Si⋅⋅⋅H Interligand Interactions in Cobalt(V) and Iridium(V) Bis(silyl)bis(hydride) Complexes

Abstract

A series of bis(silyl)bis(hydride) cobalt complexes [Cp*Co(H)2(SiR3)2] (Cp*=pentamethylcyclopentadienyl; SiR3=SiPh2H, SiMe3, SiH3, SiF3, SiCl3, SiBr3, Si(CF3)3; Co1–Co7) as well as the analogous iridium complexes [Cp*Ir(H)2(SiR3)2] (SiR3=SiEt3, SiMe3, SiH3, SiF3, SiCl3, SiBr3, Si(CF3)3; Ir1–Ir7) were studied to detect possible residual Si⋅⋅⋅H interactions. Tests of several density functionals by comparison with coupled‐cluster results indicate that the TPSSh functional performs better than B3LYP, BP86, M06, M06L, and PBEPBE. Based on molecular structures, as well as Wiberg bond indices and J(Si,H) spin–spin coupling constants as indicators of a possible Si⋅⋅⋅H interaction, at least two residual Si⋅⋅⋅H interactions in Co2, Co5, and all four possible Si⋅⋅⋅H interactions in Co3 and Co4 have been detected. Co6 and Co7 exhibit stronger Si⋅⋅⋅H bonding than the other complexes studied. On the contrary, the iridium complexes Ir1–Ir3 and Ir5–Ir7 are classical iridium(V) bis(silyl)bis(hydride) complexes with only rudimentary Si⋅⋅⋅H interactions, if any.

Reactions of Hydrosilanes with Transition Metal Complexes

“…Three papers are summarized in this section: the first is on hydrosilylation of alkenes that involve CpCo complexes, the next is on Si···H interligand interactions in Co­(V) and Ir­(V) complexes, and the last is on a CpRh complex that contains a Si···H···Si unit …”

“…The Ir–Si distances vary in the seven Ir complexes from 2.322 to 2.426, compared to the various Co–Si distances that range from 2.183 to 2.304. Therefore, the authors proposed that the larger atomic radius of iridium prevents the silyl and hydride ligands from a close interaction with each other, thus impeding a Si···H interaction …”

“…There appear to be 3 types of interactions: (a) for Co2−Co5, the presence of four Si−H interactions is clear with Si Therefore, the authors proposed that the larger atomic radius of iridium prevents the silyl and hydride ligands from a close interaction with each other, thus impeding a Si•••H interaction. 356 In a companion paper, the same authors reported the calculations for the corresponding Rh series shown in Figure 28. 363 These may also be viewed as "piano-stool" complexes, and the following examples have been synthesized and characterized spectroscopically and in some cases by X-ray or neutron diffraction: [CpRh(SiMe 3 ) 2 (H) 2 ] (X-ray), 366 [Cp*Rh(H) 2 (SiEt 3 ) 2 ], 422,424 [CpRh(SiMe 3 ) 2 (PMe 3 )H] + , 420 363 In all cases the Si 2 −H distance was longer than the Si 1 −H distance.…”

“…Co, Rh. Three papers are summarized in this section: the first is on hydrosilylation of alkenes that involve CpCo complexes, 357 the next is on Si•••H interligand interactions in Co(V) and Ir(V) complexes, 356 and the last is on a CpRh complex that contains a Si•••H•••Si unit. 363 In the study of [CpCo(CO)], the aims were to determine how a high spin [CpCo(C 2 H 4 )] species could activate hydrosilanes to generate silylcobalt hydrides and how the resulting complex can react in the presence of alkenes to ultimately produce hydrosilylation products.…”

J(Si,H) Coupling Constants of Activated Si–H Bonds

“…Indeed, also our benchmark system 7 representing a classical silyl hydride yields a positive J (Si,H) coupling which violates the rather arbitrary 20 Hz limit in theory (+34 Hz) and experiment (22 Hz; Figure ). , The situation is further complicated by the presence of bridging η 2 (H–Si)­M entities. In that case Corriou and Colomer proposed that the total coupling constant formally emerges from a competing one- and two bond coupling mechanism: J (Si,H) = 1 J (Si,H) + 2 J (Si,M,H) .…”