| The bidentate nitrile ligands DiCN-3 and DiCN-4, 1,2-bis(2-cyanophenoxy)propane and -butane, have been prepared in a manner identical to that previously reported for the synthesis of DiCN-2. All three ligands react with Mn(CO)(,5)Br to afford complexes of the type Mn(CO)(,3)(DiCN-n)Br. Where n = 2 and 3, the complexes appear to be mononuclear, and employ the ligands in ther chelated forms. The structure of Mn(CO)(,3)(DiCN-4)Br remains questionable; the ligand might be either chelating or bridging. Competition experiments show that DiCN-2 binds more efficiently to the Mn(CO)(,3)Br unit than do DiCN-3 and DiCN-4. The trinitrile TriCN, 1,3,5-tris(2-cyanophenyl)benzene, functions as either a bidentate ligand, as in M(CO)(,3)(TriCN)Br (M = Mn, Re), or as a tridentate ligand, as in {M(CO)(,3)(TriCN)}PF(,6) (M = Mn, Re).;The diisonitriles SiNC-2 and SiNC-3, 1,2-bis-(2-isocyano-3-trimethylsiloxyphenoxy)ethane and -propane, react with {Rh(COD)Cl}(,2) to afford, after metathesis with KPF(,6), complexes of the empirical formula {Rh(SiNC-n)(,2)}PF(,6). The SiNC-2 complex is dinuclear and employs SiNC-2 as a bridging ligand. The SiNC-3 complex is mononuclear and shows no tendency to associate in solutions or the solid state. Both complexes react rapidly with halogen-containing substrates to give oxidative-addition products. An improved synthesis of t-BuDiNC, 1,2-bis(4-t-butyl-2-isocyanophenoxy)ethane is reported. This ligand and the non-butylated ligand, DiNC, are shown to be capable of chelation at pseudooctahedral or pseudotetrahedral metal centers. In certain cases, the ligands bridge between two metals. Homoleptic d('6) complexes, {M(t-BuDiNC)(,3)}('z+) (PF(,6)('-))(,z) (M('z+) = Cr(DEGREES), Mn('+), Fe('2+), and Co('3+)), have also been prepared. The Co(III) complex has no known analogs in isonitrile chemistry, while only one other homoleptic Fe(II) complex containing aromatic isonitriles is known. Spectroscopic investigations of this series of compounds show that there are large variations in the degree of d(pi)-(pi)('*)(,CN) back-bonding; such bonding is quite important for the Cr(DEGREES) and Mn('+) complexes, but is essentially nonexistent for the Co('3+) complex. |
