Carbaborane‐Substituted 1,2,3‐Triphospholanes and 1‐Aza‐2,5‐diphospholane: New Synthetic Approaches

Abstract

New phosphorus-containing, five-membered P,P,P and P,N,P heterocycles were synthesized and fully characterized. The P,P,P heterocycles, 1,2,3-triphospholanes, can be synthesized by two different facile pathways, whereas the P,N,P compound, a 1-aza-2,5-diphospholane, can only be obtained with silylamine.

12‐Vertex Zwitterionic Bis‐phosphonium‐nido‐carborates through Ring‐Opening Reactions of 1,2‐Diphosphetanes

“…The second P t Bu−P t Bu group (P1−P1′) is now located between two clusters, which indicates that the reductive cleavage of the 1,2‐diphosphetane was apparently followed by intermolecular coupling. The P1−P1′ bond length (223.9(3) pm) is similar to that in 1,2‐diphosphetane Ia (224.6(3) pm) and bonds found in 1,2,3‐triphospholanes or other cyclic phosphanes …”

“…Two zwitterionic 12‐vertex bis‐phosphonium‐ nido ‐carborates, 1 a and 1 b , were obtained through a ring‐opening reaction and subsequent methylation of 1,2‐diphosphetanes with lithium and methyl iodide. Additionally, lithiated intermediate 2 a was obtained from the reaction of Ia with lithium and provided insight into this reaction and other syntheses previously reported by us . Methylation reactions of 1,2‐bis(phosphino)‐1,2‐dicarba‐ closo ‐dodecaboranes(12) also resulted in phosphonium salts and proved the crucial role of the iodide anion in the reduction of the carborane cluster.…”

“…The tert ‐butyl‐ and diisopropylamino‐substituted 1,2‐diphosphetanes Ia and Ib react with elemental lithium in THF, with cleavage of the P−P bond, to give a deep red solution of the corresponding lithium salt. This lithiated intermediate (see below) offers access to novel open‐chain (addition of HCl) or cyclic (addition of dichlorophosphines) derivatives (Scheme ). The addition of methyl iodide resulted in the formation of zwitterionic bis‐phosphonium‐ nido ‐carborates, namely, 7,10‐bis( tert ‐butyldimethylphosphonium)‐ ( 1 a ) and 7,10‐bis( N , N ‐diisopropylaminodimethylphosphonium)dodecahydro‐7,10‐dicarba‐ nido ‐dodecaborate(2−) ( 1 b ; Scheme ), which were obtained as colourless crystals in moderate to good yields (72 % ( 1 a ) and 55 % ( 1 b )).…”

“…We have previously reported several syntheses incorporating cleavage of the P−P bond through the reaction of 1,2‐diphosphetane Ia with lithium (Scheme ) . We herein report the synthesis and crystal structure of [{1‐Li(THF)P t Bu‐6‐P t Bu‐4,1,6‐ closo ‐Li(THF)C 2 B 10 H 10 }{Li(THF) 3 }] 2 ⋅ 2 THF ( 2 a ), a lithiated intermediate in this reaction.…”

P−P Condensation and P−N/P−P Bond Metathesis: Facile Synthesis of Cationic Tri‐ and Tetraphosphanes

“…Similar to related 1,2,3‐triphospholane derivatives, both cations show an envelope conformation of the five‐membered ring in the solid state in which the phenyl and the imidazoliumyl substituents adopt an all‐ trans configuration. The P−P bond lengths range from 2.2156(4) to 2.2291(4) Å and are comparable to other structurally related 1,2,3‐triphospholanes . The P1‐P2‐P3 angles with a value of 98.261(16)° for 4 a [OTf] and 101.83(4) for 4 b [OTf] are more acute compared to acyclic derivatives.…”