Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 4. Synthesis of triangulo-diplatinum–chromium and –tungsten complexes. Crystal structure of [Pt2W{µ-C(OMe)Ph}(CO)6(PBut2Me)2]
Abstract
The compounds [M{C(OMe)Ph}(CO)5](M = Cr or W) react with bis(ethylene)(trialkylphosphine)platinum complexes [Pt(C2H4)2(PR3)][PR3= PBut2Me or P(cyclo-C6H11)3] to give triangulo-trimetal compounds [MPt2{µ-C(OMe)Ph}(CO)6(PR3)2]. With [Cr{C(OMe)Ph}(CO)5], di- and tri-platinum complexes [Pt2{µ-C(OMe)Ph}(CO)2(PBut2Me)2], and [Pt3{µ-C(OMe)Ph}(µ-CO)2(PR3)3][PR3= PBut2Me or P(cyclo-C6H11)3], are also produced in the reactions. In the compound [Pt2W{µ-C(OMe)Ph}(CO)6(PBut2Me)2]13C n.m.r. studies showed that the µ-C(OMe)Ph group bridged the Pt–Pt bond, and this was confirmed by a single-crystal X-ray diffraction study. Crystals are monoclinic, with space group P21/a and Z= 4 in a unit cell of dimensions a= 16.003(5), b= 15.691(7), c= 15.261 (9)Å, and β= 93.52(4)°. The structure has been determined by heavy-atom methods from automated diffractometer data for 2.9 ⩽ 2θ⩽ 50° and refined to R 0.075 (R′ 0.082) for 3 991 reflections. A triangle of metal atoms has Pt–Pt and Pt–W separations of 2.627(1) and 2.830 (2)Å, respectively. The platinum–platinum bond is bridged by the C(OMe)Ph group [C–Pt 2.05(2)Å]. Each platinum atom is co-ordinated by a CO and by a PBut2Me group such that both PBut2Me ligands lie on the same side of the Pt–Pt bond [P–Pt–Pt 149(1)°] and are cis to the µ-C(OMe)Ph group, with the two carbonyl ligands semi-bridging across the Pt–W bonds to the formally 16-electron W(CO)4 group [Pt–C–O 148(3)°]. The ease of transfer of a carbene group from a mononuclear metal carbene complex to platinum is reflected in the reactions of [Mn{C(OMe)Ph}(CO)2(η-C5H5)] with [Pt(C2H4)2(PR3)][PR3= PMe3 or PBut2Me] from which no compounds with Mn–Pt bonds were isolated. Instead, the products were the triplatinum species [Pt3{µ-C(OMe)Ph}3(PMe3)3] and [Pt3{µ-C(OMe)Ph}2(µ-CO)(PR3)3]. These triplatinum compounds likely form via initial formation of an intermediate with a [graphic omitted]t bridged system, since it was observed that the dimetal compound [(OC)5[graphic omitted]t(PMe3)2] decomposes at 80 °C in toluene to give [Pt3{µ-C(OMe)Ph}3(PMe3)3] and [Pt3{µ-C(OMe)Ph}2(µ-CO)(PMe3)3]. Bulky phosphine groups seem to favour formation of trimetal compounds since [W{C(OMe)Ph}(CO)5] and [Pt(C2H4)(PBut2Me)2] react to give [Pt2W{µ-C(OMe)Ph}(CO)6(PBut2Me)3], rather than [(OC)5[graphic omitted]t(PBut2Me)2]. The spectroscopic properties of the new compounds are reported.
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