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Preparation and 31P and 77Se NMR spectra of platinum and palladium complexes of a P2N4Se2 ring
Chivers, Tristram,Doxsee, Daniel D.,Hilts, Robert W.
, p. 3244 - 3249 (2008/10/08)
The reaction of 1,5-Ph4P2N4Se2 with Pt(PPh3)2(CH2=CH2) or Pd(PPh3)4 in toluene at 0°C produces the η2-Se,Se′-bonded complexes M(PPh3)2(1,5-Ph4P2N 4Se2) (2a, M = Pt; 2b, M = Pd) characterized by their 31P and 77Se NMR spectra. Simulation of the 77Se NMR spectra gave detailed coupling information for 2a and 2b. Heating 2a or 2b in boiling toluene produces the corresponding η2-Se,N-μ,η1-Se′-bonded dimers [M(PPh3)(1,5-Ph4P2N4- Se2)]2 (3a, M = Pt; 3b, M = Pd). Variable-temperature 31P NMR spectra of 3a reveal a fluxional process which is proposed to involve a [1,3]-metallotropic shift. The reaction of 1,5-Ph4P2N4Se2 with [PtCl2(PEt3)]2 in CH2Cl2 produces the η′-N-bonded adducts [PtCl2(PEt3)]n(1,5-Ph4P 2N4Se2) (4a, n = 1; 5, n - 2). The two PtCl2(PEt3) groups in 5 are attached to distal nitrogen atoms of the P2N4Se2 ring, which retains a folded structure with d(Se-Se) = 2.594 A?. Treatment of 4a with Pt(PPh3)2(CH2=CH2) produces the μ3,η3-Se,Se′,N-bonded complex Pt(PPh3)2(1,5-Ph4P2N 4Se2)[PtCl2(PEt3)] identified by 31P NMR spectroscopy. Reaction of [Li[Ph4P2N4Se2Ph](THF)]2, generated from the combination of 1,5-Ph4P2N4Se2 and phenyllithium in THF, with cis-PtCl2(PEt3)2 yields the η1-Se-bonded complex trans-PtCl(PEt3)2(Ph4P2N 4Se2Ph) (7a). Variable temperature 31P NMR spectra of 7a reveal a two-site exchange process involving the two PEt3 ligands, which is proposed to occur via rotation about the Pt-Se bond. Line-fitting analysis yielded the thermodynamic parameters for this process.
