John V. Rund

Reactions of diborane with aromatic heterocycles—21 : Reactions with nitrogen-containing heterocycles related to pyridine

Abstract The reactions of solutions of B 2 H 6 in ethers with a variety of aromatic heterocycles containing one or more six-membered rings with only one nitrogen per ring have been examined. Quinoline and isoquinoline form monoborane adducts which hydroborate in the presence of an excess of B 2 H 6 . Protonolysis gives the 1,2,3,4-tetrahydro-compounds in both cases. N -Methylquinolinium and N -methylisoquinolinium iodides both hydroborate. Hydroboration and halogen loss occur with 2-, 3- or 4-haloquinolines (chlorine or bromine). Prior to hydroboration 8-hydroxyquinoline forms a borane adduct which rapidly eliminates one equivalent of hydrogen in a probable intramolecular ring closure. Sodium 8-hydroxyquinolinate combines with B 2 H 6 in an unsymmetrical cleavage reaction to form B 2 H 7 − or BH 4 − , and the same ring closed product formed by 8-hydroxyquinoline. Phenanthridine and N -methylphenanthridinium iodide both readily undergo hydroboration. The products formed by the latter with B 2 H 6 are 5-methyl-5,6-dihydrophenanthridine-borane and an iodoborane etherate. 1,8-Naphthyridine forms a transient borane complex which rapidly undergoes hydroboration; protonolysis gives 1,2,3,4-tetrahydro-l,8-naphthyridine. 2,2′-Bipyridyl undergoes a complex reaction with one equivalent of BH 3 giving a mixture of bpy·2BH 3 and hydroborated products, but 4,4′-bipyridyl does not appear to hydroborate. 1,10- and 1,7-Phenanthroline both hydroborate giving a mixture of reduced products on protonolysis. Pyridine-borane and 2-phenylpyridine-borane both decompose in refluxing diglyme, but protonolysis gives no reduced products in either case.

THE BEHAVIOR OF RIGID AND SEMI-RIGID BIDENTATE DONOR MOLECULES TOWARD SOME SIMPLE BORON ACCEPTORS

Abstract Synthesis of a series of complexes of the type LLBX2 + BX4 − where X = F− and CI− and LL = 1,10-phenanthroline, 2,2′-bipyridine and 1,8-bis(dimethylamino)naphthalene was achieved by the direct interaction of the ligand and BX3. No reaction was observed for X = CH3. The reactions provide a direct route for the preparation of tetra-coordinate boronium cations. The boron-11 nmr and infrared spectra of these complexes confirm the ionic nature of the compounds. 2,2′-Bipyridine functions as a chelating agent rather than as a bis-monodentate donor. 1,8-Bis(dimethylamino)naphthalene is found to be able to chelate cations much larger than protons. The steric implications of donor-acceptor interactions of boron with rigid and semi-rigid chelating donor molecules are discussed.

Reaction of chelating ligands with tetracarbonylnickel, nitrosyltricarbonylcobalt, and dinitrosyldicarbonyliron: a kinetics study

The kinetics of the interactions of several chelating ligands with Ni(C0)4, CONO(CO)~, and Fe(NO)2(C0)2 are examined. In all cases, two molecules of CO are evolved, being replaced by the ligand. Ni(C0)4 reacts with 1,lO-phenanthroline (phen), o-phenylenebis(dimethy1arsine) (DAS), cis- 1,2-bis(dimethyIarsino)ethylene (EDAS), and 1,2-bis(diphenyIarsino)ethane (diars) in two consecutive, first-order reactions. The first is a dissociation of CO to give the intermediate Ni(C0)3 which is rapidly attacked by one of the donor atoms of the chelate. The rate of this reaction is independent of the nature and concentration of the incoming ligand. The second reaction is first order but associatively activated and involves the displacement of a second CO ligand by the unattached donor atom of the chelating ligand. The rate of ring closure increases with the basicity of that atom, but steric influences may be important. For CONO(CO)~ and Fe(NO)2(C0)2, the ring closure reaction is not kinetically accessible, since the attachment of the first donor atom is rate determining. This reaction for CoNO(CO), exhibits mixed first- and second-order kinetics (rate = (R, + R2[AA])[CoNO(CO),]), the former resulting from the intervention of a solvent path to product. Fe(N0)2(C0)2 reacts with phen by a purely second-order associative path, but the arsines prove to give reactions poorly suited to kinetics analysis.

The effect of temperature on photoprocesses in acetone solutions of Cr(NH3)2(NCS)4

The photolysis yields and emission lifetimes for solutions of Cr(NH3)2(NCS)4− in fluid acetone have been recorded as a function of temperature in the fange −93 to 10 °C. The 2E levels are quenched by O2 and the relative contributions of the fast and slow photoreactions have been determined by comparing the photolysis yields in deaerated and O2 saturated solutions. The quantum yield of the prompt process is 0.02 and is temperature independent. The thermal enhancement of the slow photolysis correlates with depopulation of 2E and the results are consistent with back-intersystem crossing as the pathway for this process.

Excited state relaxation in Cr(CN)6−n(H2O)nn−3 complexes

The emission spectra and excited state decay rates have been recorded for Cr(CN)6−n(H2O)nn−3 (n = 0-6) complexes. Both the transition energy and relaxation rates increase with n but the large changes in transition energies are not sufficient to account for the failure of the displaced coordinate to explain the relaxation rate results.

Rigidochromism in metal-centered emission of Rh(III) complexes

Abstract A thermally induced redshift in a metal-centered 3 T 1 ⇒ 1 A 1 emission is due to population of the higher energy component of 3 T 1 , split by a low symmetry field. The population of this level is increased by solvent motion and the redshift then appears as rigidochromism.

1 H nuclear magnetic resonance study of 1,10-phenanthroline in aqueous acid. Isolation of bis(phenanthroline)–perchloric acid

The 1H n.m.r. spectrum of 1,10-phenanthroline in aqueous acid has been examined as a function of acid concentration. Changes in the spectrum are consistent with the existence of three forms of protonated phenanthroline. At the highest acid concentrations (12M-HCl), diprotonated phenathroline (phenH22+) is the dominant species. When the formal concentration of acid equals that of phenanthroline, phenanthrolinium ion (phenH+) is present and can be precipitated with perchlorate ion. Further reduction of acidity gives phen2H+, which has been isolated as a perchlorate salt.

OXIDATIVE ADDITION OF SOME HALOGENS, INTERHALOGENS AND PSEUDOHALOGENS TO [(n-C4H9)4N]2[Pt(CN)4]

Abstract The results of the treatment of [(n–C4H9)4N]2 [Pt(CN)4] with seventeen oxidizing agents, including halogens, inter halogens, and molecules such as N2O4, ICN, (SCN)2, S(CN)2 and C6 H5SCl, are reported. In cases where the reagents were not symmetrical molecules, two different ligands were added to platinum. The competition between parts of the oxidizing agent and other potential ligands in solution is also examined.

Who does what in freshman lab? A survey

During the Spring of 1986, the authors began an evaluation of the laboratory offered with the mainstream general chemistry lecture at the University of Arizona, and as a part of the evaluation undertook a survey to gather information about comparable courses at other institutions.

Reaction of diborane with benzoxazole and its sulphur and selenium analogues. A novel rearrangement to benzoxazaboroles, benzothiazaboroles, and benzoselenazaboroles

Reaction of B2H6 with the benzo-fused heteroaromatic compounds (1a–d) produces the boroles (2a–d)via a rearrangement in which BH3 adduct formation is the first step.