Palladium complexes azido

In the other study [41], Pd-bis(azido) compounds [Pd(dppn)(N3)2], [Pd(dppf)(N3)2], and [Pt(l-dpn)(SMe2)(N3)2] [dppn, l,8-bis(diphenylphosphino)naphthalene dppf, l,10-bis(diphenylphosphino)ferrocene 1-dpn 1-diphenyl-phosphinonaphthalene] underwent [2 -p 3] cycloaddition with isocyanides R NC (R = cyclohexyl, rBu, 2,6-dimethylphenyl) to convert azido ligands to five-membered, C-coordinated tetrazolate rings. In a related study [42], alkynyl palladium(II)-azido species of the type [Pd(N3)(C=CR)PMe3] reacted with rBuNC to give corresponding complexes with C-bound tetrazolates. 

Complex palladium azides are obtained by dissolving palladium salts in excess azide, e.g., palladium nitrate and sodium azide (1 4) yield a triazido anion, [Pd (N3)3]" [167]. Similarly, a tetraazido anion, [Pd (N3)4] , is obtained from K2 [PdCU] by ligand exchange [162]. Another all-azido anion is the azide-bridged, binuclear complex [Pd2(N3)6] [168]. All of these have been isolated as salts of large organic cations. 

Azide cleavage of 821, utilizing a modification in which trimethylsilylazide first forms a reactive complex with DMAP that allows the reaction to occur at room temperature, affords in 85% yield diethyl (2 S, 3R)-2-azido-3-hydroxysuccinate (822). An advantage of this synthesis is that hazardous hydrazoic acid (HN3) is avoided. A one-pot two-step conversion of 822 involving hydrogenation over palladium on charcoal in the presence of di- er -butyl dicarbonate provides enantiomerically pure 823 in 66—73% yield [238,239] (Scheme 180). 

Metal-mediated DCA between azides and isocyanides typically starts from metal-azide complexes and free isocyanides. Thus, the azido complexes [RhCp (/u-N3)(N3)]2 (Cp = rj-C Me ), trani-Rh(N3)(CO)(PPh3)2, Na2[Pd(N3)4], Na2[Pd2(/u-N3)2(N3)4], and Na[Au(N3)4], reacted with aliphatic isocyanides to give a series of new metal-carbon bonded tetrazolato complexes [40]. All azide ligands in the coordination sphere undergo this cycloaddition with isocyanides except on palladium(II), where only two tetrazol-5-ato groups are formed (12, Scheme 13.11). 

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