(Pentamethylcyclopentadienyl)iridium polyhydride complexes: synthesis of intermediates in the mechanism of formation of (pentamethylcyclopentadienyl)iridium tetrahydride and the preparation of several iridium(V) compounds

Abstract

Reaction of LiBH, with [(C,(CH3),)Ir]2(w-H)3PF6 (1) results in the formation of the borohydride-bound dimer [(C5(CH3),)IrI2H3BH4 (2, R = H), for which a single-crystal X-ray diffraction study shows the borohydride moiety bridging the two metal centers in a unique fashion. Hydrolysis of this complex yields the formally iridium(1V) dimer [(C5(CH3)5)IrH3]2. Use of the more nucleophilic reducing agent LiEt3BH in this reaction leads to the mononuclear salt (C,(CH3),)IrH3[Li(THF),1 (5), the anion of which may by hydrolyzed to the iridium(V) complex (C5(CH3),)IrH4 ( 6 ) . The overall mechanism of the formation of tetrahydride 6 is discussed on the basis of these results. Deprotonation of 6 with t-BuLi in the presence of pmdeta leads to the sequestered salt (C5(CH3),)IrH3[Li(pmdeta)] (8). Silyl-or stannylation of the anion occurs with Me3Si03SCF3, Me3SnC1, and Ph3SnBr to yield the new iridium(V) polyhydrides (C5(CH3),)1rH3SiMe3, (C5(CH3),)IrH3SnMe3, and (C5-

Activation of Organic Substrates on Multi-Metallic Sites of Transition Metal Polyhydride Clusters Having C5Me5 Groups as Auxiliary Ligands

“…The reaction of [(C 5 Me 5 )Ru(CH 3 CN) 3 ](BF 4 ) [19] with an anionic iridium hydride complex Li[(C 5 Me 5 )IrH 3 ] [20] led to a new heterobimetallic hydride cluster (C 5 Me 5 )Ru(µ-H) 3 Ir(C 5 Me 5 ) (8) [Equation (5)]. [21] The longitudinal relaxation time T 1 for the hydride ligands was determined to be 3.34 s at Ϫ80°C, which is sufficient to characterize the complex as a classical trihydride complex.…”

“…This result suggests that the coordinatively unsaturated sites are generated on 1 by way of a hydride transfer from the ruthenium center to the ethylene ligand, i.e., hydrogenation of ethylene. (12) Monitoring the reaction by NMR spectroscopy showed the formation of an intermediary mono-µ-vinyl complex {(C 5 Me 5 )Ru} 2 (CH 2 CH 2 )(µ-CHCH 2 )(µ-H) (20). Monovinyl complex 20 was highly reactive owing to coordinative unsaturation at the metal centers and could be readily converted into 19 in the presence of excess amounts of ethylene (Scheme 4).…”

“…The structure of the intermediary thiaruthenacyclohexadiene 40 was confirmed in comparison with that of the analogous thiaruthenacycle derived by the reaction of µ 3 -borylene complex 17 with benzothiophene. [31] Complex 41 underwent hydrogenolysis by treatment of 41 with dihydrogen (7.2 atm) to produce ethylbenzene and the µ 3 -sulfido complex 15 [Equation (20)]. (20) Complex 12 shows reactivity for the cleavage of the CϪS bonds in dibenzothiophene.…”

“…[31] Complex 41 underwent hydrogenolysis by treatment of 41 with dihydrogen (7.2 atm) to produce ethylbenzene and the µ 3 -sulfido complex 15 [Equation (20)]. (20) Complex 12 shows reactivity for the cleavage of the CϪS bonds in dibenzothiophene. The reaction of 12 with dibenzothiophene proceeded at 110°C to form 15 and biphenyl in high yield [Equation (21)].…”

Binuclear cyclopentadienyliridium hydride chemistry: Terminal versus bridging hydride and cyclopentadienyl ligands

“…The terminal ν(Ir-H) frequencies were found to range from 2098 to 2282 cm -1 , which lie within the established range of 1800 to 2500 cm -1 . 6,36,37 The bridging ν(Ir-H) frequencies are much lower, ranging from 1372 to 1684 cm -1 . The experimental ν(Ir-H) frequencies of the pentamethylcyclopentadienyl deriviatives, measured in KBr pellets, exhibit the same trend but are 100 to 200 cm -1 below the predicted ν(Ir-H) frequencies for their unsubstituted cyclopentadienyl analogues.…”