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2 u 1 Method for Preparation of Dialkyl Tellurium and Dialkyl 1 P 0555
Selenium This invention relates to a method for the preparation of dialkyl of the Group VI metals tellurium and selenium.
The metals Tellurium and Selenium are of importance in semiconductor technology, for example in the preparation of the infra red detector material cadmium mercury telluride (CMT) and in light sensing switches respectively.
It is well known that the presence of impurities in semiconductor materials is extremely undesirable. It is therefore useful to be able to prepare semiconductor materials and chemical precursors used in their manufacture in a high degree of purity.
An important series of such chemical precursors is the alkyls of the relevant semiconductor material, which can relatively easily be thermally dissociated to form an epitaxial layer of the material or a layer containing the material. Such alkyls have the additional advantage that they are otherwise relatively stable and may be purified further via the formation of adducts with for example lewis base adjuvants such as trialkyl or triaryl Group V compounds.
The formation of various addjucts for semiconductor purifi cation is described for example in GB 850955-A, together with a method for preparation of Group II metal alkyls. The preparation of other alkyls can present problems, and in particular the prep aration of the Group VI alkyls such as those of tellurium and selenium in a pure state has until now presented great difficulty.
At present'. methods for preparation of tellurium alkyls are known. Synthetic Communications 12(3), (1982), 163-165 describes a method for preparation of dialkyl ditellurium by reaction of the corresponding lithium alkyl and elemental tellurium in THF with atmospheric oxidation, tellurium dialkyl not being formed. Similarly J. Organometallic Chemistry 255, (1983), 61-70 describes 30 the preparation of mixtures of tellurium dialkyls and ditellurium dialkyls by reaction of the corresponding Grignard reagent RMgC1 with tellurium IV chloride. This reaction is believed to result in contamination of the product with RTeCl. The present invention seeks to overcome or alleviate the 35 problems outlined above by providing a method for the preparation of n.-) -- r.. 1 -0 2 dialkyls of tellurium and selenium in a substantially more pure state, or at least in a state that facilitates further purification. Other objects and advantages of the present invention will be apparent from the following description.
According to the present invention a method for the preparation of dialkyl tellurium or dialkyl selenium comprises reacting either elemental tellurium or elemental selenium, or a tellurium IV or selenium IV halide with a Group I metal alkyl in a solvent which is or contains at least one C'4-CIO aliphatic ether, and optionally 10 also contains a. liouic. alkane.
The reaction is preferably carried out under conditions which exclude atmospheric oxygen, for example under an inert atmosphere eg nitrogen. Oxidation by the atmosphere can result in impurities.
A preferred temperature is below 200C, especially -40 0 C to 0 0 C. Above room temperature impurities may be formed, such as neohexyl Group I metal alkyls.
The method is suitable for the preparation of all dialkyls, but is especially suitable for the preparation of di- C., - C4 alk-yis of tellurium and selenium, which may be straight chain, branched or t r--um an seleniun '- tertiary alkyls, --!-r eZa7;rz, le -1, e 11 I methyl, dietbyl.
n- 4--c-1 o-- -buty! -i-. Irzo- s-ri ter'u.-', tellurium anl i-ter+.
;1 - .e Group IT -!iet--1 i,- -Dre.e--ably lithium, so..Ii.1 or pot.. ssium., - - - e,v -1 rre-1 C-rou-, i -metr-l aU- ls a-( there'ore MeLar.' + the el.hic.:1 is a dii- C C alkyl ether, especialiy a ether. The alkyl z--ou-Ds o' the di-.-n-lkyl or- d-'n-alkvl ether Pay be It. e 5a-rie or.1i-ferent an'. a wt-ticularly -Dre'--r--e.' e-ther ic lethyl ether. ether- is/are used, it/lthey shoul. -Dre'e---?.bly have a. lo.. boi-'--n-Doint.
T an PliF.n-- is -Dresent it muEt te lij.ui a' the reaction temp- erature, suitable alka,-ie..- inclu-- n-jentane.
"he, n a 1ra-lide o- the Grour, VI element is use:! it is preferably Lhe cl- lorii-e. eR or- SeIV) k 4.
