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The "Hidden" Reductive [2+2+1]-Cycloaddition Chemistry of 2-Phosphaethynolate Revealed by Reduction of a Th-OCP
Jingzhen Du1, Gábor Balázs2, Ashley J Wooles1
1Department of Chemistry, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
Abstract:
The reduction chemistry of the newly emerging 2-phosphaethynolate (OCP)- is not well explored, and many unanswered questions remain about this ligand in this context. We report that reduction of [Th(TrenTIPS )(OCP)] (2, TrenTIPS =[N(CH2 CH2 NSiPri 3 )]3- ), with RbC8 via [2+2+1] cycloaddition, produces an unprecedented hexathorium complex [{Th(TrenTIPS )}6 (μ-OC2 P3 )2 (μ-OC2 P3 H)2 Rb4 ] (5) featuring four five-membered [C2 P3 ] phosphorus heterocycles, which can be converted to a rare oxo complex [{Th(TrenTIPS )(μ-ORb)}2 ] (6) and the known cyclometallated complex [Th{N(CH2 CH2 NSiPri 3 )2 (CH2 CH2 SiPri 2 CHMeCH2 )}] (4) by thermolysis; thereby, providing an unprecedented example of reductive cycloaddition reactivity in the chemistry of 2-phosphaethynolate. This has permitted us to isolate intermediates that might normally remain unseen. We have debunked an erroneous assumption of a concerted fragmentation process for (OCP)- , rather than cycloaddition products that then decompose with [Th(TrenTIPS )O]- essentially acting as a protecting then leaving group. In contrast, when KC8 or CsC8 were used the phosphinidiide C-H bond activation product [{Th(TrenTIPS )}Th{N(CH2 CH2 NSiPri 3 )2 [CH2 CH2 SiPri 2 CH(Me)CH2 C(O)μ-P]}] (3) and the oxo complex [{Th(TrenTIPS )(μ-OCs)}2 ] (7) were isolated.
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