cis-dioxomolybdenum(VI) and oxo(phosphine oxide)molybdenum(IV) complexes: Steric and electronic fine-tuning of cis-[MoOS](2+) precursors
Date
2005
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Doonan, C.
Millar, A.
Nielsen, D.
Young, C.
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Inorganic Chemistry: including bioinorganic chemistry, 2005; 44(13):4506-4514
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Christian J. Doonan, Andrew J. Millar, David J. Nielsen, and Charles G. Young
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Abstract
The complexes cis-Tp/<sup>Pr</sup>Mo<sup>VI</sup>O<inf>2</inf>(OAr) (Tp/<sup>Pr</sup> = hydrotris(3-isopropylpyrazol-1-yl)borate, <sup>-</sup>OAr = phenolate or naphtholate derivative) are formed upon metathesis of Tp/ <sup>Pr</sup>MoO<inf>2</inf>Cl and HOAr/NEt<inf>3</inf> in dichloromethane. The orange, diamagnetic dioxo-Mo(VI) complexes exhibit strong ν(MoO<inf>2</inf>) IR bands at ca. 930 and 905 cm<sup>-1</sup> and NMR spectra indicative of C <inf>s</inf> symmetry. They undergo electrochemically reversible, one-electron reductions at potentials in the range -0.714 to -0.855 V vs SCE (in MeCN) and react with PEt<inf>3</inf> to produce Tp/<sup>Pr</sup>Mo<sup>IV</sup>O(OAr) (OPEt<inf>3</inf>). The green, diamagnetic oxo-Mo(IV) complexes display a single ν(MoO) IR band at ca. 950 cm<sup>-1</sup> and exhibit NMR spectra indicative of C<inf>1</inf> symmetry. The crystal structures of eight dioxo-Mo(VI) complexes have been determined to assess the degree of frontal (O <inf>3</inf>-donor face) steric congestion at the Mo center, to identify complexes amenable to conversion into monomeric oxosulfido-Mo(VI) derivatives. The complexes display distorted octahedral geometries, with a cis arrangement of terminal oxo ligands, with d(Mo=O)<inf>av</inf> = 1.694 Å and 〈(MoO<inf>2</inf>)<inf>av</inf> = 103.4°. Maximal frontal steric congestion is observed in the 2-phenolate derivatives, and these are identified as precursors for strictly monomeric (solid and solution state) oxosulfido-Mo(VI) counterparts. © 2005 American Chemical Society.
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© 2005 American Chemical Society