Pyridyl‐Functionalized 1‐Phosphabarrelene: Synthesis, Coordination Chemistry and Photochemical di‐π‐Methane Rearrangement

Abstract

Dedicatedtothe element phosphorus on the 350th anniversary of its discovery.Abstract: The [4+ +2] cycloaddition of 2-(2'-pyridyl)-4,6-diphenyl-l 3 -phosphinine with the highly reactive dienophile hexafluoro-2-butyne has been studied and the first pyridylfunctionalized 1-phosphabarrelenew as obtained and structurally characterized. Although monodentate CF 3 -1-phosphabarrelenes show only ap oorc oordination ability,t he chelating nature of the novel P, N-hybrid ligand gives accesst ov arious transition-metal complexes.U pon irradiation with UV light, the pyridyl-functionalized 1-phosphabarrelene undergoes ar ather selective di-p-methane rearrangementi nt he coordination sphere of the metal center, leading to the formation of ac omplex based on ah itherto unknown pyridylfunctionalized 5-phosphasemibullvalene derivative.D FT calculations provide first insights into the mechanism of this reaction.[a] Dr.M.B ruce, Dr.M .P apke,M.W eber,Prof.

Facile One‐Step Access to Pyrrole‐Based 1,4‐Diphosphabarrelenes

“…The rather high TEP value of 1 b seems to be due to the caged structure, because the comparison of the TEP values of monophosphabarrelene V and PPh 3 shows the same trend (Table 1). [23] Nevertheless, due to the electron‐rich pyrrolyl substituents, 1,2‐diphosphabarrelene 1 b is one of the strongest donors among the phosphabarrelenes [5,23] …”

Borane Adducts of Aromatic Phosphorus Heterocycles: Synthesis, Crystallographic Characterization and Reactivity of a Phosphinine‐B(C6F5)3 Lewis Pair

“…Based on our observations and due to the strong polarization of the phosphorus heterocycle caused by the interaction with the Lewis acid, we anticipated that 6 ‐B(C 6 F 5 ) 3 might exhibit a pronounced reactivity particularly towards unsaturated substrates. Previous studies have shown that activated alkynes can react with certain phosphinines, phosphinine–metal complexes, 1‐methylphosphininium salts, phosphinine‐sulfides and phosphinine‐selenides to form 1‐phosphabarrelene derivatives [14,21–23] . This orbital controlled [4+2] cycloaddition reaction proceeds by a 1,4‐addition of the dienophile across the phosphorus heterocycle.…”

“…It is interesting to note that only one regioisomer is formed in the conversion of 6 ‐B(C 6 F 5 ) 3 with styrene. In 10 ‐B(C 6 F 5 ) 3 , the phenyl group of the former styrene substrate is pointing away from the B(C 6 F 5 ) 3 moiety, most likely due to steric effects during the [4+2] cycloaddition step, as this reaction is orbital controlled [22,23] …”

“…Previous studies have shown that activated alkynes can react with certain phosphinines, phosphinine-metal complexes, 1-methylphosphininium salts, phosphinine-sulfides and phosphinine-selenides to form 1-phosphabarrelene derivatives. [14,[21][22][23] This orbital controlled [4 + 2] cycloaddition reaction proceeds by a 1,4-addition of the dienophile across the phosphorus heterocycle. Again, this process is facilitated by increasing the polarization of the aromatic phosphinine, for example, by P coordination to a metal center or by oxidation to a formal P(V) derivative.…”

“…In 10-B(C 6 F 5 ) 3 , the phenyl group of the former styrene substrate is pointing away from the B(C 6 F 5 ) 3 moiety, most likely due to steric effects during the [4 + 2] cycloaddition step, as this reaction is orbital controlled. [22,23] Motivated by these initials results, we attempted to apply 6-B(C 6 F 5 ) 3 in typical frustrated Lewis-pair reactions. [27] As styrene derivatives react with diaryl-substituted esters in the presence of the FLP system R 3 P/B(C 6 F 5 ) 3 to form substituted olefins, we decided to treat 6-B(C 6 F 5 ) 3 first with ester 11 (Scheme 7).…”