XL-Xantphos: Design and Synthesis of a Mechanistic Probe of Xantphos <i>O</i>‑Coordination in Catalytic Reactions

The synthesis and characterization of an analog of the Xantphos ligand that is geometrically incapable of coordination of the xanthene bridging oxygen atom is reported. This new ligand, XL-Xantphos, ((9,9-dimethyl-9H-xanthene-4,5-diyl)­bis­(4,1-phenylene))­bis­(diphenylphosphane), was studied in homogeneous, catalytic reactions for comparison with Xantphos. The XL-Xantphos ligand performed essentially identically to Xantphos in Rh-catalyzed hydroformylation of 1-octene, which suggests that the high regioselectivity for linear aldehyde is due to the large bite angle of these ligands and is not influenced by oxygen coordination to the metal. The Pd-catalyzed amidocarbonylation of 4-bromoanisole with dimethylhydroxylamine hydrochloride similarly showed no difference between Xantphos and XL-Xantphos. Computations on Pd­(II) phosphine complexes at the DLPNO–CCSD­(T) level of theory indicated that these ligands have different preferences for cis and trans coordination modes. The XL-Xantphos ligand has a thermodynamic preference for trans-chelated structures, whereas the cis-[(Xantphos)­PdCl2] isomer was calculated to be thermodynamically more stable than its trans isomer. Given the key role of d8 square planar Pd intermediates in many catalytic cycles, the greater preference of Xantphos to form cis chelates may indeed be a factor which has made this ligand particularly effective.

Rights

CC BY-NC 4.0

Data and Resources

Additional Info

Field Value
Theme
Author Gregory T. Whiteker (1398331), Fangzheng Li (1398334), Robert D. J. Froese (2348245), Michael L. Tulchinsky (2870756), Amaruka Hazari (1621246), Jerzy Klosin (1508728)
Maintainer
Source https://figshare.com/articles/XL-Xantphos_Design_and_Synthesis_of_a_Mechanistic_Probe_of_Xantphos_i_O_i_Coordination_in_Catalytic_Reactions/8072219
Source Created 2019-05-02T19:13:19Z
Source Modified 2019-05-02T19:13:19
Language English
Spatial
Source Identifier 10.1021/acs.organomet.9b00141.s002
Dataset metadata created 16 May 2019, last updated 16 May 2019