Coordination of neutral, methylene bridged bis-guanidyls at palladium.

The bis-guanidyl compound H(2)C{hpp}(2) (hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) coordinates to palladium(ii) as a neutral, chelating N,N'-bidentate ligand. Structural analysis of PdMeCl(H(2)C{hpp}(2)) shows a non-planar metallacycle that is twisted relative to the square plane of the metal and an "anagostic" interaction with a C-H from the bridging methylene group. Generation of the cationic palladium complex, [PdCl(H(2)C{hpp}(2))][OTf] was achieved by halide abstraction from the dichloride PdCl(2)(H(2)C{hpp}(2)) using NaOTf. The product was identified as a mixture of different species in solution; in the solid-state, the molecular structure is dimeric, consisting of the mu,mu'-dichlorobridged dication. The new bis-guanidyl compound H(2)C{tbo}(2) (Htbo = 1,4,6-triaza-bicyclo[3.3.0]oct-4-ene) was synthesized, and structurally characterized. Coordination of this compound at palladium dichloride was accompanied by ionization of the Pd-Cl bond, and formation of the dication [Pd(H(2)C{tbo}(2))(2)][Cl](2). Structural analysis shows a significant reduction in the twisting of this ligand.

A structural, theoretical and coordinative evaluation of the bicyclic guanidinate derived from 1,4,6-triazabicyclo[3.3.0]oct-4-ene.

Partial deprotonation of the bicyclic guanidine 1,4,6-triazabicyclo[3.3.0]oct-4-ene (Htbo) is achieved using (n)BuLi. Isolation of the resulting lithium salts has resulted in the structural characterization of the mixed anion complex {[Li(tbo)(VIII)(tboH)](2)}(infinity) (where -H = 1-(2-aminoethyl)-2-imidazolidinethione) and the partially deprotonated salt Li(6)(tbo)(6)(Htbo)(3), 1b. The neutral guanidine Htbo reacts cleanly with AlMe(3) and ZnMe(2) to afford the organometallic complexes [Al(tbo)Me(2)](2) [2](2), and Zn(3)(tbo)(4)Me(2) (3). Structural characterization of these compounds enables comparison between the {5:5}-bicyclic system, [tbo](-), and the previously reported {6:6}-bicyclic system, [hpp](-) (where hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine). Results indicate that delocalization within the [tbo](-) anion is restricted to the CN(2) amidinate component, with retention of electron density in the non-bonding nitrogen lone-pair. These conclusions are supported by a DFT analysis of the neutral guanidines, Htbo and hppH.