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A Palladium-Catalyzed Stannole Synthesis


A palladium-catalyzed (2 + 2 + 1) cycloaddition reaction of two C_2H_2 and one SnR_2 to form C-unsubstituted stannoles (C_4H_4)SnR_2 [R = CH(SiMe_3)_2 2a, R_2 = {C(SiMe_3)_2CH_2}_2 2c] is described. Catalysts are (R'_2PC_2H_4PR'_2)-Pd complexes (slow reaction) and (R'_3P)_2Pd complexes (fast reaction). The mechanism of the catalysis has been elucidated in detail from stoichiometric reactions based on R = CH(SiMe_3)_2. For the [(R'_2PC_2H_4PR'_2)Pd]-catalyzed system, the starting Pd(0)-ethene complexes (R'_PC_2H_4PR'_2)Pd(C_2H_4) (R' = ~iPr (3), ~tBu (4)) react both with ethyne to give the Pd(0)-ethyne derivatives (R'_2PC_2H_4PR'_2)Pd(C_2H_2) (R' = ~iPr (5), ~tBu (6)) and with SnR_2 to yield the Pd(0)-Sn(II) adducts (R'_2PC_2H_4PR'_2)Pd=SnR_2 (R' = ~iPr (7), ~tBu (8)). The Pd-Sn bond [2.481(2) A] of 7 is very short, indicative of partial multiple bonding. Subsequent reactions of the Pd(0)-ethyne complexes 5 and 6 with SnR_2 or of the Pd(0)—Sn(II) complexes 7 and 8 with ethyne afford the 1,2-palladastannete complexes (R'_2PC_2H_4PR'_2)Pd(CH=CH)SnR_2 (Pd-Sn) (R' = ~iPr (10), ~tBu (11)). The derivative with R' = Me (9) has also been synthesized. In 10 a Pd—Sn single bond [2.670(1) A] is present. Complexes 10 and 11 (as well as 7 and 8 but not 9) react slowly with additional ethyne at 20℃ to reform the Pd(0)—ethyne complexes 5 and 6 with concomitant generation of the stannole (C_4H_4)SnR_2 (2a). Likely intermediates of this reaction are the Pd(0)—η~2-stannole complexes (R'_2PC_2H_4PR'_2)Pd(η~2-C_4H_4SnR_2) (R' = ~iPr (12), ~tBu (13)), which have been synthesized independently. The stannole ligand in 12, 13 is easily displaced by ethyne to yield 5 or 6 or by SnR_2 to yield 7 or 8. Thus, the isolated complexes 5-8 and 10-13 are conceivable intermediates of the catalytic stannole formation, and from their stoichiometric reactions the catalysis cycle can be assembled. For the [(R'_3P)_2Pd]-catalyzed system, the corresponding intermediates (Me_3P)_2-Pd(C_2H_2) (15), (~iPr_3P)_2Pd(C_2H_2) (17), (Me_3P)_2Pd=SnR_2 (18), (~iPr_3P)_2Pd=SnR_2 (20), and (Me_3P)_2Pd(CH=CH)SnR_2 (Pd-Sn) (19) have been isolated or detected by NMR, and (~iPr_3P)_2Pd(CH=CH)SnR_2 (Pd-Sn) (21) is postulated as an intermediate. The [(Me_3P)_2Pd] system (stannole formation above 0℃) is catalytically more active than any of the [(R'_2PC_2H_4PR'_2)Pd] systems (slow stannole formation for R' = ~tBu at 20℃). Most active is the [(~iPr_3P)_2Pd] system, allowing a catalytic synthesis of the stannole 2a from SnR_2 and ethyne at -30℃ [1% of 17; yield 2a: 87%; TON (turnover number): 87]. By carrying out the catalysis in pentane at 20℃ (0.04% of 17), the TON is increased to 1074 but the yield of 2a is diminished to 43% due to uncatalyzed thermal side reactions.......

【作者名称】: Jochen Krause, Karl-Josef Haack, Klaus-Richard Poerschke, Barbara Gabor, Richard Goddard, Christian Pluta
【作者单位】: Max-Planck-Institut fuer Kohlenforschung, D-45466 Muelheim an der Ruhr, Germany
【关 键 词】: A Palladium-Catalyzed Stannole Synthesis
【期刊名称】: Journal of the American Chemical Society
【期刊论文数据库】: [DBS_Articles_01]
【期刊论文编号】: 107,450,055
【摘要长度】: 2,757
【上篇论文】: 外文期刊 - Microstructure-critical Current Density Model For Mgb_2 Wires And Tapes
【下篇论文】: 外文期刊 - On the nature of the dative bond: Coordination to metals and beyond. The carbon case

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