Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 43. Carbon–tungsten triple bonds as formal four-electron donors; synthesis and reactions of the compounds [FeW(µ-CC6H4Me-4)(CO)5L]{L = HB(pz)3[tris(pyrazol-1-yl)borate] or η-C5H5} and X-ray crystal structures of [FeW(µ-CC6H4Me-4)(CO)5{HB(pz)3}] and [FeW(µ-CC6H4Me-4)(CO)(µ-Me2PCH2PMe2)(CO)2{HB(pz)3}]

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Abstract
The compounds [W(CC6H4Me-4)(CO)2{HB(pz)3}][HB(pz)3= tris(pyrazol-1-yl)borate] and [Fe2(CO)9] react in diethyl ether to give the p-tolylmethylidyne-bridged iron–tungsten complex [FeW(µ-CC6H4Me-4)(CO)5{HB(pz)3}]. The structure of this unsaturated (32 valence electron) compound has been established by X-ray diffraction. The parameters for the [graphic omitted] ring [Fe–W 2.612(2), µ-C–Fe 1.826(6), µ-C–W 2.025(7)Å] suggest partial multiple bonding in the metal–metal and µ-C–Fe bonds, as expected if the {HB(pz)3}(OC)2WCC6H4Me-4 fragment were acting formally as a four–electron donor to the tricarbonyliron group. An analogous but less stable iron–tungsten complex [FeW(µ-CC6H4Me-4)(CO)5(η-C5H5)] has been obtained from the reaction between [W(CC6H4Me-4)(CO)2(η-C5H5)] and the bis(cyclo-octene)iron complex [Fe(CO)3(η-C8H14)2]. Both 32-valence electron compounds [FeW(µ-CC6H4Me-4)(CO)5L][L =η-C5H5 or HB(pz)3] react reversibly with CO affording the electronically-saturated 34 valence electron complexes [FeW(µ-CC6H4Me-4)(CO)6L]. The equilibrium is in favour of the Fe(CO)4-containing species when L =η-C5H5, and the Fe(CO)3 species when L = HB(pz)3. The resonances for the ligated alkylidyne carbon atoms in the 13C-{1H} n.m.r. spectra of the compounds [FeW(µ-CC6H4Me-4)(CO)5L] are considerably more deshielded than those in the spectra of [FeW(µ-CC6H4Me-4)(CO)6L], and this is considered to reflect the variable electron-pair donor properties (four or two electrons, respectively) of the L(OC)2WCC6H4Me-4 fragments in these complexes. The unsaturated compounds react readily with monodentate or bidentate tertiary phosphines, and several types of product are described, some being formally electronically saturated (34 electron iron–tungsten species) while others are not. Initial attack of the phosphine groups occurs at the iron centre, but the compounds [FeW(µ-CC6H4Me-4)(CO)4(PMe3)2(η-C5H5)] and [FeW(µ-CC6H4Me-4)(CO)4(dppm){HB(pz)3}](dppm = Ph2PCH2PPh2) release CO and form [FeW(µ-CC6H4Me-4)(µ-CO)(CO)2(PMe3)2(η-C5H5)] and [FeW(µ-CC6H4Me-4)(µ-CO)(µ-dppm)(CO)2{HB(pz)3}], respectively, in which both metal centres are co-ordinated by a PMe3 ligand or by the µ-dppm group. An X-ray diffraction study on [FeW(µ-CC6H4Me-4)(µ-CO)(µ-dmpm)(CO)2{HB(pz)3}](dmpm = Me2PCH2PMe2) established that in this molecule the Fe–W bond [2.605(1)Å] is bridged by the dmpm group and by the alkylidyne ligand [µ-C–Fe 1.911(3), µ-C–W 1.951(4)], and is strongly semi-bridged by a CO ligand on tungsten [W-C-0162.1(4)°]. The iron atom carries two terminally bound CO groups and the tungsten is ligated by the HB(pz)3 – anion. Alkylation (SO3CF3Me) of the compounds [FeW(µ-CC6H4Me-4)(µ-CO)(CO)2(PMe3)2(η-C5H5)] and [FeW(µ-CC6H4Me-4)(µ-CO)(µ-L–L)(CO)2{HB(pz)3}](L–L = dppm or dmpm) affords the salts [FeW(µ-CC6H4Me-4)(µ-COMe)(CO)2(PMe3)2(η-C5H5)][SO3CF3] and [FeW(µ-CC6H4Me-4)(µ-COMe)(µ-L–L)(CO)2{HB(pz)3 2}][SO3CF3], respectively. Spectroscopic data [i.r. and n.m.r. (1H, 13C-{1H}, and 31P-{1H})] for all the new compounds are reported and discussed.

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