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Flower KR, McGown AT, Miles PJ, Pritchard RG, Warren JE: Isolation of 1,4-Li (2)-C (6) H (4) and its reaction with [(Ph (3) P) AuCl]. Dalton Trans. 2010 Apr 14;39(14):3509-20. Epub 2010 Mar 2.
The difficulty in generating 1,4-Li (2)-C (6) H (4) utilising the lithium halogen exchange reaction on 1,4-Br (2)-C (6) H (4), 1,4-I (2)-C (6) H (4) and 1-Br-4-I-C (6) H (4) is revisited and only on treatment of 1,4-I (2)-C (6) H (4) with 2 molar equivalents of n-BuLi can 1,4-Li (2)-C (6) H (4) be isolated in excellent yield. Treatment of with two equivalents of [ClAu (PPh (3))] gives [1,4-(Ph (3) PAu)(2)-C (6) H (4)] in excellent yield. Subsequent treatment of with 2.5 molar equivalents of PPh (2) Me, PPhMe (2) or PMe (3) affords the PPh (3) substituted compounds [1,4-(LAu)(2)-C (6) H (4)] (L = PPh (2) Me , PPhMe (2), PMe (3)) in essentially quantitative yields. On treatment of 1,4-Br (2)-C (6) H (4) or 1-Br-4-I-C (6) H (4) with 2 molar equivalents of n-BuLi only mono-lithiation takes place to give 1-Br-4-Li-C (6) H (4) as shown through the isolation of essentially 1 : 1 molar equivalents of Ph (2) PC (6) H (4)-4-Br and Ph (2) PBu on treatment with 2 molar equivalents of ClPPh (2). Treatment of , prepared by lithium/iodine exchange on 1-Br-4-I-C (6) H (4), with [ClAu (PPh (3))] affords [(Ph (3) P) Au (C (6) H (4)-4-Br)] as expected and in addition [(Ph (3) P) Au (n-Bu)(C (6) H (4)-4-Br)(2)] , indicating the straightforward chloride/aryl exchange at gold may proceed in competition with oxidative addition of the n-BuI, generated in the initial lithium/iodine exchange reaction, to some 'aurate' complex Li [Au (C (6) H (4)-4-Br)(2)] formed in situ followed by reductive elimination of Br-C (6) H (4)-4-n-Bu in a manner that mimics lithium diorganocuprate chemistry. All of the gold-containing compounds have been spectroscopically characterised by (1) H and (31) P-{(1) H} NMR and in addition compounds and by single crystal X-ray diffraction studies. The solid state structures observed for are dictated by non-conventional hydrogen bonding and the packing requirements of the phosphine ligands. For and there is no close AuAu approach, however for and the reduction in the number of phenyl rings allows the formation of AuAu contacts. For and the extended structures appear to be helical chains with AuAu contact parameters of 3.855 (5) A and C-Au-Au-C 104.1 (3) degrees for and 3.139 (4) A and C-Au-Au-C -92.0 (2) degrees for . The AuAu approach in is longer than is normally accepted for an AuAu contact and is dictated by ligand directed non-conventional hydrogen bonding to the aurated benzene ring and the pi-stacking requirements of the phosphine ligand. By comparison of the structures with other structures in the database it is evident that the aurophilic interaction is a poor supramolecular synthon in the presence of non-conventional hydrogen bond donors. Searches of the CCDC database suggest that the observed parameters for the AuAu contact in sit close to the cut-off point for observing this type of contact. In addition to aurophilic contacts and non-conventional hydrogen bonds there are a number of halogenated solvent C-ClAu contacts observed in the structures of and . The nature of these contacts have implications for the accepted van der Waals radius of gold which should be extended to 2 A. |
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