ABSTRACT
Purine nucleobases are excellent ligands for metal ions, forming normally coordinative Werner-type bonds by utilizing the N donor atoms of the nucleobase skeleton. Here we show that purines such as 8-chlorocaffeine and 8-bromo-9-methyladenine react with [Pt(PPh3)4] under oxidative addition of the C(8)-halogen bond to the metal center. The resulting Pt(II) complexes feature a C(8)-bound ylidene ligand. Protonation of the ylidene at the N(7/9)-atom yields complexes bearing a protic N-heterocyclic carbene ligand derived from the purine base with an NMe,NH-substitution pattern.
Subject(s)
Metals/chemistry , Purines/chemical synthesis , Heterocyclic Compounds/chemistry , Magnetic Resonance Spectroscopy , Models, Molecular , Platinum Compounds/chemical synthesis , Platinum Compounds/chemistry , Purine Nucleosides/chemistry , Purine Nucleotides/chemistry , Purines/chemistry , X-Ray DiffractionABSTRACT
The chemistry of heterocyclic carbenes has experienced a rapid development over the last years. In addition to the imidazolin-2-ylidenes, a large number of cyclic diaminocarbenes with different ring sizes have been described. Aside from diaminocarbenes, P-heterocyclic carbenes, and derivatives with only one, or even no heteroatom within the carbene ring are known. New methods for the synthesis of complexes with N-heterocyclic carbene ligands such as the oxidative addition or the metal atom template controlled cyclization of beta-functionalized isocyanides have been developed recently. This review summarizes the new developments regarding the synthesis of N-heterocyclic carbenes and their metal complexes.
ABSTRACT
Facile access to the eta2-alkyne-1-thio complexes [Tp'M(CO)2{eta2-(BnS)CC(S)}] (Tp' = hydrotris(3,5-dimethylpyrazolyl)borate; Bn = benzyl; M = Mo, W) by reductive removal of one benzyl group in the corresponding bis(benzylthio)acetylene complexes, [Tp'M(CO)2{eta2-(BnS)CC(SBn)}](PF6), has been thoroughly investigated. Experimental evidence of the intermediates, [Tp'M(CO)2{eta2-(BnS)CC(SBn)}] (M = Mo, W), and the fate of the cleaved benzyl group by isolation of the byproduct, [Tp'W(CO){C(O)Bn}{eta2-(BnS)CC(SBn)}], is provided. Neutral eta2-alkyne-1-thio complexes [Tp'M(CO)2{eta2-(BnS)CC(S)}] bearing a free terminal sulfur atom have been established as monodentate ligands L in homoleptic pentanuclear [M'L4]2+ complexes with nickel(II) and palladium(II). Comparison of the NMR and IR spectroscopic as well as cyclovoltammetric data of the heterobimetallic complexes with the free thio-alkyne complexes reveals a strong electronic coupling of the redox-active eta2-CC-bound metal centers and the sulfur-coordinated metal ion.
