Calcium complexes amides

Calcium-binding proteins, 6, 564, 572, 596 intestinal, 6, 576 structure, 6, 573 Calcium carbonate calcium deposition as, 6, 597 Calcium complexes acetylacetone, 2, 372 amides, 2,164 amino acids, 3, 33 arsine oxides, 3, 9 biology, 6, 549 bipyridyl, 3, 13 crown ethers, 3, 39 dimethylphthalate, 3, 16 enzyme stabilization, 6, 549 hydrates, 3, 7 ionophores, 3, 66 malonic acid, 2, 444 peptides, 3, 33 phosphines, 3, 9 phthalocyanines, 2,863 porphyrins, 2, 820 proteins, 2, 770 pyridine oxide, 3,9 Schiff bases, 3, 29 urea, 3, 9... 

Several aluminum biphenolate complexes have been investigated as initiators for the ROP of PO.810,935 Unlike the TPP and salen-based systems, a cis coordination site is realistically accessible and in theory an alternative cis-migratory mechanism to the backside attack pathway might operate. However, NMR analyses on the resultant PPO show that stereochemical inversion still occurs when the biphenolate initiators are used (Scheme 22). It has also been confirmed that the same process occurs with the Union Carbide calcium alkoxide-amide initiator for both PO and CHO.810... 

Calcium alkoxides synthesis, 336 Calcium complexes acetylacetone, 372 amides, 164 malonic acid, 444... 

Led by the efforts of Westerhausen and coworkers, a variety of heavy alkaline earth metal zincates or aluminates under formation of alkaline earth metal-carbon contacts have been prepared. Examples include the reaction of trialkylalanes with donor-free calcium 6i5-amides to afford dimeric aluminates, shown in Figure 30. Noteworthy is the planar Ca2N2 center of this complex, in addition to close calcium-aluminum contacts, which may indicate the presence of three-center, two-electron bonding. 

Base for C-H or N-H Deprotonation of Precursors to Carbene or Amide Ligands in the Preparation of Metal Complexes. KHMDS has been used as a base for the deprotonation of N-H or B-H bonds in imine-based ligands or trispyrazolyl borate-derived ligands to synthesize calcium complexes, which were used as initiators of the ring-opening polymerization of lactides. A first example of a two-coordinate, neutral In singlet carbene complex has been prepared via an in situ deprotonation of the imine ligand precursor with KHMDS in the presence of In I to afford the In(I) complex in 36% unoptimized yield as pale yellow, thermally stable crystals. ... 

More recent work has pressed towards even more selective sensors for calcium, stimulated by a 2 1 ligand calcium stoichiometry found by Petranek and Ryba (129) for a calcium crown ether which exhibited high calcium ion selectivity over magnesium. Thus, Shono and co-workers (130) have studied a bicyclic polyether amide derivative with enhanced selectivity for calcium, while Simon and co-workers (131) have reported a non-crown neutral carrier for calcium which forms a 3 1 ligand calcium complex with very high selectivity for calcium over sodium and potassium, that is, by factors of 10 and 10, respectively. This indicates that macrocyclic systems are not a prerequisite for high selectivity. 

Primary and secondary amines and amides are first chlorinated at nitrogen by the chlorine released by the gradually decomposing calcium hypochlorite. Excess chlorine gas is then selectively reduced in the TLC layer by gaseous formaldehyde. The reactive chloramines produced in the chromatogram zones then oxidize iodide to iodine, which reacts with the starch to yield an intense blue iodine-starch inclusion complex. 

Two equiv. of 6,6-di(cyclopropyl)fulvene react at 60 °C over a period of a week with Ca[N(SiMe3)2]2-(THF)2 bis in THF to yield the metallocene 170. The heteroleptic amido complex 171 is detected as an intermediate with 111 and 13C 1H NMR spectroscopy. A 1 1 reaction of the calcium amide and 170 also produces 171 in solution, an equilibrium involving these three derivatives exists (Equation (30)). The calcocene 170 crystallizes at — 20 °C from THF as colorless cuboids. The metal center is surrounded by the four ligands in a distorted tetrahedral manner, and the cyclopentadienyl group and the propylidene fragment are coplanar with each other.393... 

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. 

Even a cursory reading of Chapter 3 of the previous volume/ dealing with alkaline earth diorgano amides, shows that detailed information on their preparation, structure and reactivity was quite sparse. For example, there were no data available for strontium or barium amide derivatives and there was just one structure of a complex related to a calcium amide - that of [(thf)3Ca( AIH j(. - in which calcium was incorporated as part of an... 

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. 

A related reaction sequence that involves the Michael addition of a coordinated amide ion to an a,0-unsaturated malonate results in the formation of a P-carboxyaspartic acid complex. The acid is isolated as the calcium salt by reduction of cobalt(III) followed by recovery and hydrolysis of the diethyl ester (Scheme 45).215... 

Harder prepared the two bis(methanide) complexes 39 and 40 from the respective reactions between the parent methane and the relevant bis-amide [M N(SiMe3) 2].34,35 Under no circumstances could a second deprotonation be observed. In common with 38, 39 and 40 were found to contain calcium- and barium-methanide contacts in the solid state. 

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