SYNTHESIS AND REACTIONS OF STABLE 16-ELECTRON OSMIUM(0) COMPLEXES [OSCL(NO)(PR(3))(2)] INCLUDING THE X-RAY CRYSTAL-STRUCTURE OF [OSCL2(NO)(ETA(1)-CH=C=CPH(2))(P-I-PR-3)(2)]

The reaction of [OsCl(NO)(PPh(3))(3)] (1) with P-i-Pr-3 and P-i-Pr(2)Ph affords almost quantitatively the 16-electron square-planar osmium(0) complexes [OsCl(NO)(PR(3))(2)] (2, 3). In toluene at room temperature or below, compounds 2 and 3 react spontaneously with CO, H-2, and CH2N2 to give the carbonylosmium(0), dihydridoosmium(II), and methyleneosmium(0) derivatives 4-9 in excellent yields. While 2 and 3 on treatment with HC=CPh form the alkynyl(hydrido)osmium(II) complexes 10 and 11, attempts to rearrange these compounds to the vinylideneosmium(0) isomers failed. Reaction of 2 and 3 with the alkynols HC=CCMe(2)OH and HC=CCPh(2)OH also produces six-coordinate alkynyl(hydrido) complexes 12-14, which similar to 10 and 11, are inert with regard to isomerization. Compounds 13 and 14 react, however, with chloride-containing acidic alumina to give the eta(1)-allenylosmium(II) derivatives [OsCl2(NO)(eta(1)-CH=C=CPh(2))(PR(3))(2)] (15, 16) in 40-50% yield. The X-ray crystal structure analysis of 15 (monoclinic space group P2(1) with a = 9.901(1) Angstrom, b = 16.041(1) Angstrom, c = 11.812(6) Angstrom, beta = 111.59(1)degrees, and Z = 2) reveals an octahedral geometry around osmium with trans disposed phosphine and cis disposed chlorine Ligands. The C=C=C chain is nearly linear with C-C distances that are almost identical to those of allenes.