Stabilization of Calcium Hydride Complexes by Fine Tuning of Amidinate Ligands
Stabilization of Calcium Hydride Complexes by Fine Tuning of Amidinate Ligands
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DOI：
10.1021/acs.organomet.6b00566
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发表时间：
2016-10-10
期刊：
影响因子：
2.8
通讯作者：
Harder, Sjoerd
中科院分区：
文献类型：
--
作者：
Causero, Andrea;Ballmann, Gerd;Harder, Sjoerd
研究了一系列对称脒基配体RAmAr（R为骨架取代基，Ar为N取代基）对（RAmCaH）-Ca-Ar型氢化钙配合物的稳定作用。发现（RAmCaN）-Ca-Ar（SiMe 3）（2）类型的前体仅对Ar = DIPP（2，6-二异丙基苯基）的配体交换稳定。骨架取代基R的大小决定聚集和溶剂化。得到如下配合物：[（RAmCaN）-Ca-DIPP（SiMe 3）（2）]（2）（R = Me，p-Tol），（RAmCaN）-Ca-DIPP（SiMe 3）（2）中心点Et 2 O（R = Np，tBu），AdAm（DIPP）CaN（SiMe 3）（2）中心点THF，和AdAm（DIPP）CaN（SiMe 3）（2）。这些杂配型酰胺钙配合物与PhSiH 3的反应仅对较大的骨架取代基（R = tBu，Ad）产生二聚氢化钙配合物（（RAmCaH）-Ca-Ar）（2）。脒基配体的（N，芳基）-配位似乎对这些络合物的稳定性至关重要，并且发现芳基中心点Ca相互作用很强（17 kcal/mol）。通过加入极性溶剂，得到了一种新型的三聚氢化钙配合物，其晶体结构为（tBuAm（DIPP）CaH）（3）center dot 2 Et（2）O和（AdAm（DIPP）CaH）（3）center dot 2 THF.这项工作的总体结论是，空间位阻（tBu vs Ad）或配位溶剂（THF vs Et 2 O）的微小变化可能对产物形成和稳定性产生重大影响。
A range of symmetric amidinate ligands RAmAr (R is backbone substituent, Ar is N substituent) have been investigated for their ability to stabilize calcium hydride complexes of the type (RAmCaH)-Ca-Ar. It was found that the precursors of the type (RAmCaN)-Ca-Ar(SiMe3)(2) are only stable toward ligand exchange for Ar = DIPP (2,6-diisopropylphenyl). The size of the backbone substituent R determines aggregation and solvation. The following complexes could be obtained: [(RAmCaN)-Ca-DIPP(SiMe3)(2)](2) (R = Me, p-Tol), (RAmCaN)-Ca-DIPP(SiMe3)(2)center dot Et2O (R = Np, tBu), AdAm(DIPP)CaN(SiMe3)(2)center dot THF, and AdAm(DIPP)CaN(SiMe3)(2). Reaction of these heteroleptic calcium amide complexes with PhSiH3 gave only for larger backbone substituents (R = tBu, Ad) access to the dimeric calcium hydride complexes ((RAmCaH)-Ca-Ar)(2). (N,aryl)-coordination of the amidinate ligand seems crucial for the stability of these complexes, and the aryl center dot center dot center dot Ca interaction is found to be strong (17 kcal/mol). Addition of polar solvents led to a new type of trimeric calcium hydride complex exemplified by the crystal structures of (tBuAm(DIPP)CaH)(3)center dot 2Et(2)O and (AdAm(DIPP)CaH)(3)center dot 2THF. The overall conclusion of this work is that minor changes in sterics (tBu vs Ad) or coordinated solvent (THF vs Et2O) can have large consequences for product formation and stability.