Synthesis and crystal structures of guanidinatoaluminum complexes and catalytic study for MPV reduction

Bimetallic aluminum alkyl and iodide complexes stabilized by a bulky bis-guanidinate ligand

“…The Al-C bond lengths for the compounds 2 and 3 lie between 1.949(6) Å and 1.962(3) Å, these values are similar to the reported values of Al-C bond lengths. [6][7][8][9][10][11][12][13] The Al-I bond distances in 4 Al1-I1 is 2.507(2) Å and Al1-I2 is 2.521(2) Å which are well in agreement with the reported values. [6][7][8][9][10][11][12][13] The bite angles of the bridged bis-guanidine ligands N1-Al1-N2, which are 68.75 (16), 69.33 (10) and 71.19 (19) • 4 for 2-4, respectively.…”

“…5 To date, several examples of mononuclear guanidinato aluminum complexes, including aluminum alkyls and halides are known in the literature. [6][7][8][9][10][11][12][13] Recent reports suggest that dinuclear aluminum complexes are more important precursors for ring opening polymerization (ROP) of cyclic esters (e.g., lactide and ε-caprolactone), cyclic ethers (e.g., cyclohexne oxide (CHO) and propylene oxide (PO)) than their monometallic counterparts. [14][15][16] Despite the prominent role of cooperative effect between two aluminum centers, synthesis and catalytic application of well-characterized dinuclear aluminum complexes remain scarce.…”

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

“…A value of 0.15 for this parameter confirmed a slight distorted squarepyramidal structure in which four N atoms belonging to the two identical guanidinato units occupy the equatorial positions, while the apical position is occupied by the methyl group. It should be noted that the few pentacoordinated guanidinate aluminum complexes that have been published to date exhibit distorted trigonal bipyramidal geometries, 49,52 45,49 Furthermore, the Al1−C8 distance 1.972(2) Å is consistent with values previously reported. 51 Catalytic Studies for the Synthesis of 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.…”

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]…”