Reactions of 2-butyne with group 6-group 10 heterobimetallics. New mixed-metal metallacycle chemistry

Article abstract of DOI:10.1021/om00006a044

The reactions of disubstituted alkynes with the mixed-metal complexes NiCp*M(CO)₃Cp (1, M = Mo, W) are presented, and the chemistry of the resultant products is developed. Complexes 1 react with nonterminal alkynes to afford nickelacyclic products of the type NiCp*{μ-η²(1,3-Ni), η²(1,2-M)-C(R)C(R′)C(O)}M(CO)₂Cp″ (3) [M = Mo, W; R = R′ = Me; R = Me, R′ = Ph. Cp″ = Cp, Cp′; not all combinations made]. Complexes 3 may be thermally decarbonylated to the μ-alkyne (dimetallatetrahedrane) complexes NiCp*(μ-η²,η²-RC ₂R′)M(CO)₂-Cp″ (2). Complex 3a (R = R′ = Me; M = Mo; Cp″ = Cp) may be protonated or alkylated at the metallacyclic acyl-like carbonyl ligand with HBF₄·Et₂O or R₃O⁺BF₄^- (R = Me, Et), respectively, to afford the cationic species [NiCp*{μ-η²(1,3-Mo),η ²(1,2-Ni)-C(Me)C(Me)C(OH)}-Mo(CO)₂Cp]⁺BF ₄^- (4, Ni-Mo) and [NiCP*{μ-η²(1,3-Mo),η ²(1,2-Ni)-C(Me)C(Me)C(OR)}Mo(CO)₂-Cp]⁺ BF₄^- (Ni-Mo; 5a, R = Me; 5b, R = Et), respectively. On the basis of an analysis of the ¹³C NMR spectrum of 5c′, a Ni-W analog of 5a, complexes 4 and 5 are believed to contain molybdenacycle, not nickelacycle, rings - i.e. a ring flip takes place during the protonation or the alkylation reaction. The attempted substitution of a carbonyl ligand in 5a with ^tBuNC in the presense of the oxidant Me₃NO led to oxidation at the molybdenum center, loss of all carbonyl ligands, rupture of the Ni-Mo bond, and insertion of an isocyanide ligand into one of the Mo-C σ-bonds. The structure of the resulting cationic molybdenum oxo species 7, NiCp*{μ-η³(1,2,3-Ni)-C(OMe)C(Me)C(Me)C(N ^tBu)}Mo(O)Cp⁺BF₄^- was established by an X-ray diffraction study. Crystal data for 7, NiMoC₂₆H₃₈BF₄NO₂: monoclinic, P2₁/c (No. 14), a = 12.288(3) A?, b = 13.130(2) A?, c = 17.013(4) A?, β = 93.47 (1)°, Z = 4, R(F) = 0.042, and R_W(F) = 0.051. Complex 5a reacts with KHBEt₃ affording what is believed to be the hydridoacyl species NiCp*{μ-η³(1,2,3-Ni),η ²(1,4-Mo)-C(OMe)C(Me)C(Me)C(O)}MoH(CO)Cp (8, Ni-Mo). A carbonyl ligand in 5a may be substituted with an iodide ion to afford the neutral molybdenum iodo species NiCp*{μ-η³-(Ni),η ²(1,3-Mo)-C(Me)C(Me)C(OMe)}MoI(CO)Cp (9, Ni-Mo). Alkylation of 9 with MeLi afforded the very air-sensitive Mo-Me complex NiCp*{μ η³-(Ni),η²(1,3-Mo)-C(Me)C(Me)C(OMe)}MoMe(CO)Cp (10, Ni-Mo).