ISOCYANIDE INSERTION CHEMISTRY - SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF BRIDGING IMIDOYL COMPLEXES OF NICKEL AND AMIDE FORMATION BY INTRAMOLECULAR COUPLING OF ACYL AND IMIDOYL FUNCTIONALITIES

The binuclear pseudoallyl complex ns-(Me3P)BrNi(mu2-eta3:eta1-CH2-o-C6 H4)NiBr(PMe3)2 (1) inserts selectively 1 equiv of CNXy (Xy = 2,6-dimet hylphenyl) into the Ni-benzylic bond with formation of the cyclic comp lex trans-(Me3P)2BrNi(C(NXy)CH2-o-C6H4)NiBr(PMe3) (2) that contains a bridging eta2-imidoyl ligand. The analogous reaction of 1 with CNBu(t) gives a related mu2,eta2-imidoyl species 3a which, in contrast to 2, exists in solution in thermodynamic equilibrium with its isomer tran-( Me3P)BrNi(eta2-C(NBut)CH2-o-C6H4)NiBr(PMe3)2 (3b), in which the imidoy l ligand is terminally bonded in a eta2 fashion to one of the nickel c enters. Variable temperature NMR studies show 3b is the kinetic produc t of the insertion reaction and that the strongly solvent dependent eq uilibrium 3a half arrow right over half arrow left 3b is attained only at sufficiently high temperatures (ca. -20-degrees-C). At even higher temperatures (ca. 40-degrees-C), the 3a-3b mixtures convert into a th ird isomeric compound, trans-(Me3P)2Ni(C(NBut)C6H4-o-CH2)NiBr(PMe3) (4 ), in a process which formally corresponds to the deinsertion of CNBu( t) from the Ni-benzyl bond followed by reinsertion into the Ni-aryl mo iety. In a rather complex reaction 2 interacts with CO to afford the m ononuclear complex trans-Ni(C=CHC6H4C(O)NXy)Br(PMe3)2 (5) whose format ion probably involves the intramolecular coupling of acyl and imidoyl functionalities. Hydrolytic cleavage of the Ni-C bond in 5 provides th e corresponding N-aryl-1-isoquinolone 6. Compounds 2 and 3a, have been characterized by X-ray studies. 2 crystallizes in the monoclinic spac e group P2(1)/n with a = 12.437(3) angstrom, b = 16.025(2) angstrom, c = 16.015(2) angstrom, beta = 101.47(1)degrees, and Z = 4. Crystals of 3a are also monoclinic, space group P2(1)/n, with a = 26.05(1) angstr om, b = 10.226(1) angstrom, c = 12.013(2) angstrom, beta = 93.54(12)de grees, and Z = 4. The mu2,eta2-imidoyl functionalities of both complex es exhibit similar structural characteristics.