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

Abstract

The new rhodium(I) phenoxide complexes [Rh(OPh) (2,6-(CH=R 2) 2C 5H 3N)] (R 2 = i-Pr( 3), t-Bu( 4)) containing strongly electrondonating N-N′-N ligands, have been prepared by a metathesis reaction of [RhCl(2,6-(CH=R 2) 2C 5H 3N)] (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 H 2O, give with phenol the adducts [Rh(OPh) (2,6-(CH=NR 2) 2C 5H 3N)] · HOPh (R2 = 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(OC 6H 4-(NO 2-4))(2,6-(CH=R 2) 2C 5H 3N)] · HOPh (R 2 = i-Pr ( 7), t-Bu ( 8)) in which the formed phenol is hydrogen bonded to the Rh(I)-OC 6H 4-(NO 2-4) 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 RhCl 2(C(O)C 6H 3) (2,6(C(H)=N-i-Pr) 2C 5H 3N)] ( 15), and phenylbenzoate and [RhCl 2(C(O)Ph) (2,6-(C(H)=N-i-Pr) 2C 5H 3N)] ( 19), respectively. Complex 15 and the analogous complex [RhCl 2(C(O)CH 3) (2,6-(C(H)=N-t-Bu) 2C 5H 3N)] ( 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) Å, β = 92.041(4)°, 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 1H NMR measurements. When the oxidative addition of acetyl chloride to 3 was carried out at −78°C in toluene the intermediate complex [RhCl(OPh) (C(O)Me) (2,6-(C(H)=N-i-Pr) 2C 5H 3N)] ( 11) could be isolated, which at room temperature reductively eliminates phenylacetate with formation of 1. Oxidative addition of acetyl chlori de to 4 at room temperature gives [RhCl(OPh) (C(O)Me) (2,6-(C(H)=Nt-Bu) 2C 5H 3N)] ( 12) which yields phenylacetate and 2 at 70°C in benzene by inductive elimination. Treatment of 3 with two equivalents of benzyl chloride afforded a mixture of [RhCl(OPh) (CH 2Ph) (2,6-(C(H)=N-i-Pr) 2C 5H 3N)] ( 13) and [RhCl 2(CH 2Ph) (2,6-(C(H)=N-i-Pr) 2C 5H 3N)] ( 17) and some non-characterizable organic products, while 4 only yielded [RhCl(OPh) (CH 2Ph) (2,6-(C(H)=N-tBu) 2C 5H 3N)] ( 14).