Synthesis and Characterization of Ether Adducts of Thorium Tetrahydroborate Th(BH4)4 and Chemical Vapor Deposition of Thorium Boride Thin Films.

Treating ThCl4 with LiBH4 in various ethereal solvents affords the adducts Th(BH4)4(Et2O)2, Th(BH4)4(thf)2, and Th(BH4)4(dme) (thf = tetrahydrofuran and dme = 1,2-dimethoxyethane). The structures of these three compounds have been established by single-crystal X-ray diffraction: if the tetrahydroborate groups are considered as occupying one coordination site, the Et2O and thf complexes adopt trans-octahedral coordination geometries, whereas the dme complex exhibits a cis-octahedral structure. All four BH4- ligands in each compound are tridentate, rendering each thorium center 14-coordinate. The Th···B distances range from 2.64 to 2.67 Å, and the Th-O bond lengths are 2.47-2.52 Å. We propose that crystals of Th(BH4)4(thf)2 are isomorphous with those of U(BH4)4(thf)2, but owing to pseudosymmetry the latter was reported in a unit cell that was too small by a factor of 2. IR spectra and 1H and 11B NMR data are reported as well. All three adducts are volatile, subliming readily at 60 °C and 10-4 Torr, making them potentially useful as precursors for the chemical vapor deposition (CVD) of thin films of thorium boride. Passage of Th(BH4)4(Et2O)2 over glass, Si(100), and aluminum substrates heated to 350 °C yields amorphous films of approximate stoichiometry ThB2; films deposited from Th(BH4)4(thf)2 have stoichiometries closer to ThB2.5 and contain some oxygen. Auger, XPS, XRD, and SEM studies of these films are reported.

Sodium Aminodiboranates Na(H3BNR2BH3): Structural and Spectroscopic Studies of Steric and Electronic Substituent Effects.

We describe the syntheses of a series of sodium aminodiboranate salts, Na(H3B-NR2-BH3), with different substituents on nitrogen, including sodium salts of the unsubstituted aminodiboranate, H3B-NH2-BH3-, and of the N-substituted anions H3B-NRR'-BH3-, where NRR' = NHMe, NHEt, NH(SiMe3), NEt2, N(i-Pr)2, N(SiMe3)2, NMe(i-Pr), NMe(t-Bu), NMe(SiMe3), and the pyrrolidide and piperidide derivatives NC4H8, NC5H10, and NC5H8-cis-2,6-Me2. The compounds have been characterized by 1H and 11B NMR spectroscopy and IR spectroscopy; crystallographic studies have been carried out for the unsolvated N,N-dimethylaminodiboranate salt Na(H3B-NMe2-BH3) and several sodium aminodiboranate salts in which the sodium ions are solvated with ethers (dioxane, diglyme, tetrahydrofuran, and 12-crown-4) or amines (N,N,N',N'-tetramethylethylenediamine). One of the structures contains a rare example of an ether ligand in which one oxygen atom bridges between two metal ions. General structural and spectroscopic trends as a function of the substituents on nitrogen are discussed.

X-ray Crystal Structure of Thorium Tetrahydroborate, Th(BH4)4, and Computational Studies of An(BH4)4 (An = Th, U).

The crystal structure of Th(BH4)4 is described. Two of the four BH4- ions are terminal and tridentate (κ3), whereas the other two bridge between neighboring ThIV centers in a κ2,κ2 (i.e., bis-bidentate) fashion. Thus, each thorium center is bound to six BH4- groups by 14 Th-H bonds. The six boron atoms describe a distorted octahedron in which the κ3-BH4- ions are mutually cis; the 14 ligating hydrogen atoms define a highly distorted bicapped hexagonal antiprism. The thorium centers are linked into a polymer consisting of interconnected helical chains wound about 4-fold screw axes. The structures of An(BH4)4 (An = Th, U) were also investigated by DFT. The geometries of [An(BH4)6]2-, [An3(BH4)16]4-, and [An5(BH4)26]6- fragments of the polymeric structures were optimized at the B3LYP and/or PBE levels. Most calculated geometries are 14-coordinate and agree with the experimental structures, but isolated [Th(BH4)6]2- units are predicted to feature 16-coordinate ThIV centers.

