Isolation of 1,2,4,3-Triazaborol-3-yl-metal (Li, Mg, Al, Au, Zn, Sb, Bi) Derivatives and Reactivity toward CO and Isonitriles

Abstract

3,4-dihydro-2H-1,2,4,3-triazaborol-3-yl-lithium 3 was synthesized and fully characterized. The (11)B NMR spectrum, X-ray diffraction analysis, and computational studies revealed the ionic nature of the B-Li bond, and indeed 3 displays nucleophilic property which allowed preparation of a series of 1,2,4,3-triazaborol-3-yl-metal complexes (Al; 5, Au; 6, Zn; 7, Mg; 8, Sb; 9, and Bi; 10). 3 reacted with CO (1 atm) and various isonitriles under ambient condition, and mechanistic study suggests that the reactions with CO and aryl isonitriles proceed via an insertion of CO and isonitrile carbon into the B-Li bond followed by isomerization to yield transient carbene species, one of which was confirmed by trapping with S8. With PhNC, compounds 5 and 7·(thf) underwent exchange of THF molecule coordinating to the metal center with isonitrile, whereas insertion of isonitrile carbon occurred at the B-Bi bond in 10 which afforded stable bismuth (boryl)iminomethane 20.

Easy access to nucleophilic boron through diborane to magnesium boryl metathesis

“…The fourth coordination site of 11 is occupied by the [Bpin] − unit, which is ligated to magnesium through its sp 2 boron centre as a terminal boryl ligand. The Mg(1)–B(1) distance [2.324(2) Å] lies within the range observed in three reported magnesium derivatives synthesized by reactions of compound 1 with MgBr 2 [2.281(6)–2.377(4) Å] and is comparable to the Mg–B bond length of a closely related and very recently reported N- heterocyclic 1,2,4,3-triazaborol-3-yl-magnesium species [2.341(7) Å], which was prepared by an analogous salt elimination route1427. These data indicate that the Mg–B interaction within 11 possesses a similarly polarized nature.…”

“…Although this latter feature also ensures that the electropositive boron centre retains a significant partial positive charge (for 1 ; calculated natural population analysis charge on B=+0.072), these species behave as boron-centred nucleophiles by dint of a net polarization of the boron–lithium bond (in effect, B δ+ –Li δ++ ) induced by the even lower effective nuclear charge of lithium (for 1 ; calculated natural population analysis charge on Li=+0.755)913. Although a rich and varied chemistry has since arisen from the reactivity of compound 1 and related N- heterocyclic boryl anions with organic914, transition metal15161718 and main group electrophiles1419202122232425, alternative nucleophilic boron reagents remain very rare species262728293031. Notable exceptions are Braunschweig's dimetalloborylene and borolyl anions (for example, 2 and 3 )3233 Bertrand and Kinjo's carbene-stabilised monovalent boron species (for example, 4 )3435363738 and a remarkable tricyanoborandiyl dianion394041.…”

Reactivity of a Tetra(o‐tolyl)diborane(4) Dianion as a Diarylboryl Anion Equivalent

“…The major structural parameters of 2 and 3 were compared with those of 1 (Table 1). These features are consistent with those of the previously reported C-substituted diborane(4) dianions D and E, [3d,e] suggesting the formation of B=B p-bonds in 2 and 3.I ts hould be noted that the BÀLi lengths in 2 [2.243(2), 2.277(3) ]w ere slightly shorter than those in tetraaryldiborane (4) (4) ]w ere longer than those in ab orylmagnesium species, [10] boratabenzene-magnesium complexes, [11] ab orole dianion magnesium complex, [12] and unsymmetrical diborene-magnesium complexes. These features are consistent with those of the previously reported C-substituted diborane(4) dianions D and E, [3d,e] suggesting the formation of B=B p-bonds in 2 and 3.I ts hould be noted that the BÀLi lengths in 2 [2.243(2), 2.277(3) ]w ere slightly shorter than those in tetraaryldiborane (4) (4) ]w ere longer than those in ab orylmagnesium species, [10] boratabenzene-magnesium complexes, [11] ab orole dianion magnesium complex, [12] and unsymmetrical diborene-magnesium complexes.…”

A New Perspective on Borane Chemistry: The Nucleophilicity of the B−H Bonding Pair Electrons

“…[14c] As shown in Scheme 2, the key step for the formation of ADB was the substitution of the THF donor of THF·BH 3 by the B À Hb ond of NH 3 3 were formed, with most of the NH 2 BH 2 being trapped by BH 3 to form ADB.During this process,the initial nucleophilic attack of the BÀHbond at the positively charged hydrogen on the Natom and its induction of the formation of the dihydrogen complex were clearly illustrated by theoretical calculations and isotopic experiments.I nt he ADB final product, the B À NH 2 À Bb ond stabilized the B À H À Bb ond as demonstrated in case (iv)s hown in Figure 3. (7,8)],r espectively. [23,24] Form any years,t he structure of DADB puzzled the community,u ntil as eries of experiments were carried out that identified the compound as the salt [H 2 B(NH 3 ) 2 ][BH 4 ].…”

“…[4][5][6] In most cases,n ucleophilic boron compounds are unstable. Commonly applied strategies to enhance their stabilization include the installation of sterically imposing donor ligands (Figure 2), or the reaction with electrophilic reagents to transform transient nucleophiles into their main-group derivatives [7,8] and metal complexes,r espectively. [9,10] Due to their interesting properties,t he chemistry of nucleophilic boron compounds has quickly become ah ot research topic.…”