Höltzl Tibor, Szieberth Dénes, Nguyen Minh Tho, Veszprémi Tamás
Department of Inorganic Chemistry, Budapest University of Technology and Economics, Gellért tér 4, 1524 Budapest, Hungary.
Chemistry. 2006 Oct 25;12(31):8044-55. doi: 10.1002/chem.200600228.
High-level ab initio (CCSD(T), CBS-QB3 and CASSCF, CASPT2, MR-ACPF, MR-ACPF-2) and density functional theory (B3LYP) calculations were carried out to study the dimerization of phosphaacetylene or phosphaethyne (HCP). Seventeen low energy closed-shell and five open-shell phosphaacetylene dimers were found on the potential energy surface. Two head-to-head, one head-to-tail and three other dimerization reaction pathways were determined, all with high activation barriers, suggesting that closed-shell minima are usually kinetically stable. An open-shell head-to-head reaction pathway has also been found with moderate initial barrier (95.0 kJ mol(-1)) leading to 1,2- and 1,3-diphosphacyclobutadiene, suggesting that polymerization of HCP and oligomerization of its derivatives have open-shell mechanism. Formation of 1,2-diphosphacyclobutadiene is both thermodynamically and kinetically favored over 1,3-diphosphacyclobutadiene. A head-to-head reaction involving LiBr as a catalyst was also studied. It has been pointed out that LiBr catalyze the closed-shell mechanism. All the four possible reaction channels of this reaction yield 1,4-diphosphatriafulvene with a fairly low activation Gibbs-free energy (44.8 kJ mol(-1)), suggesting that this compound could be synthesized. This finding fully supports the experimental results.
进行了高水平的从头算（CCSD(T)、CBS-QB3以及CASSCF、CASPT2、MR-ACPF、MR-ACPF-2）和密度泛函理论（B3LYP）计算，以研究磷乙炔（HCP）的二聚反应。在势能面上发现了17个低能量闭壳层和5个开壳层磷乙炔二聚体。确定了两条头对头、一条头对尾以及其他三条二聚反应途径，所有途径都具有较高的活化能垒，这表明闭壳层极小值通常在动力学上是稳定的。还发现了一条具有适度初始能垒（95.0 kJ mol⁻¹）的开壳层头对头反应途径，可生成1,2 - 和1,3 - 二磷杂环丁二烯，这表明HCP的聚合及其衍生物的低聚具有开壳层机制。1,2 - 二磷杂环丁二烯的形成在热力学和动力学上都比1,3 - 二磷杂环丁二烯更有利。还研究了以LiBr作为催化剂的头对头反应。已经指出LiBr催化闭壳层机制。该反应的所有四个可能反应通道都以相当低的活化吉布斯自由能（44.8 kJ mol⁻¹）生成1,4 - 二磷杂三亚苯，这表明该化合物可以合成。这一发现充分支持了实验结果。
