SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF [CR(T-C4H9HNC-EQUIVALENT-TO-CNH-T-C4H9)(CN-T-C4H9)4I]I - REDUCTIVE COUPLING OF ISOCYANIDE LIGANDS IN A 1ST ROW TRANSITION-METAL COMPLEX

The reductive coupling of two isocyanide ligands to form a coordinated bis(alkylamino)acetylene molecule, previously known for [M(CNR)6] complexes, M = Mo, W and R = alkyl, has been extended to include the first row transition metal chromium. An improved synthesis and X-ray structure determination of the known precursor molecule, [Cr(CN-t-C4H9)6] (1), are reported. Crystal data for 1: monoclinic P2(1), a = 17.688(6) angstrom, b = 11.912(1) angstrom, c = 19.221(6) angstrom, beta = 116.65(1)degrees, Z = 4. The structure was solved by conventional direct methods and refined by full matrix least squares to R = 0.060 and R(w) = 0.070 for 4851 reflections with I greater-than-or-equal-to 3sigma(I). The coordination geometry is approximately octahedral. A noteworthy feature of the structure is the variability of isocyanide C-N-C bend angles [136.1(9)-175(1)degrees], which correlate linearly with the M-C bond lengths for M = Cr and Mo. Addition of 2 equiv of HI(aq) to [Cr(CN-t-C4H9)6] in THF resulted in carbon-carbon bond formation between two isocyanide ligands to afford [Cr(t-C4H9HNC=CNH-t-C4H9)(CN-t-C4H9)4I]I (2), which has been characterized by H-1 and C-13{H-1} NMR and IR spectroscopic, as well as elemental, analyses. The solid-state structure of 2.(toluene) was determined in a single crystal X-ray diffraction study. Crystal data for 2.(toluene): monoclinic P2(1)/n, a = 15.927(4) angstrom, b = 17.397(2) angstrom, c = 17.351(4) angstrom, beta = 111.36(1)degrees, Z = 4. The structure was solved by direct methods and refined by full matrix least-squares procedures to R = 0.035 and R(w) = 0.042 for 5523 reflections with I greater-than-or-equal-to 3sigma(I). The idealized geometry about the chromium center in 2 is C2v, capped trigonal prismatic. Reaction of 2 with