Reactivity of cyclopalladated compounds. Part 7. Syntheses of metallobicyclic compounds and their reactions with acetylenes. X-Ray crystal and molecular structures of the compounds [(NMe2CH2C6H4)Pd{C(CF3)C(CF3)(C6H4CH2NMe2)}] and [{(NMe2CH2C6H4)C(CF3)C(CF3)}Pd{C(CF3)C(CF3)(CH2C9H6N)}]

Abstract

Hexafluorobut-2-yne (hfb) reacted with [M(dmba – H)₂](dmba =NN-dimethylbenzylamine, M = Ni or Pd) to give [([graphic omitted]Me₂)}] compounds in which one acetylene was formally inserted into one of the M–C bonds, the second metallocycle being unmodified. A cis geometry has been tentatively assigned to the compound where M = Ni, whereas a trans configuration is found for M = Pd. This latter complex isomerizes slowly in solution to give the cis isomeric form which has been studied by single-crystal X-ray diffraction measurements; the complex crystallizes in the monoclinic space group P2_1/n with a= 11.705(2), b= 11.146(2), c= 16.317(5)Å, β= 93.16(2)°, and Z= 4. The two nitrogen atoms are indeed mutually cis to each other, the Pd–N distances being rather long [2.231 (3) and 2.223 (3)Å]; the phenyl ring which is a part of the seven-membered palladated ring is now perpendicular to the co-ordination plane of the Pd atom. Reaction of lithiated NN-dimethylnaphthylamine (dmna) or NN-dimethylaminotoluene (dmat) with [PdCl₂(SEt₂)₂] gave the bicyclic compounds [Pd(dmna – H)₂] and [Pd(dmat – H)₂], the latter in very low yield however. The former compound gave metallic Pd and an organic product by reaction with hfb. Asymmetric bicyclic compounds have been synthesized by reaction of lithiated dmna, dmat, or dmba with the chlorine-bridged dimers [{Pd(dmba – H)Cl}₂] or [{Pd(8Me-quin – H)Cl}₂](8Me-quin = 8-methylquinoline). Reaction between hfb and the bicyclic compound [Pd(dmba – H)(dmna – H)] afforded a compound in which again only one acetylene has reacted with the Pd–C bond of the palladated dmba moiety; the two Pd–C bonds are trans to each other and it also isomerizes into the corresponding cis species in solution. [Pd(dmba – H)(8Me-quin – H] with hfb gave a product in which the acetylene reacted with both Pd–C bonds affording a bicyclic compound with two seven-membered rings attached to the same palladium. This product exists as a mixture of cis and trans isomers but only the cis species has been isolated in a pure crystalline form. Its stereochemistry has been confirmed by an X-ray diffraction study; the complex crystallizes in the monoclinic space group P2_1/n with a= 13.948(8), b= 12.338(7), c= 16.868(6)Å, β= 107.89(4)°, and Z= 4. The seven-membered ring containing the dmba ligand resembles that described above whereas the new ring containing 8Me-quin – H is mainly described by two planes whose dihedral angle is 112.3°. [Pd(dmba – H)(8Me-quin – H)] also reacts under smooth conditions with MeO₂CCCCO₂Me to give a mixture of products from which one compound has been isolated in a pure form : it has fixed one acetylene per palladium atom and we suggest on the basis of n.m.r. data that it has reacted with the C–Pd bond of the palladated 8Me-quin moiety.