931 spectrum is due to the high reactivity of silyl radicals toward aromatic sub~titution.~ H. Sakurai and A. Hosomi, J. Am. Chem. SOC.,93, 1709 (1971). P. J. Krusic and J. K. Kochi. J. Am. Chem. SOC.,SO, 7155 (1968). A. Hudson and H. A. Hussain, Mol. Phys., 16, 199 (1969). (a) A. D.McLachlan, Mol. Phys., 2, 271 (1959); (b) ibid., 3, 233 (1960). For calculations of the n-spin population, the extended Hartree-Fock treatment with h = 1.2, CY- = (YO 0.3560and & - c = 0.4560 were finally used. Spin populations at the CHs group were then calculated by = 3.060. using the Gerson's parameters;" a,,,= (YO - 0.56, F. Gerson, "High Resolution E.S.R. Spectroscopy", Wiley Verlag Chemie, 1970, p 106. Table I and II contain only data for germy1 radicals, but we have also obtained experimental and calculated results for Ph&, PhpMeC-, and PhMepC-.Details wiii be published elsewhere. I?.W. Watson and A. J. Freeman, Phys. Rev., 123, 521 (1961); 124, 1117 (1962). J, R. Bolton, A. Carrington, and A. D. McLachlan, Mol. Phys., 5 , 31 (1962). The square root of the ratio of +(Me3Ge.)/+(Me3C.) is noteworthy in this respect, since the hyperconjugation model also predicts this value to be an approximate relative resonance integral, P - - c ~ ~ I & - c H From ~. the reported value for Me3C- (22.72 G),17 it is calculated to be 0.48, very close to the value used for the calculation of the T-spin populations. R. W. Fessenden and R. H. Schuler, J. Phys. Chem., 71, 74 (1967). We thank the referees for the constructive criticism on this point. H. Sakurai and K. Mochida, Chem. Commun., 1581 (1971).
-
Hideki Sakurai,* Kunio Mochida, Mitsuo Kira Department of Chemistry, Faculty of Science, Tohoku University, Aoba Aramaki. Sendai 980, Japan Received June 13, 1974
The reaction of 1 with phenylacetylene (2b) under similar conditions (reflux for 9.5 hr) gave the corresponding addition compound, 3b, in 84.8% yield.I0 Unsubstituted acetylene (2c) also reacted with l, when 2c was bubbled into a refluxing benzene solution of 1 in the presence of the catalyst, to give 3c in 53.3% yield.' However, diphenylacetylene and bis(trimethylsilyl)acetylene failed to react with I under similar conditions, only the starting materials being recovered. Hexamethyldisilane (4), a n example of the unstrained hexaorganodisilane, similarly undergoes the reaction but slowly. Thus, with 2a, 4 gave dimethyl 1,2-bis(trimethylsilyl)maleate ( 5 ) in 3.4% yield after refluxing for 23 hr in benzene. I * T h e cis stereochemistry of 5 was tentatively assigned by comparison of the uv spectrum with 3a.
c
C C0,Me I
Me,Si
/ \ C0,Me 5
1,1,2,2-Tetramethyl-3,4,5,6-tetraphenyl1,2-disilane (6) gave a n interesting new ring system, 7, by the reaction with 2a under similar conditions in 72.7% yield.I4
+
Novel [a 7r] Reactions of Hexaorganodisilanes with Acetylenes Catalyzed by Palladium Complexes1 Sir:
Recently Traven and West* and we3 reported the donor properties of the silicon-silicon bond as evidenced by charge-transfer complexation between organopolysilanes and tetracyanoethylene. More recently, we have described that the level of the highest occupied molecular orbital of I ,2-disilacycloalkanes is raised with decreasing ring size, and, as a result, the donor property of the silicon-silicon bond is enhanced, for example, inl, 1,2,2-tetramethyI- 1,2disilacyclopentane ( l ) . 4In this context, 1 is a convenient compound for a n investigation of reactions in which the silicon-silicon bond may act as a donor. W e report here a novel cycloaddition reaction of organodisilanes with some unsaturated compounds such as acetylenes5 catalyzed by palladium complexes. The reaction afforded mainly cis1,2-disilylethylenes and hence the mode of the reaction is ,2,] proformally analyzed as a thermally forbidden [,2, cess.6 This type of reaction for the carbon-carbon bond can be seen only for a highly strained molecule such as bicyclo[2.1 .O]pentane,' but we are not aware of any precedented example for the silicon-silicon bond. When a solution of 1 (1 mmol), dimethyl acetylenedicarboxylate (2a) ( 1 mmol), and bis(tripheny1phosphine)palladium dichloride (0.01 mmol) in benzene (10 ml) was heated at reflux for 3 hr under a nitrogen atmosphere, crystalline dimethyl 1,1,4,4-tetramethyl-1,4-disilacyclohept-2-ene2,3-dicarboxylate (3a) was obtained in 83.4% ~ i e l d . ~ , ~
7
6
We have examined various metal complexes as a possible catalyst of the reaction and have found that the palladium complexes such as PdC12(PhCN)2, [ ( ~ - a l l y l ) P d C I ] ~ , PdCI*(PEt3)2, and Pd(PPh3)4 a r e also effective. With these palladium complexes, the reaction proceeds similarly, but the details of the reaction such as the rate of the reaction, yields of the products, and the nature of the by-products are different slightly with respect of each catalyst. Thus, for ex1+Za-
PdCI.IPhCN,
PnH. reflux
+
3a
MeOOC>(
s1
Me. -Si)[CO2Me
MeOOC
S-iSi
Me.
