Diazene complex

Figure 6.15 Iron-sulfur-diazene complexes as studied in reference 49.

Copper (continued) cynates, 17 322, 323 diaminodithioether complexes, 17 185 diazene complexes, 27 232 difluoride, structure, 27 85, 86, 87, 88 dinuclear sites, 40 362-367 diphosphine complexes of, 14 235-239 electron-density distributions of complexes, 27 34, 41... 

Mdssbauer spectra of bonding and structure in, 15 184-187 reactions with diborane, 16 213 stabilization of, 5 17, 18-19 cyanates, 17 297, 298 cyanide complexes of, 8 143-144 cyclometallated bipyridine complex, 30 76 diazene complexes, 27 231-232 dinitrogen complexes, 27 215, 217 diphosphine complexes of, 14 208-219 dithiocarbamates, 23 253-254 -1,2-dithiolene complexes, 22 323-327 hydrogen bonding, 22 327 halide complexes with phosphine, etc., 6 25 hexaflouride, structure, 27 104 hydride complexes, 20 235, 248-281, see also Transition metal-hydride complexes... 

The first diazene complexes of nickel(0), namely [Ni(CNBu )2(PhNNPh)] and [Ni(PR3)2(PhNNPh)] (PR3 = PMe3, PBu3, PPh3) were simultaneously prepared by Otsuka and co-workers204,205 and Klein and Nixon154 according to equations (38)-(40). 

Sometimes an ancillary ligand is also lost upon deprotonation. Dehydrohalogenation of neutral diazene complexes is generally more difficult but can be accomplished in some cases. The nature of the base is important (equation 127). 

Other Lewis acids including transiton metals also bind to N in these complexes.386 Hydride sources can attack diazenido ligands at N forming the expected diazene complex (equation 152). 

In 1965 it was shown that diazonium salts apparently could be inserted into Pt—H bonds (267). The diazene complex thus formed can subsequently be deprotonated by base to yield the corresponding diazenido complex [Eq. (16)]. 

With the authenticated singly bent diazenido complexes, protonation (or, more generally, electrophilic attack) does occur at as predicted by the studies described above, to yield hydrazido(2-) complexes (39, 57-59, 72, 97, 114, 324) and protonation of doubly bent species gives diazene complexes (201, 218). 

There are four pathways leading to diazene complexes. These routes have been reviewed before (143, 275, 317) and therefore will only be outlined here, with pertinent examples. 

The reaction of [RhHCl2(PPh3)3] with aryldiazonium salts in the presence of LiCl gives complexes that were originally formulated as solvated rhodium arylazo complexes (21), but these have subsequently been shown by H NMR and 15N-labeling studies to be the diazene complexes RhCl3(NHNAr)(PPh3)2] (218). 

Treatment of polyhydrido complexes with diazonium salt, even in an excess, never results in the formation of more than a mono(diazene) complex (62, 218, 331) fEq. (24)1. 

The reaction of phenylhydrazine with copper(II) chloride in aqueous solution gives [Cu4Cl4(PhNNH)] (13) and the reactions of 1,2-disubsti-tuted hydrazines with copper(II) salts give complexes such as [Cu2-Cl2(MeNNMe)l (46, 142). The reaction of substituted hydrazines (or lithiated, substituted hydrazines) with halido complexes of the transition metals can yield diazene complexes. Complexes of Ni, Pd, Pt (147, 199,213), and Rh (209) have been prepared in this manner [Eq. (25)]. 

The reaction of transition metal oxo complexes with substituted hy-drazines yields the diazene complexes, containing the M—NRNC(R)0 chelate. 

Binuclear diazene complexes have been prepared in the meticulous and elegant work of Sellman and co-workers. The basis of the preparative route used in these studies is the oxidation of coordinated hydrazine by copper(II)-hydrogen peroxide mixtures] to yield dinitrogen complexes (291, 292). 

Controlled oxidation can give rise to the intermediate diazene complexes in low yield (293). 

Finally, the heterodinuclear diazene complex, (T)5-C5H5)Mn-(CO)2NHNHCr(CO)5], has been prepared (299, 300) by the pathway outlined in Eq. (31). 

In contrast to the diazene complexes, the hydrazido(2-) complexes are well-authenticated intermediates on the pathway leading to ammonia in the reactions of compounds of the type [Ml MPlJ (M = Mo or W P = monotertiary phosphine) (103). 

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