Iminoacylation. 3. Formation of Platinum(IV)-Based Metallaligands Due to Facile One-End Addition of vic-Dioximes to Coordinated Organonitriles^1-3

Abstract

The reaction of vic-dioximes with the organonitrile platinum(IV) complexes trans-[PtCl4(RCN)2] (R = Me, CH2Ph, Ph, vic-dioxime = dimethylglyoxime; R = Me, vic-dioxime = cyclohexa-, cyclohepta-, and cyclooctanedione dioximes) proceeds rapidly under relatively mild conditions and affords products of one-end addition of the dioximes to the nitrile carbon, i.e. [PtC4(NH=C(R)ON=[spacer]=NOH)2] (1-6) (R = Me, CH2Ph, Ph, spacer = C(Me)C-(Me) for dimethylglyoxime; R = Me, spacer = C[C4H8]C, C[C5H10]C, C[C6H12]C for the other dioximes), giving a novel type of metallaligand. All addition compounds were characterized by elemental analyses (C, H, N, C1, Pt), FAB mass spectrometry, and IR and 1H, 13C[1H], and 195Pt NMR spectroscopy. X-ray structure determination of the dimethylformamide bis-solvate [PtCl4(NH=C(Me)ON=C(Me)C(Me)=NOH)2] x 2DMF (la) disclosed its overall trans geometry with the dimethylglyoxime part in anti configuration and the amidine one-end (rather than N,N-bidentate) coordination mode of the N-donor ligands. When a mixture of cis- and trans-[PtC4(MeCN)2] in MeCN was treated with dimethylglyoxime, the formation of, correspondingly, cis- and trans-[PtCl4(NH=C(Me)ON=C(Me)C(Me)=NOH)2] (1) was observed and cis-to-trans isomerization in DMSO-d6 solution was monitored by 1H, 2D [1H,15N] HMQC, and 195Pt NMR spectroscopies. Although performed ab initio calculations give evidence that the trans geometry is the favorable one for the iminoacylated species [PtCl4-(ligand)2], the platinum(IV) complex [PtCl4(NH=C(Me)ON=C[C4Hs]C=NOH)2] (4) was isolated exclusively in cis configuration with the two metallaligand "arms" held together by intramolecular hydrogen bonding between the two peripheral OH groups, as it was proved by single-crystal X-ray diffractometry. The classic substitution products, e.g. [PtC12(N,N-dioximato)2] (12-15), are formed in the addition reaction as only byproducts in minor yield; two of them, [PtCl2(C7H11N2O2)2] (14) and [PtCl2(C8H13N2O2)2] (15), were structurally characterized. Complexes (12-15) were also prepared by reaction of the vic-dioximes with [PtCl4L(Me2SO)] (L = Me2SO, MeCN), but monoximes (Me2C=NOH, [C4H8]C=NOH, [C5H10]C=NOH, PhC(H)=NOH, (OH)C6H4C(H)= NOH) react differently adding to [PtCl4(MeCN)(Me2SO)] to give the corresponding iminoacylated products [PtCl4(NH=C(Me)ON=CRR')(Me2SO)](7-11).

Chemistry and Biological Activity of Platinum Amidine Complexes

“…The reaction of trans-[PtCl 2 (NCR) 2 ] (R= Me, Et, CH 2 Ph) with HN=C(NHPh) 2 gave [PtCl-{HN=C(NC(NHPh)=NPh)R}(NCR)] derivatives, but if the reaction is carried out for a prolonged time upon heating in the presence of 4 equiv HN=C(NHPh) 2 , the nucleophilic attack proceeds on both nitriles to yield the corresponding [Pt{HN=C(NC-(NHPh) = NPh)R} 2 ] derivatives containing two bidentate 1,3,5-triazapentadiene ligands. [73] The cyanoguanidine complex cis- [78,79] alcohols, [80,81] hydroxamic acid, [82] amino acid esters [83] ). Of particular synthetic relevance is the preparation of oxazolines by preliminary reaction of trans-[PtCl 4 (NCEt) 2 ] with amino alcohols H 2 NCRR 1 CR 2 R 3 OH having varying degrees of substitution at the methylene groups, which fosters selective nucleophilic attack by the ÀNH 2 moiety, subsequent liberation of the hydroxo-functionalized amidines by reaction with dppe, and final conversion of the amidine to the oxazoline promoted by zinc(II) chloride according to Scheme 12.…”

“…Pt IV centers provide a substantially stronger activation of RCN species upon metal coordination. Complexes of the type [PtCl 4 -(NCR) 2 ] are very reactive toward various protic nucleophiles HNu, achieving imino complexes [PtCl 4 {HN=C(Nu)R} 2 ] that are substantially inert toward substitution and hydrolysis (HNu = oximes, [78,79] alcohols, [80,81] hydroxamic acid, [82] amino acid esters [83] ). Of particular synthetic relevance is the preparation of oxazolines by preliminary reaction of trans-[PtCl 4 (NCEt) 2 ] with amino alcohols H 2 NCRR 1 CR 2 R 3 OH having varying degrees of substitution at the methylene groups, which fosters selective nucleophilic attack by the ÀNH 2 moiety, subsequent liberation of the hydroxo-functionalized amidines by reaction with dppe, and final conversion of the amidine to the oxazoline promoted by zinc(II) chloride according to Scheme 12.…”

Oxidative Addition of Cl2, HClO to Square‐Planar PtII Complexes: Synthesis and Structural Characterization of Platinum(II) and Platinum(IV) Bis(amidate) Complexes

“…The Pt-Cl bond lengths [2.324(8) and 2.328(7) Å for 5, 2.311(2) and 2.319(2) Å for 6] are in good agreement with other structurally characterized platinum chloride compounds. [13] The NH 3 and NH 2 groups in 5 and 6 are involved in intra-and intermolecular hydrogen bonding. The Cl-Pt-Cl angles [179.24(8) drally coordinated platinum() center in which the platinum atom is surrounded by three nitrogen and three chlorine atoms in a meridional fashion.…”

trans-Bis[(E)-acetoneO-propanimidoyloxime-κN′]tetrachloroplatinum(IV)

“…Previously, we have reported the crystal structures of trans-[PtCl 4 {NH C(R)ON CR 0 R 00 2 } 2 ] [R = R 0 = R 00 = Me (Kukushkin et al, 2000); R = Me, R 0 = Cl, R 00 = C 6 H 4 -4-NO 2 (Garnovskii et al, 2000); R = Me, R 0 = Cl, R 00 = p-Tol (Garnovskii et al, 2000); R = R 0 = Me, R 00 = C(Me) NOH (Kukushkin et al, 2000); R = Et, R 0 = Ph, R 00 = OH (Luzyanin et al, 2002); R = Et, R 0 = H, R 00 = Mes (Bokach et al, 2003); R = Et, R 0 = H, R 00 = COPh (Makarycheva-Mikhailova et al, 2003); R = Et, R 0 = MeO, R 00 = Mes (Luzyanin et al, 2004); R = Et, R 0 = Me, R 00 = C(Ph) NNH 2 (Garnovskii et al, 2004); R = Et, R 0 = Me, R 00 = C(Ph) NN CH(C 6 H 3 -2-OH-5-NO 2 ) (Garnovskii et al, 2004); R = Et, R 0 = Me, R 00 = COOEt (Luzyanin et al, 2005); R = Me, R 0 = R 00 = C 5 H 10 (Kukushkin et al, 1998)]. Here, we report the X-ray structure of one more representative of this class of compounds, the title complex trans- The coordination polyhedron of the centrosymmetric complex (I) (Fig.…”