Reactivity differences between molecular and surface silanols in the preparation of homogeneous and heterogeneous olefin metathesis catalysts

The reaction of Mo(N)(CH₂tBu)₃ (1) and SiO_2-(700) generates (SiO)Mo(NH)(CHtBu)(CH₂tBu) (2) when performed in C₆H₆ (material [1/SiO_2-(700)]_C6H6). The grafting occurs presumably by protonation of the nitrido ligand to form an intermediate (SiO)Mo(NH)(CH₂tBu)₃ (3), a pentacoordinated complex, which decomposes into 2 and 2,2-dimethylpropane. While [1/SiO_2-(700)]_C6H6 is highly active in olefin metathesis, [1/SiO_2-(700)]_CH2Cl2 and [1/SiO_2-(700)]_THF are poorly active or inactive catalysts respectively. In contrast, when Mo(N)(CH₂tBu)₃ reacts with a molecular silanol derivative, a soluble model of the surface of SiO_2-(700), it yields a very stable complex, (c-C₅H₉)₇Si₇O₁₂SiO-Mo(NH)(CH₂tBu)₃ (3m), which does not spontaneously generate 2,2-dimethylpropane and an alkylidene complex in contrast to the surface complex. Moreover, 3m does not catalyse olefin metathesis at room temperature as it does not already contain the initiating carbene ligand, and it is necessary to heat up the reaction mixture to 110 °C to obtain low catalytic activity. Nevertheless, the complex 3m generates well-defined metallocarbenes when heated in the presence of PMe₃: (c-C₅H₉)₇Si₇O₁₂SiO-Mo(N)(CHtBu)(P(CH₃)₃)₂ (4m) as a 10:1 mixture of its syn and anti rotamers with the loss of 2 equiv. of 2,2-dimethylpropane.     

Generation and Reactivity of a One-Electron-Oxidized Manganese(V) Imido Complex with a Tetraamido Macrocyclic Ligand

The synthesis and X-ray structure of a new manganese(V) mesitylimido complex with a tetraamido macrocyclic ligand (TAML), [Mn^V(TAML)(N-Mes)]⁻ ( 1 ), are reported. Compound 1 is oxidized by [(p-BrC₆H₄)₃N ]^+.[SbCl₆]⁻ and the resulting Mn^VI species readily undergoes H-atom transfer and nitrene transfer reactions.     

Anilate Tethered Neutral Tetrahedral Pd(II) Cages Exhibiting Selective Encapsulation of Xylenes and Mesitylene

The design of porous materials for the recognition of multiple hydrocarbons is highly desirable for the energy-efficient separation and recognition of chemical feedstock. Herein, three new iso-structural porous discrete metal–organic cages of formula {[Pd₃(NiPr)₃PO]₄(R-AN)₆} (R-AN=anilate linkers) for the selective recognition of substituted aromatic hydrocarbons are reported. The tetrahedral cages 1 , 2 , and 3 containing anilate, chloranilate, and bromanilate linkers exhibited selective encapsulation of mesitylene, o-xylene, and p-xylene, respectively, over other analogous aromatic hydrocarbons. These selective encapsulations were driven by the variations in the portal diameters present at each of these cages and their interactions with the hydrocarbon guests. These observations are supported by mass spectrometry, NMR studies, and theoretical binding-energy calculations.     

Molybdenum(VI) Bis(imido) Complexes: From Frustrated Lewis Pairs to Weakly Coordinating Cations

