141 Crystal structure analysis of (Et4N),. 7 . C H X N (the values in brackets represent results of a structure determination on a second data set obtained from an independently grown new crystal): a = 16.557(!) [16.563(4)], b = 18.915(6) [18.879(6)], C = 17.110(6) [17.108(5)] A, a = / f = y = 9 0 " ; space group, Pbcm, 2 = 4 , pCalcd=1.35 g cm-,, pl,hu,= 1.40 g cm-,, p=12.9 cm-', 2Q,,,=4O0 (MoKa, L=O.71069A); 2620 unique reflections; used in refinement with F~z > 3 u ( F~) : 1290 [1376]; parameters 198. Final R=0.0699 I0.07331, R, =0.0647 10.06891. The low number of observed reflections for both data sets is due to the fact that crystals of high crystallographic quality could not be isolated. This problem, coupled with positional disorders encountered with two of the three [Et4N]" cations, accounts for the rather high temperature factors obtained for some of the carbon atoms. Further details of the crystal structure investigation are available on request from the Fachinformationszentrum Energie, Physik, Mathematik GmbH, D-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-53 196, the names of the authors, and the journal citation. [IS] H. Beinert, A. Dedicated to Professor Hans Bock on the occasion of his 60th birthdayAlthough the chemistry of the silanediyls is well developed and of continuing interest,"] there are few convenient methods for generating these species on a preparative scale. We had need for a variety of methods for making di-rert-butylsilanediyl (2) and in this communication we report three convenient routes for generating this intermediate, possibly in a complexed form like 8, in high yields.'21 2 has been proposed as a product of the photolyses of hexa-tert-butylcy~lotrisilane~~~ and di-tert-butylsilyldi-a~i d e . '~] We have found [Eqn. (a)] that when di-tert-butyl-dichlorosilane ( l a ) and lithium in T H F in the presence of excess of triethylsilane, were irradiated with ultrasonic waves using an ultrasonic cleaning bath, the di-tert-butylsilanediyl insertion product l,l,l-triethyl-2,2-di-tert-butyldisilane (3) was isolated in 60% yield.[51 The same product was obtained in comparable yields from l b and l c . This is the first example of a metal-promoted a-elimination of dihalosilanes on a preparative scale. tBu2SiX2 + Li a [tBu,Si:] E13S'H * Et,Si-SiHtBu2 (a) l a , X = C1 2 Ib, X = Br lc, x = 1 3We have investigated the reactions of l a and lithium with other trapping agents and in the absence of a quenching agent. With trans-butene for example, 1,l-di-tert-butyltrans-2,3-dimethylsilirane (4), was isolated in 65-70% yield. None of the cis isomer was detected by gas chromatography. When cis-butene was used as a trap, 1,l-di-tertbutyl-cis-2,3-dimethylsilirane was also isolated in 65-70% yield.16] A small amount (< 5%) of 4 was detected along with 5 but was understood to arise from the presence of 2-5% trans-butene in our samples of cis-butene.
