title: Synchronized fluxional motion and cyclometalation of ligands in platinum(II) complexes.
abstract: Oscillation of the 2,9-dimethyl-1,10-phenanthroline (dmphen) ligand between nonequivalent exchanging sites in [Pt(Me)(dmphen)(P(o-tolyl)3)]+ and phosphane rotation around the Pt-P bond take place at the same rate. Thus, this cationic complex behaves as a molecular gear, exhibiting a fascinating synchronism between two otherwise independent fluxional motions. The process (DeltaG(3330)(#) = 68.5 +/- 0.2 kJ mol(-1)) was found to be unaffected by (i) the nature of various counteranions (X = PF6- 1, SbF6- 2, CF3SO3- 3, BF4- 4, BArf- 5), (ii) the polarity or the electron-donor properties of the solvent and, (iii) the addition of weak nucleophiles. Restricted phosphane rotation around the Pt-P bond impedes free dmphen oscillation in a 14-electron three-coordinate T-shaped intermediate, containing eta1-coordinated dmphen, generated by easy Pt-N bond dissociation from [Pt(Me)(dmphen)(P(o-tolyl)3)]+. 1-5 undergo easy orthoplatination, leading to new [Pt(dmphen){CH2C6H4P(o-tolyl)2-kappaC,P}]X cyclometalated Pt(II) compounds (X = PF6- 1, SbF6- 2, CF3SO3- 3, BF4- 4, BArf- 5). The kinetics of the cyclometalation of 3 and 4 were followed in tetrachloroethane by both 1H NMR and spectrophotometric techniques (kobs = 1.7 x 10-4 s(-1) at 333 K, DeltaH = 59.3 +/- 3 kJ mol(-1), and DeltaS = -141 +/- 8 J K(-1) mol(-1)). Ring opening of dmphen is again a prerequisite for C-H bond activation, which takes place through a multistep oxidative-addition reductive-elimination pathway. The molecular structure of cyclometalated 10 shows a butterfly shape with two o-tolyl rings projected above and below the coordination plane. Variable-temperature 1H NMR spectra revealed hindered rotation around the P-Cipso(o-tolyl) bonds at rather mild temperatures (DeltaG(3330)(#) = 55.2 +/- 0.4 kJ mol(-1)). Dmphen oscillation results very slowly and is dependent on the nature of the counteranions, of the solvents, and is strongly accelerated by the presence of weak nucleophiles that act as catalysts, according to an associative mode of activation.
authors.affiliation: Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Salita Sperone, 31-Vill. S. Agata-98166 Messina, Italy. rromeo@unime.it
authors.forename: Raffaello
authors.initials: R
authors.lastname: Romeo
authors.forename: Giuseppina
authors.initials: G
authors.lastname: D'Amico
authors.forename: Emanuela
authors.initials: E
authors.lastname: Guido
authors.forename: Alberto
authors.initials: A
authors.lastname: Albinati
authors.forename: Silvia
authors.initials: S
authors.lastname: Rizzato
mesh_terms: D018360:Crystallography, X-Ray; D003500:Cyclization; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D017671:Platinum Compounds / Q000737:chemistry*; D012997:Solvents
chemical_list: D008024:Ligands; D017671:Platinum Compounds; D012997:Solvents