Group 4 metal polyhydrides: synthesis, structure and reactivity of tetrakis(pentamethylcyclopentadienylhafnium dihydride chloride)

Abstract

The polyhydride [Cp*HfHzC1]42 waa prepared by high-pressure hydrogenation of Cp*Hf(C6Hlo)C1 (C6H10 = 2,3-dimethyl-l,3-butadiene) or Cp*Hf(COT)Cl (COT = cyclooctatetraene). The structure of [Cp*HfH2C1], was determined by X-ray diffraction. The compound crystallizes in the tetragonal space group P42'm with a = 21.454 (3) A, c = 10.525 (3) A, and Z = 4. The structure was refined to R = 0.030 and R, = 0.039 for 303 parameters and 2839 reflections with I > 2.5a(T). The molecule has four Hf atoms in a butterfly arrangement with alternating Cp* and C1 ligands (Hf-Ct = 2.15,2.23, and 2.27 A; Hf-Cl = 2.397 (3), 2.438 (3), and 2.432 (3) A). Hydride positions could not be found due to disorder in one of the Cp* ligands probably caused by the presence of a benzene solvate molecule. IR and NMR studies indicate the presence of two sets of four equivalent hydrides bridging the edges of a Hf4 butterfly arrangement. Bridging hydride ligands account for the low reactivity of the complex.

The Anionic Zirconocene Trihydride: [Cp*2ZrH3]-

“…1 H NMR (THF-d8, 25 °C): 1.95 (s, 30H), 1.46 (t, 1H, |JH-H| ) 18 Hz), 1.11 (d, 2H, |J H-H| ) 18 Hz). 13 Synthesis of [Cp* 2ZrH3]Li (4). (i) A suspension of 3 (59 mg, 0.16 mmol) and LiH (13 mg, 1.6 mmol) in THF (5 mL) was stirred at room temperature for 5 days.…”

“…1 H NMR (C7D8, -23 °C): 4.79 (s, 2H), 3.88 (s, 1H), 2.01 (s, 30H), -1.44 (s, 1H), -1.93 (s, 1H). 13 (5-d5) was prepared by the same method as above, using LiAlD 4 in the reduction. 1 H NMR (C 6D6, 25 °C): 2.08 (s, 30H).…”

“…Other Ti, Zr, and Hf metallocene hydride complexes have been prepared and characterized. While sterically less demanding ancillary ligands result in dimeric or polymeric complexes of the form [Cp 2 MH 2 ] n , − species such as Cp* 2 MH 2 are monomeric. − In a similar vein, monocyclopentadienyl complex hydrides such as [Cp*ZrH 2 (BH 4 )] 2 , Cp* 2 Zr 2 H 3 Cl 3 (PMe 3 ), and [Cp*HfH 2 Cl] 4 form dimers and tetramers, respectively. Monomeric and dimeric Zr and Hf polyhydride species such as M 2 H 3 (BH 4 ) 5 (PMe 3 ) 2 , MH(BH 4 ) 3 (dmpe), and MH 2 (BH 4 ) 2 (dmpe) 2 have also been described 14 as well as complexes of the form Hf 2 H 3 (BH 4 ) 3 (npp) 2 and Hf 2 H 4 (BH 4 ) 2 (npp) 2 …”

Syntheses and structures of Zr4tetrahedral clusters containing direct Zr–Zr bonds: the missing cluster in the series Zrn(n = 2–6)

“…8 Its Hf analog, [Cp*HfH 2 Cl] 4 , has been prepared by Teuben's group. 9 They found this hafnium polyhydride to be rather chemically inert. As zirconium and hafnium compounds always possess similar chemical properties, we were interested in exploring the reactivity of this Zr(IV) tetranuclear polyhydride.…”

“…is similar to its Hf analog, as described by Teuben's group. 9 Although an excess amount of sodium amalgam was used, the complete transformation of [(μ 2 -H)(μ 3 -H)(Cp*ZrCl)] 4 to 2 still requires a long reaction time. Pure crystals of 1 could be isolated from either hexane or toluene solutions but cluster 2 isolated from an ether solution contains a small amount of unidentified impurity.…”