Molybdenum(VI) bis(imido) complexes [Mo(NtBu)₂(L^R)₂] (R=H 1 a ; R=CF₃ 1 b ) combined with B(C₆F₅)₃ ( 1 a /B(C₆F₅)₃, 1 b /B(C₆F₅)₃) exhibit a frustrated Lewis pair (FLP) character that can heterolytically split H−H, Si−H and O−H bonds. Cleavage of H₂ and Et₃SiH affords ion pairs [Mo(NtBu)(NHtBu)(L^R)₂][HB(C₆F₅)₃] (R=H 2 a ; R=CF₃ 2 b ) composed of a Mo(VI) amido imido cation and a hydridoborate anion, while reaction with H₂O leads to [Mo(NtBu)(NHtBu)(L^R)₂][(HO)B(C₆F₅)₃] (R=H 3 a ; R=CF₃ 3 b ). Ion pairs 2 a and 2 b are catalysts for the hydrosilylation of aldehydes with triethylsilane, with 2 b being more active than 2 a . Mechanistic elucidation revealed insertion of the aldehyde into the B−H bond of [HB(C₆F₅)₃]⁻. We were able to isolate and fully characterize, including by single-crystal X-ray diffraction analysis, the inserted products Mo(NtBu)(NHtBu)(L^R)₂][{PhCH₂O}B(C₆F₅)₃] (R=H 4 a ; R=CF₃ 4 b ). Catalysis occurs at [HB(C₆F₅)₃]⁻ while [Mo(NtBu)(NHtBu)(L^R)₂]⁺ (R=H or CF₃) act as the cationic counterions. However, the striking difference in reactivity gives ample evidence that molybdenum cations behave as weakly coordinating cations (WCC).     

Synthesis and Crystal Structure of N-Phenylbis（ferrocenecarboxyl）imide

The ferrocenyl compound,N-phenylbis(ferrocenecarboxyl)imide (C28H23NO2Fe2,Mr=517.17),was synthesized and structurally characterized by means of X-ray single-crystal dif-fraction. It crystallizes in monoclinic,space group C2/c with a=21.374(14),b=10.430(7),c= 10.741(7) ,β=114.184(8)°,V=2184(2) 3,Z=4,Dc=1.573 g/cm3,F(000)=1064,μ(MoKα)= 1.355 mm–1,T=291(2) K,the final R=0.0548 and wR=0.1437 for 1524 observed reflections with I > 2σ(I). In this compound,the nitrogen atom links two ferrocenyl groups and one phenyl group forming a novel imido derivative.     

叔丁基亚胺四氯合钽(V)阴离子配合物[IPrH]+[tBuN=TaCl4(py)]-的合成与表征

[^tBuN=TaCl₃(py)₂]和氮杂环卡宾(IPr =1,3-bis(2,6-diisoproylphenyl)imidazol-2-ylidene)的反应得到预料之外的叔丁基亚胺四氯合钽(V)离子配合物[IPrH]⁺[^tBuN=TaCl₄(py)]- (1)。利用核磁共振波谱,红外吸收光谱,荧光光谱,元素分析和X-Ray单晶衍射对配合物1的结构进行了表征。X-射线单晶衍射分析表明,Ta(V)中心与4四个氯和2个分别来自亚胺和吡啶配体的氮原子以八面体构型配位。     

Synthesis, X-ray studies, spectroscopic characterization and DFT calculations of p-tolylimido rhenium(V) complexes bearing an imidazole-based ligand

Novel p-tolylimido rhenium(V) complexes [Re(p-NC₆H₄CH₃)X₂(hpb)(PPh₃)] and [Re(p-NC₆H₄CH₃)(hpb)₂(PPh₃)]X (X = Cl, Br) have been obtained in the reactions of [Re(p-NC₆H₄CH₃)X₃(PPh₃)₂] with 2-(2-hydroxyphenyl)-1H-benzimidazole (Hhpb). The compounds were identified by elemental analysis IR, UV-Vis spectroscopy and X-ray crystallography. The electronic structures of the complex [Re(p-NC₆H₄CH₃)Cl₂(hpb)(PPh₃)] and the cation [Re(p-NC₆H₄CH₃)(hpb)₂(PPh₃)]⁺ have been calculated with the density functional theory (DFT) method. Additional information about binding in the [Re(p-NC₆H₄CH₃)Cl₂(hpb)(PPh₃)] and [Re(p-NC₆H₄CH₃)(hpb)₂(PPh₃)]⁺ has been obtained by NBO analysis. The electronic spectra of [Re(p-NC₆H₄CH₃)Cl₂(hpb)(PPh₃)] and [Re(p-NC₆H₄CH₃)(hpb)₂(PPh₃)]Cl were investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.