Origin of Differences in Regioselectivity in the (Cyclo-) Polymerization of alpha, omega-Diynes and 1-Alkynes Between Tetra- and Penta-Coordinated Mo/W Imido/Oxo Alkylidene N-Heterocyclic Carbene Complexes and Implications for Ene-yne Metathesis

烯烃/炔复分解反应的区域选择性强烈地依赖于预催化剂和活性物种两者的结构和几何形状。在这方面，复分解是否从五配位或四配位的金属亚烷基开始并通过其进行的问题是至关重要的。由于在环化二炔与五配位的中性和阳离子金属亚氨基烷叉N-杂环卡宾（NHC）配合物的区域选择性与四配位的，阳离子的一个有很大的不同，它是高度感兴趣的，以揭示这些差异的区域选择性的起源。为了这些目的，我们希望详细研究的α，ω-二炔的环化聚合以及聚合的1-炔使用一组定制的四和五配位的钼/钨亚氨基/氧代亚烷基NHC配合物。除了在顺式/反式含量和重复单元结构方面阐明聚合物结构外，这些研究应主要集中在动力学研究上，以澄清缔合或解离机制是否有效。速率常数的温度依赖性NMR测量将允许另外提供关于过渡态的δ-S ε的定量热力学数据，这将提供关于过程的分子性的明确信息，从而分别提供关于缔合或解离机制的明确信息。最后，这些研究结果应与那些区域和化学选择性在烯-炔复分解催化相同的一套（前）催化剂，再次基于动力学研究。将产生的全面的图片将有助于设计未来的区域选择性烯烃和炔复分解催化剂。

The regioselectivity of olefin/alkyne metathesis reactions strongly depends on the structure and geometry of both, the pre-catalyst and the active species. In that regards, the questions, whether metathesis starts from and proceeds via pentacoordinated or tetracoordinated metal alkylidenes is of utmost importance. Since the regioselectivity in cyclopolymerization of diynes with pentacoordinated neutral and cationic metal imido alkylidene N-heterocyclic carbene (NHC) complexes differs substantially from the one of tetracoordinated, cationic ones, it is of high interest to reveal the origin of these differences in regioselectivity. For these purposes, we wish to study in detail the cyclopolymerization of alpha, omega-diynes as well as the polymerization of 1-alkynes using a tailored set of tetra- and pentacoordinated Mo/W imido/oxo alkylidene NHC complexes. Apart from the elucidation of the polymer structure in terms of cis/trans-content and structure of the repeat unit, these studies shall mainly focus on kinetic investigations to clarify whether either an associative or a dissociative mechanism is operative. Temperature-dependent NMR measurements of the rate constants will allow for additionally providing quantitative thermodynamic data on delta-S‡ at the transition state, which will provide unambiguous information about the molecularity of the process and thus about an associative or dissociative mechanism, respectively. Finally, these findings shall be correlated with those on the regio- and chemoselectivity in ene-yne metathesis catalyzed by the same set of (pre-) catalysts, again based on kinetic studies. The comprehensive picture that is to be generated will help for designing future, regioselective olefin and alkyne metathesis catalysts.