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Sequential π-ligand exchange from metallacyclopentanes: Synthesis and structure of 1,1 -bis(cyclopentadienyl)-2,3-diphenyl-1-hafnacyclopent-2-ene
Erker, Gerhard,Dorf, Ulrich,Rheingold, Arnold L.
, p. 138 - 143 (2008/10/08)
Bis(cyclopentadienyl)hafnacyclopentane was prepared by reaction of Cp2HfCl2 and 1,4-dilithiobutane. Thermolysis of the five-membered metallacycle at 80°C with butadiene results in liberation of 1 equiv of ethylene and formation of an (ethylene)hafnocene/butadiene (1:1) addition product: (1-3:6-η-2-hexenediyl)hafhocene. Similarly, the hafnacyclopentane reacted with diphenylcetylene under suitable controlled reaction conditions at 80°C in benzene to give a 36% yield of the title compound. 1,1-Bis(cyclopentadienyl)-2,3-diphenyl-1-hafnacyclopent-2-ene crystallizes in the triclinic space group P1 with cell constants a = 8.901 (2) A?, b = 9.871 (2) A?, c = 13.199 (3) A?, α = 78.19 (2)°, β = 72.49 (2)°, γ = 65.62 (2)°, V = 1003.0 (4) A?3, Z = 2, and R(F) = 2.76%. The four ring carbons are nearly planar. Bond distances within the metallacyclic five-membered ring system are Hf-C(1) = 2.255 (7), C(1)-C(2) = 1.529 (7), C(2)-C(3) = 1.513 (8), C(3)-C(4) = 1.337 (8), and C(4)-Hf = 2.268 (4) A?. Though the ring system is somewhat strained (bond angles C(1)-C(2)-C(3) = 115.6 (5)° and Hf-C(4)-C(3) = 110.6 (3)°), the strong hafnium to carbon σ-bonds protect it from rapidly reacting further with additional diphenylacetylene to give the very stable metallacycle Cp2Hf(-CPh=CPhCPh=CPh).
