β-diketiminato calcium acetylides: Synthesis, solution dimerization, and catalytic carbon-carbon bond formation

Anthony G M Barrett, Mark R. Crimmin, Michael S. Hill, Peter B. Hitchcock, Sarah L. Lomas, Mary F. Mahon, Panayiotis A. Procopiou, Kogularamanan Suntharalingam

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56 Citations (Scopus)

Abstract

The β-diketiminate-stabilized calcium amide [{ArNC(Me)CHC(Me)NAr }Ca{N(SiMe3)2 }(THF)] (1) reacts with terminal acetylenes in hydrocarbon solvents to yield the corresponding calcium acetylide complexes [(ArNC(Me)CHCN(Me)Ar)Ca(C≡CR1}]2 (R1 = n-Bu, t-Bu, Ph, 4-MeC6H4, ferrocenyl, Ar = 2,6-di-isopropylphenyl, 2a-e). Although in all instances solid and solution state data were consistent with the reaction products existing as dimeric species with aggregation occurring via three-center-two-electron bridging acetylide units, a further reaction of 1 with HC≡CSi(iPr) 3 demonstrated that both monomelic solvated [(ArNC(Me)CHC(Me)NAr} Ca(C≡CSi(Pr)3}(THF)2] (3b) or dimeric acetylide [(ArNC(Me)CHC(Me)NArJCa(C≡CSi(iPr)3]2 (3a) species could be isolated from the reaction depending upon the exact conditions of the crystallization of the reaction product from solution. Further solution studies demonstrated the presence of a monomer-dimer equilibrium in solution. A van't Hoff analysis allowed ΔG°(298 K) for the dimerization reaction to be calculated as +27.0 kJ mol-1. The reaction of these hydrocarbon-soluble kinetically stabilized calcium acetylides with 1,3-dialkylcarbodiimides gave the corresponding heteroleptic calcium C-propargyl amidinate complexes [(ArNC(Me)CHCN(Me)-Ar}Ca{(R2N) 2CC≡CR1}(THF)n] (R1 = 4-MeC6H4, n = 0, 4a; 4-MeC6H4, n = 1, 4a·THF; R2 = iPr; R1 = Si( iPr3), R2 = Cy, n = 1, 4b·THF) via insertion of the carbodiimide into the calcium-carbon σ-bond. The latter complexes have been characterized in both solution and the solid state including single-crystal X-ray analysis of 4a · THF. Extension of this reactivity to catalytic systems has allowed the application of amide 1 (5 mol %) to the catalytic hydroacetylenation of 1,3-di-isopropylcarbodiimide with phenylacetylene, yielding the corresponding propargyl amidine in 59% yield following crystallization from hexane solution.

Original languageEnglish
Pages (from-to)6300-6306
Number of pages7
JournalORGANOMETALLICS
Volume27
Issue number23
DOIs
Publication statusPublished - 8 Dec 2008

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