Unsymmetrical Zirconacyclopentadienes from Isolated Zirconacyclopropenes with 1-Alkynylphosphine Ligands

The reaction of one equiv of 1-alkynylphosphines, R2PCCR′ (R = Et, iPr, or Ph and R′ = Ph or Mes), with Cp2Zr(pyr)(η2-Me3SiCCSiMe3) resulted in formation of monoalkyne complexes. In the case where R = Et, iPr, or Ph and R′ = Ph, a “ligand free” zirconacyclopropene complex is produced. These complexes are stabilized by intermolecular donation of the phosphorus lone-pair in the dimeric complexes [Cp2Zr(η2-R2PCCPh)]2 (R = Et, iPr, or Ph). However, with R = Ph and R′ = Mes, the zirconocyclopropene-pyridine complex Cp2Zr(pyr)(η2-Ph2PCCMes) is formed. Homocoupling of the 1-alkynylphosphines was demonstrated by reaction of a second equiv of Ph2PCCPh with [Cp2Zr(η2-Ph2PCCPh)]2 to give the diphosphinozirconacyclopentadiene Cp2Zr[2,5-(Ph2P)2-3,4-Ph2C4] with high regioselectivity (77%). The zirconacyclopropene complexes also react with one equiv of PhCCPh or EtCCEt to give zirconacyclopentadienes in which the phosphino substituent preferentially adopts the 2-position (α) of the zirconacyclopentadiene ring. These unsymmetrical zirconacyclopentadienes undergo substitution of the R2PCCR′ moiety with the less bulky alkynes PhCCPh or EtCCEt. The substituents on the 1-alkynylphosphines significantly influence the rates of alkyne substitution such that sterically more demanding substituents in either the α- (-PiPr2) or β- (-Mes) position of the zirconacycle lead to faster exchange. The α-phosphinozirconacyclopentadienes were readily converted to 1-phosphinobutadienes via reaction with benzoic acid. The zirconacyclopentadiene Cp2Zr[2-Ph2P-3,4,5-Ph3C4] was converted to the corresponding thiophene oxide by the oxo-transfer reaction with sulfur dioxide. In the case of ((1Z,3E)-3-ethyl-2-phenylhexa-1,3-dienyl)diphenylphosphine and (3,4,5-triphenylthiophen-2-yl oxide)diphenylphosphine, the molecules were isolated as their phosphine oxides. Reactions of the zirconacyclopropene complexes [Cp2Zr(η2-Ph2PCCPh)]2 and Cp2Zr(pyr)(η2-Ph2PCCMes) with the diyne (F5C6)CC−1,4-C6H4−CC(C6F5) gave bis(zirconacycle)s terminated with phosphino groups. These bis(zirconacycle)s were converted to the corresponding phosphino-terminated oligomers by protonolysis with hydrochloric acid. In addition, the Ph2PCCMes moiety of Cp2Zr[2-Ph2P-3-Mes-4-(C6F5)C4]−1,4-C6H4−Cp2Zr[2-Ph2P-3-Mes-4-(C6F5)C4] was exchanged with PhCCPh to give the phenylene(zirconacyclopentadiene) Cp2Zr[2,3-Ph2-4-(C6F5)C4]−1,4-C6H4−Cp2Zr[2,3-Ph2-4-(C6F5)C4].

将1当量的炔基膦（1-alkynylphosphines）R₂PC≡CR'（其中R为乙基（Et）、异丙基（iPr）或苯基（Ph），R'为苯基（Ph）或均三甲苯基（mesityl，简称Mes））与双环戊二烯基锆配合物Cp₂Zr(pyr)(η²-Me₃SiC≡CSiMe₃)（其中pyr为吡啶（pyridine），η²为侧基配位模式）反应，可生成单炔配位配合物。当R为Et、iPr或Ph且R'为Ph时，可得到“无配体”的锆杂环丙烯（zirconacyclopropene）配合物。这类配合物以二聚体形式[Cp₂Zr(η²-R₂PC≡CPh)]₂（R=Et、iPr或Ph）通过磷原子孤对电子的分子间配位实现稳定。当R为Ph且R'为Mes时，则生成锆杂环丙烯-吡啶配合物Cp₂Zr(pyr)(η²-Ph₂PC≡CMes)。将第二当量的Ph₂PC≡CPh与二聚体[Cp₂Zr(η²-Ph₂PC≡CPh)]₂反应，可区域选择性（77%收率）得到二膦基取代的锆杂环戊二烯（zirconacyclopentadiene）Cp₂Zr[2,5-(Ph₂P)₂-3,4-Ph₂C₄]，该反应证实了炔基膦的均偶联过程。锆杂环丙烯配合物与1当量的二苯乙炔（PhC≡CPh）或二乙基乙炔（EtC≡CEt）反应，可生成膦基取代优先位于锆杂环戊二烯环2位（α位）的锆杂环戊二烯类产物。这类不对称锆杂环戊二烯可与位阻更小的炔烃PhC≡CPh或EtC≡CEt发生R₂PCCR'基团的取代反应。炔基膦上的取代基对炔烃取代反应的速率有显著影响：锆环α位（-PiPr₂）或β位（-Mes）的空间位阻越大，交换反应速率越快。α-膦基取代的锆杂环戊二烯可与苯甲酸反应，轻松转化为1-膦基丁二烯类化合物。配合物Cp₂Zr[2-Ph₂P-3,4,5-Ph₃C₄]可通过与二氧化硫的氧转移反应（oxo-transfer reaction），转化为相应的噻吩氧化物。当得到((1Z,3E)-3-乙基-2-苯基己-1,3-二烯基)二苯基膦和(3,4,5-三苯基噻吩-2-氧化物)二苯基膦时，产物以其膦氧化物形式分离得到。双锆环配合物[Cp₂Zr(η²-Ph₂PC≡CPh)]₂和Cp₂Zr(pyr)(η²-Ph₂PC≡CMes)与二炔(C₆F₅)C≡C-1,4-C₆H₄-C≡C(C₆F₅)反应，可得到末端连有膦基的双锆环化合物。这类双锆环配合物经盐酸质子解（protonolysis）后，可转化为相应的末端膦基封端的低聚物。此外，将配合物Cp₂Zr[2-Ph₂P-3-Mes-4-(C₆F₅)C₄]-1,4-C₆H₄-Cp₂Zr[2-Ph₂P-3-Mes-4-(C₆F₅)C₄]中的Ph₂PCCMes基团与PhC≡CPh进行取代交换，可得到亚苯基桥联的双锆杂环戊二烯Cp₂Zr[2,3-Ph₂-4-(C₆F₅)C₄]-1,4-C₆H₄-Cp₂Zr[2,3-Ph₂-4-(C₆F₅)C₄]。