of the the synthesis To complete (eq 7). trialkylsilylchloride bis(bis(trialkylsilyl)amide) compounds, the secondary amine was deprotonated with n-butyl lithium (eq 8), followed by salt elimination between zinc dichloride and the alkali metal bis(trialkylsilyl)amide in a 1:2 ratio (eq 9). > NH 2Si(CH 2CH 3) 3 + NH 4Cl NH 3(xs) + ClSi(CH 2CH 3)3 -----
(5)
NH 2Si(CH 2CH 3)3 + n-BuLi ----- > LiN(H)(Si(CH 2CH 3)3) + BuH
(6)
.... > HN(Si(CH 2CH 3)3 (R') + LiC1
(7)
LiN(H)(Si(CH2 CH3 )3 )
+
C1R' -
> LiN(Si(CH 2CH 3)3)(R') + BuH HN(Si(CH 2CH 3)3)(R') + n-BuLi -----
(8)
> Zn[N(Si(CH 2CH 3)3)(R')] 2 + 2LiCl 2 LiN(Si(CH 2CH 3)3)(R') + ZnC12 .----
(9)
R = dimethylsilyl (DMS), TMS, TES, tert-butyldimethylsilyl (TBDMS) RESULTS AND DISCUSSION Although it is a risky proposition to attempt to extract thermal mechanistic information involving vapor phase species from mass spectral data alone, useful trends may emerge from an exploration of a related series of compounds. Therefore, it is not our ultimate
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purpose to propose gas phase bond dissociation energy values from electron ionization data, rather to gain insight into the relative stability of selected examples of an overall compound matrix. The products isolated from the reaction sequence above (eq. 4) each are distillible viscous liquids (R = n-Pr, i-Pr, n-Bu, i-Bu, s-Bu, t-Bu, c-Hex). The utility of the designed precursor can be evaluated through analyzing the thermal decomposition mechanisms. The new series of compounds exhibit decompostion pathways quite similar to the previously reported zinc bis(alkyltrimethylsilylamide) compounds."I Investigations into the thermal decomposition mechanisms of the homoleptic zinc bis(alkyltrialkylsilylamide) compounds have shown no direct e
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