Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 23. Alkyne insertion into heteronuclear dimetal compounds with bridging tolylmethylidyne ligands; crystal structures of [FeW{µ-C(C6H4Me-4)C(Me)C(Me)}(CO)5(η-C5H5)] and [Fe2W(µ3-CC6H4Me-4)(µ-Me3SiC2SiMe3)(µ-CO)(CO)6(η-C5H5)]

Abstract

Cobalt–tungsten complexes [CoW(µ-CRCR¹CR²)(CO)₂(η-C₅H₅)(η-C₅Me₅)](R = C₆H₄Me-4; R¹= R²= Ph or Me; R¹= Ph or Me, R²= Me or Ph; R¹= Bu^t, R²= H), with allyl groups bridging the Co–W bonds, have been prepared by heating the alkynes PhCCPh, MeCCMe, MeCCPh, and Bu^tCCH with the compound [CoW(µ-CR)(CO)₃(η-C₅H₅)(η-C₅Me₅)]. Related iron–tungsten compounds [FeW(µ-CRCR¹CR²)(CO)₅(η-C₅H₅)](R¹= R²= Me, Ph, C₆H₄Me-4, or CF₃) have been prepared by heating the appropriate alkyne R¹CCR² with the cluster complex [Fe₂W(µ₃-CR)-(µ-CO)(CO)₈(η-C₅H₅)] in toluene. In contrast, the diiron–tungsten species reacts with Me₃SiCCSiMe₃ and with Bu^tCCSiMe₃ to afford compounds [Fe₂W(µ₃-CR)(µ-alkyne)(µ-CO)(CO)₆(η-C₅H₅)] which retain the µ₃-CFe₂W structural core, the product from Bu^tCCSiMe₃ being formed as a mixture of isomers. The ¹H and ¹³C-{¹H} n.m.r. data for all the compounds are reported and discussed, and the molecular structures of [FeW{µ-C(C₆H₄Me-4)C(Me)C(Me)}(CO)₅(η-C₅H₅)] and [Fe₂W(µ₃-CC₆H₄Me-4)(µ-Me₃SiC₂SiMe₃)(µ-CO)(CO)₆(η-C₅H₅)] have been established by X-ray diffraction. In the dimetal compound the Fe–W bond [2.720(1)Å] is bridged by a three-carbon chain [mean C–C 1.438(8)Å]. Whereas all the atoms of the chain are bound to the iron [2.047(6), 2.103(6), and 2.083(6)Å], only the two end carbons are attached to the tungsten [2.194(6) and 2.164(7)Å]. The iron atom carries three essentially orthogonal terminal carbonyl groups, and the tungsten is ligated by the cyclopentadienyl ring and two carbonyl groups. Crystals of [FeW{µ-C(C₆H₄Me-4)C(Me)C(Me)}(CO)₅(η-C₅H₆)] are monoclinic (space group C2/c); the structure has been refined to R 0.039 for 3 334 reflections measured to 2θ= 55° at 220 K. In the diiron–tungsten compound the metal atoms form a triangle which is bridged asymmetrically by the µ₃-CC₆H₄Me-4 ligand; one of the Fe–W edges is bridged transversely on the opposite face of the triangle by the µ-Me₃SiCCSiMe₃ ligand. The iron atoms each carry three terminal carbonyl groups, but one of those on the iron atom associated with the acetylenic bridge is strongly semi-bridging to the other iron atom. The tungsten atom carries one terminal carbonyl group (oriented approximately parallel to the acetylene fragment) and the cyclopentadienyl ligand. The unbridged Fe–W bond (ca. 2.77 Å) is significantly longer than the other two (W–Fe 2.66, Fe–Fe 2.64 Å). Crystals of [Fe₂W(µ₃-CC₆H₄Me-4)(µ-Me₃SiC₂SiMe₃)(µ-CO)(CO)₆(η-C₅H₅)] are monoclinic (space group P2₁), and are unusual in that the crystallographic asymmetric unit comprises two enantiomorphous molecules of the complex related by a non-crystallographic centre of inversion. The structure has been refined to R 0.051 for 7 443 reflections measured to 2θ= 60° at 293 K.