Structurally defined ring-opening and insertion of pinacolborane into aluminium-nitrogen bonds of sterically demanding dialkylaluminium amides

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Pollard, Victoria A. and Kennedy, Alan R. and McLellan, Ross and Ross, Duncan and Tuttle, Tell and Mulvey, Robert E. (2021) Structurally defined ring-opening and insertion of pinacolborane into aluminium-nitrogen bonds of sterically demanding dialkylaluminium amides. European Journal of Inorganic Chemistry, 2021 (1). pp. 50-53. ISSN 1434-1948 (https://doi.org/10.1002/ejic.202000919)

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Abstract

Dialkylaluminium amides iBu 2Al(TMP) and iBu 2Al(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 [iBu 2Al{OC(Me) 2C(Me) 2O}B(H)(NR 2)] 2 (NR 2=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.

ORCID iDs

Pollard, Victoria A. ORCID logoORCID: https://orcid.org/0000-0002-9149-3458, Kennedy, Alan R. ORCID logoORCID: https://orcid.org/0000-0003-3652-6015, McLellan, Ross ORCID logoORCID: https://orcid.org/0000-0001-9700-0258, Ross, Duncan, Tuttle, Tell and Mulvey, Robert E. ORCID logoORCID: https://orcid.org/0000-0002-1015-2564;
CORE (COnnecting REpositories)