Synthesis and Characterization of Strontium N,N-Dimethylaminodiboranates as Possible Chemical Vapor Deposition Precursors.

The reaction of SrBr2 with 2 equiv of sodium N,N-dimethylaminodiboranate (DMADB; Na(H3BNMe2BH3)) in Et2O at 0 °C followed by crystallization and drying under vacuum gives the unsolvated strontium compound Sr(H3BNMe2BH3)2 (1). Before the vacuum-drying step, the colorless crystals obtained by crystallization consist of the diethyl ether adduct Sr(H3BNMe2BH3)2(Et2O)2 (2). If the reaction of SrBr2 with 2 equiv of Na(H3BNMe2BH3) is carried out in the more strongly coordinating solvent thf, the solvate Sr(H3BNMe2BH3)2(thf)3 (3) is obtained. Treating the thf adduct 3 with 1,2-dimethoxyethane (dme), bis(2-methoxyethyl) ether (diglyme), or N,N,N',N'-tetramethylethylenediamine (tmeda) in thf affords the new compounds Sr(H3BNMe2BH3)2(dme)2 (4), Sr(H3BNMe2BH3)2(diglyme) (5), and Sr(H3BNMe2BH3)2(tmeda) (6), respectively, in greater than 60% yields. Treatment of 3 with 2 equiv of the crown ether 12-crown-4 affords the charge-separated salt [Sr(H3BNMe2BH3)(12-crown-4)2][H3BNMe2BH3] (7). Crystal structures of all the Lewis base adducts are described. Compounds 2-6 all possess chelating κ2-BH3NMe2BH3-κ2 groups, in which two hydrogen atoms on each boron center are bound to strontium. Compound 6 is dinuclear because each metal atom is also coordinated to one hydrogen atom on a BH3NMe2BH3- ligand that chelates to the neighboring metal center. Compound 7 possesses an unusual κ1-BH3NMe2BH3- group owing to the near-complete encapsulation of the Sr atom by two 12-crown-4 molecules; the other BH3NMe2BH3- anion is a charge-separated counterion. When they are heated, the diglyme and tmeda compounds 5 and 6 melt without decomposition and can be sublimed readily under reduced pressure (1 Torr) at 120 °C. The diglyme and tmeda adducts are some of the most volatile strontium compounds known and are promising candidates as CVD precursors for the growth of strontium-containing thin films.

Anagostic interactions under pressure: attractive or repulsive?

Square-planar d(8)-ML4 complexes might display subtle but noticeable local Lewis acidic sites in axial direction in the valence shell of the metal atom. These sites of local charge depletion provide the electronic prerequisites to establish weakly attractive 3c-2e M⋅⋅⋅H-C agostic interactions, in contrast to earlier assumptions. Furthermore, we show that the use of the sign of the (1)H NMR shifts as major criterion to classify M⋅⋅⋅H-C interactions as attractive (agostic) or repulsive (anagostic) can be dubious. We therefore suggest a new characterization method to probe the response of these M⋅⋅⋅H-C interactions under pressure by combined high pressure IR and diffraction studies.

Synthesis and characterization of calcium N,N-dimethylaminodiboranates as possible chemical vapor deposition precursors.

