On the Reactivity of Mes*P(PMe
3 ) towards Aluminum(I) Compounds - Evidence for the Intermediate Formation of Phosphaalumenes.
Chempluschem 2023;
88:e202300078. [PMID:
36824017 DOI:
10.1002/cplu.202300078]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 02/22/2023] [Accepted: 02/23/2023] [Indexed: 02/25/2023]
Abstract
Phosphaalumenes are the heavier isoelectronic analogs of alkynes and have eluded facile synthesis until recently. We have reported that the combination of a phosphinidene transfer agent, Ar TerP(PMe3 ) (Ar Ter=2,6-Ar2 -C6 H3 ), with (Cp*Al)4 (Cp*=C5 (CH3 )5 ) afforded the phosphaalumenes Ar TerPAlCp* as isolable, violet, thermally stable compounds. In here we describe attempts to utilize Mes*P(PMe3 ) (Mes*=2,4,6-tBu3 -C6 H2 ) as a phosphinidene source in combination with different Al(I) precursors, namely Dip NacnacAl (Dip Nacnac=HC[C(Me)NDip]2 , Dip=2,6-iPr2 -C6 H3 ), (Cp*Al)4 and Cp3t Al (Cp3t =1,2,4-tBu3 -C5 H2 ). In all cases the formation of phosphaalumenes was not observed, however, their intermediate formation is indicated by formation of the dimer [Cp*Al(μ-PMes*)]2 (2) and C-H-bond activation products along the putative P=Al bond, giving unusual 1,2-P,Al-tetrahydronaphtalene derivatives 1 and 4, clearly underlining the role the sterically demanding group on phosphorus plays in these transformations. The reactivity studies are supported by theoretical studies, demonstrating a thermodynamic preference for the C-H activation products. Additionally, we show that there are potential pitfalls in the synthesis of Cp*2 AlH, the precursor to make (Cp*Al)4 and give recommendations how to circumvent these.
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