SYNTHESIS AND CHARACTERIZATION OF BINUCLEAR PALLADIUM(I) COMPLEXES OF ISOCYANIDES WITH PHENYL-SUBSTITUTED CYCLOPENTADIENYL AND TRIS(PYRAZOL-1-YL)BORATE LIGANDS

The reactions of PdCl2(RNC)(2) with potassium pentaphenylcyclopentadienide (K{C(5)Ph(5)}) and potassium tetraphenylcyclopentadienide (K{C(5)HPh(4)}) gave binuclear palladium(I) complexes, Pd-2(eta-C(5)Ph(5))(2)(mu-RNC)(2) (3; R = 2,6-Me(2)C(6)H(3)) and Pd-2(eta-C(5)HPh(4))2 (mu-RNC)(2) (4a, R = 2,6-Me(2)C(6)H(3); 4b, R = 2,4,6-Me(3)C(6)H(2)), in good yields. Complexes 3 and 4 were characterized by elemental analysis, IR, UV-vis, and H-1 and C-13 NMR spectroscopies, and X-ray crystallography. Compound 3 crystallizes in the triclinic system, space group P $$($) over bar 1, with a = 13.391(8) Angstrom, b = 23.793(9) Angstrom, c = 13.681(6) Angstrom, alpha = 90.24(4)degrees, beta = 118.13(4)degrees, gamma = 90.30(4)degrees, and Z = 2 (R = 0.085 and R(w) = 0.088 for 2886 independent reflections with I > 4 sigma(I)), and compound 4b crystallizes in the triclinic system, space group P $$($) over bar 1, with a = 14.907(3) Angstrom, b = 18.794(3) Angstrom, c = 11.769(2) Angstrom, alpha = 101.88(2)degrees, beta = 97.33(2)degrees, gamma = 89.40(2)degrees, and Z = 2 (R = 0.047 and R(w) = 0.038 for 5808 independent reflections with I > 3 sigma(I)). Complexes 3 and 4 consist of two palladium atoms bridged by two isocyanides having the C-N-C linear structure. The Pd2C2 core is folded with the dihedral angles of 121.6 degrees (3) and 137.5 degrees (4b) between the two Pd2C planes. The Pd-Pd bond lengths are 2.632(5) Angstrom (3) and 2.673(1) Angstrom (4b), and the phenyl-substituted cyclopentadienyl groups coordinate to the metal in the distorted eta(5)-fashion. Complex 4 readily reacted with isocyanide to yield the ketenimine compound, Ph(4)C(4)C=C=NR (5). When potassium 1,2,4-triphenylcyclopentadienide (K{C(5)H(2)Ph(3)}) was used, the binuclear palladium(I) complex of isocyanide with bridging eta(3)-C(5)H(2)Ph(3) anions, Pd-2(mu-eta(3)-C(5)H(2)Ph(3))(2)(RNC)(2) (6a, R = 2,6-Me(2)C(6)H(3); 6b, R = 2,4,6-Me(3)C(6)H(2)), was obtained instead of the isocyanide-bridged dimer. Complex 6b crystallizes in the triclinic system, space group P $$($) over bar 1 with a = 11.511(4) Angstrom, b = 12.768(3) Angstrom, c = 10.157(2) Angstrom, alpha = 103.23(2)degrees, beta = 91.71(2)degrees, gamma = 96.83(2)degrees, and Z = 2 (R = 0.034 and R(w) = 0.033 for 5572 independent reflections with I > 3 sigma(I)). In the dimer 6, two eta-C(5)H(2)Ph(3) groups are parallel in an anti arrangement. The Pd-Pd bond length is 2.6309(9) Angstrom. The reaction of Pd2Cl2(RNC)(4) with Na(HB(pz)(3)} (pz = pyrazol-1-yl) produced the dipalladium(I) compound, Pd-2(HB(Pz)3)(mu-RNC2) (8, R = 2,4,6-Me(3)C(6)H(2)), which crystallizes in the monoclinic system, space group P2(1)/n, with a = 11.243(3) Angstrom, b = 15.871(6) Angstrom, c = 12.035(2) Angstrom, beta = 91.99(2)degrees, and Z = 2 (R = 0.062 and R(w) = 0.073 for 1142 independent reflections with I > 3 sigma(I)). Complex 8 consists of two palladium atoms bridged by two isocyanides, and the Pd2C2 core is crystallographically planar. The HB(pz)(3) anion coordinates to the metal in an asymmetrical tridentate manner. The Pd-Pd bond length is considerably elongated to 2.757(4) Angstrom. A linear correlation between the Pd-Pd bond length and the dihedral angle between the two PdC2 planes was observed in the series of Pd-2(mu-RNC)2 dimers. The present work provides an efficient route to a new series of binuclear palladium(I) complexes containing cyclopentadienyl analogues and isocyanides.