Alkali Metal Complexes of a <i>tert</i>-Butylphosphine-Bridged Biphenolate Ligand

The coordination chemistry of group 1 metals with a potentially tridentate, dianionic biphenolate phosphine ligand that carries a phosphorus-bound tert-butyl group is described. Deprotonation of bis(3,5-di-tert-butyl-2-hydroxyphenyl)-tert-butylphosphine (H2[tBu-OPO]) with two equivalents of n-BuLi, NaH, or KH in ethereal solutions produces the corresponding alkali metal complexes {[tBu-OPO]M2(solv)x}2 (M = Li, Na, K; solv = DME, THF). An X-ray diffraction study of the lithium derivative reveals a dimeric structure that contains two [tBu-OPO]Li2(DME) units linked by two dative O−Li bonds; the two lithium atoms in each monomeric [tBu-OPO]Li2(DME) are bridged by both phenolate oxygen donors with only one lithium being coordinated to the phosphorus donor. As a result, the Li4O4 moiety in {[tBu-OPO]Li2}2 constitutes three successive Li2O2 tetragons fused in an open cubane structure. The coordination of the phosphorus donor to lithium in {[tBu-OPO]Li2(DME)}2 is also confirmed by variable-temperature 31P{1H} and 7Li{1H} NMR studies. Interestingly, the sodium complex is composed of two [tBu-OPO]Na2(DME)2 units linked by a bridging DME; each [tBu-OPO]Na2(DME)2 subunit is structurally similar to its lithium analogue though adopting one more coordinated DME. The potassium complex also contains two [tBu-OPO]K2(THF)2 moieties linked with two dative O−K bridges; the structure of the monomeric [tBu-OPO]K2(THF)2 unit, however, is markedly distinct from those of its lighter congeners. In addition to the anticipated fac-coordination from the heteroatoms in the biphenolate phosphine ligand, one of the potassium atoms in monomeric [tBu-OPO]K2(THF)2 is π-bound to one of the aryl rings incorporated in the [tBu-OPO]2− backbone.本文报道了一类带有磷键合叔丁基的潜在三齿双阴离子双酚膦配体（biphenolate phosphine ligand）与第1族金属的配位化学研究。将双(3,5-二叔丁基-2-羟基苯基)-叔丁基膦（H2[tBu-OPO]）在醚类溶剂中与两当量的正丁基锂（n-BuLi）、氢化钠（NaH）或氢化钾（KH）进行去质子化反应，可得到对应碱金属配合物{[tBu-OPO]M2(solv)x}2（其中M为Li、Na、K；solv为二甲氧基乙烷（DME）、四氢呋喃（THF））。对该系列的锂衍生物开展X射线衍射（X-ray diffraction）分析，结果显示其为二聚体结构：包含两个由两条配位O-Li键桥连的[tBu-OPO]Li2(DME)单元；每个单体[tBu-OPO]Li2(DME)中的两个锂原子均被两个酚氧给体桥联，且仅有一个锂原子与磷给体配位。由此，{[tBu-OPO]Li2}2中的Li4O4结构单元由三个连续的Li2O2四元环融合而成，形成开放式立方烷结构。通过变温31P{1H}与7Li{1H}核磁共振（NMR）研究，也证实了{[tBu-OPO]Li2(DME)}2中磷给体与锂原子的配位作用。值得注意的是，该钠配合物由两个通过桥连DME连接的[tBu-OPO]Na2(DME)2单元构成；每个[tBu-OPO]Na2(DME)2亚基的结构与其锂对应物相似，但多结合了一个配位DME。该钾配合物同样包含两个由两条配位O-K键桥连的[tBu-OPO]K2(THF)2结构单元；然而，单体[tBu-OPO]K2(THF)2单元的结构与其较轻的同系物（即锂、钠配合物）存在显著差异。除双酚膦配体中杂原子的预期面式配位（fac-coordination）外，单体[tBu-OPO]K2(THF)2中的一个钾原子还与[tBu-OPO]2-骨架中的一个芳环形成π配位作用。