Vicinal diamines are important structural motifs in various natural products, ligands, drug molecules, and agrochemicals. While direct installation of two N atoms on C-C multiple bonds is the most efficient and convenient way to produce 1,2-diamine, most of the studies reported so far rely on bespoke substrates and limited N sources, which lack generality. In 2007, Mountford and co-workers reported that phenylpropyne and 1,1-diphenylhydrazine react in the presence of Ti(NNPh2)(NC2,Me)(py) (1, NC2,Me = MeN(CH2CH2NSiMe3)2) to produce a 1,2-diamine in which the N-N bond of hydrazine is formally added across the alkyne. Inspired by this result, we have further developed this alkyne diamination reaction by expanding the utility of the Ti diphenylhydrazido catalyst towards other hydrazines and alkynes. We found that this reaction can proceed through two different competing pathways: unimolecular diamination or bimolecular hydrohydrazination. Preliminary results highlight that hydrazine concentration and the reaction temperature strongly impact the selectivity, with low concentrations leading to exclusive diamine formation. It has also been observed that electron-rich alkynes favor diamination, whereas electron-poor alkynes undergo hydrohydrazination. The broader aim of this project is to develop a diamination strategy that tolerates protected hydrazines so that the -NH2 functionality of the 1,2-diamine product can be orthogonally functionalized. We are also exploring Ti catalysts with different NNN-type ligands to further develop alkyne diamination and other difunctionalization methodologies.

Ti catalyzed 1,2-diamination of Alkynes using 1,1-disubstituted hydrazines

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