Synthesis of tungsten vinyl alkylidene complexes via the reactions of WCl2(NAr)(PX3)3 (X = R, OMe) precursors with 3,3-disubstituted cyclopropenes

Article abstract of DOI:10.1021/ja00071a026

Several WCl₂(NAr)(PX₃)₃ complexes were synthesized, including WCl₂(N-2,6-C₆H₃Me₂)(PEt ₂Ph)₃ (1), WCl₂(NPh)[P(OMe)₃]₃ (2), WCl₂(N-2,6-C₆H₃Me₂) [P(OMe)₃]₃ (3), and WCl₂[N-2,6-C₆H₃(i-Pr)₂] [P(OMe)₃]₃ (4). NMR spectroscopic data for these complexes and a single-crystal X-ray diffraction study of 4 supported a meridional arrangement of the three PX₃ ligands, all lying cis to the apical imido ligand. The lability of one PX₃ ligand in complexes 1-4 was demonstrated by reactions with ethylene and phenyl- and diphenylacetylene to give the corresponding π-acceptor (L) complex WCl₂(L)(NAr)(PX₃]₂. In solution, some of the WCl₂(L)(NAr)(PX₃)₂ complexes, especially those with P(OMe)₃ ligands, were in equilibrium with WCl₂(L)(NAr)(PX₃) and free PX₃; complete removal of 1 equiv of PX₃ was achieved upon addition of CuCl. Complexes 1-4 and also WCl₂(NPh)(PMePh₂)₃ reacted with 3,3-diphenylcyclopropene and 4,8-dioxaspiro[2.5]oct-1-ene (referred to subsequently as diphenyl- and ketalcyclopropene) to give a number of η²-cyclopropene complexes and/or vinyl alkylidene complexes. Concentrated diethyl ether solutions of the reactants and use of the sterically smaller tungsten precursors enabled the clean formation of the η²-cyclopropene complexes W(η²-cyclopropene)Cl₂(NAr)(PX₃) ₂. Spectroscopic data and a single-crystal X-ray diffraction study of W(η²-diphenylcyclopropene)Cl₂(NPh) [P(OMe)₃]₂ indicated an octahedral geometry in which the two mutually trans PX₃ ligands and the cyclopropene occupy equatorial positions cis to the apical imido ligand and the substituents of the cyclopropene lie syn to the imido ligand. The η²-cyclopropene complexes were converted to the corresponding vinyl alkylidene complexes W(=CHCH=CR₂)Cl₂(NAr)(PX₃)₂ thermally, photochemically, and chemically (catalysis by HgCl₂). For the reactions of the sterically more bulky tungsten precursors with cyclopropenes, direct isolation of the vinyl alkylidene complexes was possible. A crystal structure of an alkoxide derivative W(=CHCH=CPh₂) [N-2,6-C₆H₃-(i-Pr)₂] [OCMe(CF₃)₂]₂[P(OMe)₃] confirmed the formation of a diphenylvinyl alkylidene ligand with an s-trans arrangement of the double bonds. In addition to an s-trans isomer, the ketalvinyl alkylidene ligand also formed two different s-cis isomers with one oxygen atom of the ketal ring chelating to tungsten. A crystal structure showed that, in one of these isomers, the ketal ring has been opened by a chloride ligand from tungsten, and a mechanism is proposed for this rearrangement.