Green Routes to Fluorocarbons

氟碳化合物是各种应用的重要材料。例如，小分子氢氟碳化物(HFC)具有低的臭氧消耗潜力，已取代禁用的氯氟烃(CFCs)作为制冷剂、发泡剂、溶剂等。最近，不饱和HFC正在上市，与其饱和类似物相比，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和有毒金属，如锑。氟聚合物的独特性质，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，这些材料是通过使用环境持久性氟表面活性剂的能量密集型自由基工艺或乳液聚合来制备的。因此，对于重要的单体，如偏氟乙烯(CH2=CF2)和六氟丙烯[CF2=CF(CF3)]，无法控制插入区域和立体选择性，从而无法控制聚合物的微观结构。此外，由于目前使用的聚合方法的随机性，这些单体与四氟乙烯(CF2=CF2)共聚得到的重要材料也缺乏一致的性质。在我们的研究计划中，我们的目标是：1)使用商用催化裂解装置，由廉价的本体聚四氟乙烯(PTFE)与二氟甲烷、乙炔或合成气(CO/H2)在低压(&lt；20torr)下共热解制备氢氟烯(HFA)。含碳气体被多相催化剂活化，然后与聚四氟乙烯裂解生成的气相CF2结合。固体碱，如氧化镁或水滑石，将用于从CH2F2中脱除HF以生成CHF卡宾，金属催化剂将激活乙炔进行CF2加成或插入C-H键，Fisher-Tropsch催化剂将用于在催化剂表面生成CHn单元，用于与气相CF2卡宾反应。优化的反应条件将用于扩大生产选定的氢氟烷烃以供实验室使用，并随后向行业合作伙伴转让技术。*2)开发贱金属络合物催化的HFA反应，通过金属环戊烷中间体进行，这将为生产具有技术价值的氢氟碳化物提供更环保的途径。我们关于低配位有机氟镍环的研究成果将被扩展到包括用于H_2下稳定低价催化剂的半活性N-杂环卡宾-硫醚配体，以及分别用于异源裂解二氢和可逆C-F键活化的双功能P-N和P-B配体。还将评估低配位铁络合物，以比较d5，6有机氟金属环的反应性与我们的d7，8镍的例子，特别是关于混合的HC/FC金属环的形成和官能化，以及利用HF产品的串联工艺的开发。*3)研究亲核金属氟卡宾作为HFA歧化和通过金属环丁烷中间体进行聚合的引发剂。在新开发的利用Me3SiCF3和NaI催化CF2转移到低价金属的基础上，我们将合成一些新的亲核贱金属氟卡宾，并研究它们与HFA的环加成反应以及随后的氟化物提取。目标系统包括XL2钳形配体和金属氢氟卡宾。这些基础研究将伴随着使用硅基试剂将CFRF和CHRF卡宾传递到低价金属前体以及随后催化插入C-H键的串联过程的快速吞吐量催化测试。

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.