A Palladium-Catalyzed Stannole Synthesis
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- 作者：Jochen Krause ; Karl-Josef Haack ; Klaus-Richard Pö ; rschke ; Barbara Gabor ; Richard Goddard ; Christian Pluta ; and Klaus Seevogel
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：January 31, 1996
- 年：1996
- 卷：118
- 期：4
- 页码：804 - 821
- 全文大小：754K
- 年卷期：v.118,no.4(January 31, 1996)
- ISSN：1520-5126
文摘
A palladium-catalyzed (2 + 2 + 1) cycloaddition reaction oftwo C2H2 and one SnR2 to formC-unsubstitutedstannoles (C4H4)SnR2 [R =CH(SiMe3)2 2a, R2={C(SiMe3)2CH2}22c] is described. Catalysts are(R'2PC2H4PR'2)Pd complexes (slow reaction) and(R'3P)2Pdcomplexes (fast reaction). The mechanism of the catalysis hasbeenelucidated in detail from stoichiometric reactions based on R =CH(SiMe3)2. For the[(R'2PC2H4PR'2)Pd]-catalyzedsystem, the starting Pd(0)-ethene complexes(R'2PC2H4PR'2)Pd(C2H4)(R' = iPr (3), tBu(4)) react both with ethyneto give the Pd(0)-ethyne derivatives(R'2PC2H4PR'2)Pd(C2H2)(R' = iPr (5), tBu(6)) and with SnR2 to yield thePd(0)-Sn(II) adducts(R'2PC2H4PR'2)Pd=SnR2(R' = iPr (7), tBu(8)). The Pd-Sn bond [2.481(2) Å] of7 is veryshort, indicative of partial multiple bonding. Subsequentreactions of the Pd(0)-ethyne complexes 5 and6 withSnR2 or of the Pd(0)-Sn(II) complexes7 and 8 with ethyne afford the1,2-palladastannete complexes(R'2PC2H4PR'2)Pd(CH=CH)SnR2(Pd-Sn) (R' = iPr(10), tBu (11)). Thederivative with R' = Me (9) has also beensynthesized.In 10 a Pd-Sn single bond [2.670(1) Å] ispresent. Complexes 10 and 11 (as well as7 and 8 but not 9) reactslowlywith additional ethyne at 20 
C to reform the Pd(0)-ethynecomplexes 5 and 6 with concomitant generation ofthestannole (C4H4)SnR2(2a). Likely intermediates of this reaction are thePd(0)-
2-stannole complexes(R'2PC2H4PR'2)Pd(2-C4H4SnR2)(R' = iPr (12), tBu(13)), which have been synthesized independently. Thestannole ligandin 12, 13 is easily displaced by ethyne to yield5 or 6 or by SnR2 to yield7 or 8. Thus, the isolated complexes5-8and 10-13 are conceivable intermediates of thecatalytic stannole formation, and from their stoichiometricreactionsthe catalysis cycle can be assembled. For the[(R'3P)2Pd]-catalyzedsystem, the corresponding intermediates(Me3P)2Pd(C2H2) (15),(iPr3P)2Pd(C2H2)(17), (Me3P)2Pd=SnR2(18),(iPr3P)2Pd=SnR2(20), and(Me3P)2Pd(CH=CH)SnR2(Pd-Sn) (19) have beenisolated or detected by NMR, and(iPr3P)2Pd(CH=CH)SnR2(Pd-Sn) (21) ispostulated asan intermediate. The [(Me3P)2Pd]system (stannole formation above 0 C) is catalytically more activethan any ofthe[(R'2PC2H4PR'2)Pd]systems (slow stannole formation for R' = tBu at 20C). Most active is the[(iPr3P)2Pd]system, allowing a catalytic synthesis of the stannole 2afrom SnR2 and ethyne at -30 C [1% of 17;yield 2a:87%; TON (turnover number): 87]. By carrying out the catalysisin pentane at 20 C (0.04% of 17), the TONisincreased to 1074 but the yield of 2a is diminished to 43%due to uncatalyzed thermal side reactions.
C to reform the Pd(0)-ethynecomplexes 5 and 6 with concomitant generation ofthestannole (C4H4)SnR2(2a). Likely intermediates of this reaction are thePd(0)-2-stannole complexes(R'2PC2H4PR'2)Pd(2-C4H4SnR2)(R' = iPr (12), tBu(13)), which have been synthesized independently. Thestannole ligandin 12, 13 is easily displaced by ethyne to yield5 or 6 or by SnR2 to yield7 or 8. Thus, the isolated complexes5-8and 10-13 are conceivable intermediates of thecatalytic stannole formation, and from their stoichiometricreactionsthe catalysis cycle can be assembled. For the[(R'3P)2Pd]-catalyzedsystem, the corresponding intermediates(Me3P)2Pd(C2H2) (15),(iPr3P)2Pd(C2H2)(17), (Me3P)2Pd=SnR2(18),(iPr3P)2Pd=SnR2(20), and(Me3P)2Pd(CH=CH)SnR2(Pd-Sn) (19) have beenisolated or detected by NMR, and(iPr3P)2Pd(CH=CH)SnR2(Pd-Sn) (21) ispostulated asan intermediate. The [(Me3P)2Pd]system (stannole formation above 0 C) is catalytically more activethan any ofthe[(R'2PC2H4PR'2)Pd]systems (slow stannole formation for R' = tBu at 20C). Most active is the[(iPr3P)2Pd]system, allowing a catalytic synthesis of the stannole 2afrom SnR2 and ethyne at -30 C [1% of 17;yield 2a:87%; TON (turnover number): 87]. By carrying out the catalysisin pentane at 20 C (0.04% of 17), the TONisincreased to 1074 but the yield of 2a is diminished to 43%due to uncatalyzed thermal side reactions.