Miguel A. Muñoz-Hernández

Nature of Si–H Interactions in a Series of Ruthenium Silazane Complexes Using Multinuclear Solid-State NMR and Neutron Diffraction

Three new N-heterocyclic-silazane compounds, 1a-c, were prepared and employed as bidentate ligands to ruthenium, resulting in a series of [Ru(H){(κ-Si,N-(SiMe2-N-heterocycle)}3] complexes (3a-c) featuring the same RuSi3H motif. Detailed structural characterization of the RuSi3H complexes with X-ray diffraction, and in the case of triazabicyclo complex [Ru(H){κ-Si,N-(SiMe2)(C7H12N3)}3] (3a), neutron diffraction, enabled a reliable description of the molecular geometry. The hydride ligand of (3a) is located closer to two of the silicon atoms than it is to the third. Such a geometry differs from that of the previously reported complex [Ru(H){(κ-Si,N-(SiMe2)N(SiMe2H)(C5H4N)}3] (3d), also characterized by neutron diffraction, where the hydride was found to be equidistant from all three silicon atoms. A DFT study revealed that the symmetric and less regular isomers are essentially degenerate. Information on the dynamics and on the Ru···H···Si interactions was gained from multinuclear solid-state ((1)H wPMLG, (29)Si CP MAS, and 2D (1)H-(29)Si dipolar HETCOR experiments) and solution NMR studies. The corresponding intermediate complexes, [Ru{κ-Si,N-(SiMe2-N-heterocycle)}(η(4)-C8H12)(η(3)-C8H11)] (2a-c), involving a single silazane ligand were isolated and characterized by multinuclear NMR and X-ray diffraction. Protonation of the RuSi3H complexes was also studied. Reaction of 3a with NH4PF6 gave rise to [Ru(H)(η(2)-H -SiMe2)κ-N-(C7H12N3){κ-Si,N-(SiMe2)(C7H12N3)}2](+)[PF6](-)(4aPF6) which was isolated and characterized by NMR spectroscopy, X-ray crystallography, and DFT studies. The nature of the Si-H interactions in this silazane series was analyzed in detail.

Phosphinodi(benzylsilane) PhP{(o-C6H4CH2)SiMe2H}2: A Versatile “PSi2Hx” Pincer-Type Ligand at Ruthenium

The synthesis of the new phosphinodi(benzylsilane) compound PhP{(o-C6H4CH2)SiMe2H}2 (1) is achieved in a one-pot reaction from the corresponding phenylbis(o-tolylphosphine). Compound 1 acts as a pincer-type ligand capable of adopting different coordination modes at Ru through different extents of Si-H bond activation as demonstrated by a combination of X-ray diffraction analysis, density functional theory calculations, and multinuclear NMR spectroscopy. Reaction of 1 with RuH2(H2)2(PCy3)2 (2) yields quantitatively [RuH2{[η(2)-(HSiMe2)-CH2-o-C6H4]2PPh}(PCy3)] (3), a complex stabilized by two rare high order ε-agostic Si-H bonds and involved in terminal hydride/η(2)-Si-H exchange processes. A small free energy of reaction (ΔrG298 = +16.9 kJ mol(-1)) was computed for dihydrogen loss from 3 with concomitant formation of the 16-electron species [RuH{[η(2)-(HSiMe2)-CH2-o-C6H4]PPh[CH2-o-C6H4SiMe2]}(PCy3)] (4). Complex 4 features an unprecedented (29)Si NMR decoalescence process. The dehydrogenation process is fully reversible under standard conditions (1 bar, 298 K).

Oxidative insertion into the N–H bond of carbazole, indole and pyrrole with zerovalent metals

Abstract The reactions of carbazole (C12H8NH), indole (C8H6NH) and pyrrole (C4H4NH) with the zerovalent [Pt(PEt3)3], [Pd(PEt3)3] and [Ni(PEt3)3] gave oxidative insertion into the N–H bond, affording the corresponding hydrides of the type trans-[HM(LN)(PEt3)2], LN=de-protonated heterocyclic ligand; the isolated compounds for platinum were trans-[HPt(C8H6N)(PEt3)2] (1), trans-[HPt(C4H4N)(PEt3)2] (2), and for nickel trans-[HNi(C12H8N)(PEt3)2] (3), trans-[HNi(C8H6N)(PEt3)2] (4) and trans-[HNi(C4H4N)(PEt3)2] (5); on using palladium the corresponding hydrides were also detected in solution, however, after longer reaction time the double substituted compounds: trans-[Pd(C12H8N)2(PEt3)2] (6), trans-[Pd(C8H6N)2(PEt3)2] (7) and trans-[Pd(C4H4N)2(PEt3)2] (8) were obtained. A crystal structure is reported for 6.

Synthesis of (η6-arene)tricarbonylmetal and (σ-nitrogen)pentacarbonylmetal complexes of 1,2,3,4-tetrahydroquinoline and 1,2,3,4-tetrahydroisoquinoline with chromium, molybdenum and tungsten

Abstract Thermal reactions of [M(CO)6] with 1,2,3,4-tetrahydroquinoline (1) afford the corresponding (η6-arene)tricarbonylmetal complex (M=Cr, 3; M=Mo, 4; and M=W, 5). In contrast, thermolysis of the same hexacarbonyl complexes with 1,2,3,4-tetrahydroisoquinoline (2) affords the (σ-nitrogen)pentacarbonylmetal derivatives (M=Cr, 7; M=Mo, 8; and M=W, 9). For chromium the (η6-arene)tricarbonylmetal complex (6) was also isolated. X-ray crystal structures are reported for 3, 4, 7 and 9.

Regioselective Spirostan E-Ring Opening for the Synthesis of Dihydropyran Steroidal Frameworks

The regioselective opening of the ring E in spirostan sapogenins provides new dihydropyran derivatives. This novel side chain is obtained after a Lewis acid mediated acetolysis followed by an alkaline workup. The reaction mechanism is analyzed via density functional theory computations, and both experimental and computational data support the formation of an oxacarbenium intermediate. The behavior of the title skeletons under acidic conditions is also investigated.

CCDC 947557: Experimental Crystal Structure Determination

Related Article: Katharine A. Smart, Mary Grellier, Laure Vendier, Sax A. Mason, Silvia C. Capelli, Alberto Albinati, Virginia Montiel-Palma, Miguel A. Munoz-Hernandez, Sylviane Sabo-Etienne|2014|Inorg.Chem.|53|1156|doi:10.1021/ic4027199