Cationic aluminum, gallium, and indium complexes in catalysis

The introduction of cationic charge allows cationic group 13 complexes to be excellent Lewis acid catalysts. Cationic aluminum, gallium, and indium complexes in catalysis are comprehensively reviewed based on the reaction type.

A monoanionic NNNN-type macrocyclic ligand for electropositive metal centers

The coordination of a mono(amido) triamine macrocyclic ligand Me₃TACD derived from cyclen (1,4,7,10-tetraazacyclododecane or [12]aneN₄) toward electropositive metal centers is surveyed. This NNNN-type monoanionic macrocyclic ligand is capable of stabilizing a variety of metal coordination environments that are commonly not amenable to stable coordination spheres. Metal complexes supported by Me₃TACD include hydrides, hydrocarbyls, silyls, and amides. Protection of one hemisphere of a large metal center allows, as in the case of metallocene scaffolds for early transition metals, deaggregation and control of reactivity.

Group 2 metal (Mg, Ca, Sr) silylamides supported by a cyclen-derived macrocyclic polyamine

Heteroleptic bis(silyl)amides of magnesium and calcium [(L)M{N(SiMe₃)₂}] [M = Mg, Ca; LH = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane; (Me₃TACD)H] were previously synthesized from LH and [M{N(SiMe₃)₂}₂]. Strontium bis(silyl)amides [Sr{N(SiMe₃)₂}₂(thf)₂] and [Sr{N(SiHMe₂)₂}₂(thf)_2/3] reacted with LH to give different types of products, depending on the presence of the β-SiH function. While the former underwent protonolysis to give the amido-bridged dimer [(L)Sr{N(SiMe₃)₂}]₂ (1), the latter gave the adduct [(LH)Sr{N(SiHMe₂)₂}₂] (2) as a stable solid. 2 slowly underwent an intramolecular Si-H/H-N dehydrocoupling in solution to give [{(L)SiMe₂N(SiHMe₂)}Sr{N(SiHMe₂)₂}] (3) by liberating H₂. The results of transamination of 1 with HN(SiHMe₂)₂ depended on the relative stoichiometric ratio. A 1 : 1 mixture in n-pentane gave [{(L)SiMe₂N(SiHMe₂)}Sr{N(SiMe₃)₂}] (4) and H₂, while excess HN(SiHMe₂)₂ gave the adduct 2 under similar conditions. Compounds 2 and 3 exhibit Sr↼H-Si interactions according to X-ray crystallography, NMR, and IR spectroscopy. Lighter congeners of elusive [(L)Sr{N(SiHMe₂)₂}] were isolable for Mg (5) and Ca (6).

Facile ring-opening of THF at a lithium center induced by a pendant Si-H bond and BPh3

The macrocyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane [LH = (Me₃TACD)H] formed adducts with tetramethyl-silazides [M{N(SiHMe₂)₂}] (M = Li, Na, K) of light alkali metals. Upon heating, intramolecular dehydrocoupling occurred to give [M{(L)SiMe₂N(SiHMe₂)}]. BPh₃ induced facile ring-opening of THF when reacted with [Li{(L)SiMe₂N(SiHMe₂)}].

Molecular magnesium hydrides supported by an anionic triazacyclononane-type ligand

A dimeric magnesium hydride supported by a monoanionic TACN-type ligand is formed by an unusual rearrangement of an unstable mononuclear complex with a terminal Mg–H bond.

Ring-opening of cyclic ethers by aluminum hydridotriphenylborate

Ring-opening of THF or THP in the presence of pinacolborane can be catalyzed by a molecular aluminum hydride catalyst [(L)AlH₂]₂ (L = Me₃TACD)/BPh₃ and involves an isolable intermediate [(L)AlH][HBPh₃].