Subtle Reactivities of Boron and Aluminum Complexes with Amino-Linked N-Heterocyclic Carbene Ligation

Abstract

This paper describes the synthesis and characterization of trimethylaluminum (2a), dimethylaluminum (3a), and triphenylboron complexes (7) supported by functional amine-linked NHC ligands. The chemical reactivity studies with carbodiimide and isocyanate were preformed with 2a and 3a, illustrating the noninnocent nature in Al–carbene bonding. However, the boron–carbene interaction is quite robust against addition of these substrates even at higher temperature conditions. The subtle difference in chemical reactivity between aluminum and boron is attributed from the metal–carbene bond covalency. Development of the catalytic method for Suzuki–Miyaura coupling utilizing triphenylboron reagent supported by amino-NHC is also presented.

N‐Heterocyclic Carbene Complexes of Cp*–Aluminum Triflate

“…The cleavage of Cp*–Al bond, instead of the NHC–Al interaction, is distinct from that reported previously, in which the insertion of polar C=O group to the ylidene–Al bond was observed. [6g], [6i], , The application of complex 3 in Lewis acid catalyzed organic transformations is currently under investigation.…”

Aryl-NHC group 13 trimethyl complexes : structural, stability and bonding insights

“…The steric hindrance around the aluminium center was attributed to steric crowding between the ethyl and tert-butyl groups attached to the aluminium and the amino pendant arm, respectively. 31 In a similar manner to complex 12 (see Scheme 1.3), complex 44 was subjected to reactions with electrophiles (isocyanates) to explore whether with the bidentate ligand, the stability of the Al-carbene bond would increase and reduce its susceptibility to electrophilic attack. An analogous insertion reaction to that observed for complex 12 took place.…”

“…Reactivity studies of complex 44 to electrophiles. 31 Anionic tethered N-heterocyclic carbenes have been used extensively as ligands for the stabilization of transition metals and lanthanides alike, and these ligands have also been applied to group 13 metals. 45 An example of such ligand is shown in the chiral imidazolium sulfonate compound 46, having been applied in the synthesis of dimethylaluminium complex…”

“…Prior to commencing the studies in this thesis, only four monodentate (9, 12, 15, 18), 29,30,33 and three bidentate ligands (44,47) and one tridentate ligand (50) trimethylaluminium complexes had been synthesized and fully characterized. 31,46,47 Furthermore, there are only a few known examples of saturated NHC stabilised group 13 complexes that have been fully characterized. Herein, this chapter will report the synthesis, characterization, theoretical and reactivity studies on the series of the NHC trimethylaluminium complexes.…”

“…Synthesis of chelating dimethylaluminium complex 44 from complex 12. X-ray crystal structure of the chelating dimethylaluminium complex 44 31.…”