Preparation of arylplatinum(II) complexes. The interaction of dichloro-(η-cyclo-octa-1,5-diene)platinum(II) and aryltrimethylstannanes

Abstract

One or both chloride ligands of [Pt(cod)Cl2](cod = cyclo-octa-1,5-diene) can be readily and selectively replaced by aryl groups by treatment of the complex with aryltrimethylstannanes in dichloromethane or sym-tetrachioroethane. Use of 1 mol of SnMe3R usually gives the monoaryl complexes in high yield [e.g. R = 2-furyl, 2-thienyl, benzofuran-2-yl, 2-benzothienyl, 1,2-dihydrobenzocyclobuten-3-yl, or C6H4X (X = H, p-MeO, p-Cl, p-F, p-Me3Si, or p-Me)], but for R =η6-p-MeC6H4Cr(CO)3 the diaryl complex is formed. Use of 2 mol of SnMe3R gives the diaryl complexes in good yield [e.g. R as above; plus C6H4X (X =o-MeO, m-MeO, m-F3C, p-Br, m-F, m-Cl, and p-O2N)], but, for steric reasons, with R = C6H2Me3-2,4,6 only the monoaryl complex is formed. The reactivity of the SnMe3R compounds generally parallels the ease of electrophilic substitution at the corresponding R–H bonds. The arylation method has substantial advantages over those using aryl Grignard or lithium reagents. Aryl compounds, MMe3R, of other Group 4 metals undergo analogous reactions, the reactivity decreasing in the sequence (M =) Pb > Sn Ge > Si. While mixed diaryl complexes can sometimes be made in good yield {e.g.[Pt(cod)-(2-C4H3S)(2-C4H3O)] from [Pt(cod)(2-C4H3S)Cl] and SnMe,(2-C4H3O)}, such preparations can be complicated by exchange of aryl groups between platinum centres; e.g.(i) reaction of [Pt(cod)(2-C4H3S)2] with [Pt(cod)Cl2] followed by addition of 1,2-bis(diphenylphosphino)ethane (dppe) gives [Pt(2-C4H3S)Cl(dppe)] in ca. 100% yield, (ii)[Pt(cod)(2-C8H5O)2] and [Pt(cod)(C6H4Cl-m)2] similarly give some [Pt(2-C8H5O)(C6H4Cl-m)(dppe)], and (iii)[Pt(cod)(3-C8H7)Cl] and SnMe3(C6H4Me-p) similarly give some [Pt(3-C8H7)2(dppe)] and [Pt(C6H4Me-p)2-(dppe)](3-C8H7= 1,2-dihydrobenzocyclobuten-3-yl). The olefin ligand is readily displaced from the aryl com-plexes by neutral ligands, and a wide range of [PtR(Cl)L2] and [PtR2L2] complexes with L =½ dppe or PPh3 have been made. The i.r. and 1H, 13C-{1H}, and 31P-{1H} n.m.r. spectra of the products are discussed. For cis-[ Pt(C6H4X-p)2(PPh3)2] complexes the values of 1J(Pt–P) show a good correlation with σI constants. The norbornadiene (nbd) complex [Pt(nbd)Cl2] reacts with SnMe3(2-C4H3O) to give [Pt(2-C4H3O)(nbd)Cl] in 91% yield, but the corresponding palladium complex [Pd(nbd)Cl2] reacts with SnMe3R (R = C6H4OMe-p or C6H4Me-p) to give a dimeric chloride-bridged complex in which the aryl group is attached to the organic ligand.