SYNTHESIS AND CHARACTERIZATION OF CP2ZR(CH(ME)(6-ETHYLPYRID-2-YL))(CO)+, A D(0) METAL ALKYL CARBONYL COMPLEX - COORDINATION CHEMISTRY OF THE 4-MEMBERED AZAZIRCONACYCLE CP2ZR(ETA-2-C,N-CH(ME)(6-ETHYLPYRID-2-YL))+

The cationic complex Cp2Zr(CH3)(THF)+ (1, as the BPh4- salt) reacts with 2,6-diethylpyridine to afford the chelated secondary zirconocene-alkyl complex Cp2Zr(eta2-C,N-CH{Me}{6-ethylpyrid-2-yl})+ (2). Treatment of complex 2 with CO, CH3CN, (t)BuCN, and (PhCH2)(Et)3N+Cl- affords CP2Zr(CH{Me}{6-ethylpyrid-2-yl})(CO)' (3), CP2Zr(CH{Me}{6-ethylpyrid-2yl})(CH3CN)+ (4), Cp2Zr(CH{Me}{6-ethylpyrid-2-yl})(BuCN)+ (5), and Cp2Zr(CH{Me}{6-ethylpyrid-2-yl})(Cl) (6), respectively. The thermally sensitive d0 carbonyl complex 3 is a rare example of a d0 M(alkyl)-CO adduct and is unambiguously characterized in solution by low-temperature NMR and IR spectroscopy, C-13-labeling and hydrolysis experiments, and decomposition studies. IR and NMR data establish that 3 contains a terminal CO ligand. An X-ray structure analysis of 6 establishes that the CH(Me)(6-ethylpyrid-2-yl) ligand adopts a chelated structure; the similarity of the spectroscopic data for 3-6 implies that 3-5 have similar chelated structures. At room temperature, 3 in CD2Cl2 rapidly decomposes to afford a complex mixture of products, H-1 NMR monitoring of the decomposition of 3 reveals formation of a transient cationic zirconocene-acyl intermediate 9, which undergoes 1,2-H shift to afford a mixture of isomeric/oligomeric zirconocene-enolates. Treatment of this mixture with (PhCH2)(Et)3N+Cl- affords CP2Zr(OCH=C{Me}{6-ethylpyrid-2-yl})Cl (10) as a mixture of E/Z isomers, establishing the presence of zirconocene-enolate species. Hydrolysis of the decomposition products of 3 affords a mixture of thermally sensitive tautomers, enol 11/aldehyde 11', which are characterized by NMR, FTIR, and mass spectroscopy.