Determination of the bonding preference of borane (BH3) toward aminoarsines by multinuclear nuclear magnetic resonance spectroscopy

Abstract

The reactions of BH,.thf (thf = tetrahydrofuran) with selected (dialkylamino)dimethylarsines, Me,AsNR, (R = Me, Et, Pr", or Prl) have been carried out as a function of temperature to determine the initial co-ordination site of boron and t o elucidate the nature of any As-N, As-B, and N-B bond dissociation/formation processes in solution. The reactions were monitored by rnultinuclear (IH, "B, and 13C) n.m.r. spectroscopy over a temperature range of -90 to 25 "C. With Me,AsNMe,, a N-B bonded adduct is formed at low temperature, which decomposes at 25 "C to yield (Me,N B H, ), , Me,N H-BH,, p-Me,N B, H, , and Me,AsAsMe,. Equimolar amounts of As-B and N-B adducts are formed at low temperature when Me,AsNEt, is reacted with BH,-thf. With increasing temperature, the As-B adduct converts t o the N-B adduct, which subsequently decomposes at room temperature to p-Et,NB,H,, Et,NH-BH,, (Et,NBH,),, and Me,AsAsMe,. The reaction of Me,AsNPrn, with BH,-thf yields more of the As-B adduct than of the N-B adduct at -90 "C, but the former rearranges to the latter on warming. Only the As-B adduct is formed in the reaction of Me,AsNPr+, with BH,ethf. These results suggest that the steric bulkiness of the R, N moiety plays an important role in determining the co-ordination site of the boron in this series of compounds.

Transition Metal-Catalyzed Formation of Boron−Nitrogen Bonds: Catalytic Dehydrocoupling of Amine-Borane Adducts to Form Aminoboranes and Borazines

“…The 11 B NMR spectrum of 4 displayed a triplet at δ 34.7 ( J BH = 123 Hz; lit. δ 34.2) . Previous studies on monomer−dimer equilibria of R 2 NBH 2 species by 11 B NMR indicate a general trend for the chemical shifts of both monomers (δ ≈ 37 ppm) and dimers (δ 1.9−5.4 ppm) .…”

“Spontaneous” Ambient Temperature Dehydrocoupling of Aromatic Amine–Boranes

“…The spectrum showed further resonances for BH 3 ⋅ THF ( δ =−1.5), N , N′ , N′′ ‐triphenylborazine ( 6 a ) ( δ =32.2),10b a broad resonance centered at δ =−3.6 assigned to N , N′ , N′′ ‐triphenylcyclotriborazane ( 7 a ),19 and a resonance at δ =−11.6 corresponding to an unidentified product. Additionally, a small signal at δ ≈ 36 (<1 %) was detected, which was tentatively assigned to monomeric anilinoborane ( 8 a ) (cf., e.g., PhMeNBH 2 : δ =40;19 i Pr 2 NBH 2 : δ =34.221 or 34.710b); no evidence was obtained for the formation of polyanilinoborane.…”

“…[19] The spectrum showed further resonances for BH 3 ·THF (d = À1.5), N,N',N''-triphenylborazine (6 a) (d = 32.2), [10b] a broad resonance centered at d = À3.6 assigned to N,N',N''-triphenylcyclotriborazane (7 a), [19] and a resonance at d = À11.6 corresponding to an unidentified product. Additionally, a small signal at d % 36 (< 1 %) was detected, which was tentatively assigned to monomeric anilinoborane (8 a) (cf., e.g., PhMeN=BH 2 : d = 40; [19] iPr 2 N= BH 2 : d = 34.2 [21] or 34.7 [10b] ); no evidence was obtained for the formation of polyanilinoborane. Surprisingly, when THF was added to 3 a at À20 8C and the mixture was then warmed to ambient temperature, the solution thus formed (5 m starting concentration of 3 a) showed vigorous gas evolution even in the absence of a catalyst such as 1.…”

Nature of the catalytically inactive cobalt hydride formed upon hydrogenation of aromatic substrates. Structure and characterization of the binuclear cobalt hydride [{iso-Pr2P(CH2)3PPr-iso2}Co]2(H)(.mu.-H)3

“…13C|!H| NMR (C6D6, 75.429 MHz, ppm): Cl, 98.8 (s); C2 and C2', 50.2 (s); C3 and C3', 28.6 (dt); C4, 21.1 (t); C5 and C8, 23.5 (t); C6, C7, C9 and CIO, 20.3, 20.0, 19.3, and 18. [(dippp)CoH2]2 (2). A solution of (tj3-C3H5)Co(dippp) (1) (0.516 g, 1.37 mmol) in dry hexanes (15 mL) in an 80-mL glass reactor was degassed and then stirred under an atmosphere of H2 for 24 h. The initial purple color of the solution turned dark blue instantly after hydrogen was admitted.…”