Rhodium aryloxide complexes containing terdentate nitrogen ligands, C-O bond formation, hydrogen bonding with phenol and oxidative addition reactions. Molecular structure of an Rh(III)-acetyl complex

摘要

The new rhodium(I) phenoxide complexes [Rh(OPh)(2,6-(CH=NR2)(2)C5H3N)] (R-2 = i-Pr (3), t-Ba (4)) containing strongly electron-donating N-N'-N ligands, have been prepared by a metathesis reaction of [RhCl(2,6-(CH=NR2)(2)C5H3N)] (R-2= i-Pr (1), t-Bu (2)) with NaOPh. These rhodium(I) phenoxide complexes 3 and 4, which are very sensitive to O-2 but stable towards H2O, give with phenol the adducts [Rh(OPh) (2,6-(CH=NR2)(2)C5H3N)]. HOPh (R-2 = i-Pr (5), t-Bu (6)), which contain strong O-H ... O hydrogen bonds. The hydrogen bonded phenol could not be extracted with diethyl ether, while no exchange of the hydrogen bonded phenol and the phenoxide ligand in 4 is observed on the NMR time scale, However, a small excess of phenol results in exchange of the hydrogen bonded phenol, the coordinated phenoxide ligand and free phenol on the NMR time scale. Reaction of 3 and 4 with p-nitrophenol afforded [Rh(OC6H4-(NO2-4)(2,6-(CH=NR2)(2)C5H3N)]. HOPh (R-2 = i-Pr (7), t-Bu (8)) in which the formed phenol is hydrogen bonded to the Rh(I)-OC6H4-(NO2-4) moiety, The O-H ... O bond is less strong than in 5 and 6, as the hydrogen bonded phenol could be removed by diethyl ether. Treatment of 3 with acetyl chloride and benzoyl chloride in benzene at room temperature gave phenylacetate and [RhCl2(C(O)CH3)(2,6(C(H)=N-i-Pr)(2)C5H3N)] (15), and phenylbenzoate and [RhCl2(C(O)Ph)(2,6-(C(H)=N-i-Pr)(2)C5H3N)] (19), respectively, Complex 15 and the analogous complex [RhCl2(C(O)CH3)(2,6-(C(H)=N-t-Bu)(2)C5H3N)] (16) could also be prepared directly from acetyl chloride and 1 or 2, respectively. The single crystal X-ray determination of complex 16, monoclinic, space group P2(1)/c, a=10.0477(5), b = 11.7268(6), c= 19.2336(9)Angstrom, beta = 92.041(4)degrees, Z= 4, R-1 = 0.0281, shows that the acetyl group occupies an axial position, while the N-N'-N ligand is positioned equatorially. In solution this geometry remains unchanged as was shown by variable temperature H-1 NMR measurements. When the oxidative addition of acetyl chloride to 3 was carried out al -78 degrees C in toluene the intermediate complex [RhCl(OPh)(C(O)Me)(2,6-(C(H)=N-i-Pr)(2)C5H3N)] (11) could be isolated, which at room temperature reductively eliminates phenylacetate with formation of 1. Oxidative addition of acetyl chloride to 4 at room temperature gives [RhCl(OPh)(C(O)Me)(2,6-(C(H)=Nt-Bu)(2)C5H3N)] (12) which yields phenylacetate and 2 at 70 degrees C in benzene by reductive elimination. Treatment of 3 with two equivalents of benzyl chloride afforded a mixture of [RhCl(OPh)(CH2Ph)(2,6-(C(H)=N-i-Pr)(2)C5H3N)] (13) and [RhCl2(CH2Ph)(2,6-(C(H)=N-i-Pr)(2)C5H3N)] (17) and some non-characterizable organic products, while 4 only yielded [RhCl2(OPh)(CH2Ph)(2,6-(C(H)=N-t-Bu)(2)C5H3N)](14). (C) 1998 Elsevier Science S.A. [References: 57]