Diazoalkanes complexes

A Mechanism for Alkylidene Formation. There is no unambiguous example of free-carbene capture by a metal substrate, and the mild reaction conditions used in the generation of these carbene complexes from diazoalkanes suggests that such a mechanism is highly unlikely here. Transition metal diazoalkane complexes, then, are almost certainly implicated as intermediates in these reactions. 

It is not known whether there is any carbenoid chemistry of end-on coordinated manganese-diazoalkane complexes 420 410). However, it is known that diaryldiazo-methanes 408,411 and azibenzil411 yield carbene rather than diazoalkane complexes with (n5-C5H5)Mn(CO),THF. 

Diazoalkane complexes, in preparation of diazenido complexes, 27 222 Diazoaminobenzene-copper complex, 2 39 Diazobutadiene compiexes with iron, 12 274, 275... 

Hydrazido(2-) and hydrazido(l-) complexes have also been shown to condense with aldehydes and ketones to give diazoalkane complexes containing the W=N—N=CRiR2 unit.387,388 Treatment of these complexes with LiAlFL, gives secondary amines and ammonia, whereas treatment with acid produces hydrazine, keto azines and N2-free tungsten compounds. Amines can also be produced from organohydrazido(2—) complexes.389,390... 

There is a single report of this reaction. The number of conveniently accessible diazoalkane complexes is limited (equation 142). 

Treatment of diazoalkane complexes with Li[AlH4] or LiR gives diazenido complexes (22) (dppe = Ph2PCH2CH2PPh2). For example,... 

Hydrazido(2-) complexes of Mo and W exhibit nucleophilic behavior and condense with aldehydes and ketones to give diazoalkane complexes (22), but the mechanism of these condensations has not been determined. Loss of tertiary phosphine from hydrazido(2-) intermediates to accommodate a binuclear interaction, as in Scheme 13, or to allow anion coordination are not incompatible. 

Among other C,N-donor ligand systems, the diazoalkane complexes [669,670] are widely found. The existence of three types of structures is possible due mainly to their mononuclear compounds, where either the bindings M — C (366), M—N (terminal, 367) or N — M — N (chelate, 368) are present [669,670] ... 

As in organic chemistry, diazoalkanes have found wide application as ultimate carbene sources. In contrast to the organic chemistry of diazoalkanes, however, the reactions do not proceed via free carbenes but rather via metal-mediated transformations of coordinated diazoalkanes. In some cases, diazoalkane complexes may be isolated (Figure 5.8). The parent diazoalkane, H2C=N2, has found somewhat less success in the synthesis of terminal methylene complexes LJM=CH2 however, this is primarily due to the lack of any kinetic (steric) or thermodynamic (71-dative) stabilization by carbene substituents. Thus methylene ligands... 

The intraligand bond distances in 11a are similar to those in several mononuclear tungsten diazoalkane complexes (39., 40), and the N-N (1. 35A) and C=N (1. 28A) distances are compatible with the assignment of bond orders of 1.3 and 1.9, respectively, to these bonds. Similar bond length/bond order relations suggest bond orders of ca. 1.0 for Mo2-Nl and 1.7 for Mol-Nl. The Mo-Mo bond... 

A series of aryl-substituted titanocene diazoalkane complexes, ( 5-CsMes)2Ti(N2CHAr), has also been synthesized 183.111 Dinitrogen loss affords the transient alkylidene complexes 184 that can be trapped with excess styrene to yield the titanacyclobutane complexes, (if -C5Me5)2Ti(CHArCHAr C112) 185. Measuring the rate of metallacycle formation as a function of /wra-substituent on the diazoalkane ligand has produced little effect. This observation has... 

Gp alkylidene titanium complexes have been generally generated by decomposing dialkyl and related titanium derivatives or from treatment of thioacetals with Ti(n) compounds. Thermolyzing diazoalkane complexes permits the synthesis of non-Gp alkylidene titanium derivatives (see Section 4.05.2). 

X=PF6 or BF4), 1 (M=W) gives the hydrazido(2-) complexes fra s-[WF(NNH2) (dppp)2]X and the diazoalkane complexes frans-[WF(NN=CMe2)(dppp)2]X,respectively, indicating the presence of similar species as the intermediates in conversion of the N2 ligand in 2 to NH3 or the azine. These reactions closely relate to those of 2 with MeOH or a MeOH/acetone mixture (e.g., Eq. 2). 

This reaction therefore gave a route to diazoalkane complexes by reaction of ligating dinitrogen and its discovery was particularly gratifying at the time, because attempts to produce such complexes directly by interaction of a diazoalkane with a metal complex generally caused decomposition of the diazoalkane. 

We conclude this survey of the types of reaction that were discovered by mentioning the variety of products obtained from reaction of a,cu-dibromides, Br(CH2) Br, with truns-[M(N2)2(dppe)2], which depended on the value of n. As we have already noted, for n = 1, a diazoalkane complex was formed for M = Mo. However, for M = W the complex [(WBr(dppe)2 2(jU-N2CH2N2)] was also isolated. In general, more than one type of complex was always formed, the long-chain diazenido-complexes evidently acting as alkyl bromides and attacking further dinitrogen complexes. ... 

It is clear from the products isolated from reactions in thf and related solvents discussed earlier, that as well as the alkylation reactions being a function of metal complex and halide, there is also a dependence upon solvent. If the solvent contains hydrogen atoms which are easily removed by radicals then attack on solvent might occur and the radical thereby generated can attack the M species thus yielding a diazenido-complex. This is the case, for example with thf as shown in (19), followed by a reversible reaction with protic acids to give a diazoalkane complex [Equation (20)]. 

See, for example, the following sources and references therein a) M. P. Doyle, M. A. McKervey, T. Ye, Modern Catalytic Methods for Organic Synthesis with Diazo Compounds, Wiley, New York (1998). b) J. L. Poise, A. W. Kaplan, R. A. Andersen, R. G. Bergman, Synthesis ofan n2-N2-titanium diazoalkane complex with both imido-like and metal carbene-like reactivity patterns, J. Am. 

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