Primary alkylamines 1 and hindered arylamines 1 give high yields of isocyanates 5 when reacted with carbon dioxide and the Mitsunobu zwitterions 4 generated from dialkyl azodicarboxylates and Bu 3 P in dichloromethane at -78 °C. Use of Ph 3 P still gave high yields of isocyanates from reactions of primary alkylamines, but only low yields were obtained from reactions of aromatic amines. Reactions which failed to give high yields of isocyanates gave either carbamoylhydrazines 6 and/or dicarbamoylhydrazines 10 and/or triazolinones 7. The triazolinones were shown to arise from reactions of reactive aryl isocyanates with the Mitsunobu zwitterion. The carbamoylhydrazines were shown not to arise from reaction of isocyanate with reduced dialkyl azodicarboxylates, and a mechanism for their formation is proposed. Single-crystal X-ray analyses confirmed the structures of 6, 7, and 10. 3940

The silver() iodocarbon complexes5,5-hexafluoroaceylacetonate) and [Ag 4 (hfacac) 4 (1,2-I 2 C 6 H 4 ) 3 ] 11 have been prepared and structurally characterized by single-crystal X-ray diffraction. The silver carboxylate complexes all contain carboxylate-bridged Ag 2 (carboxylate-O,OЈ) 2 dimers (Ag᎐O 2.22-2.40 Å) with the intradimer Ag ؒ ؒ ؒ Ag distance varying in the range 2.9106(12) to 3.1527(14) Å which are the values observed for the alternating dimer units Ag 2 (O 2 CCF 3 ) 2 (H 2 O) 2 and Ag 2 (O 2 CCF 3 ) 2 observed in 5. In the complexes 1-3 the silver trifluoroacetate dimers are linked by I,IЈ-bridging I 2 R ligands with one 'short' Ag᎐I bond (2.94-3.05 Å) and one 'long' Ag᎐I bond (3.13-3.14 Å) per silver. In 4, 7 and 8 the Ag 2 (carboxylate-O,OЈ) 2 dimers are extended into a chain polymer via Ag 2 O 2 rings formed by co-ordination of each silver to an oxygen atom (Ag᎐O 2.33-2.51 Å) from an adjacent dimer. The 1,2-I 2 C 6 H 4 forms an I,IЈ bridge across the two silver atoms of the dimer unit in 7 [Ag᎐I 2.918(1) and 3.024(1) Å]. Complex 8 contains an acute angle bridging IC 6 H 5 [Ag᎐I 2.927(2) and 2.970(2) Å, Ag᎐I᎐Ag 61.4(1)Њ], whilst in 4 the IC 6 H 5 is semibridging [Ag᎐I 2.853(1) and 3.309(1) Å]. In complex 5 the two structurally different dimer units are bridged in a wide-angle fashion by p-IC 6 H 4 Me [Ag᎐I 2.9200(9) and 2.9333(8) Å, Ag᎐I᎐Ag 144.53(3)Њ]. Complex 6 contains eight-atom Ag 2) rings which are interlinked to give an alternating 8646 ring chain polymer with I,IЈbridging 1,2-I 2 C 6 H 4 across the two silvers of the six-atom rings [Ag᎐I 2.722(2) and 2.980(2) Å]. The hfacac complex 10 contains a tetranuclear unit in which the hfacac ligands both chelate and bridge whilst the p-iodotoluenes each bridge two silvers via η 1 -iodocarbon and η 2 -aryl co-ordination. Complex 11 is a tetranuclear unit in which three hfacac ligands both chelate and bridge whilst the fourth hfacac ligand bridges two silvers and forms a monodentate interaction with a third silver in a µ-O, η 1 -OЈ mode. One 1,2-I 2 C 6 H 4 ligand forms a monodentate interaction with a silver atom [Ag᎐I 3.064(3) Å] whilst the other two 1,2-I 2 C 6 H 4 molecules function as highly unsymmetrical bidentate ligands [Ag᎐I 2.691(2), 3.350(2) and 2.719(2) and 3.228(2) Å]. The Ag᎐I᎐C bond angles vary from 85.9(4)Њ in 11 to 108.70(12)Њ in 3.

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