Mechanistic insights into dehydrocoupling of amine boranes using dinuclear zirconocene complexes

Catalytic dehydrocoupling of H3B center dot NMe2H using the in situ system Cp2Zr(Cl)(mu-Me3SiC3SiMe3)Zr(Cl)Cp-2 (1)/ MeLi was studied as a model for previously reported dehydropolymerisation of H3B center dot NMeH2. NMR and UVvis spectroscopic monitoring of the precatalyst activation sequence as well as a series of stoichiometric experiments showed that formation of a zirconocene dimethyl complex (2) is not relevant for activation of the precatalyst. Instead, deprotonation of H3B center dot NMe2H and reaction of thus formed Li[NMe2BH3] is proposed to result in the formation of Zr amidoborane and hydride species. DFT analysis using such complexes as active species showed a pathway for formation of H-2 and H2B.NMe2. H-1 NMR spectroscopic monitoring and stoichiometric control experiments revealed the formation of unusual diamagnetic dinuclear complexes Cp2Zr(C2SiMe3)(mu-R)ZrCp2 (R = CH(2)SiMe3, 7; R = H, 9) formed by activation of the allenediide unit of the precatalyst 1. Such species can be regarded as rare singlecomponent catalysts for the dehydrocoupling of amine boranes.

Automated summary

The catalytic dehydrocoupling of H3B·NMe2H using Cp2Zr(Cl)(μ-Me3SiC3SiMe3)Zr(Cl)Cp-2 (1)/MeLi was studied, revealing the formation mechanism of Zr amidoborane and hydride species. Unusual dinuclear complex Cp2Zr(C2SiMe3)(μ-R)ZrCp2 (R = CH(2)SiMe3, 7; R = H, 9) formed through activation of the allenediide unit of the precatalyst 1 was identified as potential single-component catalysts for the dehydrocoupling of amine boranes.