Facile Ni(II)/Ketoxime-Mediated Conversion of Organonitriles into Imidoylamidine Ligands. Synthesis of Imidoylamidines and Acetyl Amides

Abstract

Treatment of alkyl nitriles with NiX(2).6H(2)O (X = Cl, NO(3)) and 2-propanone oxime, followed by (X = Cl) addition of [i-Pr(4)N](NO(3)) for precipitation of the product, resulted in the formation of amidinium nitrates [RC([double bond]NH(2))NH(2)](NO(3)) (R = Me, Et, n-Pr). The reaction went to another direction with NiX(2).2H(2)O, i.e., the reaction between neat RCN (R = Me, Et, n-Pr, i-Pr, n-Bu, CH(2)Cl, CH(2)C(6)H(4)OMe-p) and NiCl(2).2H(2)O/2-propanone oxime (other ketoximes can also be used) gave the (imidoylamidine)Ni(II) complexes [Ni[N(H)[double bond]C(R)NHC(R)[double bond]NH](2)](2+) (1(2+)-7(2+)). The latter were isolated in good yields (65-91%) as the bis-chloride salts 1.Cl(2)-6.Cl(2) and the mixed salt 7.(Cl)(p-MeOC(6)H(4)CH(2)CO(2)). Remarkably, the latter transformation does not proceed at all if NiCl(2).2H(2)O or the ketoxime are taken alone. Liberation of imidoylamidines was performed for one alkyl-containing complex [2.Cl(2)] and one benzyl-containing complex [7.(Cl)(p-MeOC(6)H(4)CH(2)CO(2))], by (i) addition of HBF(4).Et(2)O to the acetonitrile solution of the complexes to yield [N(H)[double bond]C(R)NHC(R)[double bond]NH].2HBF(4) (R = Et 8 and R = CH(2)C(6)H(4)OMe-p 9) or (ii) substitution for ethanediamine (en) with following precipitation of the complex [Ni(en)(3)]Cl(2) with formation of free N(H)[double bond]C(R)NHC(R)[double bond]NH (R = Et 10 and R = CH(2)C(6)H(4)OMe-p 11). In contrast to the liberation in nonaqueous media, treatment of 2.Cl(2) and 7.(Cl)(p-MeOC(6)H(4)CH(2)CO(2)) with Na(2)EDTA.2H(2)O in water-methanol solutions led to substitution and hydrolysis to furnish the acyl amides [EtC([double bond]O)](2)NH (12) and [p-MeOC(6)H(4)CH(2)C([double bond]O)](2)NH (13). Alternatively, 12 and 13 were obtained by hydrolysis of 10 and 11 in water at pH ca. 8.5. It was shown that the oxime complexes trans-[NiCl(2)(C(4)H(8)C[double bond]NOH)(4)] (14) or cis-[Ni(O,O-NO(3))(2)(C(4)H(8)C[double bond]NOH)(2)] (15) can be intermediates in the formation of amidines and imidoylamidines. The sequence of the Ni(II)/oxime mediated formation of (imidoylamidine)Ni complexes and liberation (or hydrolytic liberation) of the ligands opens up a novel, facile and environmentally benign route to imidoylamidines and acyl amides.

Unsymmetrical NiII–Imidoylamidine Complexes Derived from a Novel Oxime‐Mediated Single‐Pot Reaction of Nitriles

“…We show here that a combination of previously described conversions of nitriles (mediated by oximes at Ni centers) to furnish symmetrical imidoylamidines [8] (Scheme 1, route I) and phthalocyanines [13] (route II), by using a mixture of alkylnitrile with phthalonitrile (route III), provides an easy single-pot entry to a series of new unsymmetrical bisimido- , respectively, as well as some additional vibrations due to n(CH) (2970-1850 cm À1 ) and [8][9][10] The molecular structures of complexes 1-4 ( Figure 1) show a square-planar coordination environment around a centrosymmetric Ni centre, whereas the planarity of whole molecules depends on the R substituent. Thus, those with R = Me (1) and Et (2) are entirely planar, but in complexes 3 and 4 the propyl groups lie partially in other planes.…”

