Cyclometalated N-Heterocyclic Carbene Complexes of Ruthenium for Access to Electron-Rich Silylene Complexes That Bind the Lewis Acids CuOTf and AgOTf

Abstract

The synthesis of the cyclometalated complexes Cp*Ru(IXy-H) (2) [IXy = 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene; IXy-H = 1-(2-CH2C6H3-6-methyl)-3-(2,6-dimethylphenyl)imidazol-2-ylidene-1-yl (the deprotonated form of IXy); Cp* = η(5)-C5Me5] and Cp*Ru(IXy-H)(N2) (3) was achieved by dehydrochlorination of Cp*Ru(IXy)Cl (1) with KCH2Ph. Complexes 2 and 3 activate primary silanes (RSiH3) to afford the silyl complexes Cp*(IXy-H)(H)RuSiH2R [R = p-Tol (4), Mes (5), Trip (6)]. Density functional theory studies indicated that these complexes are close in energy to the corresponding isomeric silylene species Cp*(IXy)(H)Ru═SiHR. Indeed, reactivity studies indicated that various reagents trap the silylene isomer of 6, Cp*(IXy)(H)Ru═SiHTrip (6a). Thus, benzaldehyde reacts with 6 to give the [2 + 2] cycloaddition product 7, while 4-bromoacetophenone reacts via C-H bond cleavage and formation of the enolate Cp*(IXy)(H)2RuSiH[OC(═CH2)C6H4Br]Trip (8). Addition of the O-H bond of 2,6-dimethylphenol across the Ru═Si bond of 6a gives Cp*(IXy)(H)2RuSiH(2,6-Me2C6H3O)Trip (9). Interestingly, CuOTf and AgOTf also react with 6 to provide unusual Lewis acid-stabilized silylene complexes in which MOTf bridges the Ru-Si bond. The AgOTf complex, which was crystallographically characterized, exhibits a structure similar to that of [Cp*((i)Pr3P)Ru(μ-H)2SiHMes](+), with a three-center, two-electron Ru-Ag-Si interaction. Natural bond orbital analysis of the MOTf complexes supported this type of bonding and characterized the donor interaction with Ag (or Cu) as involving a delocalized interaction with contributions from the carbene, silylene, and hydride ligands of Ru.

Reactivity of Ln(II) Complexes Supported by (C5H4Me)1– Ligands with THF and PhSiH3: Isolation of Ring-Opened, Bridging Alkoxyalkyl, Hydride, and Silyl Products

“…Although transition metal–SiH 2 Ph complexes are known, ,,,− there are no reports of rare-earth–SiH 2 Ph complexes in the literature to our knowledge. However, an alkaline earth metal–​SiH 2 Ph complex has been reported from the reaction of a tetraazacyclododecane Mg hydride complex with PhSiH 3 .…”

Expansion of the (BB)Ru metallacycle with coinage metal cations: formation of B–M–Ru–B (M = Cu, Ag, Au) dimetalacyclodiboryls

“…108 Interestingly, the Ag–Ru distance in the ruthenium silylene complex that binds Ag + across the ruthenium–silicon double bond is 2.681(1) Å. 19 The Ru1–B1 distance is typical at 2.143(3) Å while the Ru1···B2 distance is relatively short at 2.444(3) Å indicating significant interaction similarly to that in 2-Cu .…”

“…Notably, coordination of coinage metal cations to alkylidenes, silylenes, and borylenes/boryls has been reported. 16 , 19 , 20 , 118 Recently, coordination of Au + to a platinum–aryl bond has been disclosed. 119 The results reported herein also open questions whether resembling reactivity can be found in related classes of metal complexes.…”

“… 13 – 15 A distinct route to heterobimetallic complexes is also the coordination of an electrophilic metal moiety to metal alkylidene, alkylidyne, and silylene groups. 16 – 19 The isolobal analogy concept has been recently used to extend this reactivity pattern to metal borylene complexes, which have been found to coordinate electrophilic metal cations to manganese–boron double bonds. 20 …”

Half-Sandwich Silane σ-Complexes of Ruthenium Supported by NHC Carbene

“…Compound 8 was characterized by NMR spectroscopy and X-ray diffraction. Other related 16 e species, Cp′LRuCl (L = phosphine or carbene), are known from the literature. ,, Counteranion exchange between complex 7 and LiBAr F 4 (BAr F 4 = tetrakis­(pentafluorophenyl)­borate) in acetonitrile cleanly generates the related complex [Cp­(IPr)­Ru­(NCCH 3 ) 2 ]­[BAr F 4 ] ( 9 ), characterized by NMR and IR.…”