(η⁵-Pentamethylcyclopentadienyl)rhodium Complexes of Upper-Rim Monophosphinated Calix[4]arene

Abstract

A new and convenient synthesis of the upper-rim monobrominated calix[4]arene Br-calixPR2 is reported and has been used as the key precursor for the preparation of both the diphenyl- (6a) and diisopropylphosphine ligands (6b). Reactions of these new ligands with [(C5Me5)RhCl2]2 afford the complexes (calixPR2)(C5Me5)Rh(Cl)2 (8a,b), which can be converted into their corresponding dihydrides (calixPR2)(C5Me5)Rh(H)2 (9a,b) using NaBH4. 6a also reacts with (C5Me5)Rh(CO)2 to form (calixPPh2)(C5Me5)Rh(CO) (10). The X-ray structures for both 8a and 8b confirm the cone geometry of the calix[4]arene bowl and reveal the presence of the phenyl and isopropyl groups over the cavity. With respect to the Rh−P bond, a gauche conformation is depicted in the solid state. Complexes 8a,b and 9a,b appear to be fluxional in solution, as demonstrated from VT 1H and 31P NMR measurements for 8a,b. Molecular modelings confirm the presence of 13 conformers associated with the rotation around the C(calix)−P and P−Rh bonds and the cavity locking groups above it. The minimum energy conformation for the unsaturated (calixPPh2)(C5Me5)Rh complex exhibits the Rh atom well located at the opening of the free cavity.

Calix[4]arene-based Bis-phosphonites, Bis-phosphites, and Bis-O-acyl-phosphites as Ligands in the Rhodium(I)-catalyzed Hydroformylation of 1-Octene

“…After cooling to room temperature four pairs of doublets were again visible. These observations indicated dynamic processes typical of very flexible calix [4]arene molecules [17,18]. The results of both high temperature 1 H and 31 P{ 1 H} NMR studies were in good agreement.…”

Photochemistry of Styrylcalix[4]arenes

“…Solvents were dried with common methods. The calixarenes 8 ,17 11 ,22 and the model compound 4 23 were synthesized according to literature.…”

Calixarene-monophosphines as supramolecular chelators

“…This was regarded as an intriguing result, since there is no apparent reason for confining the metal unit inside the cavity, rather than orienting it outwards, as found by Harvey et al in a related cyclopentadienyl rhodium complex derived from 5. 22 On the other hand, the three bromine atoms anchored at the upper rim of calix 1, leading to a deepened calixarene, were expected to hinder rotation of the "Ph 2 PRuCl 2 (pcymene)" moiety about the P-C(calixarene) axis so as to keep the metal inside the calix cone. To gain more insight into the origin of this particular positioning, we decided to investigate whether the same ligand is also able to bind metals in an exo fashion.…”

“…Dichlorido-(g 6 -p-cymene)-{5-diphenylphosphino-17-diphenylphosphinoyl-25,26,27,28-tetrapropoxycalix [4]arene}ruthenium(II) (22). A solution of [RuCl 2 (p-cymene)] 2 (0.034 g, 0.056 mmol) in CH 2 Cl 2 (20 mL) was added to a solution of 21 (0.110 g, 0.113 mmol) in CH 2 Cl 2 (50 mL).…”

“…This is mainly due to the macrocyclic backbone of such a ligand being regarded merely as a spectator substituent, or simply as a bulky group. [20][21][22] In this study, we describe the coordination properties of five upper rim-monophosphinated calix [4]arenes built upon a cone-shaped calix [4]arene unit (1)(2)(3)(4)(5), and show that the cavity of these ligands may behave as an orienting group towards the [Ru(pcymene)Cl 2 ] moiety. This works complements a previous study in which the complexation behavior of tris-bromo substituted calixarene 1 was briefly described.…”