Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 22. Synthesis and some reactions of [bis(diphenylphosphino)methane]pentacarbonyl-µ-[methoxy(methyl)methylene]-platinumtungsten and the crystal structure of [PtW(µ-CCH2)(Ph2PCH2PPh2)(CO)5]

Abstract

Treatment of the compound [PtW{µ-C(OMe)Me}(CO)₅(cod)](cod = cyclo-octa-1,5-diene) with dppm (Ph₂PCH₂PPh₂) affords the complex [PtW{µ-C(OMe)Me}(dppm)(CO)₅]. Solutions of the latter in toluene on standing afford the isomeric species [PtW{µ-C(OMe)Me}(µ-dppm)(CO)₅] and side-products, whereas chromatography on basic alumina yields the vinylidene-bridged compound [PtW(µ-CCH₂)(dppm)(CO)5]. The structure of the latter was established by a single-crystal X-ray diffraction study. Crystals are monoclinic, space group P2₁/c (no. 14), with Z= 4 in a unit cell of dimensions a= 9.325(2), b= 17.837(3), c= 19.451(3)Å, and β= 105.74(1)°. Intensities were measured at room temperature to 2θ⩽ 50°, and the structure has been refined to R 0.036 (R′ 0.038) for 4 032 reflections. The metal–metal bond [2.774(1)Å] is asymmetrically spanned by the vinylidene ligand [C–Pt 2.012(9), C–W 2.198(8), and CC 1.363(13)Å]. The tungsten atom carries five terminal CO groups, one of which semi-bridges [W–C–O 167.8(9)°] to the platinum atom, the latter being chelated by the dppm ligand [Pt–P 2.250(2) and 2.335(2)Å]. Protonation of the compound [PtW{µ-C(OMe)Me}(µ-dppm)(CO)₅] with HBF₄·OEt₂ affords the salt [PtW(µ-CMe)(µ-dppm)(CO)₅][BF₄]. This reaction is only partially reversed by treatment of the latter with sodium methoxide in methanol, the main product being the bridged vinylidene complex [PtW(µ-CCH₂)(µ-dppm)(CO)₅]. The latter is also formed by treating [PtW(µ-CMe)(µ-dppm)(CO)₅][BF₄] with the reagent K[BH(CHMeEt)₃] in tetrahydrofuran. The n.m.r. data (¹H, ¹³C-{¹H}, ³¹P-{H}, and ¹⁹⁵Pt-{¹H}) for the new compounds are reported and discussed in relation to their structures.