Versatile coordination behavior of (N-aryliminophosphoranyl)(thiophosphoranyl) methane and its anion to platinum(II)

A Staudinger reaction of bis(diphenylphosphino) methane (dppm) with 1 equiv. of aryl-azide, gave pure mono-phosphinimine Ph2PCH2PPh2=N-aryl (1a, aryl=p-tolyl; 1b, aryl=p-anisyl), after column chromatography. A continuing reaction of 1 with sulfur afforded the new ligand, (thiophosphoranyl)(iminophosphoranyl)methane, CH2(PPh2=S)(PPh2 = N-aryl) (dppmSN(aryl)) (2a,b). By using n-BuLi, deprotonation of 2 took place, but isolation of the organometaliic derivatives M [CH(PPh2=S) (PPh2=N-aryl)] (3) failed. The reaction of 2a,b with Pt2Cl4(PEt3)(2) resulted in the formation of two isomers 4 and 5. The major product, the four-membered platinacycle trans P-Pt-C [PtCl(PEt3) {CH(PPh2=S)(PPh2-NH aryl))-C,S](+)(Y)(-) (4a, aryl=p-tolyl, Y=Cl; 4b, aryl=p-tolyl, Y=BF4; 4c, aryl=p-anisyl, Y = BF4; 4d, aryl = p-tolyl, Y = CF3CO2), contains a C,S-chelating ligand in which an H shift has taken place from the methylene group to the non-coordinated N. The minor product, the six-membered Flatinacycle [PtCl(PEt3){CH2(PPh2=S) (PPh2=N-aryl)}-S,N](+)(Y)(-) (5a-d), cannot be converted into 4a-d. The molecular structure of 4b, as determined by X-ray crystallography, shows that an intramolecular H bridge exists between the pendant P-N-H group and the Cl ligand on Ft cis to it. A deprotonation reaction of the product mixture 4/5 with NaH readily afforded the neutral four-membered platinacycle trans P-Pt-N [PtCl(PEt3) {CH(PPh2=N-pTol) (PPh2=S)}-C,N] (6), containing a C,N-coordinated anionic ligand. Remarkably, protonation of 6 did not give 4 and 5 again, but afforded trans Cl-Pt-C [PtCl(PEt3) {CH(PPh2=S) (PPh2-NH-aryl)-C,S](+)(Y)(-)(7), the geometric isomer of 4. The formation of the products 4-7, their geometry and relative (thermodynamic) stability is explained by comparing the relative sigma-donor capacity of N versus S versus C within the neutral or anionic coordinated dppmSN( aryl) ligand, with earlier reported data of related platinum complexes, (C) 1997 Elsevier Science S.A.