- Functionalization of hafnium oxamidide complexes prepared from CO-induced N2 cleavage
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Functionalization of the nitrogen atoms in the hafnocene oxamidide complexes [Me2Si(η5-C5Me 4)(η5-C5H3-3- tBu)Hf]2(N2C2O2) and [(η5-C5Me4H)2Hf] 2(N2C2O2), prepared from CO-induced N2 bond cleavage, was explored by cycloaddition and by formal 1,2-addition chemistry. The ansa-hafnocene variant, [Me2Si(η 5-C5Me4)(η5-C5H 3-3-tBu)Hf]2(N2C2O 2), undergoes facile cycloaddition with heterocumulenes such as tBuNCO and CO2 to form new N-C and Hf-O bonds. Both products were crystallographically characterized, and the latter reaction demonstrates that an organic ligand can be synthesized from three abundant and often inert small molecules: N2, CO, and CO2. Treatment of [Me2Si(η5-C5Me4) (η5-C5H3-3-tBu)Hf] 2(N2C2O2) with I2 yielded the monomeric iodohafnocene isocyanate, Me2Si(η5- C5Me4)(η5-C5H 3-3-tBu)Hf(I)(NCO), demonstrating that C-C bond formation is reversible. Alkylation of the oxamidide ligand in [(η5-C 5Me4H)2Hf]2(N2C 2O2) was explored due to the high symmetry of the complex. A host of sequential 1,2-addition reactions with various alkyl halides was discovered and both N- and N,N′-alkylated products were obtained. Treatment with Bronsted acids such as HCl or ethanol liberates the free oxamides, H(R1)NC(O)C(O)N(R2)H, which are useful precursors for N,N′-diamines, N-heterocyclic carbenes, and other heterocycles. Oxamidide functionalization in [(η5-C 5Me4H)2Hf]2(N2C 2O2) was also accomplished with silanes and terminal alkynes, resulting in additional N-Si and N-H bond formation, respectively.
- Knobloch, Donald J.,Lobkovsky, Emil,Chirik, Paul J.
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- An unprecedented study of the rearrangement of 5,5-diazidobarbituric acids under various conditions
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The unexpected parabanic acid derivatives 6a,b were obtained via unprecedented rearrangement of 5,5-diazidobarbituric acids 2a,b upon stirring in water at 50-60°C. Themolysis of diazides 2a,b in benzyl alcohol at 120-130°C afforded the tetrazole derivative 11 and/or benzyl allophanate 14.
- Khattab, Ahmed F.,Kappe, Thomas
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p. 609 - 611
(2007/10/03)
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- A new class of near-infrared electrochromic oxamide-based dinuclear ruthenium complexes
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(Chemical equation presented) We report the synthesis of a new class of symmetric and unsymmetric oxamide-based dinuclear ruthenium complexes. These complexes were characterized by NMR, ESI-MS, and electrochemical methods. Spectroelectrochemical analysis of the complexes showed broad absorptions in the NIR region for the mixed-valence state of the complexes. The introduction of a chiral group into the bridging ligand produced an optically active complex that was studied using circular dichroism.
- Rastegar, Majid F.,Todd, Erin K.,Tang, Hongding,Wang, Zhi Yuan
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p. 4519 - 4522
(2007/10/03)
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- Rational design of novel immunosuppressive drugs: Analogues of azathioprine lacking the 6-mercaptopurine substituent retain or have enhanced immunosuppressive effects
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Clinical use of the immunosuppressive drug azathioprine is limited by potentially serious toxic effects related to depression of bone marrow function. The immunosuppressive and toxic properties of azathioprine are regarded as being properties of the cytotoxicity of its metabolite, 6- mercaptopurine (6-MP). However, azathioprine has an immunosuppressive effect additional to that attributable to 6-MP alone, and we propose that this is associated with an action of the methylnitroimidazolyl substituent. This suggests a route to the rational design of nontoxic immunosuppressants by replacing the 6-MP component of azathioprine with nontoxic thiols. We have synthesized and tested in vitro 24 such analogues, with two being further tested in vivo. In the human mixed lymphocyte reaction, virtually all compounds showed some degree of activity, 10 compounds being more active than azathioprine. In vivo, two compounds were more effective than azathioprine at prolonging graft survival in mice. In an oral toxicity study in male CD1 mice at doses equivalent to those at which azathioprine caused severe bone marrow depression both analogues had no toxic effects. Our results show that the immunosuppressive effects and bone marrow toxicity of azathioprine are not a consequence of release of 6-MP alone, and with appropriate modification can be separated, an approach which may lead to less toxic immunosuppressive drugs.
- Crawford, Duncan J. K.,Maddocks, John L.,Jones, D. Neville,Szawlowski, Paul
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p. 2690 - 2695
(2007/10/03)
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- Phosphoric Carboxylic Imides. Part 6. Structure and Reactivity of 1,3,2-Diazaphospholidine-4,5-diones; Crystal Structure of 1,3-Dimethyl-2-methylamino-1,3,2-diazaphospholidine-2,4,5-trione
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1,3-Dimethyl-2-methylamino-1,3,2-diazaphospholidine-2,4,5-trione (1b) has been synthesized, and its solvolytic behaviour and X-ray crystal structure determined.Methanolysis of (1b) gives products of the cleavage of both imide P-N bonds, indicating that the ring opening in (1b) is much slower than the second P-N cleavage in the ring-opened intermediate.The low reactivity of (1b) is correlated with the small size (92.3 deg) of the endocyclic N-P-N angle, which suggests that not much energy is released upon the formation of the PV trigonal bipyramidal adduct.The molecular structure of (1b) reveals a high degree of coplanarity of the phospholidine ring with both imide N-methyl groups and both carbonyl oxygen atoms.The geometry indicates that the endocyclic nitrogen atoms in (1b) are involved in the resonance interactions not only with the adjacent carbonyl groups, but also with the phosphoryl centre. 1,3-Dimethyl-2-phenoxy-1,3,2-diazaphospholidine-2,4,5-trione (1a) has been found to react with p-anisidine or ammonia exclusively at the phosphorus atom.In the reaction with p-anisidine both P-O bond cleavage (displacement of phenol) and ring P-N bond cleavage products were obtained; this is interpreted in terms of pseudorotation of the initially formed PV intermediate.Ammonia reacts with (1a) giving exclusively the ring-retained, P-OPh bond cleavage products.Our aminolysis results for (1a) contrast with those reported in the literature.
- Hutton, Alan T.,Modro, Tomasz A.,Niven, Margaret L.,Scaillet, Sonia
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