TY - DATA T1 - Low-Valent Tungsten Aryloxide Compounds with Pyridine Ancillary Ligation:  Intramolecular Reduction of Heterocyclic and Aromatic Rings Including Formation of an η5-Cyclohexadienyl Group PY - 2003/05/01 AU - Margaret R. Lentz AU - Phillip E. Fanwick AU - Ian P. Rothwell UR - https://acs.figshare.com/articles/journal_contribution/Low-Valent_Tungsten_Aryloxide_Compounds_with_Pyridine_Ancillary_Ligation_Intramolecular_Reduction_of_Heterocyclic_and_Aromatic_Rings_Including_Formation_of_an_sup_5_sup_-Cyclohexadienyl_Group/3775323 DO - 10.1021/om030054s.s001 L4 - https://ndownloader.figshare.com/files/5886084 KW - hydrocarbon solutions KW - terminal aryloxide ligands KW - OC KW - 1 H NMR KW - η 5 KW - Cl KW - bipy ligands KW - HPh KW - VI KW - metal center N2 - The sodium amalgam reduction (2 Na per W) of hydrocarbon solutions of [W(OC6HPh4-2,3,5,6)2Cl4] in the presence of pyridine or 4-tert-butylpyridine leads to the W(IV) compounds [W(OC6HPh4-2,3,5,6)2Cl2(py)2] (1) and [W(OC6HPh4-2,3,5,6)2Cl2(4-tert-butylpyridine)2] (2) in good yields. The ambient-temperature 1H NMR spectra of both 1 and 2 were found to be sharp and to exhibit extensive contact shifts due to the paramagnetic tungsten center. The addition of 2,2‘-bipyridine to an emerald green solution of [W(OC6HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)(PEt3)] produced [W(OC6HPh4-2,3,5,6)2(bipy)2] (3), containing two bipy rings and two terminal aryloxide ligands coordinated mutually cis. The W−N(bipy) distances of 2.092(2), 2.093(2), 2.096(2), and 2.115(2) Å in 3 are among the shortest so far reported for bipy ligands bound to either molybdenum or tungsten. The solid state and solution data for 3 indicate that reduction of both bipy ligands has occurred, but whether this involves four-electron reduction to yield d0-W(VI) is unclear. The addition of 4-tert-butylpyridine to [W(OC6HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)(PEt3)] was found (1H NMR) to lead only to partial substitution of the phosphine ligand to produce [W(OC6HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)(py-But-4)] (4). The sodium amalgam reduction (4 Na per W) of hydrocarbon solutions of [W(OC6HPh4-2,3,5,6)2Cl4] in the presence of 4-tert-butylpyridine produced a mixture found to contain the expected compound 4 along with a new salt compound, [W(OC6HPh3-η5-C6H6)(OC6HPh3-η1-C6H4)(OC6HPh4-2,3,5,6)][Cl] (5), containing a total of three aryloxide ligands. Crystals were obtained containing a 1:1 ratio of 4/5. One of the aryloxides in 5 is terminally bound, the second is cyclometalated, while the third chelates to the metal center via an η5-interaction with an ortho-cyclohexadienyl ring. The formal oxidation state of the metal center in 5 is (VI), and the unit cell contains one chloride ion to balance the positive charge on the tungsten. In compound 5 the hydride ligand formed via the cyclometalation has been transferred to the ortho-position of a phenyl ring. The structural parameters for the π-bound rings in 4 and 5 and their relevance to catalytic arene hydrogenation are discussed. ER -