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 Cl2 as in phosgene chemistry. In the first step the palladium(II)
complex PdCl2L2 [L2 = 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)4N (d), CH2(CH2OCH2)CH2N (e)] and CO to produce the carbamoyl
complexes PdCl(CONHR)L2 and PdCl(2-x)(CONRR‘)xL2 (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‘)2(dipy) (6d,e) and Pd(CONRR‘)2(phen) (7d). 4d and 6d 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, Cl2, I2) 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. Cl2 and
I2 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.