The reaction of CaBr2 with 2 equiv of sodium N,N-dimethylaminodiboranate, Na(H3BNMe2BH3) in Et2O at 0 °C followed by crystallization and drying in vacuum yields the unsolvated calcium compound Ca(H3BNMe2BH3)2, 1. Before the vacuum drying step, the colorless crystals obtained by crystallization consist of the diethyl ether adduct Ca(H3BNMe2BH3)2(Et2O)2, 2. If the reaction of CaBr2 with 2 equiv of Na(H3BNMe2BH3) is carried out in the more strongly coordinating solvent tetrahydrofuran (thf), the solvate Ca(H3BNMe2BH3)2(thf)2, 3, is obtained. This compound does not desolvate as easily in vacuum as the diethyl ether compound 2. Treating the thf adduct 3 with 1,2-dimethoxyethane (dme), bis(2-methoxyethyl) ether (diglyme), or N,N,N',N'-tetramethylethylenediamine (tmeda) in thf affords the new compounds Ca(H3BNMe2BH3)2(dme), 4, Ca(H3BNMe2BH3)2(diglyme), 5, and Ca(H3BNMe2BH3)2(tmeda), 6, respectively, in greater than 60% yields. Treatment of 3 with 2 equiv of the crown ether 12-crown-4 in thf affords the charge-separated salt [Ca(12-crown-4)2][H3BNMe2BH3]2, 7. Crystal structures of all the Lewis base adducts are described. Compounds 2-6 all possess chelating κ(2)-BH3NMe2BH3-κ(2) groups, in which two hydrogen atoms on each boron center are bound to calcium. Compound 7 is the only ionic compound in the series; the Ca atom is completely encapsulated by two 12-crown-4 rings, and the anions are charge-separated counterions within the unit cell. When heated, the dme, diglyme, and tmeda compounds 4, 5, and 6 melt without decomposition, and can be sublimed readily under reduced pressure (1 Torr) at 90 °C (4) and 120 °C (5, 6). The dme adduct is one of the most volatile calcium compounds known, and is a promising CVD precursor for the growth of calcium-containing thin films.

Synthesis and single crystal structure of sodium octahydrotriborate, NaB3H8.

This paper describes a modified synthesis of NaB3H8 by the reduction of BH3·THF with sodium dispersed on silica gel. Single crystals obtained from CH2Cl2 show conclusively that the space group is Pmn21, in contrast to the Pmmn space group previously deduced from powder diffraction data.

Development of Resistance to Type II JAK2 Inhibitors in MPN Depends on AXL Kinase and Is Targetable.

PURPOSE: Myeloproliferative neoplasms (MPN) dysregulate JAK2 signaling. Because clinical JAK2 inhibitors have limited disease-modifying effects, type II JAK2 inhibitors such as CHZ868 stabilizing inactive JAK2 and reducing MPN clones, gain interest. We studied whether MPN cells escape from type ll inhibition. EXPERIMENTAL DESIGN: MPN cells were continuously exposed to CHZ868. We used phosphoproteomic analyses and ATAC/RNA sequencing to characterize acquired resistance to type II JAK2 inhibition, and targeted candidate mediators in MPN cells and mice. RESULTS: MPN cells showed increased IC50 and reduced apoptosis upon CHZ868 reflecting acquired resistance to JAK2 inhibition. Among >2,500 differential phospho-sites, MAPK pathway activation was most prominent, while JAK2-STAT3/5 remained suppressed. Altered histone occupancy promoting AP-1/GATA binding motif exposure associated with upregulated AXL kinase and enriched RAS target gene profiles. AXL knockdown resensitized MPN cells and combined JAK2/AXL inhibition using bemcentinib or gilteritinib reduced IC50 to levels of sensitive cells. While resistant cells induced tumor growth in NOD/SCID gamma mice despite JAK2 inhibition, JAK2/AXL inhibition largely prevented tumor progression. Because inhibitors of MAPK pathway kinases such as MEK are clinically used in other malignancies, we evaluated JAK2/MAPK inhibition with trametinib to interfere with AXL/MAPK-induced resistance. Tumor growth was halted similarly to JAK2/AXL inhibition and in a systemic cell line-derived mouse model, marrow infiltration was decreased supporting dependency on AXL/MAPK. CONCLUSIONS: We report on a novel mechanism of AXL/MAPK-driven escape from type II JAK2 inhibition, which is targetable at different nodes. This highlights AXL as mediator of acquired resistance warranting inhibition to enhance sustainability of JAK2 inhibition in MPN.