Alkene Metatheses in Transition Metal Coordination Spheres: Effect of Ring Size and Substitution on the Efficiencies of Macrocyclizations That Join <i>trans</i> Positions of Square-Planar Platinum Complexes

Reactions of KPPh2 and Br(CH2)nCHCH2 give the phosphines PPh2(CH2)nCHCH2 (n = a, 4; b, 6; c, 8; d, 9; 95−41%), which are combined with the platinum tetrahydrothiophene complex [Pt(μ-Cl)(C6F5)(S(CH2CH2−)2)]2 to give trans-(Cl)(C6F5)Pt(PPh2(CH2)nCHCH2)2 (3a−d, 71−54%). When treated with Grubbs' catalyst, ring-closing alkene metatheses occur to give 13- to 23-membered macrocycles with trans-spanning diphosphine ligands (96−85%, including some dimeric or oligomeric byproducts). The mixtures of CC isomers are hydrogenated (1 atm, 10% Pd/C) to give (6a−d), which are isolated in 72−50% yields. Comparable results are obtained with (1) the second-generation dihydroimidazolylidene Grubbs' catalyst and (2) a series of compounds derived from the dimethylated phosphine Ph2P(CH2)2C(CH3)2(CH2)3CHCH2, in turn prepared by sequential reactions of BrCH2CH2C(CH3)2CH2CH2Br with BrMgCH2CHCH2/Li2CuCl4 and KPPh2. The crystal structures of 6a−d are analyzed, but no special features that would promote intramolecular macrocyclizations are noted. A reaction of [Pt(μ-Cl)(C6F5)(S(CH2CH2−)2)]2 and the diphosphine Ph2P(CH2)14PPh2 leads to a multitude of products and little 6b (<15%).二苯基膦钾（KPPh2）与溴代烯烃Br(CH2)nCH=CH2反应，可得到膦类化合物PPh2(CH2)nCH=CH2（n对应a=4、b=6、c=8、d=9，产率95%~41%）；将该类膦配体与二(μ-氯)双[(五氟苯基)(四氢噻吩)合铂(II)]配合物[Pt(μ-Cl)(C6F5)(S(CH2CH2−)2)]2混合，可得到反式-氯(五氟苯基)双[二苯基(ω-烯基)膦]合铂（3a~d，产率71%~54%）。以格拉布催化剂（Grubbs' catalyst）处理该类配合物，可发生闭环烯烃复分解反应，得到带有横跨式双膦配体的13至23元大环化合物（产率96%~85%，伴随少量二聚或寡聚副产物）。所得C=C双键异构体混合物经1个大气压氢气、10%钯碳（Pd/C）催化氢化，得到6a~d，分离产率为72%~50%。采用第二代二氢咪唑亚基卡宾型格拉布催化剂，以及由BrCH2CH2C(CH3)2CH2CH2Br依次与BrMgCH2CH=CH2/四氯合铜酸二锂（Li2CuCl4）、二苯基膦钾（KPPh2）反应制得的膦配体Ph2P(CH2)2C(CH3)2(CH2)3CH=CH2，均可得到相近的实验结果。对6a~d的晶体结构进行解析后，未发现可促进分子内环化生成大环的特殊结构特征。此外，将二(μ-氯)双[(五氟苯基)(四氢噻吩)合铂(II)]配合物[Pt(μ-Cl)(C6F5)(S(CH2CH2−)2)]2与双膦配体Ph2P(CH2)14PPh2进行反应，仅得到多种复杂产物，几乎无法获得6b（产率<15%）。