Reactions of carbodi-imides with palladium(II) compounds

Reactivity of ortho‐Substituted Aryl–Palladium Complexes towards Carbodiimides, Isothiocyanates, Nitriles, and Cyanamides

“…The combination of carbodiimide insertion into a carbon–metal bond plus OH addition is an unprecedented process. Although the addition process leading to 5 bOH or 6 bOH is also unprecedented, 1) the addition of a nonmetalated phenol to a carbodiimide has been reported83 and 2) a related reaction [PdX 2 ( N ‐RNCNR′) 2 ] (X=Cl, Br; R= t Bu; R′= t Bu, Me) with MeOH giving [PdX 2 {RNHC(OMe)NR′} 2 ] has been described, although this is an intermolecular process and the bonding mode of the isourea ligand was not unambiguously established 84…”

“…Palladium complexes of type J are well‐known with nitrile ligands73, 74 but very scarce with carbodiimides, cyanamides, or isothiocyanates. Thus, the only reported Pd II complexes containing these ligands are [PdX 2 (RNCNR′) 2 ] (X=Cl, Br; R= t Bu; R′=Me, t Bu),84, 87 trans ‐[PdCl 2 (NCNR 2 ) 2 ] (R=Me, Et)88 or [PdCl(dppe){C(NHXy)Me}(SCNR)] (R=Me, Ph),72 respectively, and they coordinate as shown for intermediates J . However, formation of intermediates J must be a crucial step in our reactions since 1) in the absence of TlOTf, ToNCNTo gives a complex mixture of products and CyNCNCy does not react, 2) NCC 6 H 4 NCS‐4 inserts into the PdC bond as an isothiocyanate rather than a nitrile because it coordinates through S and 3) acrylonitrile inserts as a nitrile instead of its usual mode as an olefin because it coordinates preferentially through the N atom,89 and protonation to give intermediate K and the following steps to give 16 aOH are probably faster than the processes of coordination and insertion of the olefin.…”

“…Although the addition process leading to 5 bOH or 6 bOH is also unprecedented, 1) the addition of a nonmetalated phenol to a carbodiimide has been reported [83] and 2) a related reaction [PdX 2 (N-RN=C=NR') 2 ] (X= Cl, Br; R = tBu; R' = tBu, Me) with MeOH giving [PdX 2 A C H T U N G T R E N N U N G {RNH À C-A C H T U N G T R E N N U N G (OMe)=NR'} 2 ] has been described, although this is an intermolecular process and the bonding mode of the isourea ligand was not unambiguously established. [84] Alkyl and aryl isothiocyanates RNCS reacted with 1 aOH or 1 bOH and TlOTf in the same manner as carbodiimides, but gave only the protonation/insertion products…”

Bis(1-tert-butyl-2,3-dimethylisourea)dichloropalladium(II)

“…Since the ligands formally contain C=N, the possibility of coordination either through the imine N lone pair or through the ~t system exists; in fact, bonding is through the lone pair as in the parent carbodiimide complex and in two other cases (Khare, Little, Veal & Doedens, 1975;Gasparrini, Misiti & Cernia, 1976). Theoretically coordination through the NH nitrogen is also possible, but Bycroft & Cotton (1973) have suggested that this is unlikely for steric reasons (Stephenson, 1963). C(2)-N(1), 1.311 (8)A, is not significantly shorter than C(2)-N(2), 1.326 (8) ,/k.…”

“…Discussion. Alcohols are unreactive towards carbodiimides [RN :C :NR' (R, R' = alkyl or aryl)] at room temperature, but recent work (Bycroft & Cotton, 1973) has shown that the 1,2-addition of methanol to a carbodiimide to give the appropriate isourea is promoted by Pd Iz, e.g. by NaEPdCI 4.…”