PREPARATION AND P-31 AND SE-77 NMR-SPECTRA OF PLATINUM AND PALLADIUM COMPLEXES OF A P2N4SE2 RING

The reaction of 1,5-Ph4P2N4Se2 with Pt(PPh3)2(CH2 = CH2) or Pd(PPh3)4 in toluene at 0-degrees-C produces the eta2-Se,Se'-bonded complexes M( PPh3)2(1,5-Ph4P2N4Se2) (2a, M = Pt; 2b, M = Pd) characterized by their P-31 and Se-77 NMR spectra. Simulation of the Se-77 NMR spectra gave detailed coupling information for 2a and 2b. Heating 2a or 2b in boili ng toluene produces the corresponding eta2-Se,N-mu,eta1-Se'-bonded dim ers [M(PPh3)(1,5-Ph4P2N4Se2)]2 (3a, M = Pt; 3b, M = Pd). Variable-temp erature P-31 NMR spectra of 3a reveal a fluxional process which is pro posed to involve a [1,3]-metallotropic shift. The reaction of 1,5-Ph4P 2N4Se2 with [PtCl2(PEt3)]2 in CH2Cl2 produces the eta1-N-bonded adduct s [PtCl2(PEt3)]n(1,5-Ph4P2N4Se2) (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 angstrom . Treatment of 4a with Pt(PPh3)2(CH2 = CH2) produces the mu2,eta3-Se,S e',N-bonded complex Pt(PPh3)2(1,5-Ph4P2N4Se2)[PtCl2(PEt3)] identified by P-31 NMR spectroscopy. Reaction of [Li[Ph4P2N4Se2Ph](THF)]2, genera ted from the combination of 1,5-Ph4P2N4Se2 and phenyllithium in THF, w ith cis-PtCl2(PEt3)2 yields the eta1-Se-bonded complex trans-PtCl(PEt3 )2(Ph4P2N4Se2Ph) (7a). Variable temperature P-31 NMR spectra of 7a rev eal a two-site exchange process involving the two PEt3 ligands, which is proposed to occur via rotation about the Pt-Se bond. Line-fitting a nalysis yielded the thermodynamic parameters for this process.