Alkaline-earth metal bis

The metal to phosphorus (or arsenic) ratio varies between 1 1 (alkali metal phosphanides and arsanides) and 2 1 for bis(alkali metal) phosphanediides or arsanediides. In general, these compounds form pnictogen polyhedra with the faces being capped by monovalent metal atoms. For the alkaline-earth metal phosphorus cages, metal to phosphorus ratios between 1 2 for alkaline earth metal bis(phosphanides) and 1 1 for the phosphanediides of the divalent cations are possible. 

In contrast to the lithium amides and phosphanides, dimeric alkaline-earth metal bis(phosphanides) of the heavier group 2 metals show bicyclic structures of the... 

In Table 3.6-4 the relative energies of coligand-free dimeric alkaline earth metal bis(phosphanides) are summarized [56, 57]. Whereas for Ca and Sr the bicyclic... 

The metalation of trialkylsilylphosphane and -arsane with the alkaline earth metal bis[bis(trimethylsilyl)amides] of calcium, strontium, and barium yields the mixed phosphanides and phosphanediides as well as arsanides and arsanediides depending on the stoichiometry and the demand of the trialkylsily] substituents according to Scheme 3.6-11. The main feature is the M2E3 bipyramid with the metal atoms in apical positions. These cages are often interconnected via common faces (61, 63, 64, 65, 67, and 69). A substitution of the phosphanide substituents by other Lewis bases such as THF or benzonitrile is not possible for these compounds and, consequently, homoleptic phosphanediides and arsanediides with inner M4E4 heterocubane moieties are so far unknown for M = Ca, Sr, and Ba. In all these cases a further metalation to obtain homoleptic phosphanediides failed. 

The formation of alkaline earth metal bis[bis(tiialkylsilyl)amides] has been discussed in detail elsewhere." Like all heavier group 2 metal bis[bis(tiisalkylsilyl)amides], the complex [(Ca N(SiMe3)2 2)2] has a dimeric structure both in solution and the solid state (Figure 3.8), in which the calcium atoms are in a distorted trigonal planar environment. 

The metallation of trialkylsilyl-substituted phosphanes with the easily accessible alkaline earth metal bis[bis(trimethylsilyl)amides] in ether such as tetrahydrofuran or 1,2-dimethoxyethane yields quantitatively the alkaline earth metal phosphanides according to Eq. 1 [1]. The ether content depends on the size of the alkaline earth metal. 

Due to ab initio SCF calculations the favored bicyclic structure of the alkaline earth metal bis(phosphanides) can be explained by small, but structure dominating d orbital participation. Whereas the monocyclic magnesium bis(phosphanide) H2P-Mg(p-PH2)2Mg-PH2 with a C2/, symmetry is favored by 27.9 kJ/mol against the bicyclic Ci symmetric bicycle, the bicyclic compounds M(p-PH2)3M-PH2 of calcium and strontium are lower in energy [5]. In the case of the... 

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. 

The alkaline earth metal bis(tetraethylalanates) are also formed in the following reaction ... 

Yang D, Ding Y, Wu H, Zheng W. Synthesis and structural characterization of alkaline-earth-metal bis(amido)silane and lithium oxobis(aminolato)silane complexes. Inorg Chem. 2011 50(16) 7698-7706. 

The development of the heavy alkaline-earth metal bis(bis(trimethylsilyl)amides, M[N(SiMe3)2]2(thf)2, has been instrumental in the use of the transaminadOTi route as a viable and dependable synthetic route towards the preparadmi of alkaline-earth metal compounds. The amides, M[N(SiMe3)2]2(thf)2, can be prepared via salt metathesis involving treatment of the metal halides with alkali metal amide (Ca-Ba) [182, 183]. The heavier metal (Sr, Ba) amides can also be obtained by direct metallation in liquid, anhydrous ammonia (Sr and Ba) [83,90,91, 184-187]. 

Gartner M, Eischer R, Langer J, Gorls H, Walther D, Westeihausen M (2007) Syntheses and structmes of alkaline-earth metal bis(diphenylamides). Inorg Chem 46 5118-5124... 

