CORRELATION AMONG ALKOXIDE-]TUNGSTEN PI-BONDING, SPIN-STATE, AND REACTIVITY IN W(OCH2CF3)(2)CL-2(PME(2)PH)(2)

The reaction of WCl4(PMe(2)Ph)(2) with 2 equiv of TlOCH2CF3 gives W(OR(f))(2)Cl-2(PMe(2)Ph)(2), which is shown by solution spectroscopic and solid-state (X-ray diffraction) methods to have a trans,cis,cis stereochemistry. The resulting ligand field leaves the two d electrons spin-paired in a single orbital, which enhances O-->W pi-donation and tends to increase the metal valence electron count to (or near) 18. The electron configuration leaves the molecule surprisingly unreactive toward PMe(2)Ph, H-2, H2O, and even O-2 The W-O bonds are short (1.844(5) and 1.852(5) Angstrom), the W-Cl bonds are long (2.4865(19) and 2.4772(19) Angstrom), and the W-O-C angles are large (142.2(5) and 144.8(5)degrees). A d-orbital splitting diagram and the structural evidence for significant O-->W pi-bonding is used to rationalize some aspects of structure (e.g., W-CI bond lengths), as well as the eclipsing of the two W-O-C planes. Crystallographic data (-173 degrees C): a = 9.583(2) Angstrom, b = 14.277(3) Angstrom, c = 19.287(4) Angstrom, and beta = 102.66(1)degrees with Z = 4 in space group P2(1)/c.