N,N′-Bis(diphenylphosphino)diaminophenylphosphine Ligands for Chromium-Catalyzed Selective Ethylene Oligomerization Reactions

Reaction of 1 or 2 equiv of Ph2PCl with PhP(N(H)R)2 (R = n-propyl) yields Ph2PN(R)P(Ph)N(R)H (1) or Ph2PN(R)P(Ph)N(R)PPh2 (2), respectively. In contrast, reaction of 1 or 2 equiv of Ph2PCl with PhP(N(H)R)2 (R = isopropyl) yields exclusively Ph2PN(R)P(Ph)N(R)H (3), even under more forcing conditions. Low-temperature NMR spectroscopy and a conformational analysis of Ph2PN(iPr)P(Ph)N(iPr)H (3) reveal the lowest energy conformer to have a close N−H···P interaction of 2.95 Å, which we speculate may hinder further reactivity of this molecule. Reaction of 3 with [Cr(CO)6] yields [Cr(3)(CO)4] (5), which has been structurally characterized. Coordination of ligand 3 facilitates its conversion to Ph2PN(iPr)P(Ph)N(iPr)PPh2 (4) while bound to chromium, yielding the complex [Cr(4)(CO)4] (6), which has also been structurally characterized. Ligands 1 and 2, when reacted in situ with [Cr(acac)3] (acac = acetylacetonate) and modified methylalumoxane, and complexes 5 and 6, when activated with Ag[Al(OC4F9)4] and triethylaluminum, are moderately active and selective catalysts for the selective oligomerization of ethene to 1-hexene and 1-octene.

将1当量或2当量的二苯基氯膦（Ph2PCl）与PhP(N(H)R)2（R = 正丙基）反应，可分别得到产物Ph2PN(R)P(Ph)N(R)H（1）与Ph2PN(R)P(Ph)N(R)PPh2（2）。与之相反，当将1当量或2当量的二苯基氯膦（Ph2PCl）与PhP(N(H)R)2（R = 异丙基）反应时，即便采用更严苛的反应条件，也仅能得到产物Ph2PN(R)P(Ph)N(R)H（3）。对产物3（Ph2PN(iPr)P(Ph)N(iPr)H）开展低温核磁共振波谱（Nuclear Magnetic Resonance，NMR）分析与构象研究后发现，其最低能量构象存在键长为2.95埃的N−H···P相互作用，我们推测该相互作用可能会抑制该分子的后续反应活性。将产物3与六羰基铬（[Cr(CO)6]）反应，可得到配合物[Cr(3)(CO)4]（5），该配合物的结构已完成表征。配体3与铬配位后，在配位状态下自身会转化为Ph2PN(iPr)P(Ph)N(iPr)PPh2（4），由此得到配合物[Cr(4)(CO)4]（6），该配合物的结构同样已完成表征。配体1与配体2分别与三乙酰丙酮合铬（[Cr(acac)3]，acac = 乙酰丙酮根（acetylacetonate））及改性甲基铝氧烷进行原位反应后，配合物5与配合物6经四(全氟丁氧基)铝酸银（Ag[Al(OC4F9)4]）与三乙基铝活化后，均可作为中等活性且具有选择性的催化剂，用于乙烯选择性齐聚制备1-己烯与1-辛烯的反应。