+ C0,Me
Me,
Me, 8
WCI,( PhCI'; li
1+2a
PhH, room temp
R
I
C
SiMe,
11
C
I
1
R
2% R = R' = COOMe b, R = P h ; R = H c,
R=R'=H
SiMe, 3a, R = R' = COOMe b, R = Ph; R' = H
1
+ 2b
PdCI,( PhCS J. PhH. reflux
3b
+
c.R=R=H
Me, 10
Communications t o the Editor
932
n
ample, with PdC12(PhCN)2, the reaction of 1 and 2a gave 815 ( 1 1.9%) in addition to 3a (40.0%) by refluxing in benzene for 3 hr. A t room temperature, however, the reaction of 1 with 2a catalyzed by PdCI*(PhCN)* gave 3a (27.5%) and 916 (8.5%) after 3 days. Similarly with PdC12(PhCN)*, the reaction of 1 with 2b gave both 3b (19.3%) and 10
Me M. \
I
(14.5%).’7
W e a r e actively exploring the related reactions and the details will be reported in a forthcoming paper.
Acknowledgment. W e thank Toshiba Silicones Co., Ltd., for gifts of chlorosilanes. References and Notes (1)Chemistry of Organosilicon Compounds 79. (2)V. F. Traven and R. West, J. Am. Chem. SOC.,95, 6824 (1973). (3)H. Sakurai, M. Kira, and T. Uchida, J. Am. Chem. Soc., 95, 6826 (1973). (4)H. Sakurai and Y. Kamiyama, J. Am. Chem. Soc., 96, 6192 (1974). (5) The reaction of disilanes with dienes will be reported separately. (6)R. 6 . Woodward and R. Hoffmann, Angew. Chem., 81, 797 (1969). (7)R. Noyori, T. Suzuki, and H. Takaya, J. Am. Chem. Soc.. 93, 5896 (1971). (8)All new compounds gave correct elemental analyses. Yields described in this paper are those after isolation with TLC on silica gel.
(9)Compound 3a: mp 68.0-69.0; M+ 300 (2)m/e 89 (100);NMR 6 (CC14) 0.30 (12H, s, Si-CY), 1.04(4H. t, J = 7 Hz, SiTCH2-CH2), 1.91 (2H, q, J = 7 Hz, SiCHz-C&). 3.70 (6H, s, COOCY); ir (cm-’) (KBr) 1725, , , ,A (MeOH) 210.0(10,000) 262.0(1,500). 1715,1250; (IO) Compound 3b: an oil; +3 D 1.5365;M+ 260 (64.3)m/e 135 (100);NMR d (CCI4) 0.12(6 H, s, SiCHs), 0.16 (6 H, s. Sic&), 0.92 (2H, t, J = 6 Hz, Si-CH2-), 0.94(2H, t, J = 6 Hz, Si-CHz-), 1.88(2H, q, J = 6 Hz, SiCHz-C+), 6.44(1 H, s, =-H), 7.10(5 H, m, Ph); ir (cm-’) (neat) 1250; , , ,A (nhexane) 21 1.3(18,100), 249.0(10,000). ( 1 1 ) Compound 3c: an oil nZyD 1.4725;M+ 184 (15)m/e 141 (100);NMR 6 (CC14) 0.08(12H, s, Si-CHz), 0.80(4H, t. J = 7 Hz, Si-CH,-), 1.80(2 H, q, J = 7 Hz, SiCHp-CHZ-), 6.72(2 H, s, =-H): ir (cm-’) (neat) 1255,690, , , A, (nhexane)
