Attempts to functionalize the side-on coordinated dinitrogen ligand in [(eta; 5-C 5Me 4H) 2Hf] 2(μ 2, eta; 2 eta; 2-N 2) by addition of methyl halides such as CH 3X (X = Cl, Br, I) or alkyl halides (R-X = CH 3CH 2Br, CH 3CH 2I, and CH 3CH 2CH 2C1) resulted in 1,4-addition to yield metastable, weakly activated hafnocene end-on dinitrogen complexes, [(eta; 5-C 5Me 4H) 2HfR] (μ 2, (eta; 1, eta; 1-N 2) The product of methyl iodide addition, [(eta; 5-C 5Me 4H) 2HfCH 3](eta; 1, eta; 1-N 2) was structurally characterized and confirmed the hapticity of the N 2 ligand. Addition of the radical clocks 6-chloro-l-hexene and chloromethylcyclopropane also yielded 1,4-addition products with accompanying cyclization and ring-opening, respectively. In contrast, treatment of [(eta; 5-C 5Me 4H) 2Hf] 2-(μ 2, η 2, η 2-N 2) with benzyl chloride, benzyl bromide, or allyl bromide yielded only small quantities of the 1,4-addition product, with the majority of the mixture being the hafnocene dihalide (η 5-C 5Me 4H) 2HfX 2 and organic products of radical coupling. In benzene-d 6 solution at 23 °C, the 1,4-addition products undergo disproportionation with loss of N 2 to yield the hafnocene alkyl halide complexes (η 5-C 5Me 4H) 2Hf(R)X along with concomitant regeneration of the strongly activated side-on dinitrogen complex [(η 5-C 5Me 4H) 2(μ 2, η 2, η 2-N 2). This rearrangement is sensitive to both the halide and the alkyl substituents, where smaller groups undergo the most rapid rates of reaction, likely due to the accessibility of side-on bound N 2 intermediates.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry