CHEMISTRY OF TRIS(2,4,6-TRIMETHOXYPHENYL)PHOSPHINE (TMPP) WITH DIRHODIUM TETRAACETATE - SYNTHESIS AND SPECTROSCOPIC, ELECTROCHEMICAL, AND STRUCTURAL CHARACTERIZATION OF A BINUCLEAR COMPLEX THAT CONTAINS AN UNUSUAL PHENOXY PHOSPHINE LIGAND
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Reaction of the ether-phosphine tris(2,4,6-trimethoxyphenyl)phosphine (TMPP) with Rh2(O2CCH3)4(MeOH)2 in refluxing ethanol produces the demethylated phosphine compound Rh2(O2CCH3)3(TMPP-O)(MeOH)-EtOH in 60-65% yield (TMPP-O = oxygen metalated TMPP). The new complex has been fully characterized by 1H NMR including COSY, 31P{1H} NMR and electronic spectroscopies as well as by electrochemistry and a single-crystal X-ray analysis. Crystals of 1 are triclinic, space group P1, with unit cell parameters a = 13.730 (3) , b= 14.396 (5) , c = 11.921 (5) , a = 109.65 (2), = 95.65 (2), = 64.32 (2), V = 1997 (1) 3, and Z = 2. The molecule consists of a dirhodium unit bridged by three acetate ligands and one demethylated TMPP ligand that forms two separate metallacycle rings with the rhodium atoms. In addition, there is one axial methanol ligand in the coordination sphere and an ethanol molecule in the lattice. The structure reveals that the tertiary phosphine adopts an unusual combination bridging/chelating bonding mode that involves a formal metallation of an o-methoxy group to give a phenoxyphosphine ligand. The Rh-Rh distance is 2.4228 (3) , which is in the range found for a variety of tetrabridged Rh(II, II) complexes. Electrochemical measurements in solutions containing tetra-n-butylammonium hexafluorophosphate revealed a one-electron oxidation at E1/2 = +0.71 V in THF and at +0.78 V vs Ag/AgCl in CH3CN corresponding to the process Rh24+ Rh25+. We have prepared the paramagnetic oxidation product by chemical methods and studied its behavior by electrochemistry, NMR and EPR spectroscopy. 1991, American Chemical Society. All rights reserved.
