Carborane Complexes of Ruthenium: Studies on the Chemistry of the Ru(CO)₂(η⁵-7,8-C₂B₉H₁₁) Fragment

Abstract

Treatment of [Ru(CO)3(η5-7,8-C2B9H11)] (1) with Me3NO in THF (tetrahydrofuran) affords [Ru(CO)2(NMe3)(η5-7,8-C2B9H11)] (3b), while the salt [NEt4][RuI(CO)2(η5-7,8-C2B9H11)] (2) reacts with NCMe in the presence of AgBF4 to give [Ru(CO)2(NCMe)(η5-7,8-C2B9H11)] (3c). Related complexes [Ru(CO)2(L)(η5-7,8-C2B9H11)] (L = CNBut (3d), PPh3 (3e)) are obtained by displacement of THF from [Ru(CO)2(THF)(η5-7,8-C2B9H11)] (3a) with CNBut and PPh3, respectively. Alkenes and 3a afford the complexes [Ru(CO)2(alkene)(η5-7,8-C2B9H11)] (alkene = C2H4 (4a), MeCHCH2 (4b), Me3SiCHCH2 (4c), and C7H10 (norbornene) (4d)), whereas alkynes RC⋮CR (R = Me, Ph) give the species [Ru(CO)2(RC⋮CR)(η5-7,8-C2B9H11)] (R = Me (5a), Ph (5b)). The reaction of complex 5a with K[BH(CHMeEt)3], in Et2O solution, followed by addition of 18-crown-6, gives the salt [K(18-crown-6)][Ru{C(Me)C(H)Me}(CO)2(η5-7,8-C2B9H11)] (6), while PPh3 in CH2Cl2 affords the ylide complex [Ru{C(Me)C(Me)PPh3}(CO)2(η5-7,8-C2B9H11)] (7). Reactions between 3a and the alkynes RC⋮CH (R = But, SiMe3) yield a variety of products, in all of which the carborane ligand adopts a nonspectator role. Complex 3a and 1 mol equiv of ButC⋮CH gives a mixture of isomers [Ru(CO)2(η2:η5-9-C(H)C(H)But-7,8-C2B9H10)] (8a) and [Ru(CO)2(η2:η5-10-C(H)C(H)But-7,8-C2B9H10)] (8b). An X-ray diffraction study on 8a revealed that the ruthenium atom is η5-coordinated by the open CCBBB face of the nido-C2B9 cage and by the CC bond of the BCHC(H)But group. The reaction between 3a and 1 mol equiv of Me3SiC⋮CH is more complex due to SiMe3 group cleavage. Isomeric mixtures of [Ru(CO)2(η2:η5-9-C(H)C(H)R-7,8-C2B9H10)] (R = H (9a), SiMe3 (10a)) and [Ru(CO)2(η2:η5-10-C(H)C(H)R-7,8-C2B9H10)] (R = H (9b), SiMe3 (10b)) are obtained. Addition of PMe2Ph in heptane to 9b gives [Ru(CO)2(σ,η5-10-C(H)(PMe2Ph)CH2-7,8-C2B9H10)] (11b), the ylide structure of which was confirmed by X-ray crystallography. The Ru(CO)2 fragment is linked to the nido-C2B9 cage system by η5 bonding to the CCBBB face and by a Ru−CH2 σ-bond to the CH2C(H)(PMe2Ph)B fragment. Reactions between 3a and RC⋮CH, employing an excess of the latter, give the compounds [Ru(CO)2{η2:η5-9-C(H)C(H)R-10,11-[C(H)C(H)R]2-7,8-C2B9H8}] (R = But (12a), SiMe3 (12b)) in which all boron atoms in the open CCBBB face of the cage bonded to the ruthenium carry C(H)C(H)R substituents. Treatment of the complexes 12 with PMe3 yields respectively [Ru(CO)2(PMe3){η5-9,10,11-[C(H)C(H)But]3-7,8-C2B9H8}] (13) and [Ru(CO)2{σ,η5-9-C(H)(PMe3)C(H)SiMe3-10,11-[C(H)C(H)SiMe3]2-7,8-C2B9H8}] (14). The structure of 13 was established by X-ray diffraction. The Ru atom is coordinated by a PMe3 molecule and the two CO groups and by the nido-9,10,11-[C(H)C(H)But]3-7,8-C2B9H8 cage. All boron atoms in the pentagonal CCBBB ring ligating the metal carry C(H)C(H)But substituents. In addition to X-ray crystal structure determinations, NMR data for the new complexes are reported and discussed in relation to their structures.