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 σ_I 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.