Accessing Bioactive Hydrazones by the Hydrohydrazination of Terminal Alkynes Catalyzed by Gold(I) Acyclic Aminooxy Carbene Complexes and Their Gold(I) Arylthiolato and Gold(III) Tribromo Derivatives: A Combined Experimental and Computational Study.

Hydrohydrazination of terminal alkynes with hydrazides yielding hydrazones - were successfully catalyzed by a series of gold(I) acyclic aminooxy carbene complexes of the type [{(4-R-2,6--Bu-CHO)(N(R))}methylidene]AuCl, where R = H, R = Me (); R = H, R = Cy (); R = -Bu, R = Me (); R = -Bu, R = Cy (). The mass spectrometric evidence corroborated the existence of the catalytically active solvent-coordinated [(AAOC)Au(CHCN)]SbF (-) species and the acetylene-bound [(AAOC)Au(HC≡CPhMe)]SbF () species of the proposed catalysis cycle. The hydrohydrazination reaction was successfully employed in synthesizing several bioactive hydrazone compounds (-) with anticonvulsant properties using a representative precatalyst (). The DFT studies favored the 4-ethynyltoluene (HC≡CPhMe) coordination pathway over the -toluenesulfonyl hydrazide (NHNHSOCHCH) coordination pathway, and that proceeded by a crucial intermolecular hydrazide-assisted proton transfer step. The gold(I) complexes (-) were synthesized from the {[(4-R-2,6--Bu-CHO)(N(R))]CH}OTf (-) by treatment with (MeS)AuCl in the presence of NaH as a base. The reactivity studies of (-) yielded the gold(III) [{(4-R-2,6--Bu-CHO)(N(R))}methylidene]AuBr (-) complexes upon reaction with molecular bromine and the gold(I) perfluorophenylthiolato derivatives, [{(4-R-2,6--Bu-CHO)(N(R))}methylidene]AuSCF (-), upon treatment with CFSH.