Science of Synthesis

Negishi, E.-i.; Takahashi, T., Science of Synthesis, (2003) 2, 740.

Although the reaction of dichlorobis(η5-cyclopentadienyl)zirconium(II) and -hafnium(II) with 1,4-dimetalloalkanes, -alkenes, and -dienes is a potentially general route to five-membered zirconocene and hafnocene derivatives, its current scope is limited. 1,4-Di­metallo reagents containing lithium or magnesium are generally used; representative examples are shown in ‌Scheme 75‌. Zirconacyclopentanes ‌169‌ (M = Zr) and hafnacyclopentanes ‌169‌ (M = Hf) are formed by the reaction of butane-1,4-diylbis(magnesium bromide) (‌168‌) with dichlorobis(η5-cyclopentadienyl)zirconium(II) and -hafnium(II), further reaction with trimethylphosphine gives the corresponding three-membered bis(η5-cyclopentadi­enyl)(dimethylphosphino)zirconium(II) or -hafnium(II) derivative ‌170‌.[‌216‌] Reaction of dichlorobis(η5-cyclopentadienyl)zirconium(II) (‌49‌) with a 1,4-dimagnesioalkene gives a zirconacyclopentene ‌171‌.[‌217‌] Of particular note is the reaction of a 2,5-dimagnesiohexane derivative with dichlorobis(η5-cyclopentadienyl)zirconium(II) and -hafnium(II).[‌215‌] The reaction produces the 2,5-dimethylzircona- or hafnacyclopentane, however, treatment of the product from the reaction of dichlorobis(η5-cyclopentadienyl)zirconium(II) with bromine gives dl-2,3-dimethyl-1,4-dibromobutane (‌172‌) (≥98% dl). The product ‌172‌ would be formed from 3,4-dimethylzirconacyclopentane and formation of this intermediate has been indicated by 1H NMR spectroscopy. The corresponding reaction of dichloro­bis(η5-cyclopentadienyl)hafnium(II) permits observation of the initial, final, and intermediary hafnacyclopentanes, strongly supporting the stepwise mechanism shown in the ‌Scheme 75‌. An intramolecular ring-contraction–ring-expansion cascade is a likely mechanism for the carbon skeletal rearrangement, but this has not been established.

‌Meeeee 88‌ Meeeeeeee ee Meee-Meeeeeee Meeeeeeeeee eee Meeeeeeee Meeeeeeeeee[‌888‌–‌888‌]

Meeeeeeeeeee Meeeeeeee

8,8-Mee(η8-eeeeeeeeeeeeeeee)eeeeeeeeeeeeeeeee (‌888‌, M = Me):[‌888‌]

Me e eeeeeeeeee ee MeMe8 (88 e, 88.8 eeee) ee Me8M (888 eM) ee −88°M eee eeeee 8.88 M eeeeee-8,8-eeeeeeeeeeeee ee Me8M (88 eM, 88.8 eeee). Mee eeeeeee eee eeeeee ee −88°M, eeeeeee ee eeee eeeeeeeeeee eee 8 e, eee eeee eeeeeee ee eeee ee ee ee. Mee eeeeeee eee eeeeeee ee eeeee eee eee eeeeeee eeeeeeeee eeee eeeeeee (888 eM). Mee eeeeeee eeee eee eeeeeeee eee eeeeeeeeee ee eeeeeee ee eeee eeeeeeeeeeee eeee eeeeeeeee ‌888‌; eeeee: 8.88 e (88%). M eeee ee ‌888‌ (8.88 e) ee MM8Me8 (88 eM) eee eeeeee ee −88°M ee eeee e eeeeeeeeeee eeeeeee; eeeee: 8.8 e (88%); ee 888°M (eee); 8M MMM (eeeeeee-e8, δ): 8.88 (e, 88M, Me), 8.88 (e, 8M, β-MM8), 8.88 (e, 8M, α-MM8); 88M MMM (eeeeeee-e8, δ) 888.8 (e, M = 888 Me, Me), 88.8 (e, M = 888 Me, MM8), 88.8 (e, M = 888 Me, MM8).

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) 88/8, 888.
• 8.Meeeee-Meee, (8888) M 88e, 888.
• 8.Meeeee-Meee, (8888) M 88e, 888.