POO (WALITY 3 k Y1 0 IL 1 il The reaction is preferably carried out using about stoichiometric quantities of the reactants. Preferably the Group I metal alkyl is dissolved in the alkane, and this solution is added slowly to the element or halide suspended or dissolved in the ether. Following reaction the mixture may be stood at room temperature or refluxed if necessary to ensure completion. The solution of the dialkyl product may be separated from solid residues by filtration. Excess Group I alkyl may be destroyed by adding water. The tellurium or selenium dialkyl may then be isolated by evaporation of the solvent followed by vacuum distillation.
The method of the invention provides dialkyls of tellurium or selenium suitable for use in semiconductor formation, eg in epitaxial deposition. It may however be preferable in some cases to further purify the dialkyls by the known process of secondary adduct formation to produce an adduct with a lower dissociation temperature than that of the dialkyl itself at the pressure of secondary adduct dissociation. Other known further purification methods may be used.
-.1 invention The 'V11 us4-n,- the methe'. c, t-his - elso constitutle -. novel 1 beinr- in _ -enerall -nirer form. tillia,-i hi-. been h',-)ei.too av,-.- L1-3.ble using '-novn -p.re7,p-r--.'Uion -.r7ocess(,s. invention wil- now be '--czc-ibe--l by wa, 1 o example on-ly note: in r.i-.ent P-bl,revi-a-tiioyis- '.e = meth,.r2-, ii-t = et'- OU -1 V1 ri:r, P- 1,11 -- - 1:.
I'- = an -Su = 1, 4 EXAMPLE 1
Synthesis of di-tert-butyl telliii-iulr. fro,-i =1 -- ra'l i,- a.T2 t-Bu-. in 1---.
_,,_-Le,.en' 1 C -L __--- __ - - - 2'- A solution of tert-butyllithium (450 cu?, 1.7 moles dm-3) in pentane was added dropwise to an ethereal suspension (300 ca?) of elemental tellurium (90 g, 0.70 g atom) maintained at -40-OOC over a period of 5h. An exothermic reaction occurred and the reaction mixture was stirred for lh after the complete addition, and was then refluxed for 2h. The deep yellow ether-pentane solution of di-tertbutyl tellurium was isolated from excess tellurium and the resulting lithium telluride by.filtration. Water was added to destroy any excess tert-butyl lithium. The ether-pentane solution of di-tert- butyl tellurium was separated, dried over anhydrous calcium chloride and, after filtration, diethyl ether and pentane were removed in vacuo. The resulting deep yellow oil was purified by vacuum distillation over calcium hydride. Overall yield = 49%.
Preparation of Di-tert-butyl tellurium from t-m7--u'i in It 9- -e Lrach V) an- 1; A solution of tert-butyllithium (830 cff?, 1.7 moles dm-3) in pentane was added dropwise to an ethereal solution of tellurium(IV) chloride (100 g, 0.37 g moles) at OOC over 6h. An exothermic reaction occurred and the reaction mixture was stirred for lh after the complete addition, and was then refluxed for 2h. The pale yellow ether-pentane solution of di-tert- butyl-tellurium was isolated from the resulting lithium chloride by filtration. Water was added to destroy any excess tert-butyl-lithium. The ether pentane solution of di-tert-butyltellurium was separated, dried over anhydrous calcium chloride and after filtration, diethyl ether and pentane were removed in vacuo. The resulting deep yellow oil was purified by vacuum distillation over calcium hydride. Overall yield = 620/a.
W t U t W f EXAMPLE 3 Synthesis of dimethyltelluride from elemental tellurium - - c-"-vI lithium in I'M P. n.-,-n,. - - -20.
To a grey suspension of elemental tellurium (27.11 g, 0.2124 g atom) in diethyl ether (150 cu?) maintained at temperature between -40- OOC was added a pentane solution of methyllithium (140 cm 3, 1.5 moles dM 3) dropwise over a period of 2h. An exothermic reaction was found to occur. When the addition of methyllithium was complete the reaction mixture was brought to room under a gentle reflux for a further 2h. this stage consisted of a red supernatant amorphous residue. The red supernatant the white residue by filtration and was water (50 cu?) to destroy any unreacted solution was isolated from the aqueous 1 calcium chloride, and after filtration, were removed by fractional distillation dry nitrogen. The dimethyltelluride was 83-840C) and the resulting yellow oil was distillation (overall yield = 85%).
