Reaction environment and ligand lability in group 4 Cp₂MXY (X, Y = Cl, OtBu) complexes

Abstract

Despite their usefulness in catalytic and materials chemistry, the mixed cyclopentadienyl/alkoxide complexes of Ti, Zr, and Hf (CpM(OR)) have few reliable synthetic routes available to them. We describe the use of mechanical ball milling to promote halide metathesis from CpMCl, and compare these results to those obtained in hexanes and THF. Even without solvent, ring lability is extensive with titanium complexes, and alkoxide compounds with 0-3 Cp rings are isolated. The ball milling reactions are much faster than those in solution, but the distributions of products are similar to those obtained in hexanes, although different from those in THF. The range of compounds obtained from Zr and Hf starting materials is more limited, as Cp ring exchange does not occur.

Synthesis without solvent: consequences for mechanochemical reactivity

“…, [Ni(Ind) 2 ] 37 and ; 38 A′ = [1,3-(SiMe 3 ) 2 C 3 H 3 ] − ) are included in this group, as are the bis(dicarbollyl) complexes of cobalt( iii ), iron( iii ) and chromium( iii ), 39 and heteroleptic Cp/OR complexes of group 4 metals, [Cp 2− x M(O t Bu) 2+ x ] (M = Zr, Hf). 40 Transformation of the trimeric [{ t BuZnO t Bu} 3 ] into the tetrameric cubane [{ t BuZnO t Bu} 4 ] occurs both in solution and the solid state, 41 and even more complicated structures such as the mixed metal aggregate [Ag 12 Au 10 (CCPh) 17 (OTf) 5 (PPh 3 ) 3 ], can be formed by mixing separately prepared acetone solutions of [Au(CCPh)PPh 3 ] and Ag(OTf), or by simply grinding the two solid metal reagents together. 42…”

“…55 c A halide metathetical route for their preparation from Cp 2 MCl 2 (M = Zr, Hf) and K[O t Bu] works both in the solid state and in solution. 40 For the hafnium system, use of a 1 : 1 ratio of reagents cleanly produces the monoalkoxide product Cp 2 HfCl(O t Bu) either in hexanes or by ball milling (K[O t Bu] + Cp 2 HfCl 2 → Cp 2 HfCl(O t Bu) + KCl). In this case, the mechanochemical reaction is complete in considerably less time than the solution equivalent (15 min vs. 18 h), a partial result of the higher concentration of reagents in the solid-state environment.…”

Alternative Technologies That Facilitate Access to Discrete Metal Complexes

“…In 2016, Boyde et al performed the mechanosynthesis of Cp (cyclopentadienyl) complexes of titanium 41 , zirconium, and hafnium using halide metathesis (Scheme ). Interestingly, starting from [MCp 2 Cl 2 ] (M = Zr and Hf), the synthesis led to [MCp 2 (O t -Bu) 2 ] complexes; however, starting from the titanium complex 40 , the reaction was selective in forming compound 41 as the major product . Remarkably, when the synthesis was carried out in hexane, the selectivity of the reaction was similar, but in a polar media such as THF, the synthesis was selective.…”

“…Interestingly, starting from [MCp 2 Cl 2 ] (M = Zr and Hf), the synthesis led to [MCp 2 (Ot-Bu) 2 ] complexes; however, starting from the titanium complex 40, the reaction was selective in forming compound 41 as the major product. 81 Remarkably, when the synthesis was carried out in hexane, the selectivity of the reaction was similar, but in a polar media such as THF, the synthesis was selective. Using ball milling, reactions could be completed in minutes, whereas hours were required for reactions performed in solution.…”

Metalation Studies on Titanocene Dithiolates

“…Treatment of the known titanocene dichlorides (C 5 H 4 X)(C 5 H 4 Y)TiCl 2 (X = Y = H, 1a; X = H, Y = Cl, 1b; X = Y = Cl, 1c) [33,34] with HS-C 6 H 4 R (R = H, p-Me) in the presence of DABCO (1,4- alkyl lithiums to thermally unstable titanocene alkyls Cp2TiR2, which easily decompose to titanium(III) products [22,23] and with lithium amides to mono-cyclopentadienyl titanium tris-amides CpTi(NR2)3 [24]. In addition, with the often-used base KO t Bu, a mixture of products including those of splitting off the cyclopentadienyl ligands was observed [25]. We, therefore, decided to look at the also long-known titanocene thiolates Cp2Ti(SR)2.…”