Novel palladium-aminocarbene species derived from metal-mediated coupling of isonitriles and 1,3-diiminoisoindoline: Synthesis and catalytic application in Suzuki-Miyaura cross-coupling

摘要

The reaction between metal-bound isonitriles in cis-[PdCl_2(CNR ~1)_2] [R ~1 = cyclohexyl (Cy) 1, Bu ~t2, C_6H_4(2,6-Me_2) (Xyl)_3, CMe_2CH_2CMe_34] and 1,3-diiminoisoindoline (9) in CHCl_3 under reflux for_4 h provides the carbene species [Pd{C(N=C ~a(C_6H_4CNHN ~b))=N(H)R ~1}_2] ~(a-b) (R ~1 = Cy 10, 82% isolated yield) or cis-[PdCl{C(N=C ~a(C_6H_4CNHN _b))=N(H)R ~1}(CNR ~1)] ~(a-b) (R ~1 = Bu ~t11, 78%; Xyl 12, 84%; CMe_2CH_2CMe_313, 79%), derived from the addition of two or one equivs of 9 to the starting 1-4, respectively. The corresponding integration of cis-[PdCl_2(CNR ~1)(PPh_3)] (R ~1 = Cy_5, Bu ~t6, CMe_2CH_2CMe_38) with 1 equiv of 9 in CHCl_3 under reflux for_4 h affords the carbene species cis-[PdCl{C(N=C ~a(C_6H_4CNHN ~b))=N(H) R ~1}(PPh_3)] ~(a-b) (R ~1 = Cy 14, 84%; Bu ~t15, 76%; CMe_2CH_2CMe_316, 75%). Complexes 10-16 were characterized by elemental analyses (C, H, N), ESI ~+-MS, IR, and 1D (~1H, ~(13)C{~1H}) and_2D (~1H, ~1H-COSY, ~1H, ~(13)C-HMQC/ ~1H, ~(13)C-HSQC, 1H, 13C-HMBC) NMR spectroscopies. In addition, the structures of aminocarbene complexes 10 and 12 were elucidated by X-ray diffraction. The catalytic properties of 10-16 in the Suzuki-Miyaura cross-coupling of aryl halides, viz.,_4-R ~2C_6H_4X (X = I, R ~2 = OMe; X = Br, R ~2 = Me, OMe, and NO_2), with phenylboronic acid (in EtOH as solvent, K_2CO_3 or Cs_2CO_3 as base, 80 °C) yielding biaryl species_4-R ~2C_6H_4Ph, were evaluated. Complexes 14-16 exhibit a high catalytic activity (yields up to 98%, TONs up to 9.8 × 10 ~4, TOFs up to_3.9 × 10 ~4).