Oxidative Addition of Carbon−Chloride Bonds to Rhodium(I) Complexes Containing Terdentate Nitrogen Ligands. X-ray Analyses of Rhodium(I) Chloride and Rhodium(III) Chloromethyl Complexes

Potentially terdentate hemilabile 2,6-bis(R 2 -carbaldimino)pyridine and 2,6-bis(R 2 -ethylidyneimino)pyridine ligands (2,6-(C(R 1 ) NR 2 ) 2 C 5 H 3 N; R 1 = H, R 2 = i -Pr ( 1 ), t -Bu ( 2 ), cyclohexyl ( 3 ), p -anisyl ( 4 ); R 1 = Me, R 2 = p -anisyl ( 5 ), i -Pr ( 6 )) have been used to prepare in high yields the novel and highly nucleophilic complexes [RhCl(2,6-(C(R 1 ) NR 2 ) 2 C 5 H 3 N)] (R 1 = H, R 2 = i -Pr ( 7 ), t -Bu ( 8 ), cyclohexyl ( 9 ), p -anisyl ( 10 ); R 1 = Me, R 2 = p -anisyl ( 11 ), i -Pr ( 12 )) with [RhCl(alkene) 2 ] 2 (alkene = ethene, cyclooctene) as starting material. X-ray analyses of 7, 8, and 12 show severe steric interactions between the R 2 group and the equatorial chloride atom, leading to out-of-plane bending of the chloride atom. The angle between the N N N plane and the Rh Cl axis is 5.34(16)° for 7, 11.73(11)° for 8, and 10.04(11)° for 12 . Reaction of the Rh(I) complexes with CH 2 Cl 2, CHCl 3, benzyl chloride, and α,α-dichlorotoluene led to Rh(III) complexes by C Cl bond rupture. The Rh C bonds of the chloromethyl complexes [RhCl 2 (CH 2 Cl)(2,6-(C(R 1 ) NR 2 ) 2 C 5 H 3 N)] (R 1 = H, R 2 = i -Pr ( 13 ), cyclohexyl ( 15 )) are all short (2.052(5)−2.059(3) Å), while the C Cl bonds (range 1.728(4)−1.790(5) Å) are rather long, which indicates the contribution of a Rh CH 2 + Cl - resonance form. In solution all Rh(III) complexes exist as one isomer with the ligand bonded in a terdentate fashion (both 1 H and 13 C NMR), except for the complexes [RhCl 2 (R 3 )(2,6-(C(Me) N- i- Pr) 2 C 5 H 3 N)] (R 3 = CH 2 Cl ( 18 ), CH 2 Ph ( 24 ), CHClPh ( 27 ), Cl ( 33 )), which all contain two interconverting isomers; one five-coordinate Rh(III) isomer has a ligand which coordinates in a bidentate manner, while the other six-coordinate isomer has a ligand which coordinates in a terdentate fashion, as evidenced by low-temperature NMR measurements. Molecular modeling has shown that the formation of the five-coordinate Rh(III) species is caused by the axial ligands, which force the equatorial Cl atom into the N N N plane, resulting in an increased steric interaction of R 2 and R 1 . Reaction of the chloromethyl and dichloromethyl complexes 13 − 21 in boiling water with oxygen gave the trichloride complexes [RhCl 3 (2,6-(C(R 1 ) NR 2 ) 2 C 5 H 3 N)] (R 1 = H, R 2 = i -Pr ( 28 ), t- Bu ( 29 ), cyclohexyl ( 30 ), p -anisyl ( 31 ); R 1 = Me, R 2 = p -anisyl ( 32 ), i -Pr ( 33 )), while the chlorotolyl complex [RhCl 2 (CHClPh)(2,6-(C(Me) N- i -Pr) 2 C 5 H 3 N)] 27 gave the complex 33, benzaldehyde, and H 2 O 2 .