Applications and reactivity trends of homoleptic p-block metal amido reagents

Abstract

This review aims to develop an understanding of reactivity trends of p-block metal bases M(NR2)n (M = Sn: n = 2; M = Al, Ga, As, Sb: n = 3) towards organic substrates EHy containing one or more E-H bonds (E = B, N, P, S). These compounds not only act as good bases for the deprotonation of E-H bonds but recent advances in p-block amido chemistry have shown that, in addition, they can effect the dehydrogenic homo-coupling of primary phosphines and amines to give E-E bonded products. They have also been found to be active in stoichiometric and catalytic dehydrocoupling of amine-boranes, which has direct applications in hydrogen storage devices, revealing that these p-block catalysts offer potential alternatives to the extensive range of expensive and often highly toxic heavy metal catalysts. This perspective analyses three distinct reactivity patterns of p-block metal bases; deprotonation, stoichiometric dehydrocoupling and catalytic dehydrocoupling and attempts to rationalise reactivity in relation to the redox stability of the p-block metal.

Dehydrocoupling routes to element–element bonds catalysed by main group compounds

“…In these reactions up to two equivalents of hydrogen can be released per equivalent of starting material, offering the potential to form ring compounds such as borazanes ( t BuNHBH 2 ) 3 and borazines ( t BuNBH) 3 by elimination of either one or two equivalents of H 2 respectively, or formation of polymeric compounds such as [-(R)NQB(H)-] n . 13,25,28 2.1.3 B-N bond formation using group 4 metals. 25 Under ambient conditions (3 mol% Al(NMe 2 ) 3 or 5 mol% Ga(NMe 2 ) 3 ) further dehydrocoupling afforded the borazine ( t BuNBH) 3 in addition to an unidentified BN containing polymeric product.…”

“…Such redox instability was also observed in the reduction of tin(II) and arsenic(III) to either the metal or a Zintl phase during the homo-dehydrocoupling of phosphines. 13,25,28 2.1.3 B-N bond formation using group 4 metals. Tin(II) compounds have also been examined in the catalytic dehydrogenation of amine-boranes.…”

Synthetic Mechanisms in the Formation of SnTe Nanocrystals

“…Alternatively, a Sn-containing molecular cluster species might explain these data, particularly given divalent tin amides’ propensity to form dimers, cubanes, and larger molecular structures. 50 , 51 A cluster could be too large to resolve using solution NMR, particularly if the Sn signal is further broadened by bonding with quadrupolar 14 N nuclei.…”

“…However, a stoichiometrically equal mixture of OAm, tin silylamide, and TOPTe in deuterated THF (combined at room temperature, unheated; 150 mM Sn) showed no Sn NMR signal at any temperature between ±30 °C, suggesting resonance broadening of the NMR signal is not the cause. Alternatively, a Sn-containing molecular cluster species might explain these data, particularly given divalent tin amides’ propensity to form dimers, cubanes, and larger molecular structures. , A cluster could be too large to resolve using solution NMR, particularly if the Sn signal is further broadened by bonding with quadrupolar 14 N nuclei.…”

The role of the bis-trimethylsilylamido ligand, [N{SiMe3}2]−, in main group chemistry. Part 2: Structural chemistry of the metallic p-block elements

“…Readers may find the recent Perspective article detailing the "Application and reactivity trends of homoleptic p-block metal amido reagents" a useful compliment to this article [154].…”