Molybdenum(VI) Bis(imido) Complexes: From Frustrated Lewis Pairs to Weakly Coordinating Cations |
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| Authors: | Angela Milinkovic Dr Antoine Dupé Ao Univ-Prof Dr Ferdinand Belaj Univ-Prof Dr Nadia C Mösch-Zanetti |
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| Institution: | Institute of Chemistry – Inorganic Chemistry, University of Graz, Schubertstraße 1, 8010 Graz |
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| Abstract: | Molybdenum(VI) bis(imido) complexes Mo(NtBu)2(LR)2] (R=H 1 a ; R=CF3 1 b ) combined with B(C6F5)3 ( 1 a /B(C6F5)3, 1 b /B(C6F5)3) exhibit a frustrated Lewis pair (FLP) character that can heterolytically split H−H, Si−H and O−H bonds. Cleavage of H2 and Et3SiH affords ion pairs Mo(NtBu)(NHtBu)(LR)2]HB(C6F5)3] (R=H 2 a ; R=CF3 2 b ) composed of a Mo(VI) amido imido cation and a hydridoborate anion, while reaction with H2O leads to Mo(NtBu)(NHtBu)(LR)2](HO)B(C6F5)3] (R=H 3 a ; R=CF3 3 b ). Ion pairs 2 a and 2 b are catalysts for the hydrosilylation of aldehydes with triethylsilane, with 2 b being more active than 2 a . Mechanistic elucidation revealed insertion of the aldehyde into the B−H bond of HB(C6F5)3]−. We were able to isolate and fully characterize, including by single-crystal X-ray diffraction analysis, the inserted products Mo(NtBu)(NHtBu)(LR)2]{PhCH2O}B(C6F5)3] (R=H 4 a ; R=CF3 4 b ). Catalysis occurs at HB(C6F5)3]− while Mo(NtBu)(NHtBu)(LR)2]+ (R=H or CF3) act as the cationic counterions. However, the striking difference in reactivity gives ample evidence that molybdenum cations behave as weakly coordinating cations (WCC). |
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| Keywords: | frustrated Lewis pair H2 activation hydrosilylation Mo(VI) bis(imido) weakly coordinating cation |
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