Formation of B−P Bonds through the Reaction of nido-Monophosphinocarboranes with Palladium(II) Complexes. The First Example of a Chelating R₂P−C−B−PR₂ Diphosphine

Abstract

Reaction of [NMe4][7-PPh2-8-R-7,8-C2B9H10] (R = Me, H, Ph) with cis-[PdCl2(PPh3)2] in ethanol yielded [PdCl(7-PPh2-8-R-11-PPh2-7,8-C2B9H9)(PPh3)] (R = Me, H, Ph). The Pd(II) is in a square-planar arrangement. The carborane ligand chelates the Pd through two phosphorus atoms, one from C−PPh2 and the second from the generated B(11)−PPh2. The remaining two positions are filled by a PPh3 and one chloride. In the complexation process, a previously nonexistent B(11)−P bond is generated in the ligand. This is unambiguously demonstrated by a doublet in the 11B{1H} NMR spectrum and a 1:1:1:1 quartet in the 31P{1H} spectrum. The structure was fully elucidated by a crystal diffraction analysis of [PdCl(7-PPh2-8-Me-11-PPh2-7,8-C2B9H9)(PPh3)]·C7H8. By this reaction the hitherto unknown R2P−C−B−PPh2 chelating unit has been formed.

Germa- and Stanna-closo-dodecaborate in Reaction with [PdCl2(Xantphos)]: P–C and B–H Bond Activation

“…In the complexes [Pd 2 (C 33 H 27 P 2 O)(SnB 11 H 10 )(κ 2 -Xantphos)] ( 3 ) and [Bu 3 NH][PdCl 2 (SnB 11 H 10 )(Xantphos)] ( 4 ) we have found the remarkable activation of a B–H bond and formation of a B–P bond. Like in compound 3 the evolution of benzene and B–PPh 2 formation was reported in the literature for the reaction of [PdCl 2 (PPh 3 ) 2 ] with sulfur- or phosphorus-substituted nido -dicarboranes. , In compound 4 we have found the formation of a B–PAr 3 adduct, and this type of reaction was also reported in the literature. − …”

“…The longer interatomic distance might be due to the tension inside the four-membered ring: Sn–Pd1–P1–B. The bond between the phosphorus atom and the boron atom of 1.933(5) Å can be compared with other molecules containing phosphorus connected at a borane. , The Pd–P distances show a slight variation from 2.2854(9) to 2.3770(9) Å but are within the typical range of this ligand …”

Palladium‐Catalyzed Cascade Deboronation/Regioselective B−P Coupling of closo‐Carboranes

“…Considering the oxidative B−H functionalization is incompatible with the unsymmetric nido ‐carboranes, [7] this protocol provides a valuable method with which to synthesize phosphonionido‐ nido ‐carboranes from readily available closo ‐carborane precursors. Notably, closo ‐carboranes bearing other directing groups, such as benzoxazole, and diphenylphosphine, [6e,f] also afforded the site‐selectivity governed by the directing groups ( 28 and 29 ). Therefore, the cascade deboronation/regioselective B−P coupling provides a new route to the convenient and versatile synthesis of phosphine‐containing carboranes.…”

Mechanistic Features of Boron−Iodine Bond Activation of B−Iodocarboranes

“…Moreover, our attempts to extend the Pd-catalyzed arylation of Ph 3 P with ArI to the synthesis of [9- m -C 2 B 10 H 11 PPh 3 ] + I - from 9-iodo- m -carborane and triphenylphosphine failed. Not even traces of carboranyl phosphonium salts were detected illustrates the difference in trends for reductive elimination from σ-phenyl and σ-B−carboranyl Pd iodo complexes.…”