Carborane complexes of ruthenium: Studies on the chemistry of the Ru(CO)(2)(eta(5)-7,8-C2B9H11) fragment

Treatment of [Ru(CO)(3)(eta(5)-7,8-C2B9H11)] (1) with Me(3)NO in THF (tetrahydrofuran) affords [Ru(CO)(2)(NMe(3))(eta(5)-7,8-C2B9H11)] (3b), while the salt [NEt(4)][RuI(CO)(2)(eta(5)-7,8-C2B9H11)] (2) reacts with NCMe in the presence of AgBF4 to give [Ru(CO)(2)(NCMe)(eta(5)-7,8-C2B9H11)] (3c). Related complexes [Ru(CO)(2)(L)(eta(5)-7,8-C2B9H11)] (L = CNBu(t) (3d), PPh(3) (3e)) are obtained by displacement of THF from [Ru(CO)(2)(THF)(eta(5)-7,8-C2B9H11)] (3a) with CNBu(t) and PPh(3), respectively. Alkenes and 3a afford the complexes [Ru(CO)(2)(alkene)(eta(5)-7,8-C2B9H11)] (alkene = C2H4 (4a), MeCH=CH2 (4b), Me(3)SiCH=CH2 (4c), and C7H10 (norbornene) (4d)), whereas alkynes RC=CR (R = Me, Ph) give the species [Ru(CO)(2)(RC=CR)(eta(5)-7,8-C2B9H11)] (R = Me (5a), Ph (5b)). The reaction of complex 5a with K[BH(CHMeEt)(3)], in Et(2)O solution, followed by addition of 18-crown-6, gives the salt [K(18-crown-6)][Ru{C(Me)=C(H)Me}(CO)(2)(eta(5)-7,8-C2B9H11)] (6), while PPh(3) in CH2Cl2 affords the ylide complex [Ru(C(Me)=C(Me)PPh(3))(CO)(2)(eta(5)-7,8-C2B9H11)] (7) Reactions between 3a and the alkynes RC=CH (R = Bu(t), SiMe(3)) yield a variety of products, in all of which the carborane ligand adopts a nonspectator role. Complex 3a and 1 mol equiv of Bu(t)C=CH gives a mixture of isomers [Ru(CO)(2)(eta(2):eta(5)-9-C(H)=C(H)Bu(t)-7,8-C2B9H10)] (8a) and [Ru(CO)(2)(eta(2):eta(5)-10-C(H)=C(H)Bu(t)-7,8-C2B9H10)] (8b). An X-ray diffraction study on 8a revealed that the ruthenium atom is eta(5)-coordinated by the open CCBBB face of the nido-C2B9 cage and by the C=C bond of the BCH=C(H)Bu(t) group. The reaction between 3a and 1 mol equiv of Me(3)SiC=CH is more complex due to SiMe(3) group cleavage. Isomeric mixtures of [Ru(CO)(2)(eta(2):eta(5)-9-C(H)=C(H)R-7,8-C2B9H10)] (R = H (9a), SiMe(3) (10a)) and [Ru(CO)(2)(eta 2:eta(5)-10-C(H)=C(H)R-7,8-C2B9H10)] (R = H (9b), SiMe(3) (10a)) are obtained. Addition of PMe(2)Ph in heptane to 9b gives [Ru(CO)(2)(sigma,eta(5)-10-C(H)(PMe(2)Ph)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 eta(5) bonding to the CCBBB face and by a Ru-CH2 sigma-bond to the CH2C(H)(PMe(2)Ph)B fragment. Reactions between 3a and RC=CH, employing an excess of the latter, give the compounds [Ru(CO)(2){eta(2):eta(5)-9-C(H)=C(H)R-10,11-[C(H)=C(H)R](2)-7,8- C2B8}] (R = Bu(t) (12a), SiMe(3) (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 PMe(3) yields respectively [Ru(CO)(2)(PMe(3)){eta(5)-9,10,11-[C(H)=C(H)Bu(t)](3)-7,8- C2B9H8}] (13) and [Ru(CO)(2){sigma,eta(5)-9-C(H)(PMe(3))C(H)SiMe(3)-10,11-[C(H)=C (H)SiMe(3)](2)-7,8-C2B9H8}] (14). The structure of 13 was established by X-ray diffraction. The Ru atom is coordinated by a PMe(3) molecule and the two CO groups and by the nido-9,10,11-[C(H)=C(H)Bu(t)]3-7,8-C2B9H8 cage. All boron atoms in the pentagonal CBBB ring ligating the metal carry C(H)=C(H)Bu(t) substituents. In addition to X-ray crystal structure determinations, NMR data for the new complexes are reported and discussed ill relation to their structures.