Synthesis and oxidation of d6 tungsten pincer complexes: a complete series of tungsten(ii) hydridocarbonyl and halocarbonyl pincer complexes

Abstract

Reaction of the neutral P^HNP ligand [HN(SiMe₂CH₂PPh₂)₂] with tungsten hexacarbonyl resulted in coordination of P^HNP through both phosphorus donor atoms to form the tungsten complex [W(P^HNP)(CO)₄] (1). Reaction of P^HNP with tris(acetonitrile)tricarbonyl tungsten gave both facial and meridional tridentate isomers [W(P^HNP)(CO)₃] (2-fac and 3-mer). These three d⁶ tungsten complexes could be interconverted under appropriate conditions. The thermodynamically favored isomer 3 was protonated to form seven-coordinate [W(P^HNP)(CO)₃H][BF₄] (4). A related series of cationic tungsten(II) halide complexes was synthesized, [W(P^HNP)(CO)₃X]⁺ (6, X = I; 7, X = Br; 8, X = Cl; 9, X = F), by various routes. All of the tungsten(II) complexes underwent deprotonation at the amine site of the P^HNP ligand when triethylamine was added, resulting in neutral seven-coordinate complexes. Variable temperature ¹H, ³¹P{¹H}, and ¹³C{¹H} NMR spectroscopy showed fluxional behavior for all the seven-coordinate complexes reported here. Analysis of IR and NMR spectroscopic data showed trends through the series of coordinated halides. Crystal structures of tetracarbonyl 1, meridional tricarbonyl 3, and cationic hydride 4 were determined to confirm the coordination mode of the P^HNP ligand.