Pop-the-Cork Strategy in Synthetic Utilization of Imines:  Stabilization by Complexation and Activation via Liberation of the Ligated Species

Abstract

Treatment of trans-[PtCl(4)(RCN)(2)] (R = Me, Et) with ethanol allowed the isolation of trans-[PtCl(4)[E-NH[double bond]C(R)OEt](2)]. The latter were reduced selectively, by the ylide Ph(3)P[double bond]CHCO(2)Me, to trans-[PtCl(2)[E-NH[double bond]C(R)OEt](2)]. The complexed imino esters NH[double bond]C(R)OEt were liberated from the platinum(II) complexes by reaction with 2 equiv of 1,2-bis(diphenylphosphino)ethane (dppe) in chloroform; the cationic complex [Pt(dppe)(2)]Cl(2) precipitates almost quantitatively from the reaction mixture and can be easily separated by filtration to give a solution of NH[double bond]C(R)OEt with a known concentration of the imino ester. The imino esters efficiently couple with the coordinated nitriles in trans-[PtCl(4)(EtCN)(2)] to give, as the dominant product, [PtCl(4)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)] containing a previously unknown linkage, i.e., ligated N-(1-imino-propyl)-alkylimidic acid ethyl esters. In addition to [PtCl(4)[NH[double bond]C(Et)N[double bond]C(Et)OEt](2)], another compound was generated as the minor product, i.e., [PtCl(4)(EtCN)[NH[double bond]C(Et)N[double bond]C(Et)OEt]], which was reduced to [PtCl(2)(EtCN)[NH[double bond]C(Et)N[double bond]C(Et)OEt]], and this complex was characterized by X-ray single-crystal diffraction. The platinum(IV) complexes [PtCl(4)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)] are unstable toward hydrolysis and give EtOH and the acylamidine complexes trans-[PtCl(4)[Z-NH[double bond]C(Et)NHC(R)[double bond]O](2)], where the coordination to the Pt center results in the predominant stabilization of the imino tautomer NH[double bond]C(Et)NHC(R)[double bond]O over the other form, i.e., NH(2)C(Et)[double bond]NC(R)[double bond]O, which is the major one for free acylamidines. The structures of trans-[PtCl(4)[Z-NH[double bond]C(Et)NHC(R)[double bond]O](2)] (R = Me, Et) were determined by X-ray studies. The complexes [PtCl(4)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)] were reduced to the appropriate platinum(II) compounds [PtCl(2)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)], which, similarly to the appropriate Pt(IV) compounds, rapidly hydrolyze to yield the acylamidine complexes [PtCl(2)[NH[double bond]C(Et)NHC(R)[double bond]O](2)] and EtOH. The latter acylamidine compounds were also prepared by an alternative route upon reduction of the corresponding platinum(IV) complexes. Besides the first observation of the platinum(IV)-mediated nitrile-imine ester integration, this work demonstrates that the application of metal complexes gives new opportunities for the generation of a great variety of imines (sometimes unreachable in pure organic chemistry) in metal-mediated conversions of organonitriles, the "storage" of imino species in the complexed form, and their synthetic utilization after liberation.

Four-coordinate and pseudo five-coordinate Hg(II) complexes of a new bidentate phosphorus ylide: X-ray crystal structure and spectral characterization

“…These compounds have been used as reducing agents in coordination chemistry. The utility of metalated phosphorus ylides in synthetic chemistry has been well documented [2][3][4][5]. The a-keto stabilized ylides derived from bisphosphines, viz., Ph 2 PCH 2 PPh 2 @C(H)C(O)R, Ph 2 P-(CH 2 ) 2 PPh 2 @C(H)C(O)R (R = Me, Ph or OMe) [6] and PhC(O)C(H)@ PPh 2 CH 2 CH 2 PPh 2 @C(H)C(O)Ph [7] form an important class of hybrid ligands containing both phosphine and ylide functionalities, and can exist in ylidic and enolate forms.…”

Chemistry and Biological Activity of Platinum Amidine Complexes

“…[94] Notably, the strategy based on stabilization by complexation, activation toward designed reactions, and liberation of the ligated species appears to be a general tool in the synthetic use of imines. [95] Biological Activity…”

Crystal Structure of Diiodo, (4'-Chlorobenzoylmethylenetriphenylphosphorane), (dimethylsulfoxide), Mercury(II) Complex, C28H26ClHgI2O2PS

“…2,3 Single-crystal X-ray diffraction analysis was performed on a STOE IPDS-II two-circle diffractometer at 293 K, using graphite-monochromated Mo Ka X-ray radiation (l = 0.7107 Å). Data collection was performed at room temperature using the q-scan technique and the STOE X-AREA software package.…”

“…Table 1 vary from 81.73(19) to 132.80(13), indicating a greatly distorted tetrahedral environment. This distortion must be due to the higher s character of the sp 3 hybrid mercury orbitals involved in the above-mentioned bonds and the steric effects of the phosphine group, needing the C-Hg-I angle to be larger. A structural study also indicates that DMSO had unprecedented bonded to the metal via its O atom.…”