Synthesis and Structure of a Distorted Octahedral Palladium(II) Complex Coordinated with a Tetrathioether Ligand Tethered with Bulky Substituents Nobuhiro Takeda, Daisuke Shimizu, and Norihiro Tokitoh* Institute for Chemical Research, Kyoto UniVersity, Gokasho, Uji, Kyoto 611-0011, Japan Received June 11, 2005 A new type of an o-phenylene-bridged tetrathioether ligand tethered with extremely bulky substituents, 2,4,6-tris- [bis(trimethylsilyl)methyl]phenyl (Tbt) groups, at its terminal sulfur atoms, TbtS[(o-phenylene)S] 3 Tbt (1), was synthesized by taking advantage of the coupling reaction of thiols with iodobenzenes using Cu 2 O in 2,4,6-trimethylpyridine. Complexation of 1 with Na 2 PdCl 4 gave the corresponding dichloropalladium(II) complex, [PdCl 2 (1)] (7). The X-ray structural analysis of 7 indicated that the central palladium metal is in a distorted octahedral environment, where the two inner sulfur atoms of 1 and the two chlorine atoms form a square planar arrangement around the palladium metal and the two terminal sulfur atoms of 1 weakly coordinate to the palladium center at the axial positions. In addition, a phenyl analogue of 1, PhS[(o-phenylene)S] 3 Ph (2), was synthesized by a method similar to that for 1. Reaction of 2 with Na 2 PdCl 4 gave the corresponding dichloropalladium(II) complex, [PdCl 2 (2)] (8). X-ray crystallography of 8 showed a type of the structure different from the distorted octahedral structure in 7, i.e., a square planar arrangement around the central palladium atom with the one terminal sulfur atom of 2, its neighboring sulfur atom, and the two chlorine atoms. The results of the NMR studies on 8 in a CDCl 3 solution were not consistent with the results of the X-ray crystallography and suggested the coordination of the two inner sulfur atoms of 2 to the palladium metal, although a possibility of the existence of the rapid interconversion among isomers could not be excluded. Introduction Palladium(II) complexes generally have square planar geometry around the palladium atom, and six-coordinate complexes of palladium(II) are very rare. Cyclic poly- thioether (crown thioether) ligands such as 1,4,7-trithia- cyclononane (9S3), 1 1,4,7,10,13,16-hexathiacyclooctadecane (18S6), 2 and 1,4,7-trithiacyclodecane (10S3) 3 reportedly complexed with palladium(II) metals to give the correspond- ing five- or six-coordinate palladium(II) complexes, in which the four sulfur atoms are arranged in a square planar fashion around the palladium(II) atom and the remaining one or two sulfur atoms weakly coordinate to the palladium(II) atom [Pd‚‚‚S: 2.96-3.27 Å] at the axial positions. In addition, the 9S3 ligand has been known to stabilize mononuclear palladium(III) species, 4 which are generally known to be unstable. These unique properties of cyclic polythioether ligands are considered to be caused by their moderate, geometric preference of facial coordination and their ability to adjust the coordination modes and conformations to the geometric preference of the oxidation states of the metals. 5 Acyclic polythioethers can more easily change their coor- * To whom correspondence should be addressed. E-mail: tokitoh@ boc.kuicr.kyoto-u.ac.jp. (1) (a) Wieghardt, K.; Ku¨ppers, H.-J.; Raabe, E.; Kru¨ger, C. Angew. Chem., Int. Ed. Engl. 1986, 25, 1101-1103. (b) Blake, A. J.; Holder, A. J.; Hyde, T. I.; Roberts, Y. V.; Lavery, A. J.; Schro¨ der, M. J. Organomet. Chem. 1987, 323, 261-270. (2) Blake, A. J.; Gould, R. O.; Lavery, A. J.; Schro¨ der, M. Angew. Chem., Int. Ed. Engl. 1986, 25, 274-276. (3) (a) Grant, G. J.; Sanders, K. A.; Setzer, W. N.; VanDerveer, D. G. Inorg. Chem. 1991, 30, 4053-4056. (b) Chandrasekhar, S.; McAuley, A. Inorg. Chem. 1992, 31, 2663-2665. (4) Blake, A. J.; Holder, A. J.; Hyde, T. I.; Schro¨der, M. J. Chem. Soc., Chem. Commun. 1987, 987-988. (5) For reviews on crown thioethers, see: (a) Cooper, S. R. Acc. Chem. Res. 1988, 21, 141-146. (b) Blake, A. J.; Schro¨der, M. AdV. Inorg. Chem. 1990, 35,1-80. (c) Cooper, S. R.; Rawle, S. C. Struct. Bonding (Berlin) 1990, 72,1-72. (d) Kellogg, R. M. In Crown Compounds: Toward Future Applications, Cooper, S. R., Ed.; Wiley VCH: New York, 1992. (e) Levason, W.; Reid, G. In ComprehensiVe Coordination Chemistry II, from Biology to Nanotechnology; Lever, A. B. P., Ed.; Elsevier Ltd.: Oxford, U.K., 2004; Vol. 1, pp 399-410. Inorg. Chem. 2005, 44, 8561-8568 10.1021/ic050944v CCC: $30.25 © 2005 American Chemical Society Inorganic Chemistry, Vol. 44, No. 23, 2005 8561 Published on Web 10/01/2005