Synthesis and Catalytic Applications of Chiral Hydridoiridium(III) Complexes with Diamine/Bis(monophosphane) and Diamine/Diphosphane Coordination

Abstract

The P2/N2‐coordinated cis‐dihydridoiridium(III) chelate complexes (OC‐6‐13)‐[IrH2(H2N∩NH2)(PR3)2]BF4 [PR3 = PPh3, H2N∩NH2 = 1,2‐(H2N)2C6H4 (1a); (1R,2R)‐(H2N)2C6H10 {(R,R)‐dach} (1b); (R)‐2,2′‐diamino‐1,1′‐binaphthyl {(R)‐dabin} (1c); PR3 = PiPr3, H2N∩NH2 = (R,R)‐dach (2a), (R)‐dabin (2b); PR3 = PCy3, H2N∩NH2 = (R)‐dabin (3)] were obtained by treating the respective diamine ligands with labile precursors such as [IrH2(OCMe2)2(PPh3)2]BF4, [(η4‐1,5‐C8H12)Ir(PPh3)2]BF4, or [IrH5(PR3)2]/HBF4 (R = iPr, Cy). While oxidative addition of HCl to [(η4‐1,5‐C8H12)Ir{(S,S)‐bdpcp}]BF4 [(S,S)‐bdpcp = (1S,2S)‐(Ph2P)2C5H8] yields the usual mononuclear adduct [(η4‐1,5‐C8H12)Ir(H)(Cl){(S,S)‐bdpcp}]BF4 (4), similar treatment of [(η4‐1,5‐C8H12)Ir{(R)‐binap}]BF4 furnishes the triply chlorido‐bridged diiridium complex [{(R)‐binap}2Ir2H2(μ‐Cl)3]BF4 (5). Opening of the μ‐Cl bridges of 5 by N,N nucleophiles was used to synthesise the three diamine/(R)‐binap complexes [Ir(H)(Cl)(H2N∩NH2){(R)‐binap}]BF4 [H2N∩NH2 = (1R,2R)‐H2NCH(Ph)CH(Ph)NH2 {(R,R)‐dpen} (6a), (R,R)‐dach (6b), and H2NCMe2CMe2NH2 {tmen} (6c). Whereas the dihydrides [IrH2{(R,R)‐dach}(PR3)2]BF4 and [IrH2{(R)‐dabin}(PR3)2]BF4 (R = iPr, Ph) are only poor (pre)catalysts for the enantioselective hydrogenation of acetophenone, complexes 6a–c catalyze the formation of 1‐phenylethanol in good enantiomeric excess [eemax = 82–84 % (S)] in the presence of base. The crystal structures of 1a, 4, and 5 have been determined. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Ketone Hydrogenation with Iridium Complexes with “non N–H” Ligands: The Key Role of the Strong Base

“…[5][6][7][8][9][10] Of these, the family of [RuCl2(diphosphine)(diamine)] molecules developed by Noyori, Ikariya, Ohkuma and coworkers stands out. [11][12][13][14] Efficient enantioselective catalysts based on rhodium, [15][16][17] iridium, [18][19][20][21][22][23][24][25][26] and iron [27][28][29][30][31][32][33][34][35][36] have also been reported in the literature. Interest in iridium as a catalytic metal is sparked by the observation that it outperforms rhodium for the ionic hydrogenation of particularly difficult substrates such as imines and industrial processes based on Ir-catalyzed ketone hydrogenation have been implemented.…”

Triply Halide‐Bridged Dinuclear Iridium(III) Complexes with Chiral Diphosphine Ligands as New Easy‐to‐Handle Iridium Catalysts for Asymmetric Hydrogenation of Imines and N‐Heteroaromatics

“…Similar anionic triply halide‐bridged bifacial octahedral complexes of ruthenium were reported to display a similar AABB pattern 19. After our report, Dahlenburg and his collaborators determined the crystal structure of the triply chloride‐bridged dinuclear iridium(III) complex bearing ( R )‐BINAP 20. Bromide and iodide variants were also synthesized by the same synthetic method using aqueous HBr or aqueous HI instead of aqueous HCl [Eq.…”

Enantioselective Synthesis of Alcohols and Amines by Iridium‐Catalyzed Hydrogenation, Transfer Hydrogenation, and Related Processes

“…Dalenburgh and co-workers have prepared a large number of iridium complexes bearing N,N-and P,P-ligands (125 a-c, Scheme 69). [154,155] The best enantioselectivity was obtained with the Ir chloro hydride 125 a (N,N = (R,R)-DPEN and P,P = (R)-BINAP), either preformed or generated in situ, which afforded (S)-phenylethanol with ee values of 82-84 % at low catalyst loadings (0.2 mol %) under 20 bars of H 2 in methanol. Also in this case, the authors were able to exclude a catalytic cycle through transfer hydrogenation conditions by using D 2 instead of H 2 .…”