Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 89. Tetra- and penta-nuclear tungsten–rhodium complexes: crystal structures of [W3Rh2(µ-CO)2(µ-CMe){µ-C(Me)C(O)}(µ-PPh2)2(µ3-CMe)(CO)2(η-C5H5)3] and [W3Rh2(µ-CO)3(µ-CMe){µ-C(Me)PPh2}(µ3-CMe)-(CO)2(ηC5H5)3

Abstract

Treatment of [Rh2(µ-PPh2)2(cod)2](cod = cyclo-octa-1,5-diene) in thf (tetrahydrofuran) at room temperature with 2 equivalents of [W(CMe)(CO)2(η-C5H5)] rapidly affords the tetranuclear metal complex [W2Rh2(µ-CMe)2(µ-PPh2)2(CO)4(η-C5H5)2](4). If the same reaction is carried out using an excess of the ethylidynetungsten complex two metal cluster compounds are obtained: [W2Rh2(µ-CO){µ-C(Me)C(O)}(µ-PPh2)2(µ3-CMe)(CO)2(η-C5H5)2](5)(formed as a separable mixture of two diastereoisomers) and [W3Rh2(µ-CO)2(µ-CMe){µ-C(Me) C(O)}(µ-PPh2)2(µ3-CMe)(CO)2(η-C5H5)3](6). The structure of the latter was established by X-ray diffraction. The molecule has an essentially planar W(1), Rh(1), W(2), Rh(2), W(3) framework. Carbonyl groups bridge the Rh(1)–W(1) and Rh(2)–W(2) bonds, and PPh2 ligands span the Rh(1)–W(2) and Rh(2)–W(3) linkages. Ethylidyne groups edge-bridge the Rh(1)–W(1) bond and triply bridge the atoms Rh(1)W(2)Rh(2), but the Rh(1)⋯ Rh(2) separation [3.115(4)A] is non-bonding. The Rh(2)–W(3) bond is bridged by a C(Me)C(O) ketenyl group, and the terminal W atoms in the chain each carry a CO ligand and a C5H5 ring. A third C5H5 group ligates W(2). The metal–metal distances fall into two groups [Rh(1)–W(2) 2.791(6), Rh(2)– W(3) 2.813(4); and Rh(1)–W(1) 2.696(5), Rh(2)–W(2) 2.664(5)A], with the shorter separations corresponding to double bonds and the longer to single bonds. Compound (6) is produced by addition of a molecule of [W(CMe)(CO)2(η-C5H5)] to (5), while the latter is formed by isomerisation of (4), a process necessitating migration of µ-CMe and µ-PPh2 between the metal centres. After several hours solutions of (6) in thf afford quantitatively the complex [W3Rh2(µ-CO)3(µ-C(Me){µ-C(Me)PPh2}(µ-PPh2)(µ-CMe)(CO)2(η-C5H5)3](7) an isomer of (6). The structure of (7) was established by X-ray diffraction. An essentially planar metal atom chain W(1), Rh(1), W(2), Rh(2), W(3) forms the spine of the molecule. The various ligands ligate the rhodium and tungsten atoms in a similar manner to those in (6), with the exception of the groups which span the Rh(2)–W(3) bond. This bond is now bridged by a λ5- phospha-alkyne C(Me) PPh2 fragment such that the phosphorus atom ligates W(3) and the carbon atom CMe is bonded to Rh(2) and W(3). The Rh(2)–W(3) bond is also bridged by a CO ligand. Thus the conversion of (6) into (7) involves a novel interchange of CO and PPh2 fragments such that in the former a µ-C(Me)C(O) group is present and in the latter a µ- C(Me)PPh2 moiety. The n.m.r. data (1H, 13C-{1H), and 31P-{1H}) for the new compounds are reported and discussed.