Optically Active Mixed Unsymmetric Imine Platinum(II) Complexes – Utilization of the Liberated Imines for Further Syntheses of Mixed Imine‐Diazadiene Complexes and of (E)‐Cyanoalkenes

Abstract

Treatment of trans‐[PtCl2(NCR)2] (1) {R = CH2CO2Me (1a), Ph (1b)} with (R*)‐camphor oxime (C9H16)C=NOH (2) gives access to the optically active mixed imine‐nitrile complexes trans‐(R*)‐[PtCl2{NH=C(R)ON=C(C9H16)}(NCR)] (4), which, on reaction with ketoximes R1R2C=NOH (3) {R1 = R2 = Me (3a), C4H8 (3b)}, give the chiral unsymmetric bis(imine) complexes trans‐(R*)‐[PtCl2{NH=C(R)ON=C(C9H16)}{NH=C(R)ON=CR1R2}] (6) in moderate yields. An alternative route involves the reaction of the starting complexes 1 with ketoximes 3 to give the mixed imine‐nitrile complexes trans‐[PtCl2{NH=C(R)ON=CR1R2}(NCR)] (5), followed by reaction of the latter with (R*)‐camphor oxime (2) to afford products 6 in similar yields. Treatment of complexes 1 or 4 with two or one equivalent of 2, respectively, gives the symmetrical bis(imine) complexes trans‐[PtCl2{NH=C(R)ON=C(C9H16)}2] (7). These reactions are accelerated by microwave irradiation to afford, in better yields (71–50 %), the same products. The new optically active diimine compounds NH=C(R)ON=C(C9H16) (8) are quantitatively liberated upon reaction of complexes 7 with a diphosphane. The chiral diimino ester 8a (R = CH2CO2Me) acts as a protic nucleophile and efficiently couples with the coordinated nitrile in 4 to give the new optically active, mixed, unsymmetric imine‐1,3‐diaza‐1,3‐diene complexes trans‐(R*,R*)‐[PtCl2{NH=C(R)ON=C(C9H16)}{NH=C(R)N=C(CH2CO2Me)ON=C(C9H16)}] (9). Diimino ester 8a with an acidic α‐methylene group also reacts with acyclic nitrones –O+N(Me)=C(H)R′ (10) to afford stereoselectively the (E)‐cyanoalkenes (N≡C)C(CO2Me)=C(H)R′ (11) {R′ = 4‐MeC6H4 (11a), 2,4,6‐Me3C6H2 (11b)}. All of these compounds were characterized by IR and NMR (1H, 13C, and 195Pt for metal complexes) spectroscopy, ESI‐MS or FAB‐MS, elemental analysis, and X‐ray diffraction analysis (for 5c and 7b). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Metal-Involving Synthesis and Reactions of Oximes

“…Pombeiro and co-workers reported the nucleophilic addition of a series of ketoximes R 1 R 2 CNOH ( 74 ) to the nitrile ligands in the platinum­(II) complexes trans -[PtCl 2 (NCR 3 ) 2 ] ( 75 ). − This addition proceeded in CH 2 Cl 2 under reflux for 15–60 min (Scheme ) and led to the mono- and bis-addition trans -[PtCl 2 (NCR 3 )­{H N C­(R 3 )­ONCR 1 R 2 }] products ( 76 ; 40–62%; a) and trans -[PtCl 2 {H N C­(R 3 )­ONCR 1 R 2 } 2 ] ( 77 ; 45–52%; b and c), respectively, featuring monodentate coordinated O -iminoacylated oximes. These reactions were reported to give a 1:1 mixture of trans - and cis -isomers of the bis-addition products [PtCl 2 {H N C­(R 3 )­ONCR 1 R 2 } 2 ], but this statement requires additional confirmation, as cis/trans -isomerization has never been observed under similar conditions in similar systems. ,− The unstable imine HNC­(CH 2 CO 2 Me)­ONCMe 2 was liberated from 77 (R 1 /R 2 = Me/Me) by treatment of the complex with 2 equiv of dppe in CDCl 3 …”

Crystal structures of (E)-1-naphthaldehyde oxime and (E)-phenanthrene-9-carbaldehyde oxime

“…Oximes, HO-N CR 1 R 2 , are also valuable and simple reagents containing the O-N C moiety (Kukushkin & Pombeiro, 1999), which easily adds to nitrile ligands, to form a variety of nitrogen-containing products e.g. iminoacylated compounds (Kopylovich et al, 2009;Lasri et al, 2007Lasri et al, , 2008, amidines (Kopylovich et al, 2001), carboxamides (Kopylovich et al, 2002), phthalocyanines (Kopylovich et al, 2004), or 1,3,5-triazapentadiene species (Kopylovich et al, 2007). In this work, we report the synthesis and crystal structures of two aldoximes, viz.…”

Highly Stereoselective 1,3-Dipolar Cycloaddition of Nitrones to (Nitrile)2PtIISpecies Furnishing Diastereomerically Pure 2,3-Dihydro-1,2,4-oxadiazole Ligands

“…Given that one can envisage the preparation of a spectrum of chiral nitrones (or, on the contrary, chiral nitriles), it follows that the Pt II -mediated cycloaddition reactions could provide efficient routes to diastereomerically pure ligand systems. Previously, a relevant example of diastereomericaly pure (imine) 2 Pt II complex generated from (nitrile) 2 Pt II species via nucleophilic addition of chiral camphor-derived oxime was reported …”

“…Previously, a relevant example of diastereomericaly pure (imine) 2 Pt II complex generated from (nitrile) 2 Pt II species via nucleophilic addition of chiral camphor-derived oxime was reported. 63 Special attention should be drawn to the fact that platinum(II) complexes with 2,3-dihydro-1,2,4-oxadiazoles, where the heterocycles are mixtures of stereomers, are of biological importance, exhibiting antitumor properties. 64,65 Furthermore, we found a route for the decoordination of tetrahydro-5,8-methanocyclohexa[3 0 ,2 0 :4,5][1,3]oxazolo-[3,2-b][1,2,4]oxadiazoles to form a single enantiomer.…”