Synthesis and Reactivity of [PCCP]-Coordinated Group 5 Alkyl and Alkylidene Complexes Featuring a Metallacyclopropene Backbone
Synthesis and Reactivity of [PCCP]-Coordinated Group 5 Alkyl and Alkylidene Complexes Featuring a Metallacyclopropene Backbone
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DOI：
10.1021/acs.organomet.9b00577
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发表时间：
2019-11-11
期刊：
影响因子：
2.8
通讯作者：
Ballmann, Joachim
中科院分区：
文献类型：
--
作者：
Federmann, Patrick;Richter, Tim;Ballmann, Joachim
利用r2p功能化的甲基烷1a （R = Ph）和1b （R = Pr-i）合成了[PCCP]配位的5族配合物。在钒的情况下，制备了d(1)构型的二烷基化合物[PCCP]V(CH2SiMe3)(2) (3a和3b)，并发现它们具有抗氧化性，即在各种氧化剂处理下均未观察到相应的烷基烯配合物。然而，对于铌和钽，(Pr2P)- pr -i取代配体得到了高价d(0)构型的烷基-烷基烯配合物[PCCP]M(=CHSiMe3)(CH2SiMe3) （M = Nb: 6b, M = Ta: 7b）。这两种烷基烯，即6b和7b，用于张力烯烃的开环复分解聚合（ROMP）。虽然6b和7b中的eta(2)-炔基最适合描述为金属环丙烯，但在这些聚合过程中，不饱和配体主链既没有降解也没有共聚。然而，在7b的氢解作用下，金属环丙烯主链部分氢化，形成具有金属环丙烷亚结构的双核（mu-H）(3)桥接钽(V)配合物8。该反应中的中间体可催化萘中的一种或两种芳烃氢化，而分离的二聚体物种8在相同的反应条件下无活性。
The R2P-functionalized tolanes 1a (R = Ph) and 1b (R = Pr-i) were employed for the synthesis of [PCCP]-coordinated group 5 complexes. In the case of vanadium, the d(1)-configured dialkyl species [PCCP]V(CH2SiMe3)(2) (3a and 3b) were prepared and found to be resistant toward oxidation, i.e., the corresponding alkylidene complexes were not observed upon treatment with various oxidants. For niobium and tantalum, however, the high-valent d(0)-configured alkyl-alkylidene complexes [PCCP]M(=CHSiMe3)(CH2SiMe3) (M = Nb: 6b, M = Ta: 7b) were obtained for the (Pr2P)-Pr-i-substituted ligand. Both these alkylidenes, i.e., 6b and 7b, were employed for ring-opening metathesis polymerizations (ROMP) of strained olefins. Although the eta(2)-alkyne motifs in 6b and 7b are best described as metallacyclopropenes, the unsaturated ligand backbone was neither degraded nor copolymerized over the course of these polymerizations. Upon hydrogenolysis of 7b, however, the metallacyclopropene backbone was partially hydrogenated, and the dinuclear (mu-H)(3)-bridged tantalum(V) complex 8 featuring a metallacyclopropane substructure was formed. An intermediate in this reaction was shown to catalytically hydrogenate one or both arenes in naphthalene, while the isolated dimeric species 8 was found to be inactive under identical reaction conditions.