“…At the same time, following our studies on the Zn II -and Co II -ketoxime-mediated transformations of nitriles to carboxamides, carboxylic acids and amidines, [7] and applying a similar synthetic strategy to the Ni II -ketoxime system, we have achieved an easy conversion of various alkylnitriles (RCN) into imidoylamidine complexes [Ni{N(H)= C(R)NHC(R)=NH} 2 ] 2 + . [8] The family of such compounds has been recently extended [9,10] to other metals and various substituent groups (R) by using direct synthetic procedures based on nitriles, which include the solvothermal transformation of RCN [9a,b] and arylnitrile coupling with LiN-…”

“…Although some of the above-mentioned pathways for imidoylamidines are quite attractive (especially those which involve direct transformations of cheap and industrially available synthons like nitriles), [6,8,9] many of them still display significant drawbacks, such as the harsh reaction condi-A C H T U N G T R E N N U N G tions, [9a,b] low yields and selectivities, [6, 9a,b] require uncommon, expensive or/and moisture sensitive chemicals [9c, 10d-f] or particular metal complexes with complicated ligands, [6] and/ or involve amidines [4, 5a, 10a,e,f] and triazines, [5b, 10b,c] compounds obtained by the hazardous two-stage Pinner syntheses. [11] All the more important is that most of the synthesised "genuine" imidoylamidine complexes are symmetrical (B with equal R groups; Scheme 1, route I) and only rare examples of unsymmetrical imidoylamidines (namely generated on Pt centers by nitrile-amidine coupling) have been obtained.…”

Crystal structure of dichloro{[anilino(phenylimino)methyl]- (propanimidoyl)azanide}-[η2-(N,N′-diphenylguanidinato)]platinum(IV) – deuterochloroform (1:1), PtCl2(C13H12N3)(C16H17N4) · CDCl3

“…However, this interatomic distance is typical (within 3s)for this type of 1,3,5-triazapentadiene-and/or 1,3,5-triazapentadienato-containing metallacycles, and is comparable with the lengths of the corresponding C=N double bonds in the monochelated and bischelated (1,3,5-triazapentadienato)Pt II complexes [1]a nd the monochelated (1,3,5-triazapentadienato)Pt IV complex [2]. The N=C double bond lengths and the N-Csingle bond lengths in the metallacycle, in contrast to complexes of the types (1,3,5-triazapentadiene)M and/or (1,3,5-triazapentadienato)M (M =Pt II or Ni II ) [1,3,4], are indicative of ahigher degree of delocalization in the metallacycle. The N3-C7 bond distance (1.370 (2) Å)issimilar to the length of the corresponding N-Csingle bond in Pt II and Pt IV complexes containing the analogous structural fragment, i.e.…”

“…The N4-C14 and N4-C7 bond lengths (1.330(3) and 1.334(2) Å,r espectively) are close to the N-C bond lengths in Pt II and Pt IV complexes containing the Pt-N(H)=C(Et)NC(N(H)Ph)=NPh moiety [1,2]. The N1-C7 distance (1.333(2) Å)islonger than atypical N=C double bonds in the (1,3,5-triazapentadiene)M and/or (1,3,5-triazapentadienato)M (M =Pt II or Ni II )complexes [1,3,4], due to the influence of the N(H)Ph group. However, this interatomic distance is typical (within 3s)for this type of 1,3,5-triazapentadiene-and/or 1,3,5-triazapentadienato-containing metallacycles, and is comparable with the lengths of the corresponding C=N double bonds in the monochelated and bischelated (1,3,5-triazapentadienato)Pt II complexes [1]a nd the monochelated (1,3,5-triazapentadienato)Pt IV complex [2].…”