July 5 , 1964
1,1,2-TRIPHENYL-1-SILACYCLOBUTANE AND
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-PENTANE
Recrystallization of 2.28 g . of the "crude" ester from 80 ml. of hot methanol a: rapidly as possible gives 1.16 g. (527' yield) of yellow ester. LVith 105' preheat and a heating rate of 6"/min. the ester sinters a t 116" and melts a t 118-120' with gas evolution. When heated from room temperature a t a rate of 14'/rnin., the m . p . is 112-113". Anrii.31 Calcd. for C,HpSnOl: C, 48.98; H , 4.11; N , 14.28. Found: C , 19.11; H , 4.06; li,14.62. Thc recrystallized ester, when kept a t -78" for 4 months, shows no change in m . p . When held a t 25' for a month in the light (or dark) in Pyrex, soft glass or plastic vials, the m . p . falls about tlircc degrees. The n.m.r. spectrum of a deuteriochloroform solution of the recrystallized ester exhibits, in addition to the aromatic hydrogen peaks ( a doublet a t 8.25 and a doublet a t 8.00 a), a lone vinyl singlet a t 7.20 and a lone methoxy hydrogen singlet a t 3.88 6 . Thus only the predominant isomer is present. The peak areas of the aromatic, vinyl, and methoxy hydrogcris are in the expected 4 : 1 . 3 ratio, respectively. The solution was kept a t c u . 24' and the n.m.r. spectrum recorded a t frequent intervals; one-half of the predominant isomer remains after 5 days, and only after 15 days has it completely decomposed. Method B.-In the procedure referred to in footnote 14, a solution of the sodium salt of pnitrophenylnitromethane in D M F is treated with ethereal diazomethane and then 1 equiv. of fluoroboric acid is added dropwise a t 0'. Nitrogen evolves as fast as the acid is added. The D M F is largely removed by vacuum evaporation a t 20" and the resulting sirup is taken u p in benzene, washed with water, and dried. Removal of the benzene below 35' gives a tan solid which, on recrystallization from methanol, yields the nitronic ester, m . p . 118-120' dec. In retrospect it is clear that D M F is a poor choice for the reaction medium. .I simple procedure for the preparation of m h y drous ~ o l u t i o n sof fluoroboric acid in ethers has recently bpen published32and it irould appear that the use of anhydrous diethyl ether as the reaction medium will enhance the convenience and utility of this method. T h e methyl nitronic ester of p-bromophenylnitromethane was prepared by method A using a reaction time of 4 days. The "crude" methyl ester is a yellow oil (100% yield) which, upon cooling to -80" and then warming t o O o , crystallizes; m.p. 20 to 43" with gas evolution a t about 95". Anal. Caicd. for C&X02Br: C , 41.76; H, 3.50; N, 6.09; Br, 34.74. Found: C, 41.65; H , 3.46; K , 5.95; Br, 34.80. The n . m . r . spectrum of a carbon tetrachloride solution of the "crude" nitronic ester reveals, in addition to aromatic hydrogen peaks, two vinyl hydrogen singlets ( a t 6.90 and 6.72 6 in about a ______
4 : l ratio, respectively) and two methoxy hydrogen singlets (at 3.75 and 3.85 6 in about a 4 : l ratio, respectively). Therefore both stereoisomers are present. The n.m.r. spectrum was recorded a t frequent intervals. One-half of the minor-isomer decomposed in about 1.5 hr., while the half-life of the major isomer was about 2 days. A 1.12-g. sample of the "crude" ester was dissolved in about 8 ml. of methanol a t 2 5 " , filtered t o remove dust, cooled to -60°, and the resulting slurry filtered. After washing with about 5 ml. of cold ( a .-60') methanol, the white, crystalline solid was sucked partially dry in the funnel and then dried in z'acuo a t 25" for about 15 min.; yield 0.10 g . Anal. Calcd. for: C8H8N02Br:C , 41.76; H , 3.50; S ,6.09; Br, 34.74. Found: C, 41.89; H, 3.53; X, 6.36; Br, 35.00. With 50" preheat and a heating rate of So/min. the recrystallized ester sintered a t 65", melted a t 66.5-67.5", and evolved gas above about 100'; lit. m . p . 