Synthesis of Ortho-Palladated Phenol Derivatives. Study of Their Reactivity with Carbon Monoxide and Isonitriles

The reaction of 2-ROC6H4I with [Pd2(dba)3]·dba (“Pd(dba)2”; dba = dibenzylideneacetone)
in the presence of the appropriate ligand results in the formation of the arylpalladium
complexes trans-[Pd(C6H4OR-2)I(PPh3)2] (R = H (1a), C(O)Me (1b), C(O)CHCH2 (1c)) and
[Pd(C6H4OR-2)I(bpy)] (bpy = 2,2‘-bipyridine; R = H (2a), C(O)Me (2b)). Complexes 1b and
1c react with bpy in the presence of Tl(OTf) (OTf = OSO2CF3) to give the cationic species
[Pd(C6H4OR-2)(bpy)(PPh3)]OTf (R = C(O)Me (3b), C(O)CHCH2 (3c)). Complex 1a reacts
with carbon monoxide, yielding the insertion complex trans-[Pd{C(O)C6H4OH-2}I(PPh3)2]
(4a). Complexes 2a and 2b can also be carbonylated to give [Pd{C(O)C6H4OR-2}I(bpy)] (R
= H (5a), C(O)Me (5b)). Complex 4a reacts with bpy and Tl(OTf), giving [Pd{C(O)C6H4OH-2}(bpy)(PPh3)]OTf (6a). The reaction of 2-ROC6H4I with Pd(dba)2 and isonitriles R‘NC gives
rise to the complexes trans-[Pd{C(NR‘)C6H4OR-2}I(CNR‘)2] (R = H, R‘ = Xy = 2,6-dimethylphenyl) (7a), R‘ = tBu (7a*); R = C(O)Me, R‘ = Xy (7b), R‘ = tBu (7b*)). Complexes
7a and 7b* can also be prepared by ligand displacement from 2a and 2b and XyNC and
tBuNC, respectively. Complexes 2a and 2b react with R‘NC (1:1) to give [Pd{C(NR‘)C6H4OR-2}I(bpy)] (R = H, R‘ = Xy (8a), R‘ = tBu (8a*); R = C(O)Me, R‘ = Xy (8b)). Complex 7a
reacts with bpy in the presence of Tl(OTf), yielding [Pd{C(NR‘)C6H4OH-2}(CNR‘)(bpy)]OTf (9a). Reaction of 5a with R‘NC gives trans-[Pd{C(O)C6H4OH-2}I(CNR‘)2] (R‘ = Xy (10a),
tBu (10a*)), which, in turn, react with further R‘NC in the presence of Tl(OTf) to give [Pd{C(O)C6H4OH-2}(CNR‘)3]OTf (R‘ = Xy (11a), tBu (11a*)). Finally, the reaction of 7a with
Pd(OAc)2 results in the tetrameric [Pd{κ2(C,O)-μ2(O)-C(NXy)C6H4O-2}(CNXy)]4 (12) and
trans-[PdI2(CNXy)2]. Most of the reported aroyl (4−6, 10, 11) and iminoaroyl (7−9, 12)
derivatives are new types of palladium complexes. The crystal structures of complexes 5a,
7a, 7b, 8b, 9a, and 12 have been determined by X-ray diffraction methods. The following
scale of trans influence has been established:  bpy < I < C(NXy)C6H4OC(O)Me-2 ≈
C(O)C6H4OH-2 < C(NXy)C6H4OH-2.