Formation of New σ-Norbornenylrhodium(III) Complexes Promoted by Quinoline-8-carbaldehyde and Their Rearrangement into Nortricyclylrhodium(III) Derivatives. Formation of Norbornene and Nortricyclene
2011-03-28T00:00:00Z (GMT) by
[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 mol1 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.
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