Synthesis and reactivity of benzyne derivatives of rhenium formed by facile ortho-hydrogen abstraction in a homoleptic rhenium aryl. X-ray structure of the cationic benzyne [Re(η2-2-MeC6H3)(2-MeC6H 4)2(PMe3)2][I5]

Article abstract of DOI:10.1021/om00104a023

The paramagnetic benzyne complexes Re(η²-2-MeC₆H₃)(2-MeC₆H ₄)₂(PMe₂R)₂ (R = Me, 2a; R = Ph, 2b) are formed at low temperature via ligand-induced ortho-hydrogen abstraction on addition of phosphine to the homoleptic aryl Re(2-MeC₆H₄)₄ (1). Complexes 2 are oxidized under mild conditions to the benzyne cations [2][X] (X = PF₆^-, BPh₄^-, OTf^-, Co(CO)₄^-, I₅^-) with E_1,2 = -0.90 V (relative to Cp₂Fe at 0.00 V). The cations are reduced by strong nucleophiles, e.g., LiBEt₃H, Me₃SiCH₂MgCl, in THF, back to the neutral species. NMR data for [2][X] are in agreement with the solid-state structure, determined for [2a][I₅] by X-ray crystallography. Crystals are orthorhombic, space group Pna2₁. with a = 18.735 (2), b = 13.954 (5), c = 14.193 (2) A?, Z = 4, D_calcd = 2.23 g cm^-3. The geometry of the cation can be described as distorted trigonal bipyramidal with the benzyne symmetrically η²-bound at an equatorial site (Re-C(benzyne) = 2.02 (2) A?) and with axial phosphines (Re-P = 2.421 (5) and 2.435 (51 A?); the equatorial Re-C(2-MeC₆H₄) distances are 2.09 (1) A?.