65",'" 65.5'.1° When the recrystallized nitronic ester was kept a t - 7 8 " , no change in the m . p . occurred after 1 month. When kept a t 24' in a plastic vial, exposed to light, the m.p. drops about a degree in 24 hr. and after 11 days it has fallen t o 60-63". The n.m.r. spectrum in CCI4 shows only one vinyl singlet ( a t 6.90 6 ) and only one methoxy singlet ( a t 3.75 6 ) , in addition to the aromatic hydrogen peaks (two doublets a t 7.46 and 7.71 a). The peak areas of the aromatic, vinyl, and methoxy hydrogens are i n the expected 4 : 1 : 3 ratio, respectively. The n.m.r. spectrum was recorded a t frequent intervals; one-half of this (predominant) isomer remains after about 2 days. The ultraviolet spectrum of the recrystallized nitronic ester in 95% ethanol a t 19" shows XmnX 288 mp ( ~ ~ ~ ~X 3l o. 42) ; 7h s h 299 fnp esti (2.73 X IO4). From the rate of decrease of intensity of the peak a t 285 mp, the half-life of the major isomer of the nitronic ester is ca. 7 days a t 19' in 957' ethanol. 3-Phenyl-1-nitropropane and Diazomethane.--An ice-cold solution of 8.26 g . (50 mmoles) of 3 - p h e n y l - l - n i t r 0 p r o p a n e ~in~ 50 ml. of ether was allowed to stand with 65 mmoles of diazomethane in 190 ml. of dry ether a t 0" (in the dark) for 5 days. The nitro compound was recovered quantitatively (8.40 g , ) and shown by V.P.C.to be contaminated by a small amount of ethyl ether; other than this it was identical (v.P.c., %*OD 1.5205) with the original nitro compound.
(31) W e a r e i n d e b t e d to Dr. D. E. Hardies for t h i s experiment, (32) R Daniels a n d C. G . K o r m e n d y , J . O r g . C h e m . , 27, 1860 (1962).
( 3 3 ) N. K o r n b l u m , H . 0. L a r s o n , R. K . Blackwood, D. D. M o o b e r y , E. P . Oliveto, a n d G. E . G r a h a m , J . A m . Chem. S O L .78, , 1500 (1966).
[CONTRIBUTION FROM
THE
Acknowledgment.-We are indebted to Mr. William E. Baitinger for determining many of the n.m.r. spectra and to Mr. Baitinger and Professor Norbert Muller for much assistance in interpreting these spectra.
CHEMISTRY DEPARTMEST, IOWASTATE UNIVERSITY, AMES,
IOlVA]
Small-Ring Organosilicon Compounds. I. A Comparison of the Reactivities of 1,1,2-Triphenyl-l-silacyclobutaneand 1,1,2-Triphenyl-l-silacyclopentane BY HENRYGILMAN A N D LVILLIAMH. ATWELL RECEIVED SEPTEMBER 16. 1963 T h e preparation of 1,1,2-tripheiiyl-l-silacyclobutane(11) and 1,1,2-triplieiiyl-l-silacyclopentane (111) and a comparison of the reactivities of these two compounds toward a variety of reagents is described Compound I1 was found to undergo facile ring opening with most of the reagents used. I n direct contrast, however, no cleavage could he observed with 111 under similar reaction conditions. A theoretical consideration of the factors contributing to the enhanced reactivity of silacyclobutanes is prcscnted.
Introduction Recently in this laboratory, attention has been given to the preparation, structural determination, and reactions of a compound originally prepared by Kipping' and desigiiatcd by him as compound " A " This compound has been shown to be octaphenylcyclotetrasilane (I).273 ( 1 ) ( a ) I' S Kipping a n d J E. S a n d s , J . C h e m Soc , 119, 830, 848 (1%21), (11) F S K i p p i n g , i b i i i , 123, 2 5 0 0 , 2,598 (lC123j. (c) F. S Kipping. ibid , 126, 22!)1 (1!124). ( d ) I' S Kipping, i b i 0 , 2719 (1927); (e) F S Kip-
pinR. "Ilakerian I.ecture," Pror R o y . SOL ( I n n d o n ) , A169, 139 (1937)
Ph+'
I'li,Si-Si
SiPh2 I
1
Ph?
The highly reactive nature of this compound toward a variety of reagents' proinpted an investigation into 1 2 ) €I Gilman. I ) . J Peterson. A W Jarvie. a n d H J S Winkler, J A m Chein S o c , 82, 207fi (I9ciOj ( 3 ) A W . P Jarvie. H J S Winkler, 1) J Peterson, a n d H G i l m a n , ibid , 83, 1'321 (1!101) (4) For a review of t h e chemictry r,f octaphenylcyc1otetrasil;lne i e e IT Gilman and G I.. Schwebke. in F G A S t o n e and il \&-est tiil ".bl
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HENRYGILMAN A N D WILLIAMH . ATWELL
PROPERTIES O F THE
Vol. 86
TABLEI KNOWNSILACYCLOBUTANES1"
B.p.-----
7--
Compound"
"C.
mm.
