Synthesis and Reactivity of Ortho-Palladated Arylureas. Synthesis and Catalytic Activity of a C,N,C Pincer Complex. Stoichiometric Syntheses of Some N-Heterocycles

Abstract

1-(2-Iodophenyl)-3-p-tolylurea (1) reacts with Pd(dba)2 ([Pd2(dba)3]·dba; dba = dibenzylideneacetone) in the presence of the appropriate ligands to give the ortho-palladated arylureas [Pd{C6H4NHC(O)NHTo-2}IL2] (To = C6H4Me-4; L2 = tbubpy (4,4‘-di-tert-butyl-2,2‘-bipyridine) (2a), tmeda (N,N,N‘,N‘-tetramethylethylenediamine) (2b); L = PPh3 (2c)). Reaction of 2b with Tl(TfO) (TfO = triflate, CF3SO3) results in the formation of cyclopalladated [Pd{κ2C,O-C6H4NHC(O)NHTo-2}(tmeda)]OTf (3b). The latter reacts with PPh3 to yield [Pd{C6H4NHC(O)NHTo-2}(tmeda)(PPh3)]OTf (4b). Treatment of 2b with CO gives the corresponding acyl derivative [Pd{C(O)C6H4NHC(O)NHTo-2}I(tmeda)] (5b). If Tl(TfO) is added after the bubbling of CO, the C,N coupling product 3-p-tolyl-1H-quinazoline-2,4-dione (6) is formed. Complex 5b reacts with XyNC (Xy = 2,6-dimethylphenyl) to yield trans-[Pd{C(O)C6H4NHC(O)NHTo-2}I(CNXy)2] (7). Both 5b and 7 decompose in solution to give 6. Complex 2b reacts with isocyanides to give the iminoacyl derivatives trans-[Pd{C(NR)C6H4NHC(O)NHTo-2}I(CNR)2] (R = Xy (8x), tBu (8t)). The complex 8x gives the C,N coupling product 4-(xylylimino)-3-p-tolyl-3,4-dihydro-1H-quinazolin-2-one (9) after treatment with TlOTf. 8x also reacts with bases (K2CO3 and Tl2CO3) to yield the iminoacyl amido carbene C,N,C pincer palladium complex [Pd{κ3C,N,C-C(NXy)C6H4NC(O)NToC(NHXy)-2}(CNXy)] (10); this complex is an active precatalyst in Heck and Suzuki reactions. The reaction of 2b with R‘C⋮CR‘ ‘ and TlOTf gives [Pd{κ2C,N-CR‘CR‘ ‘C6H4NHC(O)NHTo-2}(tmeda)]OTf (R‘ = R‘ ‘ = Et (11be), CO2Me (11bm), Ph (11bp); R‘ = Ph, R‘ ‘ = CO2Me (11bq)). These complexes decompose in solution, and in the case of 11bp, 2,3-diphenylindole-1-carboxylic acid p-tolylamide (12p) was isolated. 11bq reacts with PPh3 to give 3-phenyl-1H-indole-2-carboxylic acid methyl ester (13q). 11bp and 11bq decompose in the presence of CO to yield 3,4-diphenyl-2-quinolone (14po) and 2-oxo-4-phenyl-1,2-dihydroquinoline-3-carboxylic acid methyl ester (14qo), respectively. Similarly, when 11bq is reacted with XyNC, the C,N coupling compound 2-xylyl-4-phenyl-1,2-dihydroquinoline-3-carboxylic acid methyl ester (14qnx) is formed. The crystal and molecular structures of 3b, 10·0.5CDCl3, 11bp·OEt2, 11bq, and 14po have been determined.