C₂-Symmetric P,N Ligands Derived from Carborane-Based Diphosphetanes: Synthesis and Coordination Chemistry

Abstract

Racemic carborane-based bisphosphanes were obtained by dismutation reactions between a carborane-based diphosphetane and diaryl dichalogenides. NMR spectroscopic and theoretical studies revealed a two-step mechanism explaining the high stereoselectivity of these reactions. The coordination chemistry of the multidentate P,N ligands 6c and 6d in copper(I) and silver(I) complexes was studied. While 6d acted exclusively as tetradentate ligand, 6c showed either tridentate or tetradentate coordination depending on the metal and the counterion.

Exploiting the Ring Strain of Diphosphetanes: A Synthetic and Computational Approach towards 1,2,5‐Selenadiphospholanes

“…Both compounds show an envelope conformation of the C 2 P 2 Se ring and a trigonal‐pyramidal geometry around the phosphorus atoms (Figure ). The C cluster −C cluster bond length as well as the bond angles around the phosphorus atoms in both compounds have similar values to those found in diphospholane diselenide III and are comparable to previously published carborane‐substituted bisphosphanes ,,. The P−Se and P=Se bond lengths as well as the P−Se−P angles observed in both compounds are within the range of published values for diphospholane diselenides Ia , Ib and III , as well as the open‐chain diphosphaselenanes VI .…”

“…Due to the broadness of the signal at 76.8 ppm and partial overlap of the satellite signals with the doublets, 1 J P‐Se coupling constants could not be deduced reliably from the 31 P{ 1 H} NMR spectrum. The observed coupling constants are consistent with through‐space interactions between the phosphorus atoms which are commonly observed in carborane‐substituted bisphosphanes ,,,. The 77 Se{ 1 H} NMR spectrum shows two resonances at 338.3 ( 1 J Se−P =285 Hz) and 340.2 ppm ( 1 J Se−P =281 Hz).…”

“…The 77 Se{ 1 H} NMR spectrum shows two resonances at 338.3 ( 1 J Se−P =285 Hz) and 340.2 ppm ( 1 J Se−P =281 Hz). The shifts and coupling constants are very similar to the one observed in rac ‐1,2‐bis[ tert ‐butyl(phenylseleno)phosphanyl]‐ ortho ‐carborane (338.6 ppm ( 1 J Se−P =284 Hz)) . Crystals suitable for X‐ray diffraction were obtained by recrystallisation of 8 from a mixture of acetonitrile and toluene; the randomly selected crystal was shown to be 8‐ trans .…”

“…8‐ trans and 8‐ cis have the same energy, supporting an isomerisation process after formation of 8‐ trans . Interestingly, rac ‐1,2‐bis[ tert ‐butyl(phenylseleno)phosphanyl]‐ ortho ‐carborane, in which the methyl group at the phosphorus atom in 8 is formally replaced by a phenylselenyl moiety, is configurationally stable …”

Coordinating Ability of the Iminophosphorane Group in ortho‐Carborane Derivatives

“…Although the (P, N) ligands are the most abundant types of non‐carboranyl hybrid ligands, in the field of carboranes, only three examples of (P, N) donor ligands are known. The phosphine–amino ligand closo ‐1‐PPh 2 ‐2‐CH 2 NMe 2 ‐1,2‐C 2 B 10 H 10 was used to obtain rhodium and iridium complexes that were isolated and used in catalytic hydrogenation reactions; the ligands 1‐PR 2 ‐2‐(4‐ i Pr‐oxazolin‐2‐yl)‐1,2‐C 2 B 10 H 10 , R = Ph, Cy, were also used in rhodium‐catalyzed asymmetric hydrogenation processes, although the metal complexes were not isolated; and finally, very recently, a (P, N) bis(phosphane) derivative of carborane was used to obtain copper(I) and silver(I) complexes . Besides these few examples, the literature also describes some phosphine‐imine and phosphite‐imine carborane compounds that could be used as (P, N) chelating ligands, although no attempts have yet been made to obtain their metal complexes .…”