Formation of New σ-Norbornenylrhodium(III) Complexes Promoted by Quinoline-8-carbaldehyde and Their Rearrangement into Nortricyclylrhodium(III) Derivatives. Formation of Norbornene and Nortricyclene

[RhCl(Nbd)]₂ (Nbd = norbornadiene) reacts with quinoline-8-carbaldehyde (C₉H₆NCHO) in the presence of N-donor ligands to give dinuclear rhodium(III) complexes [Rh(μ-Cl)(C₉H₆NCO)(Nbyl)L]₂ (L = pyridine, 1; 4-methylpyridine, 2; or isoquinoline, 3), where Nbyl is a σ-coordinated norbornenyl ligand. The reaction of 2 with chelating N-donor ligands affords mononuclear η¹-coordinated norbornenyl rhodium(III) compounds [RhCl(C₉H₆NCO)(Nbyl)(LL′)] (LL′ = 8-aminoquinoline, 4; 2-aminomethylpyridine, 5; biacetyldihydrazone, 6; 2,2′-bipyridine, 7) as a mixture of two isomers, a and b. Complex 2 reacts with monodentate ligands such as PPh₃ or CO to afford the hydroacylation product C₉H₆NC(O)Nbyl (8). The reaction of [RhCl(Nbd)]₂ with C₉H₆NCHO (Rh:C₉H₆CHO = 1:2) in benzene solution leads to H transfer from the aldehyde of one molecule of C₉H₆NCHO to norbornadiene and to the κ²-N,O coordination of the second C₉H₆NCHO molecule, giving the σ-norbornenyl derivative [RhCl(C₉H₆NCO)(Nbyl)(κ²-C₉H₆NCHO)] (9). In dichloromethane solution 9 undergoes H transfer from the aldehyde of the κ²-coordinated C₉H₆NCHO to the σ-norbornenyl group to afford [Rh(μ-Cl)(C₉H₆NCO)₂]₂ (10) and norbornene. In methanol solution two competitive reactions occur: (i) formation of 10 and norbornene as in CH₂Cl₂ or (ii) ring closure of the norbornenyl group in 9 to form a nortricyclyl group (Ntyl) to afford [RhCl(C₉H₆NCO)(Ntyl)(κ²-C₉H₆NCHO)] (11). In dichloromethane solution 11 undergoes H transfer from the coordinated aldehyde to the nortricyclyl group to afford 10 and nortricyclene. The reaction of 11 with 2,2′-bipyridine affords [RhCl(C₉H₆NCO)(Ntyl)(bipy)] (12). [RhCl(Nbd)]₂ reacts with C₉H₆NCHO in the presence of PPh₃ to yield pentacoordinated [RhCl(C₉H₆NCO)(Nbyl)(PPh₃)] (13), which in dichloromethane solution transforms into [RhCl(C₉H₆NCO)(Ntyl)(PPh₃)] (14). A proposal for this transformation is presented. The activation parameters ΔH^‡ = 22.7 ± 0.2 kcal mol^1 and ΔS^‡ = 5.3 ± 0.5 cal K⁻¹ mol⁻¹ have been determined. The complexes have been fully characterized. X-ray diffraction structures of complexes 1, 4a, 10, and 14 are also reported.