Polynuclear rhodium(II) compounds with phosphino-phenoxide ligands Academic Article uri icon

abstract

  • The syntheses, spectral properties, and molecular structures of compounds isolated from the reaction of Rh2(O2- CCF3)4(acetone)2 with the ether phosphine tris(2,4,6-trimethoxyphenyl)phosphine (TMPP) are described. Two products are formed, the relative yields of which are determined by reaction conditions and stoichiometry. The tetranuclear compound [{Rh2(O2CCF3)3[{C6H2(OMe)3}2P{C6H2(OMe)2O}]2 (1) is favored under mild conditions with 2 equiv of phosphine ligand whereas the dinuclear product Rh2(O2CCF3)2{C6H2(OMe)3}2P{C6H2(OMe)2O}2 (2) is obtained from further reaction of 1 with TMPP or by reaction of the trifluoroacetate complex with 4 equiv of TMPP. The excess phosphine in these reactions aids in the demethylation of an ortho-methoxy substituent and, if absent, results in a low yield of substitution products. Compound 1 crystallizes as a CH2Cl2 solvate in the monoclinic space group P21/n with unit cell dimensions a = 14.718(7) Å, b - 24.040(5) Å, c = 24.260(6) Å, β = 98.78(3)°, V - 8484(5) Å3, and Z = 4. Final refinement of 937 parameters gave residuals of R = 0.058 and Rw = 0.090 with a quality-of-fit = 3.06. An X-ray structure revealed that the molecule exhibits a new binding mode for the TMPP ligand wherein a phenoxide bridge spans two dirhodium units to give a “dimer-of-dimers”. The compound dissolves in coordinating solvents with disruption of the intermolecular Rh-phenoxide bonds to give two molecules of the dinuclear species Rh2(O2CCF3)3(TMPP-O)(S) (S = solvent). The tetranuclear structure of 1 is in equilibrium with the dimer form in noncoordinating solvents such as CHCl3, as evidenced by two independent sets of phosphine resonances in the NMR and 31P NMR spectra. Compound 2 crystallizes as a CH2Cl2 solvate in the monoclinic space group P21/n with unit cell dimensions a = 14.146(4) Å, b = 19.56(1) Å, c = 23.822(6) Å, β - 101.90(2)°, V = 6449(4) Å3, and Z = 4. Residuals of R = 0.066 and Rw = 0.099 were obtained with 805 parameters and a quality-of-fit = 2.94. In 2, each Rh center is bonded to a face-capping TMPP (η3-P,O,O) and to cis-trifluoroacetate ligands in the usual bridging mode. The solid-state structure of 2 is preserved in solution, as judged by NMR spectroscopy, which reveals one type of TMPP ligand with magnetically inequivalent arene groups. The results of these studies are in contrast to previous findings for the the corresponding reactions of Rh2(O2CCH3)4 with TMPP that produce a dinuclear complex with the ligand arrangement found in 1 but no tetranuclear or bis-substituted products. Details of the syntheses, full characterization of compounds 1 and 2, and a comparison of this work to related chemistry are described. © 1994, American Chemical Society. All rights reserved.

author list (cited authors)

  • Dunbar, K. R., Matonic, J. H., & Saharan, V. P.

citation count

  • 25

publication date

  • January 1994