Syntheses and structural characterization of [2.2]paracyclophane complexes of rhodium and iridium supported by diene ligands

We systematically prepared nine [2.2]paracyclophane complexes of Rh and It, [Rh(eta(6)-PCP)(C2H4)(2)]BF4.THF 1 . THF (pcp = [2.2]paracyclophane),[Rh(il pcp)(diene)]BF4 (diene = 1,5-cyclooctadiene (cod) 2-CH2O2; 2,5-norbornadiene (nbd) 3), [RhAyl, Ti pcp)(diene)(2)](BF4)(2) (diene = cod 4; nbd 5), [Ir(eta(6)-PCP)(cod)]X (X = BF4 6a; ClO4 6b . CH2Cl2) and [Ir-2(eta(6), eta(6)-pcp)(cod)(2)]X-2 (X = BF4 7a; ClO4 7b), seven structures of which were crystallographically characterized. In complexes 1 . THF, 2 . CH2Cl2, 3 and 6b CH2Cl2, each of the Rh or It atoms are eta(6)-bonded to the upper side of the two decks in the pcp ligand to afford a mononuclear structure. The Rh or Ir atoms are supported by ethylene or diene ligands. The average C(pcp)=C(pcp) distance with the Rh or Ir atom of 1.411 (1.THF), 1.413 (2.CH2Cl2), 1.411 (3) and 1.419 Angstrom (6b.CH2Cl2) is longer than those (1.393, 1.393, 1.390 and 1.400 Angstrom) without a Rh or Ir atom, respectively. The average interannular distances between the two decks are 3.03 (1 . THF), 3.01 (2 . CH2Cl2), 3.04 (3) and 3.01 A (6b . CH2O2), respectively. In contrast, in complexes 4, 5 and 7b, two Rh or Ir atoms are eta(6)-coordinated to the upper and lower decks in the pcp ligand to provide a dinuclear structure. The Rh or Ir atoms are similarly supported by diene ligands. Two coordinating cod ligands in pcp complexes 4 and 7b are located in a staggered conformation against the pcp ligand, whereas two nbd ligands in complex 5 are located in an eclipse conformation. The average C(pcp)=C(pcp) distances with the Rh or Ir atom of 1.416 (4), 1.417 (5) and 1.420 Angstrom (7b) are longer than that (1.385 Angstrom) of the metal-free pcp ligand. The average interannular distances between the two decks are 3.04 (4), 3.05 (5) and 3.05 A (7b), respectively. On complexes 1.THF-7b, the average interannular distances of 3.01-3.05 A between the two decks were found to be shorter than that (3.09 A) of the metal-free pcp ligand, suggesting that the repulsive pi-interaction between the two decks is reduced by the coordination of the metal fragment with the diene ligand to the pcp ligand. In addition, the relationships between the intramolecular distances and the configuration of the two ethylenic bridges were quite obvious. If the interannular distance was shorter than 3.05 Angstrom, the configuration of the two ethylenic bridges was more likely a twisted cross type, and if the interannular distance was shorter than 3.01 Angstrom, the configuration was more likely a parallel type, accompanying with the structure conversion of the two ethylenic bridges and the slide of the two decks. In the 1 H NMR study, the stoichiometric 1: 1 reaction solution of [M(diene)](+) (M = Rh and It; diene = cod and nbd) and the pcp ligand in CD2Cl2 or (CD3)(2)CO at 23 degreesC showed two kinds of H-1 NMR signals, which led to assign as a major mononuclear pcp complex [M(eta(6)-pcp)(diene)] (+) and a minor metal-free pcp ligand. On the other hand, the stoichiometric 2:1 reaction solution of [M(diene)](+) and the pcp ligand in CD2Cl2 or (CD3)(2)CO at 23 degreesC revealed two kinds of H-1 NMR signals, which led to assign as a minor dinuclear pcp complex [M-2(eta(6)-pcp)(diene)(2)](2+) and a major mononuclear pcp complex [M(eta(6)-pcp)(diene)](+). These results suggest that the mononuclear pcp complex [M(eta(6)-pcp)(diene)](+) is more stable in solution. (C) 2002 Elsevier Science B.V. All rights reserved.