Density
1, o c :
llD
Ref.
1-Methyl-1-silacyclobutane 63 733 1,4313 20 5 7 1-Chloro-1-ethyl-1-silacyclobutane 133.5 14/ 1.4572 20 die" 0 , 9 7 9 1 9 1-Cliloro-1,3-dimethyl-1-silacyclobutane 118 740 1 4428 20 dr*0 0.9473 9 1,l-Dimethyl-1-silacyclobutane 81 730 1 4270 20 dao20 0.7746 6 1-Ethyl-1-methyl-1-silacyclobutane 109 745 1 ,4388 20 diazo0.7965 9 1,1,3,3-Tetramethyl-l,3-disilacyclobutaneb 117-119 1.4380 27 7 , 8a, 8b, 8d The preparation of 1,1,3,3-tetrachloro-2,4,4,4-tetrakis(trichlorosily~~-l,3-disilacyclobutane has been recently reported" ; R.Mueller arid W. Mueller, Chenz. B e r . , 96, 2894 (1963), report m.p. 168-169" sub. For a recent report concerned with the preparation of other silacyclobutanes, see L*.M. Vdovin, N . S. Nametkin, and P. L. Grinberg, Dokl. Aknd. Nauk S S S R , 150, 799 (1963) [ Chem. Abstr., The physical constants given are those reported in ref. 7. 59, 8781 (1963)],
the chemistry of other four-membered silicon-containing distilled) V with magnesium in tetrahydrofuran ( T H F ) heterocycles. A literature search showed that relaafforded I1 in yields ranging from 40-55%. Surpristively few such compounds had been prepared, and ingly, no reaction could be observed when ether was little information was available concerning the reacsubstituted for T H F as the solvent in the cyclization tivity of these compounds. The silacyclobutane ring step. system has been shown to be extremely susceptible to NBS Ph(CHd3SiPhz PhCH=CHCHgSiPhl cleavage by polar reagents. Facile ring opening has I I been observed with: (1) ethanolic b a ~ e ,(2) ~ ' sulfuric ~ k Br acid,6 (3) ethanolic silver nitrate,? (4) b r ~ m i r i e , ' , ~ ~ , ~ I V 1 1 VI and (5) hydrogen halides.8 PhCH (CH2)2SiPhz A collection of the known silacyclobutanes together 1, LIAIH. I I with the available physical properties is given in Table Br 2, HaQ" Br I. n V We now wish to report the synthesis of 1;1>2-triMg/EtzO PhLgiPhn MdTHF phenyl-1-silacyclobutane (11) and 1,1,2-triphenyl-lI1 no reaction silacyclopentane (111), and a comparison of the reactivities of these two compounds toward a variety of reaReactivity of 11.-Cleavage of I1 with lithium gents. aluminum hydride was found to occur under mild conditions giving high yields of the initial starting material Results and Discussion IV. This appears to be the first reported cleavage of a Preparation of 11.-The ability of N-bromosucsilacyclobutane using lithium aluminum hydride, and ciriiinide (NBS) to effect bromination of silicon hythis reagent promises to be of general utility for the drides'! - - I 1 as well as allylic bromination14 was utilized in proof of structure of such compounds. the prcparation of I1 and 111. The synthetic method Compound I1 was found to decolorize a solution of ciriployed for the preparation of I1 and I11 was esbromine in carbon tetrachloride slowly a t room temsciitially the same and will be described in detail for the perature and to reduce ethanolic solutions of silver iornler. salts, such as silver nitrate and silver acetate, often with ( ;iPliciiylpropy1)dipheiiylsilane (IV) was treated witli S 13s to give bromo-(3-bromo-3-phenylpropyl)di- the formation of a silver mirror. These observations are in agreement with the high degree of reactivity prepliciiylsilanc (V). Attempts to purify this latter mateviously reported for other silacyclobutane c o m p o ~ n d s . ~ rial by (listillation resulted in decomposition with the In addition to the above, I1 was found to undergo S L I ~ ~ S C ~t~ Iisolation ~CII of bromo-(3-phenyl-2-pr,openyl)exothermic ring opening on an alumina's column. On tli~~lieilylsilane (VI). However, reaction of crude (unthe basis of infrared analysis and by analogy with the V : I I I C L \ i n Ot gan
