Amines coordinated secondary

Oxidative dehydrogenations of many macrocyclic ligand complexes have now been documented. Typically, these reactions involve conversion of coordinated secondary amines to imine groups. 

Coordinated secondary amines can also be alkylated, but only after deprotonation by a strong base generates a suitable nucleophile. Work on rhodium(III) complexes of ethylenediamine12 has been extended to nickel(II) complexes of various fully saturated macrocycles such as cyclam (Scheme l).13,14 The methylated cyclam complex is kinetically inert, unlike the isomer with all four methyl groups on the same side of the ring, which is obtained on reaction of the preformed tetramethyl cyclam with nickel ions. 

It is likely that the Lewis acidity of the/ac-[99mTc(CO)3]+ moiety is the reason for cleavage. It is assumed that one remaining water molecule is acidified and attacks intramolecularly the tertiary N-C bond, resulting in a hydroxo group on the cleaved carbon and a secondary amine coordinated to technetium. 

The structure of the cages sep and sar is such that to invert the overall configuration of the complex, simultaneous inversion of all six coordinated secondary amines is necessary. This leads to the extraordinary configurational stability even the Co(II) sar complex is not race-mized in solution over 2 hours (6, 7). 

In the absence of a kinetically stable M—N bond the asymmetry is lost due to rapid pyramidal inversion of the free amine (AG<25 kjmol ), unless the asymmetrically substituted nitrogen atom is part of a rigid organic ring system. The simplest and earliest studied coordination compound incorporating an asymmetric coordinated secondary nitrogen as the sole source of chirality is [Co(sarcosine)(NH3)4] (sarcosine = N-methylglycinate) (28). Numerous reports... 

Typical examples of the rich coordination chemistry of saturated tetraaza macrocycles are the complexes given by 1,4,8,11-tetraazacyclotetradecane, also known as cyclam, with nickel(II) (Table 103). Isomerism is expected to occur in the Ni-cyclam system due principally to the different configurations about the asymmetric coordinated secondary amines which, in turn, influence the possible conformations which can be adopted by the chelate rings. In the tram octahedral complexes [NiX2(cyclam)] (373 X = Cl, and [NiI(cyclam)]I-H20 ... 

Imines. The hydrogenation of imines is challenging because is difficult to find catalysts providing high enantioselectivity, broad applicability and acceptable rates at moderate pressures of hydrogen. Additional complications are the interconversions between the E and Z isomers in case of the acyclic substrates, the tendency to racemisation of the secondary amines obtained after the reaction and the inhibition of the catalyst by amine coordination. Iridium-based catalysts are finding increased application in this reaction. The most common substrates are ( )-imines derived from acetophenone (35, Scheme 7.15). 

There are five basic forms for the trans or planar metal complexes which contain 1,4,8,11-tetraazacyclotetradecane, cyclam, or the hexamethyl analog, CTH. These forms arise due to the combinations of the configurations of the four asymmetric coordinated secondary amine nitrogens present in these systems. Each secondary amine proton is approximately in an axial position and either resides above or below the plane containing the nickel and four nitrogen atoms. Three of these forms are nonenantiomeric (I, II, and III, Fig. 1) and two are enantiomeric (IV and V, Fig. 1). The numerals 3 and 2 in Fig. 1 represent the three and two carbon chains, respectively, which span adjacent coordinated secondary amines. The + and — notation represents secondary amine protons above and below the plane,... 

Secondary amines react readily with dichlorocarbene to yield secondary formamides in good yield [17, 18]. Apparently, the secondary amine coordinates with dichlorocarbene, and after proton transfer a dialkylaminodichloromethane is produced. The latter undergoes basic hydrolysis under phase transfer conditions which evidently stops before appreciable cleavage of the formamide occurs. The reaction is formulated in equation 3.12 and several examples are tabulated in Table 3.5. 

The majority of U(V1) coordination chemistry has been explored with the trans-ddo s.o uranyl cation, UO " 2- The simplest complexes are ammonia adducts, of importance because of the ease of their synthesis and their versatihty as starting materials for other complexes. In addition to ammonia, many of the ligand types mentioned ia the iatroduction have been complexed with U(V1) and usually have coordination numbers of either 6 or 8. As a result of these coordination environments a majority of the complexes have an octahedral or hexagonal bipyramidal coordination environment. Examples iuclude U02X2L (X = hahde, OR, NO3, RCO2, L = NH3, primary, secondary, and tertiary amines, py n = 2-4), U02(N03)2L (L = en, diamiaobenzene n = 1, 2). The use of thiocyanates has lead to the isolation of typically 6 or 8 coordinate neutral and anionic species, ie, [U02(NCS)J j)/H20 (x = 2-5). 

The heavier chalcogens are more prone towards secondary interactions than sulfur. In particular, the chemistry of tellurium has numerous examples of intramolecular coordination in derivatives such as diazenes, Schiff bases, pyridines, amines, and carbonylic compounds. The oxidation state of the chalcogen is also influential sulfur(IV) centres engender stronger interactions than sulfur(II). For example, the thiazocine derivative 15.9 displays a S N distance that is markedly longer than that in the corresponding sulfoxide 15.10 (2.97 A V5. 2.75-2.83 A, respectively). ... 

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