Preparation, Structures, and Some Reactivities of Five-Coordinate Alkyne Complexes of Mo with Tetraphosphine or Diphosphine Coligand [Mo(RCCR′){<i>meso</i>-<i>o</i>-C₆H₄(PPhCH₂CH₂PPh₂)₂}] and [Mo(RCCR′)(Ph₂PCH<sub>2</sub

The five-coordinate alkyne complexes [Mo(η2-RCCR′)(κ4-P4)] (3; P4 = meso-o-C6H4(PPhCH2CH2PPh2)2) were synthesized by treatment of the Mo(0) tetraphosphine complex [Mo(κ4-P4)(dppe)] (1; dppe = Ph2PCH2CH2PPh2) with internal alkynes RCCR′. The X-ray analysis of 3a (R = Me, R′ = COOMe) and 3b (R = R′ = Ph) has disclosed their trigonal-bipyramidal geometry in a solid state, whereas their fluxional feature in solution has been demonstrated by the VT-NMR study. New closely relating diphosphine complexes [Mo(η2-RCCR′)(dppe)2] (4) have also been obtained analogously from the reactions of trans-[Mo(N2)2(dppe)2] with RCCR′, and their trigonal-bipyramidal structures have been confirmed by the X-ray diffraction for 4a (R = Me, R′ = COOMe). Complexes 3a, 3b, 4a, and 4b were allowed to react with aqueous HCl in THF to give hydrogenation products from coordinated alkynes including cis/trans-alkenes and/or alkanes, the yields of which depend upon the nature of the alkyne complexes and the amounts of acid. From the reactions of 3a with HBF4·Et2O under the controlled conditions, two intermediate complexes were isolated, namely, a hydridoalkyne complex [MoH(η2-MeCCCOOMe)(κ4-P4)][BF4] and an η3-allyl complex [Mo(η3-CH2CHCHCOOMe-κO)(κ4-P4)][BF4], and the mechanism for the formations of hydrogenation products of alkynes via these intermediate stages has been proposed. Reaction of 3a with H2S gas also resulted in the hydrogenation of the coordinated alkyne to the alkene, which was further converted to the H2S adduct smoothly under the reaction conditions. Oxidation of 3a by I2 yielding a cationic alkyne complex [MoI(η2-MeCCCOOMe)(κ4-P4)]I is also described.五配位炔烃配合物[Mo(η²-RC≡CR′)(κ⁴-P₄)]（3；P₄ = 内消旋邻苯二基双(2-二苯基膦乙基)膦，即meso-o-C₆H₄(PPhCH₂CH₂PPh₂)₂）通过零价钼四膦配合物[Mo(κ⁴-P₄)(1,2-双(二苯基膦)乙烷)]（1；1,2-双(二苯基膦)乙烷简称dppe）与内炔烃RC≡CR′反应合成得到。对3a（R=Me，R′=COOMe）和3b（R=R′=Ph）的X射线衍射分析表明，其固态结构均为三角双锥几何构型；而变温核磁共振（VT-NMR）研究证实了它们在溶液中的流变特性。通过类似反应路径，由反式-[Mo(N₂)₂(dppe)₂]与RC≡CR′反应，还得到了一系列结构相近的新型二膦配合物[Mo(η²-RC≡CR′)(dppe)₂]（4）；其中4a（R=Me，R′=COOMe）的X射线衍射分析确认了其三角双锥分子结构。将配合物3a、3b、4a与4b置于四氢呋喃（THF）中的盐酸水溶液中反应，可得到配位炔烃的加氢产物，包括顺/反式烯烃和/或烷烃，产物收率取决于炔烃配合物的结构与酸的投料量。在可控反应条件下，使3a与氟硼酸乙醚加合物（HBF₄·Et₂O）反应，分离得到两种中间体配合物：分别为氢合炔烃配合物[MoH(η²-MeC≡CCOOMe)(κ⁴-P₄)][BF₄]与η³-烯丙基配合物[Mo(η³-CH₂CHCHCOOMe-κO)(κ⁴-P₄)][BF₄]；据此提出了炔烃加氢产物经上述中间体路径生成的反应机理。3a与硫化氢气体的反应同样实现了配位炔烃的烯烃加氢，生成的烯烃在该反应条件下可进一步顺利转化为硫化氢加合物。本文还报道了3a经碘（I₂）氧化得到阳离子炔烃配合物[MoI(η²-MeC≡CCOOMe)(κ⁴-P₄)]I的反应。