Synthesis of the cationic bis(but-2-yne) complex [W(CO)(NCMe)(S2CNC4H8)-(η2-MeC2Me)2]BF4 and its reactions with neutral bidentate donor ligands (L–L) to give [W(CO)(S2CNC4H8)(L–L)(η2-MeC2Me)]BF4: X-ray crystal structure determination of [W(CO)(S2CNC4H8)(Ph2PCH2PPh2)(η2-MeC2Me)]BF4

Abstract

Silver tetrafluoroborate reacts with an equimolar quantity of [WI(CO)(S₂CNC₄H₈)(η²-MeC₂Me)₂] in acetonitrile at room temperature to give the cationic mono(acetonitrile) compound [W(CO)(NCMe)(S₂CNC₄H₈)(η²-MeC₂Me)₂]BF₄(1) in good yield. Equimolar quantities of (1) and L–L [L–L = Ph₂P(CH₂)_nPPh₂(n= 1 or 2), Ph₂P(CH₂)₂PPh(CH₂)₂PPh₂, 2,2′-bipyridine, 1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, or S₂CP(C₆H₁₁)₃] react in CH₂Cl₂ at room temperature to give the highly coloured mono(but-2-yne) complexes [W(CO)(S₂CNC₄H₈)-(L–L)(η²-MeC₂Me)]BF₄(2)–(8) in high yield. The structure of [W(CO)(S₂CNC₄H₈)(Ph₂PCH₂PPh₂)-(η²-MeC₂Me)]BF₄(2) was determined by X-ray crystallography. Crystals of (2) are monoclinic, space group P2₁/c with a= 11.638(1), b= 12.400(2), c= 25.165(3)Å, and β= 90.40(1)°. The structure was refined to R= 0.069 (R′= 0.094) for 2 031 reflections with F_o > 5σ(F_o). The geometry about the tungsten atom in (2) can be described as pseudo-octahedral, with the but-2-yne ligand trans to one of the phosphorus atoms of the Ph₂PCH₂PPh₂ ligand. The other phosphorus atom, the two sulphur atoms of the dithiocarbamate ligand, and the carbon monoxide ligand all lie approximately in the equatorial plane. The barrier to rotation of the but-2-yne ligand in complexes (2)–(6) was determined by variable-temperature ¹H n.m.r. spectroscopy. The results are discussed in terms of the steric and electronic effects of the bidentate donor ligands in (2)–(6). Carbon-13 n.m.r. spectroscopy suggests that the two but-2-yne ligands in (1) are donating a total of six electrons to the metal whereas the but-2-yne ligand in (2)–(8) acts as a four-electron donor to the metal centre.