Synthesis of Phosphinines from Co^II-Catalyzed [2+2+2] Cycloaddition Reactions

Abstract

The Co II -catalyzed [2+2+2] cycloaddition of functionalized diynes and phosphaalkynes resulting in the formation of an array of structurally interesting phosphinines is reported. A combination of 1,2-bis(diphenylphosphino)benzene (dppbenz) and CoI 2 turned out to be the most suitable and active catalyst system under microwave reaction conditions. Chemoselective cyclizations of phosphaalkynes in the presence of nitriles have been observed, and a number of carbonyl functionalities are tolerated as well. The reaction can successfully be conducted with a 1:1 ratio of phosphaalkyne/diyne substrate. Model reactions with benzonitrile and diyne demonstrated that Co II catalysts in the presence of bisphosphines prefer carbocyclization, while reduction to lower oxidation states promotes heterocyclization to the corresponding pyridine. A reaction mechanism comprising a Co II oxidation state for the cyclotrimerization process is proposed and rationalized based on control experiments and theoretical calculations.

Photochemical C(sp)–C(sp2) Bond Activation in Phosphaalkynes: A New Route to Reactive Terminal Cyaphido Complexes LnM–C≡P

“…Mes-CP ( 3 ), on the other hand, is both less thermodynamically and kinetically stable than 1 and should be more similar to Ph–CP. This was demonstrated by Scheer and co-workers, who reported the coordination compound ((PPh 3 ) 2 Pt-η 2 (Mes-CP) in 2004 …”

“…In terms of stability and steric demand, phosphaalkyne 2 is expected to be in between 1 and 3 . Phosphaalkynes 1 and 3 , as well as the 1,3,5-triisopropylphenyl-substituted phosphaalkyne Tripp-CP ( 2 ), were synthesized on multigram scale according to modified literature procedures . At ambient conditions, compound 3 is a colorless oil with a freezing point of T = 10.5 °C.…”

Elimination reactions in 1,4-diphosphinine chemistry: mixed-valence intermediates and 1,1- vs. 1,4-elimination pathways

“…2–4 A plethora of functionalisation facets are known to date, ranging from 1,4-addition reactions to give II or III , 5–7 or 1,1-oxidations furnishing phosphoranes ( IV ) or phosphane oxides ( V ). 8–10 Research on phosphinines remains very active, 11,12 and a very interesting example of water addition was published by Müller in 2024 13 (Chart 1, bottom): pyridinyl-substituted VI reacted reversibly with H 2 O to form VII , but applying vacuum returned VI at ambient temperature.…”

“…[2][3][4] A plethora of functionalisation facets are known to date, ranging from 1,4-addition reactions to give II or III, [5][6][7] or 1,1-oxidations furnishing phosphoranes (IV) or phosphane oxides (V). [8][9][10] Research on phosphinines remains very active, 11,12 14 the first isolation of a 1,4-diphosphinine was not achieved until 2017 when Streubel et al synthesised a tricyclic, imidazole-2-thione-fused derivative (IX, Chart 2). 15 Since then, the scope of fused five-membered heterocycles has expanded, i.e., incorporating 1,3-thiazole-and 1,3-dithiole-2thiones 16,17 as well as different substitutions in C 2 -position, i.e., selones, 18 TTF-motifs 19 and a 2-phenylimidazolium-fused example, the latter was reported by Ghadwal et al 20 Several different reactivity studies on 1,4-diphosphinines IX have been performed, such as [4 + 2]-cycloaddition [21][22][23] and 1,4-addition reactions, 16,22 the latter yielding σ 3 λ 3 -1,4-dihydro-1,4-diphosphinine structural motifs.…”