Dimeric Phosphinoboranes [R′(Hal)B‐PHR] 2 and some of their Reactions

Reactions of organylboron halides RBX 2 (R = t Bu, i Pr, Et, Me; X = Cl, Br) with lithium organylphosphides LiPHR′ (R′= mes, Ph, t Bu) in a 1:1 ratio lead to the corresponding 1,3,2,4‐diphospha‐dibora‐cyclobutanes [R′(H)P‐B(Hal)R] 2 . Further substitution to 2,4‐diphosphino derivatives has only be achieved for [ t Bu(H)P‐B( t Bu)PH t Bu] 2 ( 12 ). Its exocyclic PH t Bu groups can be metallated by LiPH t Bu, but it is more convenient to use the 1 : 3 reaction of t BuBCl 2 with LiPH t Bu for the preparation of [ t Bu(H)P‐B( t Bu)PLi t Bu] 2 ( 16 ), which was isolated as a diethyl ether solvate. Compound 12 on irradiation with a mercury vapour lamp splits off t BuPH 2 and generates the bicyclic t BuP[B t Bu‐PH t Bu] 2 ( 17 ). The new compounds have been characterized by NMR and Mass spectral data. The t Bu groups of compound [Br( t Bu)B‐PH t Bu] 2 ( 7 ), are present in an all‐ trans ‐configuration. Its B 2 P 2 ring is planar.