Syntheses and Characterization of Upper Rim 1,2- and 1,3-Diphosphinated Calix[4]arenes and Their Corresponding 1,5-Cyclooctadienylrhodium(I) Complexes:  Comparison of the Catalytic Hydroformylation Properties of Terminal Alkenes

Abstract

The 5,11- (1,2-isomer) and 5,17-bis(dialkylphosphino)-25,26,27,28-tetra-n-propoxycalix[4]arene (1,3-isomer) ligands (alkyl = Me, i-Pr) have been prepared and coordinated to Rh(COD)+ fragments (COD = 1,5-cyclooctadiene). The ligands 5,17-bis(diphenylphosphino)-11,23-dibromo-25,26,27,28-tetra-n-propoxycalix[4]arene and 5,11-bis(diphenylphosphino)-25,26,27,28-tetra-n-propoxycalix[4]arene have been coordinated to M(COD)+ (M = Rh, Ir) and RhCl(CO) fragments, as well. On the basis of mass spectrometry and 31P NMR spin−lattice relaxation time measurements (T 1), all of the complexes are found to be dimers. Molecular modeling provides evidence that ring stress favors the dimer over the monomer, and the modeled structures for both 1,2- and 1,3-isomers have been corroborated by the comparison of the photophysics of the Ir(COD)+ species at 77 K. The decrease in emission lifetimes of the P2Ir(CC)2 + lumophore in the presence of 1-hexene is more pronounced for the 1,3-isomer, indicating reduced steric hindrance about the metallic center. The catalytic hydroformylation of five terminal alkenes using all six Rh(COD)+ catalyst precursors has been investigated under various conditions in order to extract the turnover frequencies (tof as defined as the number of moles of products divided by the total number of moles of rhodium used per hour) and the ratios of the product distribution (n/ i, normal vs internal). The comparison of the data suggests that the basicity and the cone angle of the phosphines influence the n/i ratios. The tof's are generally larger for the 1,2-series for 1-hexene, but depend on the nature of the phosphine for styrene, vinyl acetate, vinyl benzoate, and vinyl p-tert-butylbenzoate. All in all, these complexes are good catalysts with respect to literature data, notably those containing the (i-Pr2P)− groups. During the course of this study, one hydride carbonyl complex has been synthesized and characterized from 1H and 31P NMR, IR, and T 1 measurements.

An Original Calix[4]arene‐Containing Oligomer/Polymer Catalyst for Homogeneous Hydroformylation

“…The steric hindrance/ring stress-driven ROP process is also supported by the fact that the catalytic intermediates are 5-and 6-coordinate species that require room around the metal atom. [13] In this respect, a linear coordination polymer offers less steric problems than the dimer as one can deduce in the models (Figure 1 and 2). With more ring stress in 1-8 and less in 10, the induction period to produce the more active species, where there is less steric hindrance, is shorter for the former than for 10.…”

“…The same hydroformylation conditions employed by Plourde et al [13] were used for hex-1-ene in the presence of a catalytic amount of 10. The reaction is complete within 48 h (>99%) with no evidence for the hydrogenated product, hexane.…”

“…[10][11][12] This group has anchored Rhcontaining fragments at diphosphinated calix [4]arene macrocycles at the upper-rim, but these amorphous materials that appear as polymers in the solid state, are essentially dimers in solution that exhibit obvious ring stress and steric hindrance (see compounds 1-8 in Scheme 1). [13] The equilibrium between the polymer (solid state) and the 'stressed' dimer (solution) is not unprecedented ({Pd 2 (dmb) 2 Cl 2 } n (solid) versus Pd 2 (dmb) 2 Cl 2 (solution); dmb ¼ 1,8-diisocyano-p-menthane). [14] Consequently, the catalytic properties should be a function of the ring opening polymerization (ROP) process prior to efficient catalysis.…”

“…, and n/i is 1.71 (50 8C/THF/70 atm H 2 /CO 1: 1), [13] little is gained with 10 (except for a modest change in n/i ratio). However, the long induction period is indicative that the more active catalyst is formed slowly for 10 in comparison with 1-8 where no induction was observed at all.…”

The Spectroscopy and Photophysical Behavior of Diphosphine- and Diisocyanide-Containing Coordination and Organometallic Oligomers and Polymers: Focus on Palladium and Platinum, Copper, Silver, and Gold

“…In solution, the polymer becomes a binuclear complex as is demonstrated by the estimation of the molecular dimension from the measurements of spin-lattice relaxation time (T 1 ) and nuclear Overhauser enhancement (NOE) constants using closely related binuclear palladium complexes. The technique was recently established [20,21], and used successfully on several occasions thereafter [12,22,23]. The driving force for such phenomena is the the ease of dissolving small molecules-with better solute-solvent interactions-rather than large polymers, particularly when the polymers do not incorporate soluble side-chains.…”