Carborane Complexes of Ruthenium: Studies on the Chemistry of the Ru(CO) 2 (η 5 -7,8-C 2 B 9 H 11 ) Fragment

Treatment of [Ru(CO) 3 (η 5 -7,8-C 2 B 9 H 11 )] ( 1 ) with Me 3 NO in THF (tetrahydrofuran) affords [Ru(CO) 2 (NMe 3 )(η 5 -7,8-C 2 B 9 H 11 )] ( 3b ), while the salt [NEt 4 ][RuI(CO) 2 (η 5 -7,8-C 2 B 9 H 11 )] ( 2 ) reacts with NCMe in the presence of AgBF 4 to give [Ru(CO) 2 (NCMe)(η 5 -7,8-C 2 B 9 H 11 )] ( 3c ). Related complexes [Ru(CO) 2 (L)(η 5 -7,8-C 2 B 9 H 11 )] (L = CNBu t ( 3d ), PPh 3 ( 3e )) are obtained by displacement of THF from [Ru(CO) 2 (THF)(η 5 -7,8-C 2 B 9 H 11 )] ( 3a ) with CNBu t and PPh 3, respectively. Alkenes and 3a afford the complexes [Ru(CO) 2 (alkene)(η 5 -7,8-C 2 B 9 H 11 )] (alkene = C 2 H 4 ( 4a ), MeCH CH 2 ( 4b ), Me 3 SiCH CH 2 ( 4c ), and C 7 H 10 (norbornene) ( 4d )), whereas alkynes RC⋮CR (R = Me, Ph) give the species [Ru(CO) 2 (RC⋮CR)(η 5 -7,8-C 2 B 9 H 11 )] (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 (η 5 -7,8-C 2 B 9 H 11 )] ( 6 ), while PPh 3 in CH 2 Cl 2 affords the ylide complex [Ru{C(Me) C(Me)PPh 3 }(CO) 2 (η 5 -7,8-C 2 B 9 H 11 )] ( 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 (η 2:η 5 -9-C(H) C(H)Bu t -7,8-C 2 B 9 H 10 )] ( 8a ) and [Ru(CO) 2 (η 2:η 5 -10-C(H) C(H)Bu t -7,8-C 2 B 9 H 10 )] ( 8b ). An X-ray diffraction study on 8a revealed that the ruthenium atom is η 5 -coordinated by the open CCBBB face of the nido -C 2 B 9 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 (η 2:η 5 -9-C(H) C(H)R-7,8-C 2 B 9 H 10 )] (R = H ( 9a ), SiMe 3 ( 10a) ) and [Ru(CO) 2 (η 2:η 5 -10-C(H) C(H)R-7,8-C 2 B 9 H 10 )] (R = H ( 9b ), SiMe 3 ( 10b )) are obtained. Addition of PMe 2 Ph in heptane to 9b gives [Ru(CO) 2 (σ,η 5 -10-C(H)(PMe 2 Ph)CH 2 -7,8-C 2 B 9 H 10 )] ( 11b ), the ylide structure of which was confirmed by X-ray crystallography. The Ru(CO) 2 fragment is linked to the nido- C 2 B 9 cage system by η 5 bonding to the CCBBB face and by a Ru−CH 2 σ-bond to the CH 2 C(H)(PMe 2 Ph)B fragment. Reactions between 3a and RC⋮CH, employing an excess of the latter, give the compounds [Ru(CO) 2 {η 2:η 5 -9-C(H) C(H)R-10,11-[C(H) C(H)R] 2 -7,8-C 2 B 9 H 8 }] (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 ){η 5 -9,10,11-[C(H) C(H)Bu t ] 3 -7,8-C 2 B 9 H 8 }] ( 13 ) and [Ru(CO) 2 {σ,η 5 -9-C(H)(PMe 3 )C(H)SiMe 3 -10,11-[C(H) C(H)SiMe 3 ] 2 -7,8-C 2 B 9 H 8 }] ( 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-C 2 B 9 H 8 cage. All boron atoms in the pentagonal CCBBB 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 in relation to their structures.