temperature and was heated The reaction product at solution and a white solution was isolated from then treated with distilled methyllithium. The ethereal ayer dried over anhydrous diethyl ether and pentane at 1 atmos. pressure under distilled at 1 atm (B.P. purified by vac um 6 -Dreik-ration o' i=.lkyl tellurium or -ialkyl I. A ietho or the selenium clu---acte-4lsp-' by reacting either ele-;ie-i.'IC-.1 te'-'1-, iriu-,,n oe" e. % 1 m e ntal selenium, or a telluriu-,ri (Ilr) 1-alidle or Eelen--u-.,,i (IV) a Group JT in a solvent whic-1 Is or con-;---ns Wi+1. -/ Me-'%,C-:Ll;-:'-IK7jl 1- 1 L_- - ea 'io _t one al-r,,at-c ether aniL ont- nally also contains a 2. A metho accor.!!--i,- to claip 1 ch,----rac,,te::-sed in ti;-:t the clialkyl tellurium cr selleen uz is 2 -1, f L U0 C14. alkyl -in 'a' d! ih method-:-c-cor &. tc claim 2 characterisel in th L.--ter, - h - ' - --- W.'k_i i-ne- =. ace-,.,-ii--ir to cha-racterir-z,'i In th-lt.
to clain 1 characterise in. that thr C ur.-rir ) or o -1. 1.1 IS the c-,,lori"e.
to Pn-Y o - -- 1 1.. - -- - ---C4. - - -!: 4 "' U71.
e-it-e th7- tl.e-;ro,,-,) i) --iet7- E.E.2-UT c- s o"--.
in tn:t the Grour A iet-o- <--cco--i,-1,t:- to cirin- A z-ccor-lin-r-- to claim Q characterise- in that the mt 2 e alk-1 or -.)otL<-Lz,siu-n -,.ne-Lth-kr-, --t'n,, _1 -1 1 in tY.-.r-t tne Grow A e', o a: c c or ng t o c! i 7, 1 or nethyllithium.
is -- m A to 1 characterise- in 'Ulkit the solvent i ' al r --a - v c th em.
i -netho- 'c, 10 ch-.rF,te-,--e, In that the solvent -- 1, - - 11 is '-eth.,, ether.
j A - 1 L, 1 im 1 char--c'e,-is--e' in that the ree-c-ion m rctho-1 accorilin- to cla- is cut un'e- con,5tio.c: which excluie a-';lmo--pheri-c ox-ei -1 n 3 -- z, V.. - - :..e' Lhe -ietlic' to ' chara-tnrised 2n 'li-it the -eactio- -1 L, 1. -. -1 L L, 1 on't- be'Lo.- 2^02.
1 o., 5- cmrr.,5e-- out at -'-0 -- to ^i --- 1 it POOR QUALITy 1 ú:.,, method accorlin,fT to clalm 1 character! e-e ', in that i te-,-'-bu.L'. ', t tion o -riUP. -!- y the reac L.-'-]U is prepare - L- - elementil at C.c,', in a r-:olverit that 1-1-etl-,,il etilhe:
E ccor-ll-- to clain 1 cli--rac'Leris.e-1 in that rli- A m. e t - 7 tert-butyl tel.luriu.r.1 is prepared bv the -reic-.'--5on c' t-Bu--- - 0 ' _].j;rjU,T1 (TV, tetrE ci-lcrc'---1 \_):A a temperatUre ^belo,,.., 20 -' in a solvent ivz.t coatainR iiethrl ether 17 A netho - accor.l-np, to claim 1 characterise-- in that i methyll tellurium. is -Dre-Eare--'. bv the reaction o-" meth,-llithium with element-1 a 're'oq 2,3 C in a t of or --eleniun when -Dre-Da--e- br -,roces J -Loan.,,,, ore o claims 1, 22. ' 1'. 15. 14- 17.
P()01k (LUALITY Published 1989 at The Patent Office, State House, 66 71 High HOlborn, London WClR 4TP. Further copies may be obtained from The Patentofftce. - Balas Branch, St Mar7 Cray, Orpington. Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con- 1197 -,---u uy Davuraplex technicues ltd. St M-- rl--,- ---- --,--