Bismuthides. Many intermetaUic compounds of bismuth with alkafl metals and alkaline earth metals have the expected formulas M Bi and M Bi, respectively. These compounds ate not saltlike but have high coordination numbers, interatomic distances similar to those found in metals, and metallic electrical conductivities. They dissolve to some extent in molten salts (eg, NaCl—Nal) to form solutions that have been interpreted from cryoscopic data as containing some Bi . Both the alkafl and alkaline earth metals form another series of alloylike bismuth compounds that become superconducting at low temperatures (Table 1). The MBi compounds are particularly noteworthy as having extremely short bond distances between the alkafl metal atoms. 

A mercury cathode finds widespread application for separations by constant current electrolysis. The most important use is the separation of the alkali and alkaline-earth metals, Al, Be, Mg, Ta, V, Zr, W, U, and the lanthanides from such elements as Fe, Cr, Ni, Co, Zn, Mo, Cd, Cu, Sn, Bi, Ag, Ge, Pd, Pt, Au, Rh, Ir, and Tl, which can, under suitable conditions, be deposited on a mercury cathode. The method is therefore of particular value for the determination of Al, etc., in steels and alloys it is also applied in the separation of iron from such elements as titanium, vanadium, and uranium. In an uncontrolled constant-current electrolysis in an acid medium the cathode potential is limited by the potential at which hydrogen ion is reduced the overpotential of hydrogen on mercury is high (about 0.8 volt), and consequently more metals are deposited from an acid solution at a mercury cathode than with a platinum cathode.10... 

The heavy alkaline earth metals Ca, Sr, and Ba react with 2 equivalents of NJ -bis(2,6-diisopropylphenyl)formamidine in the presence of bis(pentafluorophenyl)-mercury to afford the bis(formamidinato) species as THF adducts in good to moderate yield (Scheme 23). When the same reactions are carried out in a 1 1 molar ratio, N-p-tetrafluorophenyl-N,N -bis(2,6-diisopropylphenyl)formamidine is isolated as the sole product in all cases (Scheme 23). Other substituted N -bis(aryl)formamidinate complexes of the heavy alkaline earth metals were synthesized accordingly. ... 

It is also possible to isolate bis(carbene) complexes involving the heavier alkaline earth metals. Thus, the reaction of two equivalents of 4 (R = Me or (Bu, R = H) with calcium, strontium and barium bis(trimethylsilyl)amides [M N(SiMe3)2 2(thf)2] (M = Ca, Sr, Ba) resulted in the displacement of two thf molecules to afford the corresponding biscarbene species, 19 (19). The solubilities and stabilities of these complexes were found to decrease from calcium to barium. 

Tab. 3.6-4. Relative energies obtained by ab initio SCF calculations of dimeric alkaline-earth metal dihydrides and bis(phosphanides) (kj mol-1).

The synthesis of heterobimetallic cages which contain alkaline-earth metals and tin(+2) atoms succeeds by the metalation of trialkylsilyl substituted phosphanes with the bis(trimethylsilyl)amides of tin(+2) and of calcium, strontium, or barium according to Scheme 3.6-13. Heterobimetallic cages of tin and magnesium are unknown, instead their formation mixtures of the homometallic phosphanides are observed [75],... 

An elegant access to larger cluster units is to make use of preformed smaller clusters as they occur, e.g., in Zintl phases [8, 9]. The phase KSi (or K4Si4) contains homoatomic Si4 tetrahedra, and thus a salt-like formulation (Na )4[Si4]" with a formal electron transfer is appropriate (Fig. 1) [10]. Such homoatomic anionic building blocks occur in binary or ternary intermetallic phases A E and A Pn j with A being an alkali and alkaline-earth metal, and E = Si-Pb and Pn = P-Bi. These phases are generally available in good quantities, and - since a few members... 

The same transformation was reported to follow treatment of 17 with excess sodium hydroxide (Sequiv), in aqueous acetone. In this case, the product yield was lower. With a reduced amount of alkali, 0.5 equiv KOH, both the hydroxy derivative 140 and the difurazanyl ether-linked bis(triazolooxadiazole) 37 resulted (Scheme 21) <1999RJ01525>. As a precaution it should be noted that the strongly acidic nature of hydroxyfurazans means they readily form stable salts with amines and alkali or alkaline earth metals, and such salts show a tendency to decompose with explosion on shock, friction, or fast heating, and so should be handled with care <1999RJ01525>. 

This chapter describes the various ways that the rates of acyl transfer reactions can be enhanced in supramolecular complexes or by supramolecular catalysts in which the crucial ingredients are such simple and relatively featureless chemical species as alkaline-earth metal ions, mainly Sr and Bi ions, and occasionally Ci . ... 

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