Synthesis and Metal Complexation Reactions of Bis-Dioxocyclams from Photochemical Reaction of Bis-Chromium Alkoxycarbene Complexes with Imidazolines

Photoinduced Reactions of Metal Carbenes in Organic Synthesis

“…Bis-carbene complexes underwent photoreaction with imidazolines to give bis-azapenams as 1:1 mixtures of diastereoisomers. (The relative configuration of each azapenam had the two heteroatoms trans, as expected, but a 1:1 mixture of [(R,R)(S,S)] and (R,S) diastereomers resulted) 160 L. S. Hegedus [28,29]. Bis-carbenes linked through the alkyl (rather than alkoxy) groups reacted similarly but in lower yields [30].…”

“…(26) (27) Photoinduced Reactions of Metal Carbenes in Organic Synthesis 183 Table 15 Photo-driven reactions of hydroxycarbene complexes with alcohols 184 L. S. Hegedus Table 16 Photo-driven reactions of aminocarbenes to produce a amino acids (28) Activated esters for use in peptide-coupling reactions were produced by photolysis of optically active chromium aminocarbenes with alcohols which are good leaving groups, such as phenol, pentafluorophenol, 2,4,5-trichlorophenol, and N-hydroxysuccinimide (Table 17) [109]. Since arylcarbenes bearing the op- tically active oxazolidine auxilliary are difficult to synthesize and often unstable, the above chemistry does not afford an effective approach to aryl glycines.…”

Synthesis of Macropolycyclic Ligands Based on Tetraazacycloalkanes

“…Recently, an unusual and efficient syntives, the protection reaction leads simultaneously to monoprotected, cis and trans diprotected, tri-and tetraprotected thesis of C-substituted 5,12-dioxocyclams and bis(dioxocyclams) was reported, based on acid-catalysed dimerization macrocycles, and hence a laborious chromatographic purification step is necessary. Moreover, disubstituted tetraaza-of azepenams [83] [84] . However, the 2,6-dioxocyclen and 5,12-dioxocyclam starting materials can be obtained on a cycloalkanes have previously been prepared according to the Richman and Atkins cyclization [62] [79] , but this method-larger scale according to literature procedures, and only two nitrogens are available for connection to a bridging group, ology is far from optimal as many chemical functions cannot survive the harsh conditions required in the detosyl-the two trans-amide groups inducing a trans-"autodiprotection" of the macrocycles.…”

trans-Dioxocyclam (1,4,8,11-tetraazacyclotetradecane-2,9-dione) dihydrate and its NiIIcomplex

“…The NiÐN amide bonds are slightly shorter than the NiÐN amine bonds, at 1.892 (5) and 1.902 (5) A Ê , respectively, as might be expected due to the increased charge attraction between the amidate N atoms and the cation. This bond-length difference is about twice that found in the Ni II complex of the octa-C-substituted ligand analogue having the same size and amide placement (L 7 ), where the bond distances are 1.915 A Ê for NiÐN amine and 1.911 A Ê for NiÐN amide (Dumas et al, 1995). Steric interactions between the ring substituents may account for these rather longer NiÐN bond lengths.…”

“…Although the synthesis of L 1 is quite simple, by a Michael addition between ethylenediamine and methyl acrylate (Tomalia & Wilson, 1985), and the ligand has been known for 15 years, no work on its transition metal complexes has been published. However, some substituted analogues (L 6 ±L 8 ) of the same trans-dioxo con®guration have been synthesized by a different method, and their Ni II complexes have been reported (Betschart & Hegedus, 1992;Dumas et al, 1995). We report here the crystal structures of L 1 H 2 ÁH 2 O, (I), and the corresponding Ni II complex, [NiL 1 ]Á2H 2 O, (II).…”