Green Routes to Fluorocarbons

碳氟化合物是用于各种应用的重要材料。例如，小分子氢氟碳化合物（HFC）具有低的臭氧消耗潜力，并且已经取代了被禁止的氯氟烃（CFC）作为制冷剂、发泡剂、溶剂等。最近，不饱和HFC正在销售，其相对于其饱和类似物已经大大降低了全球变暖潜力。然而，这些分子的工业生产包括使用对环境有问题的氯碳化合物和有毒金属如锑。含氟聚合物的独特性能，如低表面能、高热稳定性和化学稳定性，使其特别适用于热塑性塑料、涂料、弹性体膜和功能材料。不幸的是，这些材料是通过能源密集型自由基工艺或乳液聚合制备的，这些工艺采用环境持久性含氟表面活性剂。因此，对于重要的单体如偏二氟乙烯（CH 2 = CF 2）和六氟丙烯[CF 2 =CF（CF 3）]，没有办法控制插入的区域和立体选择性，从而控制聚合物的微观结构。此外，衍生自这些单体与CF2（CF2=CF2）的共聚的重要材料也遭受缺乏一致性质的问题，这是由于目前采用的聚合方法的无规性质。在我们的研究计划中，我们的目标是：1）使用商业催化热解装置在低压（< 20 ℃）下通过廉价的散装聚四氟乙烯（PTFE）和二氟甲烷，乙炔或合成气（CO/H2）的共热解制备氢氟烯烃（HFA）。含碳气体被多相催化剂活化，然后与PTFE热解产生的气相CF 2联合收割机结合。固体碱如MgO或水滑石将用于从CH 2F 2中除去HF以产生CHF卡宾，金属催化剂将活化乙炔以用于CF2加成或插入C-H键，并且费托催化剂将用于在催化剂表面上产生CHn单元以用于与气相CF2卡宾反应。优化的反应条件将用于扩大实验室使用的选定氢氟烷烃的生产规模，并随后将技术转让给行业合作伙伴。 2)通过金属环戊烷中间体，开发贱金属络合物催化的氢氟碳化合物反应，这将为生产具有技术价值的氢氟碳化合物提供更环保的途径。我们的有前途的结果与低协调的有机氟镍杂环将扩展到包括半不稳定的N-杂环卡宾硫醚配体的稳定的低价催化剂下H2和双功能的P-N和P-B配体异裂的二氢和可逆的C-F键活化，分别。低配位铁配合物也将进行评估，以比较d5，6有机氟金属配合物的反应性与我们的d 7，8镍的例子，特别是关于形成和官能化的混合HC/FC金属杂环和发展的串联过程，使生产性使用的HF产品。 3)研究亲核金属氟卡宾作为HFA复分解和聚合的引发剂，通过金属环丁烷中间体。基于新开发的CF2转移到低价金属使用Me 3SiCF 3和催化NaI，我们将合成一些新的亲核碱金属氟卡宾，并研究其与HFA的环加成反应性和随后的氟化物提取。靶系统包括XL 2钳形配体和金属氢氟卡宾。这些基础研究将伴随着使用甲硅烷基试剂将CFRF和CHRF卡宾传递到低价金属前体和随后催化插入C-H键的串联过程的快速通量催化测试。

Fluorocarbons are important materials for a variety of applications. Small molecule hydrofluorocarbons (HFCs), for example, have a low ozone depletion potential and have replaced banned chlorofluorocarbons (CFCs) as refrigerants, blowing agents, solvents, etc. More recently, unsaturated HFCs are being marketed that have greatly diminished global warming potential relative to their saturated analogs. Industrial production of these molecules, however, includes use of environmentally problematic chlorocarbons and toxic metals such as antimony. The unique properties of fluoropolymers such as low surface energy, high thermal and chemical stability make them especially useful as thermoplastics, coatings, elastomer membranes and functional materials. Unfortunately, these materials are prepared by energy-intensive radical processes or emulsion polymerization that employs environmentally persistent fluorosurfactants. As a result, for important monomers such as vinylidene fluoride (CH2=CF2) and hexafluoropropene [CF2=CF(CF3)] there is no way to control the insertion regio- and stereoselectivity and thus the polymer microstructure. Moreover, important materials derived from copolymerization of these monomers with tetrafluoroethylene (CF2=CF2) also suffer from a lack of consistent properties resulting from the random nature of the currently employed polymerization methods. In our research program we aim to: 1) Prepare hydrofluoroalkenes (HFAs) from co-pyrolysis of inexpensive bulk polytetrafluoroethylene (PTFE) and difluoromethane, acetylene or syngas (CO/H2) at low pressures (< 20 torr) using a commercial catalytic pyrolysis unit. The carbon-containing gases are activated by the heterogeneous catalyst and then combine with gas phase CF2 generated by the PTFE pyrolysis. Solid bases such as MgO or hydrotalcite will be used to remove HF from CH2F2 to generate CHF carbene, metal catalysts will activate acetylene for CF2 addition or insertion into a C-H bond, and Fisher-Tropsch catalysts will be used to generate CHn units on the catalyst surface for reaction with the gas phase CF2 carbenes. Optimized reaction conditions will be used for scaled-up production of selected HFAs for lab use and subsequent technology transfer to industry partners. 2) Develop base metal complex-catalyzed reactions of HFAs, proceeding through metallacyclopentane intermediates, that will offer greener routes to technologically valuable HFCs. Our promising results with low-coordinate organofluoronickelacycles will be extended to include hemilabile N-heterocyclic carbene-thioether ligands for stabilization of the low-valent catalyst under H2 and bifunctional P-N and P-B ligands for heterolytic cleavage of dihydrogen and reversible C-F bond activation, respectively. Low-coordinate Fe complexes will also be evaluated to compare the d5,6 organofluorometallacycle reactivity with our d7,8 nickel examples, particularly with regard to formation and functionalization of mixed HC/FC metallacycles and development of tandem processes that make productive use of the HF product. 3) Investigate nucleophilic metal fluorocarbenes as initiators for HFA metathesis and polymerization via metallacyclobutane intermediates. Building on newly developed CF2 transfer to low-valent metals using Me3SiCF3 and catalytic NaI, we will synthesize a number of new nucleophilic base metal fluorocarbenes and investigate their cycloaddition reactivity with HFAs and subsequent fluoride abstraction. Target systems include XL2 pincer ligands and metal hydrofluorocarbenes. These fundamental studies will be accompanied by rapid throughput catalytic testing of tandem processes using the silyl reagent to deliver CFRF and CHRF carbenes to low-valent metal precursors and subsequent catalyzed insertion into C-H bonds.