Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 32. Reactions of the rhodium–tungsten complex [RhW(µ-CC6H4Me-4)(CO)3(η-C5H5)(η-C9H7)] with alkynes; X-ray crystal structure of [RhW{µ-C(C6H4Me-4)C(Ph)C(Ph)}(CO)2(η-C5H5)(η-C9H7)]

Abstract

The bimetal compound [RhW(µ-CR)(CO)₃(η-C₅H₅)(η-C₉H₇)](R = C₆H₄Me-4, C₉H₇= indenyl) reacts with the alkynes R¹CCR²(R¹= R²= Ph or Me; R¹= Ph, R²= H or Me) in toluene at ca. 50–80 °C to give the bridged complexes [RhW{µ-C(R)C(R¹)C(R²)}(CO)₂(η-C₅H₅)(η-C₉H₇)]. The molecular structure of the species obtained from PhCCPh was established by a single-crystal X-ray diffraction study. A Rh–W bond [2.754(1)Å] is bridged by a three-carbon chain [mean C–C 1.439(8)Å]. Whereas all the atoms of the chain are bound to the rhodium [2.105(6), 2.135(6), and 2.103(5)Å], only the two end carbons are attached to the tungsten [2.175(5) and 2.196(6)Å]. The tungsten atom carries two essentially orthogonal terminal carbonyl groups, as well as the cyclopentadienyl ring. The indenyl group is asymmetrically attached to the rhodium atom, with three short Rh–C [2.185(7), 2.198(7), and 2.204(7)Å] and two long Rh–C [2.334(7) and 2.330(7)Å] separations to the C₅ ring, implying slippage towards an η³-bonding mode. Formation of [RhW{µ-C(R)C(Ph)C(Ph)}(CO)₂(η-C₅H₅)(η-C₅Me₅)] from [RhW(µ-CR)(CO)₃(η-C₅H₅)(η-C₅Me₅)] and PhCCPh requires forcing conditions (100 °C, 5 d in toluene), and side-reactions occur to yield hexaphenylbenzene, [Rh(CO)₂(η-C₅Me₅)], and the tetraphenylcyclopentadienone complex [Rh(µ-C₄Ph₄CO)(η-C₅Me₅)]. The reaction between [RhW(µ-CR)(CO)₃(η-C₅H₅)(η-C₉H₇)] and [W(CR)(CO)₂(η-C₅H₅)] has also been investigated. With heptane as solvent, the products are the trimetal complex [Rh₂W(µ₃-CR)(µ-CO)(CO)₂(η-C₅H₅)(η-C₉H₇)₂], the alkyne-bridged complex [W₂(µ-RC₂R)(CO)₄(η-C₅H₅)₂], and a compound formulated as [W₂{µ-C(R)C(O)C(R)}(CO)₄(η-C₅H₅)₂]. Spectroscopic data (i.r., ¹H and ¹³C-{¹H} n.m.r.) for the new compounds are reported and discussed.