HALIDE-PROMOTED CO LABILIZATION APPLIED TO THE SYNTHESIS OF ALKYNE-SUBSTITUTED DERIVATIVES OF RU3(CO)12

Among the three halide-promoted complexes [PPN][Ru3(Cl)(CO)11] ([PPN][1], [PPN][Ru3(mu-Cl)(CO)10] ([PPN][2]), and [PPN][Ru3(mu-3-Cl)(CO)9] ([PPN][3]) (the last complex is observed here for the first time), which are readily obtained by addition of [PPN][Cl] (PPN = bis(triphenylphophoranylidene)ammonium) to Ru3(CO)12, the complexes [PPN][2] and [PPN][3] react with alkynes ((a) acetylene, (b) phenylacetylene, (c) diphenylacetylene, (d) dimethylacetylene) to produce the activated species [PPN][Ru3(mu-Cl)(mu-3-eta-2-RCCR')(CO)9] ([PPN][4]; THF, 25-degrees-C, 10 min, 100% spectroscopic yield), in which the halide behaves as a good leaving group whose displacement can be catalyzed by a protic solvent. The scope of this synthetic procedure is examined. The complex [PPN][Ru3(mu-Cl)(mu-3-eta-2-(C6H5)CC(C6H5))(CO)9] ([PPN][4c]) has been crystallized in 87% yield, and its X-ray structure is reported. Crystal data: triclinic, P1BAR (No. 2), a = 15.913 (4) angstrom, b = 16.307 (4) angstrom, c = 10.992 (4) angstrom, alpha = 82.73 (2)-degrees, beta = 98.55 (3)-degrees, gamma = 103.21 (4)-degrees, V = 2733 angstrom-3, Z = 2, mu-(Mo K-alpha) = 9.65 cm-1; Enraf-Nonius CAD4 diffractometer; final R(w) = 0.046 and R = 0.045 (from 6490 observations and 340 variables). The structure consists of an open triruthenium cluster unit where the alkyne ligand is coordinated in a mu-3-eta-2- parallel-to fashion. The bridging halide spans the open edge of the metal triangle and is slightly shifted below this plane. The reactivity of [PPN][4b-d] has been investigated. Protonation of the anion [4c]- at -78-degrees-C gives the corresponding neutral hydrido complex Ru3(mu-H)(mu-Cl)(mu-3-eta-2-(C6H5)CC(C6H5))(CO)9 (5c). The complex [PPN][4d] reacts with CO at 25-degrees-C in dichloromethane/methanol solution to yield Ru3(mu-3-eta-2-CH3CCCH3)(mu-CO)(CO)9 (6d) selectively. This complex can be isolated in pure form by extraction from a biphasic methanol/hexane mixture, a procedure avoiding chromatographic workup (yield, crystallized, 60%). Its X-ray structure is reported. Crystal data for 6d: monoclinic, P2(1)/c (No. 14), alpha = 14.716 (1) angstrom, b = 14.153 (2) angstrom, c = 18.226 (2) angstrom, beta = 96.70 (2)-degrees, V = 3770 angstrom-3, Z = 8 (two independent cluster molecules in the asymmetric unit); final R = 0.030 and R(w) = 0.037 (from 6362 observations and 523 variables). The alkyne is coordinated in a mu-3-eta-2- parallel-to mode, and there is one bridging carbonyl spanning the metal-metal edge parallel to the alkyne. Attempts to isolate the elusive nonacarbonyl derivative ''Ru3(mu-3-eta-2-RCCR)(CO)9'' are described: the addition of methanol or ethanol to THF solutions of [PPN][4b] gives instantaneously the known acetylide species [PPN][Ru3(mu-3-eta-2-CC(C6H5))(CO)9] ([PPN][7b]; yield, crystallized, 80%). In the case of internal alkynes such as diphenylacetylene, the reaction of [PPN][4c] with methanol requires more forcing conditions and results in a simple substitution of the halide by a hydrido ligand to give the complex [PPN][Ru3(mu-H)(mu-3-eta-2-(C6H5)CC(C6H5)(CO)9] ([PPN][8c]). In addition, attempts to release one carbonyl ligand from the decacarbonyl derivative 6c by a controlled thermolysis result in an aggregation of the metal framework, leading to the formation of the known butterfly complex Ru4(mu-4-eta-2-(C6H5)CC(C6H5))(CO)12 (9c) in 25% yield. The disubstituted-alkyne triruthenium derivative (''violet isomer'') Ru3(mu-3-eta-2-(C6H5)CC(C6H5))2(CO)8 (10c) is obtained by treatment of [PPN][4c] with [Ag][BF4] in the presence of an excess of alkyne (yield 54%). The X-ray structure of this complex is reported. Crystal data for 10c: monoclinic, C2/c (No. 15), a = 38.440 (7) angstrom, b = 8.544 (2) angstrom, c = 22.002 (2) angstrom, beta = 114.67 (1)-degrees, V = 6566 angstrom-3, Z = 8; R = 0.025 and R(w) = 0.032 (from 4843 observations and 423 variables). The differences between the catalytic halide-promoted incorporation of phosphines into Ru3(CO)12 and the stoichiometric reactions reported here are discussed.