Synthesis and Characterization of a Stable trans-Dioxo Tungsten(IV) Complex and Series of Mono-Oxo Molybdenum(IV) and Tungsten(IV) Complexes. Structural and Electronic Effects of π-Bonding in trans-[M(O)(X)(dppe)2]+/0 Systems

• Published in: Inorganic chemistry Vol. 37; no. 23; pp. 5992 - 6001
• Main Authors: Bendix, Jesper, Bøgevig, Anders
• Format: Journal Article
• Language: English
• Published: American Chemical Society 16.11.1998
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic980342u

trans-[W(O)(F)(dppe)2](BF4) (dppe = Ph2PCH2CH2PPh2, 1,2-bis(diphenylphosphino)ethane) (10) has been synthesized. From this, the neutral trans-[W(O)2(dppe)2]·2CH3OH (11) was prepared by a hydrolysis and deprotonation reaction with Et4NOH in methanol/water. Together with the analogous molybdenum compound (2) this compound afforded by substitution under acid conditions salts of trans-[M(O)(X)(dppe)2]+ ions (M = Mo, W; X = OH, OCH3, Cl, Br, I, NCS) and trans-[Mo(O)(N3)(dppe)2](CF3SO3) (9). All the compounds have low-spin d2 electronic configuration. The compounds were characterized by 31P{1H} NMR, positive FAB-ionization mass spectrometry, UV−vis spectroscopy, and vibrational spectroscopy. X-ray crystallographic studies were carried out on compounds 10, 11, trans-[W(O)(OH)(dppe)2](ClO4) (12), and trans-[W(O)(NCS)(dppe)2](BPh4) (16). The electronic spectra of the mono-oxo species are consistent with the lowest energy transitions being of d xy → {d zx , d yz } character. No ligand-field transitions are observed for the dioxo tungsten complex. Identical π-spectrochemical series were found for the two metals. The shielding of the phosphorus nuclei determined by 31P{1H} NMR is significantly influenced by the nature of the axial ligands.