Klaus Eichele Publication Abstracts 2005

The cationic tropylium [(PCP')Ir(CO)(H)(Cl)]⁺ complex (4) (PCP' = [2,7-(CH₂P^tBu₂)₂C₇H₄]⁺) is generated from the neutral cycloheptatriene pincer complex (PCP)Ir(CO)(H)(Cl) (1) (PCP = 2,7-(CH₂P^tBu₂)₂C₇H₅) by a hydride abstraction from the CH-Ir fragment with 1 equiv of trimethylsilyl trifluoromethanesulfonate. Interestingly, the tropylium ligand backbone in complex 4 is deprotonated by a base to give the neutral Ir(III) compound (PCP'')Ir(CO)(H)(Cl) (5) (PCP'' = 2-(CHP^tBu₂)-7- (CH₂P^tBu₂)C₇H₄) with a p-system that extends into one of the phosphine bridges. Finally treatment of 5 with a further equivalent of a base removes HCl from the iridium center, forming the Ir(I) complex 6 with the same ligand backbone as in 5. The HCl elimination and the deprotonation reactions are reversible. Thus addition of 2 equiv of HCl to 6 gives at first 5 then the tropylium complex 7, which differs from 4 only by the counterion. The seven-membered aromatic tropylium system in 4 coordinates to the Mo(CO)₃ fragment, generating the bimetallic complex [(CO)₃Mo(h⁷-PCP')Ir(CO)(H)(Cl)]⁺ (8). Quantum chemical calculations at various levels of theory illustrated the relative energetic stabilities of all iridium complexes.

The 2-methylenimidazolines ImC(CN)₂ (6a–c, Im = 1,3-dialkyl-4,5-dimethylimidazol-2-ylidene) are prepared by the reaction of the imidazolium salts [ImBr]Br (5) and malodinitrile while ImC{C(O)Ph}₂ (7) is obtained from ImCH₂ (2) and benzoic fluoride. Both the structural data of 6b, 6c, and 7 and the ¹³C NMR data demonstrate the influence of steric and electronic effects on the charge separation and the nonplanar arrangement of the substituents attached at the carbon atoms of the central olefinic bond.