Metal Template Controlled Formation of [11]ane-P₂C^NHC Macrocycles

The synthesis of N-heterocyclic carbene-diphosphine macrocycles by metal template assisted cyclization reactions has been explored. Attempts to prepare the facial tungsten tricarbonyl precursor complex containing an NH,NH-functionalized carbene and a suitable diphosphine resulted in displacement of the coordinated carbene and the isolation of the corresponding diphosphine tungsten tetracarbonyl [3]. The ReI chloro tetracarbonyl complex bearing an NH,NH-functionalized carbene ligand [5] can be prepared and is a suitable precursor for the subsequent formation of the carbene-diphosphine tricarbonyl intermediate [H2-6]Cl bearing reactive 2-fluoro substituents at the phosphine-phenyl groups. Two of these fluoro substituents are displaced by a nucleophilic attack upon deprotonation of the coordinated NH,NH-functionalized carbene resulting in new C−N bonds resulting in the partially coupled intermediate, [10], followed by the desired complex with the macrocyclic ligand [8]Cl. Compounds [H-7]Cl and [8]Cl are also formed during the synthesis of [H2-6]Cl as a result of spontaneous HF elimination. Complex [8]+ may be converted to the neutral dicarbonyl chloro analog [11] by action of Me3NO. Related chemistry with analogous manganese complexes is observed. Thus, from the NH,NH-functionalized carbene manganese bromo tetracarbonyl [12], the diphosphine manganese carbene tricarbonyl cation [H2-13] may be readily prepared which provides the macrocyclic carbene-diphosphine tricarbonyl cation [14]+ following base promoted nucleophilic intramolecular displacement of fluoride. Again, [14]+ is converted to the neutral bromo dicarbonyl upon reaction with Me3NO. All complexes with the exception of the reaction intermediate [10] have been characterized by spectroscopic and analytical methods in addition to X-ray crystallographic structure determinations for complexes [3], [5], [H2-6]Cl, [H2-6][9], [8]Cl, [10], [11], [12], and [14]Br.