Tris hydroborate

A convenient route to three-carbon carboranes is the hydroboration of an alkyne with a preformed dicarbaborane. For example, reaction of ethyne (or propyne) with arachno-4,5-C2B7Hi3 (70) in hexane at 120°C gives a mixture of tri- and tetra-carbaboranes, e.g. (71), (72), (73), (74) in modest yield. Access to other... 

The required working time is 3 to 4 hours. All equipment is thoroughly dried prior to use and is flushed with an inert gas (argon or nitrogen). Commercial sodium hydroborate is used without purification. The dimethyl ether of diethylene glycol (diglyme) is refluxed over calcium hydride for 8 hours and subsequently distilled over lithium tetrahydroaluminate (lithium aluminum hydride). Commercial tri-n-butylamine is refluxed with acetic anhydride and distilled at atmospheric pressure. 

One example was reported by Tolman and coworkers (78) who found that the copper(I) complex C Tp112 (TpR2=tris(3-(R2)-5-methylpyrazol-l-yl)hydroborate) promotes NO disproportionation via a weakly bound CuITpR2(NO) intermediate (formally a MNO 11 species). The products are N20 and a copper(II) nitrito complex (Eq. (36)). The rate law established the reaction to be first-order in copper complex concentration and second-order in [NO], and this was interpreted in terms of establishment of a pre-equilibrium between NO and the Cu(I) precursor and the Cux(NO) adduct, followed by rate-limiting electrophilic attack of a second NO molecule (mechanism B of Scheme 5) (78b). 

A series of polyether macrocycles [59]—[66] (Fig. 33) that contain a coordinated reducible, redox-active 16-electron molybdenum nitrosyl (Mo(NO)(3+ group have been prepared (Al-Obaidi et al, 1986 Beer et al., 1987). Compounds [59]—[63] were synthesized from the reactions between [Mo(NO)LX2] (L = tris(3,5-dimethylpyrazolyl)hydroborate X = Cl or I ) and the appropriate amine substituted benzo-crown ether. Compounds... 

Various tris(pyrazolyl)borato aUsyhnagnesium derivatives have been prepared and were structurally characterized in the solid state. X-ray crystal-structure determinations of methyhnagnesium tris(3-tcrt-butylpyrazolyl)hydroborate (227) isopropyhnagnesium... 

The X-ray crystal-structure determination of ethylmagnesium tris(3-phenylpyrazolyl) hydroborate (232) (Figure 94) shows that the magnesium atom is penta-coordinate as the result of one a-bonded ethyl group, three magnesium-nitrogen bonds with the tris(3-phenylpyrazolyl)hydroborate moiety and one additional, coordinating THF molecule. 

Aldehydes are prepared by the hydroboration-oxidation of alkynes (see Section 5.3.1) or selective oxidation of primary alcohols (see Section 5.7.9), and partial reduction of acid chlorides (see Section 5.7.21) and esters (see Section 5.7.22) or nitriles (see Section 5.7.23) with lithium tri-terr-butox-yaluminium hydride [LiAlH(0- Bu)3] and diisobutylaluminium hydride (DIBAH), respectively. 

The bis(mercaptoimidazolyl)(pyrazolyl)hydroborato unit present in 193 (Figure 93) coordinates via both sulfur atoms [Zn—S 2.404(1) and 2.410(1) A] of the two mercap-toimidazolyl moieties and the nitrogen atom [Zn—N 2.043(4) A] of the pyrazolyl group to zinc. Because this ligand system is more flexible than the tris(pyrazolyl)hydroborate, the bond angles around zinc are closer to the tetrahedral value than in 190. 

Armaroli, N. Balzani, V. Barigelletti, F. Ward, M. D. McCleverty, J. A. Luminescence properties of Eu3 +, Tb3+ and Gd3+ complexes of the hexadentate N-podand tris-[3-(2-pyridyl)pyrazol-lyl]hydroborate. Chem. Phys. Lett. 1997, 276, 435-440. 

The aminoboranes do not form stable complexes with neutral Lewis bases (see Section 24.2.2), but the amidotrihydroborates, M[BH3NR2], are relatively stable. Monophosphidobor-ates are also known but, apparently, hydroborates with more NR2 or PR2 groups are not stable. However, di- and tri-amidoborates derived from amines containing spz N (i.e. pyrrole, pyrazole, indole, indazole) are well known. 

Hydroboration of a variety of alkenes and terminal alkynes with catecholborane in the fluorous solvent perfluoromethylcyclohexane was performed using fluorous analogs of the Wilkinson catalyst.135 136 Recycling of a rhodium-based alkene hydrosilylation catalyst was also successful.137 Activated aromatics and naphthalene showed satisfactory reactivity in Friedel-Crafts acylation with acid anhydrides in the presence of Yb tris(perfluoroalkanesulfonyl)methide catalysts.138... 

The hydroboration of an olefin involves a cis addition of a boron-hydrogen bond to an alkene linkage, and for unsymmetric olefins occurs in a counter-Markownikoff fashion. 1-Alkenes and simple 1,2-disubstituted olefins undergo rapid conversion to the corresponding trialkylborane, whereas addition of diborane to tri- and tetrasubstituted olefins may be conveniently terminated at the respective di- and monoalkylborane stage. 1-Alkenes yield trialkylboranes in which there is a preponderant (approximately 94%) addition of the boron atom to the terminal carbon.2,3... 

We were able to direct the rearrangement 23—24 so that no disproportion into 9. and 30. occurred (13). The adducts 24 are stable and can now be used for hydroboration reactions whereby a suitable method for the elimination of triphenylphosphane from complex 24 must be used. This can be achieved with benzyl-iodide jjj. On a cIcTi-tion of the iodo compound 25 and an olefin 2 to a solution of 2 in tetrahydrofuran, the benzyl-triphenylphosphonium iodide precipitates and the free R-BH2 adds to the olefin 2 forming the tri-... 

Recently several new active site model compounds have been prepared (Carrier et al., 1991) using sterically hindered tris(pyrazoyI)hydroborate (L) and tris(thioethyl)amine (L2) as ligands. The copper nitrite complex LCu11 (N02) models the enzyme substrate complex and X-ray studies confirm that the complex is tetrahedral. A mononuclear copper—nitrosyl complex similar to postulated NO adducts of copper proteins has also been prepared from LCu1 (MeCN) and NO, which has been tentatively identified as a Cu11 -NO species on the basis of IR (v NO 1711 cm 1) and ESR evidence. 

The first isolated and characterised species that could be envisioned as intermediates in the initiation step for the coordination polymerisation of epoxides when using metal carboxylate catalysts were complexes formed between cadmium carboxylates, solubilised in organic solvents by the tris-3-phenylpyrazole hydroborate ligand, and epoxides such as propylene oxide and cyclohexene oxide [68]. Other epoxide complexes with various metal derivatives have also been reported in the literature [69-72],... 

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