Synthesis and solid state and solution characterization of mono- and Di-(η1-C) carbamoyl-palladium complexes.: New efficient palladium-catalyzed routes to carbamoyl chlorides:: Key intermediates to isocyanates, carbamic esters, and ureas

Pd complexes have been used in catalytic conversion of primary and secondary amines into isocyanates or carbamoyl chlorides, respectively. The latter have been used as intermediates for the synthesis of carbamates and ureas. The palladium-based catalytic system is very active and operates in two steps, avoiding the synthesis of phosgene (COCl2), but making use of CO and Cl-2 as in phosgene chemistry. In the first step the palladium(II) complex PdCl2L2 [L-2 = 2,2' dipyridine (dipy) or 1,10-phenantroline (phen); L = triphenylphosphine (PPh3)] reacts with the amine [NH2R, R = n-C3H7 (a), n-C4H9 (b), n-C5H11 (C); NHRR' NRR' = CH2(CH2)(4)N (d), CH2(CH2OCH2)CH2N (e)] and CO to produce the carbamoyl complexes PdCl(CONHR)L-2 and PdCl(2-x)(CONRR')(x)L-2 (x =1, 2). When primary amines NH2R, (a, b, and c) are used, only monocarbamoyl complexes [PdCl(CONHR)(dipy) (1a-c), PdCl(CONHR)(phen) (2a-c), and PdCl(CONHR)(PPh3)(2) (3a,b)] are isolated. Secondary amines NHRR' (d and e) afford both monocarbamoyl PdCl(CONRR')(dipy) (4d,e) and PdCl-(CONRR')(phen) (5d,e) and dicarbamoyl complexes, Pd(CONRR')a(dipy) (6d,e) and Pd(CONRR')(2)(phen) (7d). 4d and ed have been structurally characterized: they are the first example of mono- and dicarbamoyl complexes, respectively, of the same metal system for which the solid state structure is reported. The carbamoyl complexes are subsequently reacted with halogen donors (CuCl2, N-chlorosuccinimide, Cl-2, I-2) with elimination of the carbamoyl ligand as isocyanate (primary amines complexes 1-3) or carbamoyl chloride (secondary amines complexes 4-7) and quantitative formation of the starting Pd(II) complex. Cl-2 and It are most effective and selective. They do not generate byproducts and allow an easy and quantitative recovery of the catalyst, making the reaction of potential utility.