Alkyldiazenido complexes

Alkyldiazenido complexes, mechanisms of formation, 27 223-225 Alkylfluorophosphines, 13 367-378 Alkyl ftillerides, 44 38 Alkylidiboranes cyclic, 16 215, 216 electron diffiaction studies of, 16 216 NMR of, 16 216 preparation of, 16 214, 215 Alkyllithium compounds, crystal structures, 37 83-85... 

Their proton base strengths are less than that of the dinitrogen complex, but greater than that of the hydrazido(2 -) complexes.139 Their structures are likely to be similar to those of the alkyldiazenido complexes discussed below, that is trans octahedral with a linear MoNN system and NNH = 120°, but definite evidence is lacking. 

The alkyldiazenido complexes [MoX(N2R)(dppe)2] are generally synthesized by reaction of alkyl halides with [Mo(N2)2(dppe)2]. The reaction mechanism has been elucidated in some detail,140 and is believed to involve a step in common with substitution reactions of the bis(dinitrogen) species, namely rate-controlling reversible thermal loss of N2 (equation 14). The full reaction sequence is set out in equation (15). 

This reaction offers attractive possibilities for preparing alkyldiazenido complexes. However, this reaction may be limited as only one hydride is known to work well, CpMH(CO)3 (M = Mo, W), see equation 146. 

In the same manner, the addition of acid to alkyldiazenido complexes of this type gives rise to hydrazido(2-) complexes (76) fEq. (40)1. 

The increased basicity of a ligand when coordinated to the heavier metals in a transition metal triad has been appreciated for some time (311). This is manifest in (1) the rate of alkylation of alkyldiazenido complexes (kw/kMo = 5.4) (93), and (2) the rate of formation of hydra-zido(2-) complexes by the reaction of dinitrogen complexes with acid, in methanol ( w// Mo = 9.2 x 102) (186), and in tetrahydrofuran (kw/ kMo = 29-85, dependent upon the acid and substrate employed) (187). Clearly the electron-releasing capability of the metal has conflicting influences on the rate, but as in Section VI,El the basicity influence dominates. 

Low-valent complexes of Mo and W undergo photochemistry, e.g., the Nj complexes M(N2)2(dppe)2 [M = Mo or W, dppe = l,2-bis(diphenylphosphino)ethane] react with alkyl bromides to form alkyldiazenido complexes, e.g. ... 

In the next section, we will discuss several alkyldiazenido complexes which were obtained by alkylation of dinitrogen complexes with strongly nucleophilic alkylation reagents. At least one such case is also known for aryldiazenido complexes. Sellmann and Weiss (1978) showed that a (dinitrogen)manganese complex reacts with phenyllithium (see Sect. 3.3). 

For these reasons, we start this section not with a discussion of structural types of alkyldiazenido complexes, but with the syntheses. Here, it is remarkable, that, in two early reviews and in three specific papers published in the 1970 s and 1980 s, the first synthesis of alkyldiazenido complexes was claimed in various papers published in 1967, 1969, 1972, 1978, and in the mid-1980 s. These uncertainties are, in the opinion of the present author, related to the two reasons mentioned in the preceding paragraph. 

Lappert and Poland (1969) were the first authors who reported on the discovery and characterization of mononuclear alkyldiazenido complexes by reaction of (tri-methylsilyl)diazomethane with tricarbonyl(cyclopentadienyl)molybdenum hydride and the analogous tungsten hydride. Scheme (10-18) demonstrates that these reactions are not simple substitutions of a carbonyl by a diazenido ligand, but that they are insertions of the diazoalkane into the M-H bond (see also Lappert and Lorberth, 1967). 

In Section 10.2, Sutton (1993) was quoted because all attempts to synthesize aryldiazenido complexes of nickel were without success. Nevertheless, alkyldiazenido complexes are known, as seen below. 

Some alkyldiazenido complexes of nickel, palladium, molybdenum, and ruthenium were obtained by ligand exchange or by ligand addition. They were later demonstrated not to have end-on structures, but a side-on (t ) coordination at both diazo N-atoms. Itsuka and coworkers demonstrated that in bis( r butylisocyanide)... 

Another synthesis of alkyldiazenido complexes is due to Chatt et al. (1977 b), and independently to the work of Hidai et al. (1976 b), namely a route by condensation of hydrazido(2 —) metal complexes with aldehydes or ketones. The original work of Hidai et al. (1976 a) concentrated on molybdenum complexes, that of Chatt et al. (1977 b) on tungsten, but both groups used the same type of ligands as their starting material complexes, namely [Mo(NNH2)(dppe)2] X (X = F, Cl, Br or I). The... 

Simple alkyl bromides and iodides react at room temperature to give alkyldiazenido complexes (Equation... 

Interestingly, l-bromo-4-chlorobutane also cyclizes with 15 to produce [MoBr(NNCH CH CH H2)(dppe)2]Cl in which bromine is attached to molybdenum, and chloride is the anion. Recently, the secondary alkylation of alkyldiazenido complexes to form dialkylhydrazido complexes has been reported. " However, when 20 is treated with MeBr or EtBr, no alkyldiazenido complex is isolated, but instead a dialkylhydrazido complex is produced (Equation 18) ... 

Hussain, H., Leigh, G.J., Modh-Ali, H. and Pickett, C.J. Mechanism of alkylation of alkyldiazenido-complexes of molybdenum(II) and tungsten(II) influence of metal and co-ligands on the nucleophilicity of a diazenido-group J.Chem.Soc. Dalton Trans., (1986), 1473-1477... 

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