Convenient Routes to Di‐tert‐butylsilanediyl: Chemical, Thermal and Photochemical Generation

Abstract

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.

Silver‐Catalyzed Silylene Transfer

“…Strongly reducing conditions [Li(0) and t-Bu 2 SiCl 2 ] are needed to access the requisite lithium silylenoid (57). 67 Alternatively, free silylene 60 could be generated thermally or photochemically from cyclic silanes, such as 58 or 59. 12j,68-73 Each of these methods, however, limited the functionality that could be introduced on the silacyclopropane.…”

Silylenes

“…An important step forward was made by Boudjouk and coworkers when they found that bulky substituents (such as t-butyl) on silicon increased the stability of the silirane without preventing its thermolysis (equation 35) 56 . To explain the formation of the expected product of insertion into the H Si bond of HSiEt 3 in similar yields from different precursors, it was suggested that t-Bu 2 Si • • also arises by ultrasound-promoted lithio-dehalogenation of t-Bu 2 SiX 2 (X D Cl, Br, I); see also Section II.E.…”

“…Another conceivable, but probably less likely, explanation of these experimental results 56 is that the triethylsilane somehow catalyzes the decomposition of silylenoid into free silylene, which can then insert into the Si H bond. In any case, the intermediacy of silylenes in˛-dehalogenations remains an open question, worthy of further study.…”

Theoretical Studies on the Alkylidene Silylenoid H2C = SiLiF and Its Insertion Reaction with R-H (R = F, OH, NH2)

“…5,6 Since then people tried to detect, even to obtain some silylenoid species as well as to probe into their structures and properties. [7][8][9][10][11][12][13] However, as a kind of very reactive species, the preparation of silylenoids is very difficult. Until 1995, Tamao et al 14 reported the first experimental study of silylenoid chemistry, detected the existence of [(tert-butoxy)diphenylsilyl]lithium, Ph2SiLi(OBu-t), and investigated its chemical properties.…”