I. The Reduction of Molecular Nitrogen in Binuclear Dinitrogen Complexes of Titanium and Zirconium. II. Hydrogen Reduction of Carbon Monoxide Promoted by Mononuclear Carbonyl and Hydride Complexes of Bis(Pentamethylcyclopentadienyl) Zirconium

I. The Reduction of Molecular Nitrogen in Binuclear Dinitrogen Complexes of Titanium and Zirconium. II. Hydrogen Reduction of Carbon Monoxide Promoted by Mononuclear Carbonyl and Hydride Complexes of Bis (pentamethylcyclopentadienyl) Zirconium. PART I The synthesis and characterization of (ƞ5-C5Me5) 2ZrCl2 (1), (ƞ5-C5Me5) 2ZrN22N2 (2), (ƞ5-C5Me5) 2Zr (CO) 2N2 (3), and (ƞ5-C5Me5) 2Zr (PF3) 2N2 (4) are described. 1 is prepared from lithium pentamethylcyclopentadienide and zirconium tetrachloride. Sodium amalgam reduction of 1 under N2 yields 2. 3 and 4 are prepared by substitution of the two terminal dinitrogen ligands by CO and PF3, respectively. In solution 2 (and 4) exhibits fluxional behavior. The dynamics of 2 in solution as studied by 1H and 15N NMR shows that 2 undergoes ƞ5-C5Me5 ring site exchange as a result of the !ability of the terminal dinitrogen ligands. A re-investigation of the titanium system analog in solution showed that the complex, originally assigned the formula (ƞ5-C5Me5) 2TiN2, is in fact analogous to the zirconium complex i. e. ƞ5-C5Me5) 2TiN22N2 (5). The product distribution (N2H4, NH3) for the reaction of 2, 3, 4, 5, and ƞ5-C5Me5) 2TiN22N2 (6) with anhydrous HCl in toluene is reported. Hydrazine obtained in high yields obtained from the reaction of 2 and 5 with HCl. 6 also gives hydrazine but in much lower yield. Under the same conditions the reaction with HCl for the complexes 3 and 4 results in the quantitative release of the dinitrogen and partial reduction of the terminal ligands. The product distribution for the reaction of 2 with HBr, HCl, and H2SO4 each being carried out in toluene, diethyl ether and methanol is also reported. 2- (15N2) 3 exchanges only terminal dinitrogen ligands with free 14N2 in toluene solution at -23°. Treatment of 2 which is labelled with 15N2 exclusively in the bridge position yields 1. 5 mols 14N2, 0. 5 mol 15N2, 0. 5 mol 14N2H4. The implications of these data with regard to the N2 reduction sequence are discussed. The reactions of 2, 3, 4, and 6 with LiAlH4 are reported. 2 gives hydrazine (0. 5 mol) and ammonia (1 mol) after hydrolysis of the reaction products with HCl. 6 also gives hydrazine and ammonia but in lower yield. Under the same conditions the reaction of 3 and 4 results in the evolution of most of the dinitrogen. A study of the reaction of 2 labelled with 15N2 exclusively in the bridge position showed that the hydrazine and ammonia originate from the bridge position. PART II The synthesis and characterization of (ƞ5-C5Me5) 2Zr (CO) 2 (1), (ƞ5-C5Me5) 2ZrH2 (2), and C5 (CH3) 5 C5 (CH3) 4CH2ZrH prepared from ƞ5-C5Me5) 2ZrN22N2 are described. Both 1 and ƞ5-C5Me5) 2Zr (CO) 2N2 react with H2 forming (ƞ5-C5Me5) 2Zr (H) (OCH3) (4) in high yield. 2 reacts with CO and PF3 at -80° to yield (ƞ5-C5Me5) 2Zr (H) 2 (CO) (3) and (ƞ5-C5Me5) 2Zr (H) 2 (PF3). 3 dimerizes to (ƞ5-C5Me5) 2ZrH2 (µ-OCH=CHO) aboce -50°. In the presence of 2, 3 may be reduced to 4. These observations are interpreted in terms of a reaction sequence mediated by the formyl hydride complex (ƞ5-C5Me5) 2Zr (H) (CHO) derived from 3 via migratory insertion. The reaction of 2 with formaldehyde on an equal molar basis produces a mixture of 4 and (ƞ5-C5Me5) 2Zr (OCH3) 2. The implications of these results with respect to the possible intermediacy of formaldehyde in the formation of 4 and the plausible mechanisms for the formation of 4 and (ƞ5-C5Me5) 2ZrH2 (µ-OCH=CHO) are discussed. The synthesis of (ƞ5-C5Me5) 2HfCl2 and (ƞ5-C5Me5) 2HfH2 are reported. A comparison of the bis (pentamethylcyclopentadienyl) hydrides of group IV with the bis (cyclopentadienyl) hydrides of groups V, VI, and VII is made. The possible determining factor in the rearrangement of 3 to (ƞ5-C5Me5) 2Zr (H) (CHO) is discussed.