Enantioselective Intramolecular Cyclopropanation of cis-Alkenes by Chiral Ruthenium(II) Schiff Base Catalysts and Crystal Structures of (Schiff base)ruthenium Complexes Containing Carbene, PPh₃, and CO Ligands

Abstract

The enantioselective intramolecular cyclopropanation of cis-substituted allylic diazoacetates catalyzed by the chiral ruthenium Schiff base complexes [Ru(Schiff base)(PPh 3 ) 2 ] (1) is described. Among this class of complexes examined, [Ru(2-Br-salen)(PPh 3 ) 2 ] (1a) is the most effective, catalyzing intramolecular cyclopropanation of cis-allylic diazoacetates cis-(CRHdCH)CH 2 OC(O)CHN 2 (R ) alkyl, aryl) in CHCl 3 solution to give [3.1.0]-bicyclic lactones with yields and ee values up to 71 and 90%, respectively. The analogous reactions of cis-alkenyl diazoacetates using [Ru(Schiff base)(CO)] (2) as catalyst gave comparable enantioselectivities (up to 91% ee) but lower product yields of 20-38%. Treatment of [Ru-(2,4-X-salen)(PPh 3 ) 2 ] (1d, X ) Br; 1e, X ) Cl; 1f, X ) I) with N 2 C(p-YC 6 H 4 ) 2 (Y ) H, MeO) and N-methylimidazole (MeIm) or pyridine (py) gave the monocarbene complexes [Ru(2,4-X-salen)(C(p-and [Ru(2,4-Br-salen)(CPh 2 )(py)] (4, H 2 (2,4-Br-salen) ) bis(3,5-dibromosalicylidene)-(1R,2R)-cyclohexanediamine), respectively. X-ray crystal structure determinations revealed RudC(carbene) distances of 1.921(12) Å for 3a, 1.913(5) Å for 3b, 1.919(14) Å for 3c, 1.910(2) Å for 3d, and 1.917(4) Å for 4. A comparison of the structures and electrochemistry of 1, [Ru(Schiff base)(CO)(MeIm)], 3, and 4 with those of the porphyrin analogues is presented.

Syntheses and Crystal Structures of Ruthenium-Salen Complexes Containing Triphenylphosphine Ligands

“…1.881(3)Å) [28], and [Ru(2-Br-salen)(CO)(MeIm)] (MeIm = N-methylimidazole) (1.846(13)Å) [14], but slightly shorter than that in cis-,cis[Ru{η 2 -N(O)C 10 H 6 )} 2 (CO)(PPh 3 )] (1.919(4)Å) [29].…”

“…To design rationally transformations catalyzed by ruthenium-salen complexes, the knowledge of their redox and structural properties is desirable [13]. A few ruthenium-salen complexes containing carbene, nitride, nitrosyl, oxo, hydrate, carbonyl, and halide groups, which show catalytic activity and wherein the ruthenium oxidation states vary from +2 to +6, have been investigated in recent years [14][15][16][17][18]. However, ruthenium-salen complexes with triphenylphosphine ligands have been less explored [18,19].…”

Synthesis, Crystal Structures and Preliminary Antibacterial Activities of Nickel(ii) and Zinc(ii) Complexes Derived From 2-Bromo-6-[(3-Cyclohexylaminopropylimino) Methyl]phenol

“…[1][2][3] Schiff bases derived from the condensation of salicylaldehyde with primary amines represent an important class of chelating ligands, the metal complexes of which have been widely studied. [4][5][6][7][8][9] A detailed search of literature indicates that only two ruthenium complexes, 10 three zinc complexes, 11,12 and one titanium complex 13 with the Schiff bases derived from 3-bromosalicylaldehyde have been reported so far. Moreover, no complexes have been reported with the Schiff base ligand 2-bromo-6-[(3-cyclohexylaminopropylimino)methyl]phenol (L; Scheme 1).…”

Synthesis, characterization, and structures of two new tetranuclear copper complexes with azido/dicyanamide bridges containing chiral Schiff base ligand

“…Chiral Schiff base ligands, obtained by condensing between a number of chiral amines and aldehydes or ketones, are a very important class of ligands to con struct molecule materials with various novel structures and interesting properties [1][2][3]. In their family, tet radentate Schiff base ligands containing N, O donors have been widely utilized to form polynuclear com plexes with interesting structures [4][5][6].…”