117754-09-3Relevant articles and documents
Intramolecular activation of arene CH bonds by tungsten(II) metal centers and the possible role of metal π-arene intermediates
Kerschner, Judith L.,Fanwick, Philip E.,Rothwell, Ian P.,Huffman, John C.
, p. 1431 - 1438 (2008/10/08)
The reduction of toluene solutions of the tungsten(VI) bis(aryloxide) W(OAr-2,6-Ph2)2Cl4 (1) (OAr-2,6-Ph2 = 2,6-diphenylphenoxide) with sodium amalgam (4Na/W) in the presence of phosphine ligands results in the formation of the bis-cyclometalated compounds W(OC6H3PhC6H4)2L 2 (2; a, L = PMe2Ph; b, L = PMePh2; c, L = PMe3; d, L2 = dppe). A structural study of 2b confirms the cyclometalation of the two 2,6-diphenylphenoxide ligands involving the activation and cleavage of one of the ortho-CH bonds of a substituent aryl ring. The solid-state structure of 2b involves a pseudooctahedral WO2C2P2 core with cis phosphine ligands and trans oxygen atoms. The two six-membered metallacycles maintain a comfortable bite at the metal center close to 90° with little puckering of the chelate ring due to the large 145° angle associated with the W-O-Ar linkage. Spectroscopic data on compounds 2 are consistent with them all adopting a structure in solution identical with that found in the solid state for 2b. Particularly informative is the presence in the 13C NMR spectrum of a resonance for the new W-C bond as a doublet of doublets due to coupling to one cis and one trans phosphorus nuclei. Also isolated as a minor component from the reaction mixture involving PMePh2 was a 16-electron tungsten(II) compound W(OC6H3Ph-η6-C6H 5)-(OAr-2,6-Ph2)(PMePh2) (3). Deep green crystals of 3 were obtained from a toluene solution, and a structural study shows the presence of one of the 2,6-diphenylphenoxide ligands chelated to the metal in a π-fashion with one of the side aryl rings. The overall structure of 3 is best described as a three-legged piano stool with two oxygen atoms and one phosphorus atom forming the feet. The 1H NMR spectra of 3 show it to be fluxional involving rapid room-temperature exchange of π-bound and free aryl groups of the OAr-2,6-Ph2 ligands. Reduction of 1 in the presence of dppm (Ph2PCH2PPh2) allows the isolation of a deep green compound (4). Despite the chelating potential of the dppm, both spectroscopic and structural data on 4 show it to be the 16-electron compound W(OC6H3Ph-η6-C6H 5)(OAr-2,6-Ph2)(η1-dppm). Although the η6-arene compound 3 does not readily convert thermally to the bis-cyclometalated compound 2b, its treatment with excess PMePh2 or smaller phosphines does lead to the formation of 2 along with H2 gas. These observations are interpreted from a mechanistic view point. Crystal data for WC62H50P2O2 (2b) at -140°C: a = 19.828 (8) A?, b = 26.214 (13) A?, c = 10.380 (4) A?, β = 111.53 (2)°, Z = 4, dcalcd = 1.490 g/cm-3 in space group P21/a. For WC49H39PO2 (3) at -155°C: a = 15.162 (6) A?, b = 14.096 (5) A?, c = 10.246 (4) A?, α = 61.25 (2)°, β = 101.92 (2)°, γ = 100.75 (2)°, Z = 2, dcalcd = 1.544 g cm-3 in space group P1. For WC61H48P2O2 (4) at 20°C: a = 15.008 (2) A, b = 39.449 (3) A?, c = 9.854 (2) A?, β = 105.86 (1)°, Z = 4, dcalcd = 1.253 g cm-3 in space group P21/c.
