Novel Palladium–Aminocarbene Species Derived from Metal-Mediated Coupling of Isonitriles and 1,3-Diiminoisoindoline: Synthesis and Catalytic Application in Suzuki–Miyaura Cross-Coupling

The reaction between metal-bound isonitriles in cis-[PdCl2(CNR1)2] [R1 =
cyclohexyl (Cy) 1, But 2, C6H4(2,6-Me2) (Xyl) 3, CMe2CH2CMe3 4] and 1,3-diiminoisoindoline (9) in CHCl3 under reflux for 4 h provides the carbene species [Pd­{C­(NCa(C6H4CNHNb))N­(H)­R1}2]a−b (R1 = Cy 10, 82% isolated
yield) or cis-[PdCl­{C­(NCa(C6H4CNHNb))N­(H)­R1}­(CNR1)]a−b (R1 = But 11, 78%; Xyl 12, 84%; CMe2CH2CMe3 13, 79%), derived from the addition of two or
one equivs of 9 to the starting 1–4, respectively. The corresponding integration of cis-[PdCl2(CNR1)­(PPh3)]
(R1 = Cy 5, But 6, CMe2CH2CMe3 8) with 1 equiv of 9 in CHCl3 under
reflux for 4 h affords the carbene species cis-[PdCl­{C­(NCa(C6H4CNHNb))N­(H)­R1}­(PPh3)]a−b (R1 = Cy 14, 84%; But 15, 76%; CMe2CH2CMe3 16, 75%). Complexes 10–16 were characterized by elemental
analyses (C, H, N), ESI+-MS, IR, and 1D (1H, 13C­{1H}) and 2D (1H,1H-COSY, 1H,13C-HMQC/1H,13C-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-R2C6H4X
(X = I, R2 = OMe; X = Br, R2 = Me, OMe, and
NO2), with phenylboronic acid (in EtOH as solvent, K2CO3 or Cs2CO3 as base, 80
°C) yielding biaryl species 4-R2C6H4Ph, were evaluated. Complexes 14–16 exhibit a high catalytic activity (yields up to 98%, TONs
up to 9.8 × 104, TOFs up to 3.9 × 104).