Showing papers on "Diborane published in 1969"

Molecular Energetics of Borane Carbonyl and the Symmetric Dissociation Energy of Diborane

Abstract: Large concentrations of borane, BH3, are produced upon the pyrolysis of borane carbonyl. Ionization efficiency measurements using a fast inlet mass‐spectrometric technique, have led to I(BH3) as well as A(B+), A(BH+), A(BH2+), and A(BH3+) from BH3CO. These numbers permit a complete development of the molecular energetics of BH3CO and a confirmation of the symmetric dissociation energy of diborane of 59 kcal/mole. Earlier equilibrium data on the BH3CO decomposition, combined with these electron‐impact data, also confirm D(BH3–BH3) = 59 kcal/mole. Earlier kinetic studies that suggest a very much lower dissociation energy are shown to be equivocal at best.

Stabilized tetrahydrofuran solutions of diborane

Abstract: SOLUTIONS OF DIBORANE IN TETRAHYDROFURAN CAN BE PREPARED WITHOUT HANDLING THE GAS BY TREATINGSUSPENSIONS OF SODIUM BOROHYDRIDE IN TETRAHYDROFURAN WITH BORON TRIFLUORIDE, FOLLOWED BY DECANTING, FILTERING, OR CENTRIFUGING ITATED SODIUM FLUOBORATE. SUCH SOLUTIONS ARE NORMALLY UNSTABLE AT ORDINARY TEMPERATURES, UNDERGOING REDUCTIVE CLEAVAGE OF THE SOLVENT. CONSEQUENTLY, THEY CANNOT BE STORED FOR ANY APPRECIABLE TIME OF SHIPPED ANY APPRECIABLE DISTANCE. HOWEVER, THESE SOLUTIONS ARE STABILIZED TOWARD SUCH REDUCTIVE CLEAVAGE BY BY UTILIZING IN THE SYNTHESIS A SLIGHT EXCESS OF SODIUM BOROHYDRIDE OR OTHER IONIC BOROHYDRIDES. THESE DICOVERIES NOW MAKE PRACTICAL THE MANUFACTURE, SHIPPING, STORING AND APLICATION OF SUCH SOLUTIONS OF DIBORANE IN TETRAHYDROFURAN, HIGHLY USEFUL FOR HYDROBORATIONS AND HYDROGENATIONS.

Selective Reduction of Peptide-ester Groups in Aqueous Solution

Abstract: For the selective reduction of carboxyl groups in peptides, diborane and sodium borohydride were examined Because of accompanying reductive side reaction, the reduction of carboxyl groups with diborane in tetrahydrofuran was unsatisfactory On the other hand, by the use of sodium borohydride in aqueous solution, certain model peptide esters were easily reduced to corresponding alcohols without any appreciable side reaction

Silicon–phosphorus hydrides. Part II. A comparative study by proton magnetic resonance spectroscopy of the isomers disilanyl- and disilyl-phosphine

Abstract: Complex triple mixed hydrides are formed when disilanyl- and disilyl-phosphine react with diborane. Their formation is confirmed by 1H n.m.r. spectroscopy and comparisons are drawn of features in the spectra before and after adduct formation. Specific deuteriation indicates hydrogen exchange between the SiH2 and BD3 sites in SiH3·SiH2·PH2,BD3. A new silicon phosphorus hydride, tris(disilanyl)phosphine is produced instead of disilanylphosphine–borane by a slight variation of conditions.

Nuclear‐Spin Entropy and Librational Degeneracy. Application to Ethane and Diborane

Abstract: A treatment of the problem of nuclear‐spin entropy in symmetrical molecules is given. Symmetries of the acceptable nuclear‐rotational states for molecules in the solid are calculated by applying the Pauli principle to the nuclear wavefunctions, and the numbers of such nuclear states are obtained from group theoretical considerations. Expressions for the nuclear‐rotational partition functions and low‐temperature entropies are given for rapid conversion of nuclear‐spin symmetry species as well as the more usual case of nonconversion. After applying the general theory to ethane and diborane, it is shown that the results obtained for the low‐temperature entropy depend sensitively upon the degeneracies and spacings of the librational states in the solid. When the symmetry of the potential field for librational motion in solid ethane and diborane is estimated from the known crystal structures, it is found that the librational degeneracies can exist which would give rise to sufficient randomness to cancel a calculated loss in nuclear entropy for the ethanes and to account for the experimental zero‐point entropy in diborane. The implications of this work concerning the nature of molecular motion in these and similar solids at low temperature are briefly discussed.

The electronic states of the diborane ion determined by photoelectron spectroscopy

Abstract: Five electronic states of the diborane ion are observed in the photoelectron spectrum of diborane using the 584 A He resonance line and a planar retarding-field, spectrometer.

Bonding in triphenylphosphine borane and related molecules

Abstract: The enthalpies of reaction of diborane and boron trifluoride with several tertiary alkyl and aryl phosphines in benzene solution have been measured by direct calorimetry Correlation of the results with the sums of the Taft polar substitution constants of the bases indicates that a special small stabilization factor operates in the triarylphosphine boranes, but is absent in the trialkyl analogues and in triphenylphosphine boron trifluoride The stabilization amounts to ∼38 ± 13 kcal mole–1 and may be attributed to enhanced back-π-bonding between the borane group and a vacant d-orbital on the phosphorus The fact that this enhanced stabilization does not occur in the triphenylphosphine-boron trifluoride adduct inducates that it is not due to conjugation of the aromatic π-electrons of the base with a suitable orbital on the phosphorus Our results also show that : (i) the donor-acceptor bonds in the trialkylphosphine borane adducts are significantly stronger than those in the triarylphosphine boranes; (ii) the donor-acceptor bonds in the phosphine-boron trifluoride adducts are much weaker (∼20 kcal mole–1) than those in the phosphine borane adducts

Rearrangement on borohydride reduction of a nitrophenoxy-ester

Abstract: Reduction of ethyl-2-methyl-2-(4-nitrophenoxy)-propionate (3a) with lithium borohydride in diglyme led to rearrangement to give the nitrophenoxy-alcohol (8); the unrearranged nitrophenoxy-alcohol (4) was produced by diborane reduction of the acid (3b).

Compounds obtained from the products of the hydroboration of isoprene and 1,5-hexadiene

Abstract: 1. By the hydroboration of isoprene with diborane a 24∶76 mixture of 1,1′-(1,2-dimethyltrimethylene)-bis[3-methylborolane] and 1,1′-(2-methyltetramethylene)bis[3-methylborolane] was obtained. 2. By the reaction of boron trichloride with the product of the hydroboration of isoprene 1-chloro-3-methylborolane was obtained. 3. The reaction of 1-chloro-3-methylborolane with boron trichloride leads to (2-methyltetramethylene)bis [dichtoroborane]. 4. The hydroboration of 1,5-hexadiene with diborane gave a mixture of isomeric 1,1′-(C6-alkylene)-bisborepanes. In reactions with boron trichloride this mixture, and also the crude product of the hydroboration of 1,5-hexadiene, is converted into a mixture of isomeric 1-chloroboracycloalkanes and (C6-alkyl-ene)-bis [dichloroboranes].