Amidines Derived from Pt(IV)-Mediated Nitrile−Amino Alcohol Coupling and Their Zn(II)-Catalyzed Conversion into Oxazolines

Abstract

The reaction between the platinum(IV) complex trans-[PtCl(4)(EtCN)(2)] and the amino alcohols NH(2)CH(2)CH(2)OH, NH(2)CH(2)CH(Me)OH-(R)-(-), NH(2)CH(Ph)CH(2)OH-(R)-(-), NH(2)CH(Et)CH(2)OH-(R)-(-), NH(2)CH(Et)CH(2)OH-(S)-(+), and NH(2)CH(Pr(n)())CH(2)OH proceeds rapidly at room temperature in CH(2)Cl(2) to furnish the amidine complexes [PtCl(4)(HN=C(Et)NH(arcraise;)OH)(2)] (1-6) in good yield (70-80%). The related reaction between the platinum(II) complex trans-[PtCl(2)(EtCN)(2)] and monoethanolamine in a molar ratio of 1:2 in CH(2)Cl(2) results in the addition of 4 equiv of NH(2)CH(2)CH(2)OH per mole of complex to give [Pt(HN=C(Et)NHCH(2)CH(2)OH)(2)(NH(2)CH(2)CH(2)OH)(2)](2+) (7). Formulation of 1-6 is based upon satisfactory C, H, N elemental analyses, electrospray mass spectrometry, IR spectroscopy, and (1)H, (13)C((1)H), (15)N, and (195)Pt NMR spectroscopies, while the structures of trans-[PtCl(4)((Z)-NH=C(Et)NHCH(2)CH(2)OH)(2)] (1), trans-[PtCl(4)((Z)-NH=C(Et)NHCH(2)CH(Me)OH-(R)-(-))(2)] (2), and trans-[PtCl(4)((Z)-NH=C(Et)NHCH(Et)CH(2)OH-(R)-(-))(2)] (4) were determined by X-ray single-crystal diffraction. The Z-amidine configuration of the ligands is preserved in CDCl(3) solutions as confirmed by gradient-enhanced (15)N,(1)H-HMQC spectroscopy and NOE experiments. The amidines, formed upon Pt(IV)-mediated nitrile-amino alcohol coupling, were liberated from their platinum(IV) complexes 1, 3, and 4 by reaction with Ph(2)PCH(2)CH(2)PPh(2) (dppe) giving free NH=C(Et)NHCHRCH(2)OH (R = H 8, Et 9, Ph 10), with the substituents R of different types, and dppe oxides; the P-containing species were identified by (31)P((1)H) NMR spectroscopy. NOESY spectroscopy indicates that the liberated amidines retained the same configuration relative to the C=N double bond, i.e., syn-(H,Et)-NH=C(Et)NHCHRCH(2)OH. The liberated hydroxo-functionalized amidines 8-10 were converted into oxazolines (11-13) in the presence of a catalytic amount of ZnCl(2). A similar catalytic effect has also been reached using anhydrous MSO(4) (M = Cu, Co, Cd), CdCl(2), and AlCl(3).

Hetarylamidines derived from PtIV-mediated coupling of nitriles with aminoheterocycles

“…The 195 Pt{ 1 H} NMR spectra contain one broad singlet at δ 120-173, whose position is characteristic of Pt IV com plexes. 26 The 1 H, 13 C{ 1 H}, and 195 Pt{ 1 H} NMR spectro scopic data are in complete agreement with the structure containing the hetarylamidine fragment as the ligand. This structure is additionally confirmed by X ray diffraction study of complex 1.…”

“…These reactions readily proceed if nitrile substrates are coordinated to metal centers, such as Co III , 18 Cu I , 19 Rh III , 20 W II , 21 Re IV , 22 Ir I , 23 Pt II , or Pt IV . [24][25][26] Amino derivatives of heterocycles have found limited use in metal mediated reactions. 27-30 This is apparently associated with the fact that most of reactions of metal salts with aminoheterocycles stop at complexes, in which amino ligands are coordinated by the endocyclic nitrogen atom.…”

Chemistry and Biological Activity of Platinum Amidine Complexes

“…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. [84] Interestingly, the conversion of Pt II -coordinated nitriles to oxazolines [85] and oxazines [86] was previously reported to occur through addition of ClCH 2 The study of the addition of diphenylguanidine to Pt IV -coordinated nitriles shows that the reaction proceeds more rapidly (completion within a few minutes) than for Pt II (completion in a few hours), with the formation of the corresponding 1,3,5-triazapentadienate derivative according to Scheme 13.…”

Coordination Aspects in Modern Inorganic Chemistry

“…Reactions of coordinated inorganic and organic ligands are of the high interest. In particular, in 1998-2007 reactivity of such ligands as nitriles (RCN) and oximes, coordinated to the ion Pt(IV) is intensively studied [50][51][52][53][54][55][56][57][58][59][60][61][62]. The main attention in these studies is given to the reactions of nucleophylic addition of various nucleophiles on the carbon atom of triple CN-bond of the nitrile fragment, whose electrophylic activation was reached because of its coordination to Pt(IV) 96.…”