The First Metal Complexes of the Proton Sponge 1,8-Bis(N,N,N′,N′- tetramethylguanidino)naphthalene: Syntheses and Properties

In this work we report on the syntheses and properties of the first transition metal complexes of the proton sponge 1,8-bis(N,N,N',N'-tetramethylguanidino)naphthalene (btmgn). Of the three complexes [(btmgn)PdCl2], [(btmgn)PtCl2] and [(btmgn)PtCl2(C2H4)], the first two feature a chelating btmgn ligand that is bound to the metal atom through two nitrogen atoms. Only one metal-N bond is established in [(btmgn)-PtCl2(C2H4)]. The molecular structures of [(btmgn)PdCl2] and [(btmgn)PtCl2] show some interesting details. X-ray crystallographic studies reveal that the naphthyl aromatic systems in both complexes are not planar, the metal atoms reside above the best-plane of the naphthyl systems and the compounds adopt a chiral conformation in the crystalline phase. Several dynamic processes of the two guanidinyl groups in solution were identified by line-shape analysis of the temperature-dependent NMR spectra. The complex [(btmgn)-PtCl2(C2H4)] eliminates ethylene at elevated temperature to give [(btmgn)PtCl2]. Quantum chemical (DFT) calculations indicate that the Delta G(0) value for this reaction is close to zero. Indeed the compound [(btmgbp)PtCl2] {btmgbp = 2,2'-bis(N,N,N',N'-tetramethylguanidino)biphenyl} in which the naphthyl group is replaced by a biphenyl group is not amenable to ethylene elimination. First experiments; point to interesting catalytic properties of the new complexes. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)