John D. Carpenter

Matrix isolation study of the mechanism of the reaction of diborane with ammonia : pyrolysis of the H3B.NH3 adduct

Abstract Gas-phase pyrolysis of the H3B·NH3 adduct followed by trapping of the reaction product(s) in an argon matrix at 14 K was conducted to provide support for an earlier proposed mechanism for the reaction of B2H6 with NH3. As the pyrolysis temperature increased from 65 to 300°C, a decrease in yield of adduct was noted, along with a concomitant growth in H2BNH2. The results obtained here support a mechanism for the reaction of B2H6 with NH3 in which the 1:1 adduct H3B·NH3 is formed in an initial slow step, and is followed by rapid elimination of H2 to form H2BNH2.

Matrix isolation investigation of the reaction of B2H6 with carbon–carbon multiple bonds

B2H6 was copyrolyzed at 335°C in separate experiments with C2H2 and C2H4 in a flow reactor followed by trapping into an argon matrix at 14 K. Small but distinct and reproducible yields of C2H4 and C2H6, respectively, were observed in these experiments indicating that some hydrogenation is occurring, while no evidence for alkylboranes was obtained. Extensive experiments with C2D2 and C2D4 yielded B2H5D, C2HD and several additional species indicative of extensive hydrogen isotope exchange. Possible reaction mechanisms are discussed.

The search for H2BOH: a matrix isolation study

Abstract Merged jet copyrolysis of samples of Ar/B 2 H 6 with either Ar/H 2 O or Ar/O 2 followed by trapping into an argon matrix has led to the formation and isolation of the known species boroxin, H 3 B 3 O 3 . These results differ from the gas phase microwave study of this system, where H 2 BOH was identified and characterized. Local density functional calculations of the vibrational spectrum of this compound were carried out to aid in the search for absorption of H 2 BOH, and are reported. The difference between the microwave study and the present study persisted despite very similar reaction conditions. Possible origins of this discrepancy are discussed.

The search for phosphinoboranes: a matrix isolation study

Abstract Merged jet copyrolysis reactions of diborane, B2H6, with PH3, (CH3) 3P and PF3 were attempted, followed by trapping into argon matrices. Contrary to previous studies of the reactions of B2H6 with nitrogen, oxygen and sulfur bases, only the H3B · P (CH3)3 adduct was observed, with no further elimination products. The lack of observation of the H3B · PH3 and H3B ·PF3 adducts under these conditions indicates that the equilibrium constant for adduct formation is very small at room temperature. The absence of H2 or HF elimination products (e.g. H2BPH2) provides indirect support for the previously proposed reaction mechanism involving initial adduct formation.