Cobalt complexes dinitrogen

Figure 7.10 Electronic structures of a series of bis(imino)pyridine cobalt dinitrogen complexes across three formal oxidation states.

The synthesis of the reduced bis(imino)pyridine cobalt dinitrogen complex (iPrpDijCoNj and related derivatives has prompted studies into the oxidative... 

Ding K, Pierpont AW, Breimessel W W, et al. Cobalt-dinitrogen complexes with weakened N-N bonds.J zlm Chem Soc. 2009 131 9471-9472. 

Bowman AC, Mdsmann C, Atienza CCH, Lobkovsky E, Wieghardt K, Chirik PJ. Synthesis and molecidar and electronic structures of reduced bis(imino)pyridine cobalt dinitrogen complexes bgand versus metal reduction. J Am Chem Soc. 2010 132 1676-1684. 

With the ligand dbp similar reactions yielded CoCl(dbp)3 and Co(dbp)4, but no Co(BH4)(dbp)3. Triphenyl-arsine and -stibine and CoCl2 were reduced to black products, probably cobalt metal. From NaBH3CN is afforded a Co(BH3CN)(Ph2-PCH2CH2PPh2) complex, but this does not subsequently yield a dinitrogen complex. 

Our scheme calls for the preparation of coordinatively unsaturated, or at least substitution labile, cobalt complexes that will bind O2. Reduction of halide precursor TpCo-I with magnesium metal under N2 yielded the corresponding dinitrogen complexes, see eq. 2.[8,9]... 

In dinitrogen complexes, polarization of the N2 ligand occurs with an electron-rich metal center on one side and a strongly polarizing, hard cation on the other [13]. As an example, the following resonance structure can be given for the cobalt complex [ KCo(N2)(PMe3)3 g] ... 

Relatively few compounds of this type exist. Only two simple alkene Ti-complexes are known, both prepared from the cobalt(I) complex Tp Co(N2) (19, obtained by magnesium reduction of Tp CoX (X = Cl, I) under dinitrogen)with excess H2C = CHR (R = H, CH3 Scheme 1). The ethylene complex 20 was readily isolated from solution at —30 °C, while the propene analogue 21 was only observed spectroscopically, since it proved unstable toward loss of propene upon removal of excess alkene and exposure to N2, leading to the regeneration of 19. This lability of the propene ligand was attributed to the significant steric hindrance imposed by the... 

Ding K, Brennessel WW, Holland PL. Three-coordinate and four-coordinate cobalt hydride complexes that react with dinitrogen. J/lm ChemSoc. 2009 131 10804-10805. 

The symmetrical dimer [(Me3P)3CoH]2(//-N2) is formed by protonation of the dinitrogen cobaltate precursor and its crystal structure is reported.131 The complex reversibly binds N2, forming the monomer CoH(N2)(PMe3)3. 

These radical species may (slowly) combine to form the ju-peroxodico-balt species or, as in the preparation of [CH3Co(NH3)5]2+, react (more rapidly) with the alkyl hydrazine to form the alkylated cobalt(III) species and dinitrogen. Schiff base complexes such as these are discussed in more detail later in this article. 

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