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

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 st able 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 a nd the phenoxide ligand in 4 is observed on the NMR time scale, Howeve r, a small excess of phenol results in exchange of the hydrogen bonded phenol, the coordinated phenoxide ligand and free phenol on the NMR t ime 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 whic h the formed phenol is hydrogen bonded to the Rh(I)-OC6H4-(NO2-4) moie ty, 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 ga ve 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 a cetyl chloride and 1 or 2, respectively. The single crystal X-ray dete rmination 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 N MR measurements. When the oxidative addition of acetyl chloride to 3 w as carried out al -78 degrees C in toluene the intermediate complex [R hCl(OPh)(C(O)Me)(2,6-(C(H)=N-i-Pr)(2)C5H3N)] (11) could be isolated, w hich at room temperature reductively eliminates phenylacetate with for mation of 1. Oxidative addition of acetyl chloride to 4 at room temper ature gives [RhCl(OPh)(C(O)Me)(2,6-(C(H)=Nt-Bu)(2)C5H3N)] (12) which y ields phenylacetate and 2 at 70 degrees C in benzene by reductive elim ination. Treatment of 3 with two equivalents of benzyl chloride afford ed 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-character izable 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.