155826-39-4Relevant academic research and scientific papers
Platinum(II) complexes with monocoordinated 2,9-dimethyl-1,10-phenanthroline and phosphine ligands. Exchange of the donor nitrogen and rotation about the Pt-P and P-C bonds studied by NMR spectroscopy: Arene stacking as an intramolecular brake
Fanizzi, Francesco P.,Lanfranchi, Maurizio,Natile, Giovanni,Tiripicchio, Antonio
, p. 3331 - 3339 (2008/10/08)
The structure and dynamic behavior of the platinum complexes cis- and trans-[PtX2(Me2-phen)(PPh3)] (X = Cl (1), Br (2), I (3); cis isomer, a; trans isomer, b), trans-[PtX(Me2-phen)(PPh3)2]X (X = Cl (4), Br (5), I (6)), and trans-[PtX(Me2-phen)(PBun3)2]X (X = Cl (7), Br (8), I (9)) containing monocoordinated 2,9-dimethyl-1,10-phenanthroline (Me2-phen) are reported. Exchange of the donor atom (flipping) for the singly bonded Me2-phen and rotations about the Pt-P and P-C bonds of the phosphine have been investigated by NMR spectroscopy. For the first time the ΔG* for flipping of a bidentate ligand with converging lone pairs of electrons has been measured and found to be strongly dependent upon the nature of the trans ligand (trans effect). The ΔG* for rotation about the Pt-P bond is unusually high in the case of PPh3 ligands (Δ* > 10 kcal/mol) and does not change significantly among the different compounds examined, although the Pt-P bonds are 0.1 A? longer in complexes 4-6 (phosphine trans to another phosphine) than in complexes 1a-3a (phosphine trans to a halogen atom). The PBun3 complexes 7-9 exhibit much smaller ΔG* values for phosphine rotation (2-phen ligand. One phenyl ring of PPh3 (the most shielded one) exhibits restricted rotation about the P-Cipso bond with ΔG* in the range 7.1-7.8 kcal/mol. The two remaining phenyls of PPh3 are not equivalent, and for one of them restricted rotation about the P-Cipso bond is also observed. The crystal structures of the complexes cis-[PtCl2(Me2-phen)(PPh3)] (1a) and trans-[PtCl(Me2-phen)(PPh3)2]Cl (4), as chloroform solvates, have been determined by X-ray diffraction methods. One phenyl of each phosphine ligand overlaps with the coordinated end of Me2-phen, the Cipso atom eclipsing the nitrogen atom of the phenanthroline; a second phenyl of the phosphine comes close to the second end of Me2-phen. A stacking interaction between a phenyl ring of PPh3 and the Me2-phen aromatic system appears though to be responsible for the high-energy barrier to phosphine rotation, thus simulating an electromagnetic brake. Crystal data of 1a·CHCl3: space group P21/n, a = 15.996(6) A?, b = 17.996(6) A?, c = 12.314(4) A?, β = 111.23(2)°, Z = 4, 3726 reflections, R = 0.0322. Crystal data of 4·CHCl3: space group P21, a = 11.727(6) A?, b = 11.825(7) A?, c = 17.091(8) A?, β = 94.96(2)°, Z = 2, 4338 reflections, R = 0.0333.
