Studies of amidines and their complexes with the nickel elements

Abstract

Amidines [RNC(R')NR, I] and their complexes of the nickel group metals have been studied. Accurate mass spectrometry applied to (R'=H, R=Ph; R'=CH(_3), R=Ph; R'=Ph=R) have given detailed fragmentation patterns which form the basis for the interpretation of related amidines. Differences in skeletal fragmentation patterns were noted between formamidines and acetamidines/benzamidines, (^1)H, (^13)C and (^19)F n.m.r. and mass spectroscopy of lithioamidines indicate a bidentate symmetrically bonded amidine. The reactions of amidines [RN(X)C(R^)NR] X=H, Li) with compounds of the nickel group metals, results in a wide variety of complexes; their nature depending on the amidine substituents, the metal and the synthetic route used. Complexes with N,N'chelate, or't/20-metallated, and bridging groups were prepared and characterised together with complexes containing new N,N'chelate and bridging groups, resulting from nucleophilic attack of an amidine at a coordinated nitrile. The reactions of M(PhCN)(_2)C1(_2) (M=Pd, Pt) and anhydrous NiC1(_2) with lithioamidines result in yellow Pt(Am)(_2), where Am = RNC(R')NR, red Pd(_2)(Am)(_4) and dark green Ni(_2)(Am)(_4) complexes. The platinum complexes are monomeric for the acetamidine (R'=CH(_3)), and benzamidine (R(_6)H(_5)) ligands, though for palladium the benzamidine complexes are dimeric. The nickel complexes are dimeric for the acetamidine,and benzamidine ligands. Spectroscopic studies indicate that the amidino-groups adopt a carboxylate type mode of bonding through the two nitrogen atoms, and the structure of one of the complexes, bis, N,N'diphenylbenzamicline-platinum(II) has been characterised by X-ray crystallography. The structure showed a monomeric PtN(_4) square planar unit. N.m.r. ((^19)F and (^13)C) studies have indicated fluxionality when M=Pd, R'=C(_6)H(_5), R=C(_6)H(_4)-F-p. With K(_2)MCl(_4)(M=Pd, Pt) and NiC1(_2), N,N'diarylamidines form polymeric ortho-metallated complexes, N,N' diarylformamidines and acetamidines form six-membered rings, benzamidines five-membered. Treatment of Pt(PhCN)(_2)C1(_2) with HN(Li)(C(_6)H(_5))NH results in nucleophilic attack at the nitrile and formation of Pt[HNC(C(_6)H(_5))NC(C(_6)H(_5))NH](_2). A similar reaction occurred with Pd(PhCN)(_2)C1(_2) and HNLiC(C(_4)(_9))NH.