Recoil 31Si atom reactions with PF3 resulted in the formation of both singlet and triplet 31SiF2 in the ratio of 1.0:3.3. Singlet 3'SiFz reacted with 1,3-butadiene to give difl~orosilacyclopent-3-ene-~~Si, but triplet 31SiFz only gave this product in the presence of paramagnetic molecules such as NO, NO2, or 0 2 .The nuclear recoil technique1-* and the thermal vaporization method9-lS account for all the silicon atom reactions studied to date. Both processes have also been proven to be very effective in generating silicon analogues of carbenes. Using the nuclear recoil method of formation, silylene, SiH2, has been shown to undergo Si-H2-6 and possibly Si-Si bond i n s e r t i~n .~ Both singlet and triplet SiHz also add to 1,3-butadiene, giving s i I a~y c I o p e n t -3 -e n e .~~~ On the other hand, silicon difluoride, the best characterized carbene analogue, has been extensively studied by Margrave and co-workers employing the thermal vaporization method through the following formation I Si + SiF, -2SiFi(1) Spectroscopic evidence indicates that SiF2 possesses a singlet ground electronic stateI2 with a bond angle of 100' 59'.13 It is extraordinarily stable having a half-life a t 0.1 Torr of 150 s. Even in the presence of 1 Torr of oxygen, its half-life is still 6 s.I4 However, in the majority of cocondensation studies where the SiFz thus formed is allowed to react with other substrates, the products always contained a dimeric unit of SiF2, indicating that dimerization predominates whenever SiF2 is in high concent ration.ZSiF, -(SiFJ2Accordingly, in the study of SiF2 reactions with 1,3-butadiene, Thompson and Margravels have found that the major product formed was 1, I ,2,2-tetrafluorodisilacyclohex-4-ene.Using the nuclear recoil method by employing the transmutation, 3'P(n,p))'Si, we have found that energetic 3iSi abstracts fluorine atoms from PF3 yielding 31SiF2. Due to its extremely low concentration, the 31SiF2 thus formed reacts with 1,3-butadiene in its monomeric form to give difluorosila~yclopent-3-ene-~~Si (DFSCP*).'
(4)In the present work, we have studied the effect of seven inorganic and organic additives on the yield of DFSCP* from eq 4. From these studies, the possible existence of the previously unknown triplet 31SiF2 has been deduced.lb Such experiments also reveal certain interesting chemical properties of both singlet and triplet silicon difluoride.
Experimental SectionGeneral Procedure. The general procedure used in this study was the same as that used in other typical nuclear recoil experiments.I6 Phosphorus trifluoride and 1,3-butadiene along with other desired additives were sealed in Pyrex bulbs using high vacuum techniques. Sample analysis was performed using standard radio-gas chromatography.I6Silicon-31 from the 3'P(n,p)31Si nuclear transmutation3 was formed using fast neutrons from twodifferent sources. ( 1 ) A 16-or 20-MeV deuteron beam from the Texas A&M University cyclotron was focused on a beryllium target initiating the nuclear transformation, gBe(d,n)loB. (2) Fast neutrons from a Tri...