Chemistry of carbon monoxide free monocyclopentadienylvanadium(I) alkene and alkyne complexes

The compounds CpV(L)(PMe3)2 (L = η2-ethene (2), η2-alkyne) form a new class of highly reactive CO-free CpVI complexes. Paramagnetic 2 was prepared from CpVCl(PMe3)2 and 0.5 mol of BrMg(CH2)4MgBr. An X-ray structure determination shows a relatively short ethene C=C distance of 1.365 (5) A. The η2-alkyne complexes are readily available by Mg reduction of CpVCl2(PMe3)2 in the presence of the alkyne. The X-ray structure of CpV(η2-PhC≡CPh)(PMe3)2 (4) shows the alkyne ligand to be asymmetrically oriented relative to the other ligands in the complex. The ethene ligand in 2 is readily replaced by CO or PhC≡CPh. 2,2'-Bipyridine displaces a phosphine as well to produce the paramagnetic CpV(η2-bpy)PMe3 (5). C,C coupling is observed in the reaction of 2 with CO2 to form the vanadalactone CpV[CH2CH2C(O)O]PMe3 (6). PhSSPh oxidatively adds to 2 to form [CpV(μ-SPh)2]2. 1-Hexene is slowly catalytically dimerized by 2. The alkyne complex 4 reacts with various hydrocarbon substrates through initial phosphine loss and subsequent C,C coupling. With 1,3-butadiene the hexadienediyl complex CpV(η1,η3-C2Ph2C4H6)PMe3 (9) is formed. With ethene 2:1 cotrimerization with the alkyne ligand occurs to produce an η4-diphenylhexadiene complex, CpV[η4-CH2=CHC(Ph)=C(Ph)Et]PMe3 (10), which was characterized by X-ray diffraction. With 2-butyne, 4 reacts to give CpV(η2-MeC≡CMe)(η2-PhC≡CPh)PMe3 (13), which subsequently forms the metallacycle CpV(C4Me2Ph2)PMe3 (14). An X-ray structure determination shows 14 to have a bent metallacyclopenta-1,3,5-triene structure (formally an V(V) dicarbene) with V=C bond distances of 1.891 (3) and 1.893 (3) A. Analogous bicyclic products are formed through reduction of CpVCl2(PMe3)2 in the presence of diynes. A summary of the crystal data is as follows: for 2, Pbca, a = 12.351 (3) A, b = 15.526 (4) A, c = 16.948 (3) A (130 K), Z = 8; for 4, P21/n, a = 8.249 (2) A, b = 17.619 (2) A, c = 16.278 (2) A, β = 100.61 (2)° (130 K), Z = 4; for 10, P1, a = 8.875 (3) A, b = 9.589 (2) A, c = 15.081 (6) A, α = 90.95 (3)°, β = 91.54 (3)°, γ = 117.44 (2)° (130 K), Z = 2; for 14, P212121, a = 12.957 (3) A, b = 19.205 (5) A, c = 9.155 (2) A (170 K), Z = 4.