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