Monomeric Strontium Amides

As exemplified by the complex [Sr N(SiMe3)2 2(dme)2], a coordination number of six rather than four is often observed in monomeric strontium amides because of the relatively 

The six-coordinate diphenylamido compound [Sr(NPh2)2(thf)4] (and its Ba congener) was obtained by a salt elimination method. The compound [Sr l,2-(NDipp)2Ci2H6 -( 4] was prepared similarly to its Ca analogue (see Section 3.4.2) with acetonitrile, it formed a dinuclear complex containing the bridging primary amido ligand [NC—C(H) = C(Me)-NH]-.  

A seven-coordinate Sr compound, having chelating imino-bis(2-pyridyl)phosphoranea-mido ligands, was prepared as shown in Equation (3.13) the Ba analogue was similarly prepared. 

---

It was shown that narrow-rim CMPO derivatives form stronger 1 1 lanthanide complexes than their wide-rim counterparts. However, lanthanide extraction results display a stronger extracting ability. This discrepancy can be explained by the fact that, contrary to the wide-rim CMPO calixarenes that form polymeric species, a part of less lipophilic monomeric narrow-rim CMPO calixarene piles up at the interface instead of being extracted, as predicted by Wipff for the extraction of strontium by mixed amide calixarenes (see Section 4.4.1.1). This assumption is all the more... 

A comparison of these compounds with the corresponding zinc derivatives should clarify the influence of the empty d orbitals involved in the bonding situation of the alkaline earth metal bis(phosphanides). Whereas zinc bis[bis(trimethylsilyl)amide] is monomeric due to the steric demand of the bulky amide ligand [6], the trimethylsilyl substituted phosphanide leads to oligomers such as dimers or trimers [7], The influence of the pnicogen atom is small, thus the phosphorus and arsenic derivatives (Fig. 5.) look very similar [8] or even crystallize isotypically. In contrast to the d metals calcium, strontium and barium, zinc derivatives solely build up monocyclic ring systems. 

---