Coordination and oligomerization of alkynes at mononuclear tungsten aryloxide metal centers

Article abstract of DOI:10.1021/om00030a014

Reduction of either [W(OC₆H₃Ph₂-2,6)₂Cl₄] (OC₆H₃Ph₂-2,6 = 2,6-diphenylphenoxide) or [W(OC₆H₃Prⁱ₂-2,6)₂Cl ₄] (OC₆H₃Prⁱ₂-2,6 = 2,6-diisopropylphenoxide) in toluene with sodium amalgam in the presence of alkynes (EtC≡CEt; PhC≡CPh; 4Me-PhC≡CPh-4Me) leads to a series of alkyne (ac) adducts of general formulae [(ArO)₂WCl₂(ac)] (1) and [(ArO)₂W(ac)₂] (2). The ¹³C NMR spectra of 1 and 2 show downfield shifts for the coordinated alkyne carbon atoms. A single crystal X-ray diffraction analysis shows five coordinate [W(OC₆H₃Ph_2-2,6)₂Cl ₂(C₂Et₂)] (1a) to adopt a square pyramidal geometry about tungsten with trans aryloxide ligands and an axial 3-hexyne. The solid state structure of [W(OC₆H₃Ph-2,6)₂(C₂Et ₂)₂] (2a) shows a pseudotetrahedral environment about tungsten with the two 3-hexyne ligands arranged parallel with each other. Reaction of the η⁶-arene complex [W(OC₆H₃Ph-η⁶-C₆H ₅)(OC₆H₃Ph₂-2,6)(dppm)] with 3-hexyne generates the compound [W(OC₆H₃Ph₂-2,6)₂(C ₄Et₄)] (3) which contains a tungstacyclopentatriene ring. This ring is nonplanar both in the solid state and solution (NMR). The bis-cyclometalated compounds [W(OC₆H₃Ph-C₆H₄)₂(L) ₂] (L = PMe₂Ph, PMePh₂, and py) react with alkynes to form a number of products. From the reaction with 3-hexyne, two new compounds of formula [W(OC₆H₃PhC₆H₄)₂(C ₄Et₄)] (4) and [W(OC₆H₃PhC₆H₄H₄) ₂(C₆Et₆)] (5) were isolated. Structural studies on 4 and 5 show them to contain multiple metallacyclic rings formed by transfer of one of the metalated aryloxide carbon atoms to an α-carbon of an intermediate tungstacyclopenta-2,4-diene complex. Crystal data at -100°C for WCl₂O₂C₄₂H₃₆ (1a): a = 9.331(2), b = 12.271(2), c = 16.334(3) A?; α = 107.48(1), β = 101.78(2), γ = 95.13(2)°; Z = 2, d_calcd = 1.595 g cm^-3 in space group P1; for WO₂C₄₈H₄₆ (2a) at 20°C: a = 11.458(1), b = 17.961(4), c = 10.915(2) A?; α = 104.65(1), β = 115.23(1), γ = 92.08(1)°; Z = 2, d_calcd = 1.437 g cm^-3 in space group P1; for WO₂C₄₈H₄₆ (3) at -114°C: a = 11.086(2), b = 18.400(7), c = 19.453(5) A?; α = 98.96(2), β = 97.14(2), γ = 98.67(2)°; Z = 4, d_calcd = 1.454 g cm^-3 in space group P1; for WO₂C₄₈H₄₄ (4) at 20°C: a = 10.805(7), b = 11.662(1), c = 17.008(3) A?; α = 80.12(1), β = 84.71(3), γ = 63.07(3)°; Z = 2, d_calcd = 1.476 g cm^-3 in space group P1; for WO₂C₅₄H₅₄ (5) at 20°C: a = 9.835(2), b = 11.8298(7), c = 19.620(2) A?; α = 104.748(6), β = 98.717(9), γ = 104.478-(8)°; Z = 2, d_calcd = 1.467 g cm^-3 in space group P1.