Structurally Defined Ring‐Opening and Insertion of Pinacolborane into Aluminium‐Nitrogen Bonds of Sterically Demanding Dialkylaluminium Amides

Abstract

Dialkylaluminium amides iBu2Al(TMP) and iBu2Al(HMDS) can perform catalytic hydroboration of ketones with pinacolborane to form the expected boronic esters. However, repeating the same reactions stoichiometrically without a ketone leads unexpectedly to ring‐opening of pinacolborane and insertion of its open chain into the Al−N(amido) bond. To date there has been limited knowledge on decomposition pathways of HBpin despite its prominent role in hydroboration chemistry. X‐ray crystallography shows these mixed Al−B products [iBu2Al{OC(Me)2C(Me)2O}B(H)(NR2)]2 (NR2=TMP or HMDS) form dimers with an (AlO)2 core and terminal B−N bonds. Since the bond retention (B−H) and bond breaking (B−O) in these transformations seemed surprising, DFT calculations run using M11/6‐31G(d,p) gave an energy profile consistent with a σ‐bond metathesis mechanism where London dispersion interactions between iBu and (amide) Me groups play an important stabilising role in the final outcome.

Hydrocarbon Soluble Alkali‐Metal‐Aluminium Hydride Surrog[ATES]

“…These results support the existence of the observed short contacts [AM⋅⋅⋅H−C(TMP)] in the donor‐free heavy alkali‐metal aluminates ( 3 and 4 ). Surprisingly, considering the high utility of TMP and the numerous structures it is found in, [41] the effects of non‐covalent interactions arising from it within structures has been rarely mentioned previously.…”

The Unusual Structural Behavior of Heteroleptic Aryl Copper(I) Thiolato Molecules: Cis vs Trans Structures and London Dispersion Effects

“…In effect, there is intrusion of electronic wave functions on each other’s space contrary to the Pauli exclusion principle, i.e., Pauli repulsion. However, in addition to this repulsion, there is growing evidence that attractive London dispersion (LD) interactions between the C–H moieties of the hydrocarbyl substituents of the ligands − can generate unexpected effects and enable the formation of species with unusual structures. Such effects are manifested, for example, in the stable hexaphenylethane derivative {C­(C 6 H 3 -3,5- t Bu 2 ) 3 } 2 of Grimme and Schreiner, the divalent group 14 chalcogenetates, high oxidation state mid- to late transition metal alkyls, , or in the low coordinate copper­(II) amides .…”

Reactivity of a quasi-four-coordinate butylmagnesium cation

“…There are reports of ring opening of pinacolborane by the hydrides of group 2 metals and aluminium. 20,21 However, 4a is a rare example of a ring-opened pinacolborane product retaining the hydride within the aggregate.…”