Synthesis and Structural Characterization of Double Metal Cyanides of Iron and Zinc: Catalyst Precursors for the Copolymerization of Carbon Dioxide and Epoxides

Several synthetic approaches for the preparation of double metal cyanide (DMC) derivatives of iron(II) and zinc(II)
are described. These include (1) metathesis reactions of ZnCl2 or ZnI2 with KCpFe(CN)2CO in aqueous solution,
(2) reactions of KCpFe(CN)2CO and its phosphine-substituted analogues with Zn(CH3CN)4(BF4)2 and subsequent
displacement of acetonitrile at the zinc centers by the addition of a neutral (phosphine) or anionic (phenoxide)
ligand, and (3) reactions of the protonated HCpFe(CN)2(phosphine) complexes with Zn(N(SiMe3)2)2, followed by
the addition of phenols. All structures are based on a diamond-shaped planar arrangement of the Fe2(CN)4Zn2
core with various appended ligands at the metal sites. Although attempts to replace the iodide ligands in
[CpFe(μ-CN)2PPh3ZnI(THF)]2 with acetate using silver acetate failed, two novel cationic mixed-metal cyanide salts
based on the [CpFe(PPh3)(μ-CN)2Zn(NC5H5)]22+ framework were isolated from pyridine solution and their structures
were defined by X-ray crystallography. The anionic ligand bound to zinc in these derivatives, which serve as an
anionic polymerization initiator, was shown to be central to the catalytic copolymerization reaction of CO2/epoxide
to provide polycarbonates and cyclic carbonates. The structurally stabilized phosphine-strapped complexes
[CpFe(μ-CN)2Zn(X)THF]2(μ-dppp), where X = I or phenolate, were shown to be thermally stable under the conditions
(80 °C) of the copolymerization reaction by in situ infrared spectroscopy. Both of these derivatives were proposed
to serve as mimics for the heterogeneous DMC catalysts in the patent literature, with the derivative where the
initiator is a phenolate being more active for the production of polycarbonates.

本文详细阐述了制备双金属氰化物（DMC）衍生物的铁（II）和锌（II）的多种合成方法。这些方法包括：（1）在水溶液中，将ZnCl2或ZnI2与KCpFe(CN)2CO进行置换反应；（2）KCpFe(CN)2CO及其膦取代类似物与Zn(CH3CN)4(BF4)2反应，随后通过加入中性（膦）或阴离子（苯氧基）配体来置换锌中心的乙腈，以及（3）将质子化的HCpFe(CN)2(膦)配合物与Zn(N(SiMe3)2)2反应，随后加入酚。所有结构均基于Fe2(CN)4Zn2核心的菱形平面排列，金属位点上连接有各种配体。尽管尝试使用乙酸银将[ CpFe(μ-CN)2PPh3ZnI(THF)]2中的碘化物配体替换为乙酸失败，但基于[CpFe(PPh3)(μ-CN)2Zn(NC5H5)]22+框架的两种新型阳离子混合金属氰化物盐从吡啶溶液中分离出来，其结构通过X射线晶体学得到确定。这些衍生物中与锌配位的阴离子配体，作为阴离子聚合引发剂，在催化共聚反应（将CO2/环氧物共聚生成聚碳酸酯和环状碳酸酯）中起着核心作用。结构稳定的膦配位配合物[CpFe(μ-CN)2Zn(X)THF]2(μ-dppp)，其中X = I或苯氧基，通过原位红外光谱证实，在共聚反应条件（80 °C）下具有热稳定性。这两种衍生物均被提议作为专利文献中非均相DMC催化剂的模拟物，其中含有苯氧基引发剂的衍生物在聚碳酸酯的生产中活性更高。