959902-97-7Relevant academic research and scientific papers
Aryl, methyl-diplatinum complexes each with a metal-metal donor-acceptor bond and bridging 2-diphenylphosphinopyridine (PN) ligands: General synthetic approach and mechanism of isomerization
Shafaatian, Bita,Akbari, Alireza,Nabavizadeh, S. Masoud,Heinemann, Frank W.,Rashidi, Mehdi
, p. 4715 - 4725 (2008/03/13)
A general synthetic method has been designed to prepare a series of unsymmetrical cationic organo-diplatinum complexes each containing two bridging 2-diphenylphosphinopyridine (PN), PPh2py, ligands and a platinum-platinum donor-acceptor bond. Thus, reaction of cis-[PtR 2(SMe2)2] (R = Ph, p-MeC6H 4 or p-FC6H4), 1, or cis,cis-[R 2Pt(-SMe2)2PtR2](R = Me) with 2 equiv. or 4 equiv., respectively, of PN in CH2Cl2 gave cis-[PtR2(PN-κ1P)2], 2. When complex 2 was reacted with 1 equiv. of HX (X = CF3COO) in CH2Cl 2, an approximately 2: 1 mixture of trans-[PtRX(PN- κ1P)2], 3, and [PtR(η2-PN)(PN- κ1P)]X, 4, was obtained. The reaction of one equiv. of the latter monomeric mixture with 0.5 equiv. of cis,cis-[R′2Pt(- SMe2)2PtR′2] (R′ = Me) or one equiv. of cis-[PtR′2(SMe2)2] (R′ = p-MeC6H4) in CH2Cl2 immediately gave the head-to-head (HH) stereoisomer of the diplatinum complex hh-[RPt(-PN) 2PtR′2]X, 6. However, the same reaction in benzene gave the corresponding head-to-tail (HT) stereoisomer ht-[RPt(-PN)(-NP) PtR′2]X, 9, in pure form after a few hours. The conversion of the HH isomer 6 to the HT isomer 9 in CH2Cl2 took place very slowly during 10 d, while the conversion in C6H6 was much faster and took place over 5 h. Based on the observations, a mechanism for the conversion of the kinetic HH stereoisomer to the thermodynamic HT stereoisomer is suggested which involves association of X- with the N2PtR′2 center following by one-arm dissociation of one of the PN bridging ligands from the nitrogen terminal in the HH isomer, and subsequent exchange of the ligating atom and reformation of the HT arrangement. The methyl-di p-tolyl dimer ht-[MePt(-PN)(-NP)Pt(p-MeC6H 4)2]X, 9e, in solution gradually isomerizes to ht-[(p-MeC6H4)Pt(-PN)(-NP)PtMe(p-MeC6H 4)]X, 11, by an aryl ligand transfer. All the complexes were fully characterized using multinuclear (1H, 31P and 195Pt) NMR spectroscopy and the complexes ht-[PhPt(-PN)(-NP)PtMe 2]X, 9a, and ht-[(p-MeC6H4)Pt(-PN)(-NP)PtMe(p- MeC6H4)]X, 11, were further characterized by single crystal X-ray crystallography. The Royal Society of Chemistry 2007.
