Three asymmetric guanidinato metal complexes: Synthesis, crystal structures and their use as pre-catalysts in the Meerwein–Ponndorf–Verley reduction

Recent Developments on the Use of Group 13 Metal Complexes in Catalysis

“…Recently,s everal readily accessible aluminum compounds supported by polydentate ligands, sometimes bearing bulky substituents, were shown to be effective MPV reduction catalysts (6-10, Scheme 6). [44][45][46][47][48][49] Among these new compounds, the silanolate derivative 6 was the most active with catalystl oadings of 0.5-1.0 mol %a nd temperatures rarely above 50 8C. [44]…”

Aluminum complexes of β-hydroxy-imino ligands: Synthesis, structures and application in the Tishchenko reaction

“…Recently, we report a series of amidinatoaluminum complexes [3], asymmetric guanidinato aluminum complexes [4] and bidentate N, O-aluminum complexes [5] as pre-catalysts for the Tishchenko reaction or the Meerwein-Ponndorf-Verley (MPV) reaction. As our continuous interest in developing aluminum alkoxide complexes as catalysts/initiators, here we report the synthesis and structural features of four aluminum alkoxide complexes containing β-hydroxyimino ligands with different bonding modes, and their catalytic activity for the Tishchenko reaction with a range of aromatic aldehydes.…”

Mono- and Dinuclear Asymmetric Aluminum Guanidinates for the Catalytic CO2 Fixation into Cyclic Carbonates

“…39−42 Several aluminum complexes with related guanidinato ligands can be obtained through various reaction pathways: (i) carbodiimide insertion in Al−N bonds, 43−49 (ii) salt metathesis reactions between Al-X (X = halide) and lithium guanidinates, 50−55 and (iii) protonolysis of Al−Y bonds (Y = alkyl or amide) and a neutral guanidine. 55−60 It should be noted that only in very few cases has their use as catalysts it been reported, in aldehyde reduction processes, 49,54,59 ring-opening polymerization, 60 or, curiously, guanylation of aromatic amines, 47,50 but never as catalysts for the formation of cyclic carbonates. Continuing our interest in the chemistry of guanidines and their derivatives, some of us have studied the reaction of trimethylaluminum (AlMe 3 ) with N-phosphinoguanidine ligands, which yields stable phosphinimine-amidinato compounds, after the rearrangement of the Nphosphinoguanidinato intermediates initially detected.…”

“…Several aluminum complexes with related guanidinato ligands can be obtained through various reaction pathways: (i) carbodiimide insertion in Al–N bonds, − (ii) salt metathesis reactions between Al-X (X = halide) and lithium guanidinates, − and (iii) protonolysis of Al–Y bonds (Y = alkyl or amide) and a neutral guanidine. − …”

“…It should be noted that only in very few cases has their use as catalysts it been reported, in aldehyde reduction processes, ,, ring-opening polymerization, or, curiously, guanylation of aromatic amines, , but never as catalysts for the formation of cyclic carbonates. Continuing our interest in the chemistry of guanidines and their derivatives, some of us have studied the reaction of trimethylaluminum (AlMe 3 ) with N -phosphinoguanidine ligands, which yields stable phosphinimine-amidinato compounds, after the rearrangement of the N -phosphinoguanidinato intermediates initially detected. , Very recently, we have also described the use of aromatic guanidines such as those depicted in Scheme , as catalysts for the preparation of cyclic carbonates.…”