Metal nitrogen—hydrogen bonds

With the compounds that contain nitrogen-hydrogen bonds there are highly reactive or unstable metal compounds formed. Thus with hydrazine ... 

The most widely used methods for the syntheses of monohydrazido(2—) complexes have been from the parent hydrazide and metal oxo or halide complexes with formal elimination of water (equation 168), hydrogen halide (equation 169) or trimethylchlbrosilane (equation 170). The preparation of the hydrazido(2—) complexes, shown in equation (169) and (170), shows that the driving force for the formation of metal-nitrogen multiple bonds is such that the N hydrogens are lost. 

Reactive centers in a cyclic or chelated alkyl or aryl metal silizane, such as compounds 31-54, are (1) the polar metal-carbon bond, (2) the polar metal-nitrogen bond, and (3) other bonds in the silazane, especially nitrogen-hydrogen bonds. We have been interested in reaction centers (1) and (3) and have... 

In these compounds the transition state to rotation is more or less planar whereas the ground state is twisted, but in contrast to unbridged bipyridyl the transition state is the one in which the two nitrogen atoms will pass in front. Complexation by a metal or hydrogen bonding stabilizes the planar transition state. The lowering of the barrier for racemization is at least 33.5 kJ mol-1 with complexation with PdCl2 The results are summarized in Table XV. 

This latter reaction only occurs when there is at least one monodentate phosphine coordinated to the metal. For the purpose of discussion, the remainder of this section will be divided into reactions that (i) form nitrogen-carbon bonds (ii) form nitrogen-hydrogen bonds and (iii) reactions of polynuclear complexes. 

The basicity of these nitrogen atoms facilitates protonation, coordination to metals, or hydrogen bonding to water or other protic solvents. For example, the pol3nner [NP(NHCH3)2]n forms acid-base "salts with hydrohalides, functions as a polymeric ligand for transition metals such as platinum,and at the same time is soluble in water or alcohols. 

Nitriles. Nitriles can be prepared by a number of methods, including ( /) the reaction of alkyl haHdes with alkaH metal cyanides, (2) addition of hydrogen cyanide to a carbon—carbon, carbon—oxygen, or carbon—nitrogen multiple bond, (2) reaction of hydrogen cyanide with a carboxyHc acid over a dehydration catalyst, and (4) ammoxidation of hydrocarbons containing an activated methyl group. For reviews on the preparation of nitriles see references 14 and 15. 

For a review, see Harada, K. in Patai The Chemistry of the Carbon-Nitrogen Double Bond, Ref. 40, p. 276. For a review with respect to catalytic hydrogenation, see Rylander, P.N. Catalytic Hydrogenation over Platinum Metals, Ref. 165, p. 123. 

Formally, the lone pairs on molecular nitrogen, hydrogen cyanide, and carbon monoxide are sp hybrid orbitals, whereas NLMO hybridizations calculated even lower p contributions. Hence, these lone pairs have low directionality, the electron density remains close to the coordinating atom and interaction between the lone pair and the Be2+ is comparatively weak. The Be-L bonds are easily disrupted and ligand exchange consequently can proceed with a low activation barrier. A high degree of p character, on the other hand, means that the lone pair is directed toward beryllium, with electron density close to the metal center, and thus well suited for coordination. 

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