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Published June 24, 2013 | Supplemental Material
Journal Article Open

Alkyne Hydroamination and Trimerization with Titanium Bis(phenolate)pyridine Complexes: Evidence for Low-Valent Titanium Intermediates and Synthesis of an Ethylene Adduct of Titanium(II)


A class of titanium precatalysts of the type (ONO)TiX_2 (ONO = pyridine-2,6-bis(4,6-di-tert-butylphenolate); X = Bn, NMe_2) has been synthesized and crystallographically characterized. The (ONO)TiX_2 (X = Bn, NMe_2, X_2 = NPh) complexes are highly active precatalysts for the hydroamination of internal alkynes with primary arylamines and some alkylamines. A class of titanium imido/ligand adducts, (ONO)Ti(L)(NR) (L = HNMe_2, py; R = Ph, ^tBu), have also been synthesized and characterized and provide structural analogues to intermediates on the purported catalytic cycle. Furthermore, these complexes exhibit unusual redox behavior. (ONO)TiBn_2 (1) promotes the cyclotrimerization of electron-rich alkynes, likely via a catalytically active Ti^(II) species that is generated in situ from 1. Depending on reaction conditions, these Ti^(II) species are proposed to be generated through Ti benzylidene or imido intermediates. A formally Ti^(II) complex, (ONO)Ti^(II)(η^2-C_2H_4)(HNMe_2) (7), has been prepared and structurally characterized.

Additional Information

© 2013 American Chemical Society. Received: January 29, 2013; Published: June 3, 2013. We thank Lawrence Henling and Dr. Michael Day for assistance with the X-ray studies. The Bruker KAPPA APEXII X-ray diffractometer was purchased via an NSF CRIF:MU award to the California Institute of Technology (CHE- 0639094). This work has been supported by USDOE Office of Basic Energy Sciences (Grant No. DE-FG03-85ER13431) and by the KAUST Center-In-Development at King Fahd University of Petroleum and Minerals (Dhahran, Saudi Arabia).

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