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Mononuclear Metallacyclic Silver(I) Complexes of Third Generation Bis(1-pyrazolyl)methane Ligands

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journal contribution
posted on 02.02.2009, 00:00 by Daniel L. Reger, Elizabeth A. Foley, Mark D. Smith
The third-generation bis(1-pyrazolyl)methane ligands p-C6H4[CH2OCH2CH(pz)2]2 (Lp, pz = pyrazolyl ring) and m-C6H4[CH2OCH2CH(pz)2]2 (Lm) have been synthesized by the reaction of (pz)2CHCH2OH with NaH followed by α,α′-dibromo-p-xylene or α,α′-dibromo-m-xylene. The reaction of Lp with AgBF4, AgPF6, and AgO3SCF3 yields the new compounds {Ag[p-C6H4(CH2OCH2CH(pz)2)2]}BF4, {Ag[p-C6H4(CH2OCH2CH(pz)2)2]}PF6, and {Ag[p-C6H4(CH2OCH2CH(pz)2)2]}O3SCF3, respectively. A similar reaction of Lm with AgBF4 and AgPF6 yields {Ag[m-C6H4(CH2OCH2CH(pz)2)2]}BF4 and {Ag[m-C6H4(CH2OCH2CH(pz)2)2]}PF6. These compounds were crystallized from both acetone and acetonitrile to yield nine crystalline forms of (LAg)+ that differ in counterion and solvent of crystallization. In all complexes, the four pyrazolyl rings of the ligand chelate a single silver(I) cation in a distorted tetrahedral environment to form mononuclear metallacycles. This arrangement has not previously been observed with the analogous ligands based on tris(1-pyrazolyl)methane units and is unique because of the ring sizes (16-member rings in Lm and 17-member rings in Lp). The dominant feature in all of these solid state structures, regardless of solvent or anion, is this cationic metallacyclic architecture, which does not readily lend itself to strong supramolecular organization.