Issue 41, 2007

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

Abstract

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-[PtR2(SMe2)2] (R = Ph, p-MeC6H4 or p-FC6H4), 1, or cis,cis-[R2Pt(µ-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 CH2Cl2, 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(µ-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(µ-PN)2PtR′2]X, 6. However, the same reaction in benzene gave the corresponding head-to-tail (HT) stereoisomer ht-[RPt(µ-PN)(µ-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(µ-PN)(µ-NP)Pt(p-MeC6H4)2]X, 9e, in solution gradually isomerizes to ht-[(p-MeC6H4)Pt(µ-PN)(µ-NP)PtMe(p-MeC6H4)]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(µ-PN)(µ-NP)PtMe2]X, 9a, and ht-[(p-MeC6H4)Pt(µ-PN)(µ-NP)PtMe(p-MeC6H4)]X, 11, were further characterized by single crystal X-ray crystallography.

Graphical abstract: 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

Supplementary files

Article information

Article type
Paper
Submitted
11 Jun 2007
Accepted
02 Aug 2007
First published
23 Aug 2007

Dalton Trans., 2007, 4715-4725

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

B. Shafaatian, A. Akbari, S. M. Nabavizadeh, F. W. Heinemann and M. Rashidi, Dalton Trans., 2007, 4715 DOI: 10.1039/B708769A

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