Facile Synthesis of Organolanthanide Hydrides with Metallic Potassium: Crystal Structures and Reactivity

Synthesis and Crystallographic Characterization of a Reduced Bimetallic Yttrium ansa-Metallocene Hydride Complex, [K(crypt)][(μ-CpAn)Y(μ-H)]2 (CpAn = Me2Si[C5H3(SiMe3)-3]2), with a 3.4 Å Yttrium-Yttrium Distance

The reduction of a bimetallic yttrium ansa-metallocene hydride was examined to explore the possible formation of Y-Y bonds with 4d¹ Y(II) ions. The precursor [Cp^AnY(μ-H)(THF)]₂ (Cp^An = Me₂Si[C₅H₃(SiMe₃)-3]₂) was synthesized by hydrogenolysis of the allyl complex Cp^AnY(η³-C₃H₅)(THF), which was prepared from (C₃H₅)MgCl and [Cp^AnY(μ-Cl)]₂. Treatment of [Cp^AnY(μ-H)(THF)]₂ with excess KC₈ in the presence of one equivalent of 2.2.2-cryptand (crypt) generates an intensely colored red-brown product crystallographically identified as [K(crypt)][(μ-Cp^An)Y(μ-H)]₂. The two rings of each Cp^An ligand in the reduced anion [(μ-Cp^An)Y(μ-H)]₂^1- are attached to two yttrium centers in a "flyover" configuration. The 3.3992(6) and 3.4022(7) Å Y···Y distances between the equivalent metal centers within two crystallographically independent complexes are the shortest Y···Y distances observed to date. Ultraviolet-visible (UV-visible)/near infrared (IR) and electron paramagnetic resonance (EPR) spectroscopy support the presence of Y(II), and theoretical analysis describes the singly occupied molecular orbital (SOMO) as an Y-Y bonding orbital composed of metal 4d orbitals mixed with metallocene ligand orbitals. A dysprosium analogue, [K(18-crown-6)(THF)₂][(μ-Cp^An)Dy(μ-H)]₂, was also synthesized, crystallographically characterized, and studied by variable temperature magnetic susceptibility. The magnetic data are best modeled with the presence of one 4f⁹ Dy(III) center and one 4f⁹(5d_z²)¹ Dy(II) center with no coupling between them. CASSCF calculations are consistent with magnetic measurements supporting the absence of coupling between the Dy centers.

E-H Bond Activation and Insertion Processes in the Reactions of the Unsaturated Hydride [W2Cp2(μ-H)(μ-PPh2)(NO)2]

The reactions of the title complex (1) with different p-block element (E) molecules was examined. Compound 1 reacted with BH₃·THF at room temperature to give the trihydride [W₂Cp₂(μ-H)H₂(μ-PPh₂)(NO)₂], which formally results from hydrogenation of 1, a reaction that actually does not take place when neat dihydrogen is used. Clean E-H bond oxidative addition, however, took place when 1 was reacted with HSnPh₃, to give the related dihydride stannyl derivative [W₂Cp₂(μ-H)H(μ-PPh₂)(NO)₂(SnPh₃)]. In contrast, the reaction of 1 with HSPh involved H₂ elimination to give the thiolate-bridged complex [W₂Cp₂(μ-SPh)(μ-PPh₂)(NO)₂], while that with (p-tol)C(O)H resulted in insertion of the aldehyde to yield the related alkoxide complex [W₂Cp₂{μ-OCH₂(p-tol)}(μ-PPh₂)(NO)₂]. Insertion also prevailed in the reactions of 1 with CN^tBu, which, however, involved the competitive formation of new C-H or N-H bonds, to give a mixture of formimidoyl and aminocarbyne derivatives, [W₂Cp₂(μ-κ¹:η²-HCN^tBu)(μ-PPh₂)(NO)₂] (W-W = 3.0177(2) Å) and [W₂Cp₂{μ-C(NH^tBu)}(μ-PPh₂)(NO)₂] (W-W = 2.9010(4) Å), respectively, even though the latter was thermodynamically preferred, according to density functional theory calculations. The former represents the first structurally characterized complex displaying a formimidoyl or iminoacyl ligand in the alkenyl-like μ-κ¹:η² coordination mode. The reaction of 1 with diazomethane proceeded with N₂ elimination and C-H coupling to yield the agostic methyl-bridged complex [W₂Cp₂(μ-κ¹:η²-CH₃)(μ-PPh₂)(NO)₂] (calculated W-W = 2.923 Å), whereas the reaction with N₂CH(SiMe₃) proceeded with insertion of the diazoalkane to give the corresponding hydrazonide complex [W₂Cp₂{μ-NH(NCHSiMe₃)}(μ-PPh₂)(NO)₂] (W-W = 2.8608(4) Å). The latter was converted under alkaline conditions to the methyldiazenide derivative [W₂Cp₂{μ-N(NMe)}(μ-PPh₂)(NO)₂] (W-W = 2.8730(2) Å), in a process involving hydrolysis of the C-Si bond coupled with a 1,3-H shift from N to C.

