Sodium amalgam reduction of NiC1(C6H4Br-2)(Cy2PCHzCHzPCyz)-0.5THF (6) (Cy = cyclohexyl, C6H1,) gives a mononuclear nickel(0) complex, Ni(qz-C6H4)(Cy3PCHzCHzPCy2) (3), which has been characterized by microanalysis, by mass, infrared, and NMR ('H, ' C, 31P) spectroscopy, and by single-crystal X-ray structural analysis. Crystals of 3 are orthorhombic, space group Pbca, with a = 16.068 (1) A, b = 17.189 (1) A, c = 22.358 (1) A, and 2 = 8. The structure was solved by heavy-atom methods and refined by least-squares methods to R = 0.035 and R, = 0.055 for 4203 independent reflections. The molecule consists of a central nickel atom coordinated by a symmetric q2-benzyne ligand [Ni-C(l) = 1.870 (4) A, Ni-C(2) = 1.868 (4) A the coordination geometry being close to trigonal planar. The coordinated C-C bond length of 1.332 (6) k is significantly larger than those observed in alkyne complexes of zerovalent nickel and latinum. The remaining C-C bonds of the six-membered ring are almost equal in length (average 1.385 i), consistent with a delocalized aromatic structure for the benzyne ligand. Complex 3 reacts with iodine and methyl iodide at room temperature to give, respectively, the 2-iodophenyl and o-tolyl complexes NiI(C6H4Y-2)(CyzPCHzCHzPCyz) (Y = I (71, Me (8)). Carbon dioxide, ethylene, and dimethyl acetylenedicarboxylate insert into the nickel-benzyne bond of 3 to give the nickelacycles Ni(C6H4COO)-(CyzPCHzCH2PCyz) (lo), Ni(CH2CHzC6H4-o)(CyzPCHzCHzPCyz) (111, and Ni(C(C02Me)=C-(COzMe)C6~4-o)(CyzPCH~cH~Pcyz) (12), respectively, whereas diphenylacetylene displaces benzyne to give Ni(PhCd!Ph)(CyzPCHzCHzPCyz) (13). Crystals of 11 are monoclinic, space group P2,/n, with a = 15.792 (6) A, b = 17.471 (6) A, c = 12.104 (4) A, p = 104.09 ( 2 ) O , and 2 = 4. The structure was solvedand refined as for 3 to R = 0.070 and R, = 0.071 for 2379 independent reflections. The nickel atom is coordinated in an approximately planar arrangement by the bidentate di(tertiary phosphine) and by two carbon atoms of a five-membered, half-chair-shaped chelate ring, the Ni-C(ary1) and Ni-C(alky1) bond lengths being 1.951 (12) and 1.988 (12) A, respectively. , .
