Reaction of C5(CH3)5Hf(2,3-dimethyl-1,3-butadiene)Cl with Acetylene: Formation of an Asymmetric, Disubstituted 1,3-Dihafnacyclobutane

Cp*Hf(2,3-dimethyl-1,3-butadiene)Cl (Cp* = η5-C5Me5) reacts with 1 mol of acetylene to form a disubstituted 1,3-dihafnacyclobutane complex, {Cp*Hf(Cl)[μCHCHCH2C(Me)=C(Me)CH2]}2, which was characterized by X-ray analysis (triclinic space group P1, a = 8.446 (7) Å, b = 10.518 (2) Å, c = 10.792 (1) Å, α = 108.25 (1)°, β = 103.51 (3)°, γ = 103.66 (4)°, Z = 1). The Hf2C2 ring is asymmetrical, with two different Hf-C distances (2.246 (6) and 2.134 (5) Å). An agostic C-H→M interaction is present over the shorter Hf-C bond. The acetylene triple bond is reduced to a single bond (1.538 (6) Å), with one acetylene carbon bound to two Hf atoms and the other one to the two methylene carbon atoms of the former dimethylbutadiene ligand.

Asymmetric Diels-Alder Reactions with 5-Menthyloxy-2(5H)-furanone

A new class of chiral dienophiles, 5-alkoxy-2(5H)-furanones, has been developed. Both enantiomers of 5-menthyloxy-2(5H)-furanone are readily available in enantiomerically pure form, starting from furfural and d- or l-menthol. Excellent diastereoselectivities (d.e. ≥99%) are obtained in thermal Diels-Alder reactions with several cyclic and acyclic dienes. The use of silyl dienol ethers has resulted in new routes to enantiomerically pure cyclohexanones in a highly regioselective manner.

Novel Diamagnetic and Paramagnetic Hydrides of Vanadium(II)

Apart from V(I) complexes like [CpVH(CO)3]- and HV(CO)4(PP) (PP = chelating diphosphine), very few vanadium hydride species are known which are as follows: one V(III) compound, (C5Me5)2VH, and its CO adduct and two dimeric species, [CpV(μ-H)]2(μ-C6H6) and V2H4Zn2(BH4)2(PPh2Me)4. Here we wish to report two new vanadium(II) hydride species, diamagnetic [CpV(μ-H)dmpe]2 (1) (dmpe = 1,2-bis(dimethylphosphino)ethane) and paramagnetic [CpVH(dmpe)]2(μ-dmpe) (2), produced in the reaction of the V(II) alkyl complex CpV(n-Pr)dmpe (3) with molecular hydrogen.