Rare-earth metal hydrides supported by silicon-bridged boratabenzene fluorenyl ligands: synthesis, structure and reactivity

The first boratabenzene derivatives of rare-earth metal hydrides were synthesized, and their reactivity was studied.

Carbon-nitrogen bond construction and carbon-oxygen double bond cleavage on a molecular titanium oxonitride: a combined experimental and computational study

New carbon-nitrogen bonds were formed on addition of isocyanide and ketone reagents to the oxonitride species [{Ti(η(5)-C5Me5)(μ-O)}3(μ3-N)] (1). Reaction of 1 with XylNC (Xyl = 2,6-Me2C6H3) in a 1:3 molar ratio at room temperature leads to compound [{Ti(η(5)-C5Me5)(μ-O)}3(μ-XylNCCNXyl)(NCNXyl)] (2), after the addition of the nitrido group to one coordinated isocyanide and the carbon-carbon coupling of the other two isocyanide molecules have taken place. Thermolysis of 2 gives [{Ti(η(5)-C5Me5)(μ-O)}3(XylNCNXyl)(CN)] (3) where the heterocumulene [XylNCCNXyl] moiety and the carbodiimido [NCNXyl] fragment in 2 have undergone net transformations. Similarly, tert-butyl isocyanide (tBuNC) reacts with the starting material 1 under mild conditions to give the paramagnetic derivative [{Ti3(η(5)-C5Me5)3(μ-O)3(NCNtBu)}2(μ-CN)2] (4). However, compound 1 provides the oxo ketimide derivatives [{Ti3(η(5)-C5Me5)3(μ-O)4}(NCRPh)] [R = Ph (5), p-Me(C6H4) (6), o-Me(C6H4) (7)] upon reaction with benzophenone, p-methylbenzophenone, and o-methylbenzophenone, respectively. In these reactions, the carbon-oxygen double bond is completely ruptured, leading to the formation of a carbon-nitrogen and two metal-oxygen bonds. The molecular structures of complexes 2-4, 6, and 7 were determined by single-crystal X-ray diffraction analyses. Density functional theory calculations were performed on the incorporation of isocyanides and ketones to the model complex [{Ti(η(5)-C5H5)(μ-O)}3(μ3-N)] (1H). The mechanism involves the coordination of the substrates to one of the titanium metal centers, followed by an isomerization to place those substrates cis with respect to the apical nitrogen of 1H, where carbon-nitrogen bond formation occurs with a low-energy barrier. In the case of aryl isocyanides, the resulting complex incorporates additional isocyanide molecules leading to a carbon-carbon coupling. With ketones, the high oxophilicity of titanium promotes the unusual total cleavage of the carbon-oxygen double bond.

Metallacyclic yttrium alkyl and hydrido complexes: synthesis, structures and catalytic activity in intermolecular olefin hydrophosphination and hydroamination

Metallacyclic neutral and ionic yttrium alkyl complexes coordinated by a dianionic ene-diamido ligand ([2,6-iPr2C6H3NC(Me)=C(Me)NC6H3iPr2-2,6] = L(1)) [L(1)]Y(CH2SiMe3)(THF)2 (2), {[L(1)]Y(CH2SiMe3)2}(-){Li(THF)4}(+) (3), [L(1)]Y(OEt2)(μ-Me)2Li(TMEDA) (4) were synthesized using a salt-metathesis approach starting from the related chloro complex [L(1)]Y(THF)2(μ-Cl)2Li(THF)2 (1) in 70, 85 and 72% yields respectively. The reactions of 2 with H2 or PhSiH3 afford the dimeric hydride {[L(1)]Y(THF)(μ-H)}2(μ-THF) (5) containing two μ-bridging hydrido and one μ-bridging THF ligands (91 and 85% yields). The X-ray studies of complexes 2, 3 and 5 revealed η(2)-coordination of the C=C fragment of an ene-diamido ligand to a Y cation. DFT calculations were carried out to give an insight into the metal-ligand bonding and especially the interaction between the metal and the ene-diamido ligand. The observed bonding of the ene-diamido fragment is found to reflect the acidity of the metal center in the complex that is partially overcome by a better donation from the double bond (better overlap with an empty d orbital at the yttrium center). The treatment of complex 4 with DME resulted in the C-O bond cleavage of DME and afforded a three nuclear methoxide oxide complex [{[L(1)]Y}3(μ(2)-OMe)3(μ(3)-O)](2-)[Li(DME)3](+)2 (6). Complexes 2, 3, 5 and 7 proved to be efficient precatalysts for the intermolecular hydrophosphination of styrene, 4-vinylpyridine, and 1-nonene with PhPH2 and Ph2PH as well as hydroamination of styrene and pyrrolidine.