TRIOSMIUM CLUSTERS FORMED BY OXIDATIVE ADDITION AND DECARBONYLATION OF 2-FORMYLPYRROLE - CRYSTAL-STRUCTURES OF 3 TRIOSMIUM CLUSTERS CONTAINING AROMATIC OR NONAROMATIC HETEROCYCLIC LIGANDS DERIVED FROM PYRROLE

The μ-acyl cluster [Os3H(μ2-NHCH==CHCH==CCO)(CO)10] (1) is formed by oxidative addition of 2-formylpyrrole to [Os3(CO)10(MeCN)2] in refluxing cyclohexane in the same manner as with other aldehydes. The crystals of 1 are triclinic, space group P1, with cell dimensions a = 14.882 (2) Å, b = 15.626 (4) Å, c = 9.447 (3) Å, α = 107.39 (2)°, β = 97.29 (2)°, γ = 97.84 (2)°, and Z = 4. The structure was refined to RW = 0.034. The pyrrolylacyl ligand bridges two osmium atoms through the C and O atoms of the original formyl group. Thermal loss of two COs from 1 gives two isomers of the cluster [Os3H2(μ3-C4H3N)(CO)9] (2 and 3), isomer 2 converting to 3 thermally. Isomer 2, [OS3H2(μ3-NHCH==CHC==C) (CO)9], retains the NH bond and is directly related to the N-methyl analogue of 2, [Os3H2(μ3-MeNCH==CHC==C)(CO)9] (5), and closely related to the benzyne cluster [Os3H2(C6H4)(CO)9], both of known X-ray structure. Cluster 2 converts to 3 by cleavage of N-H and Os-C bonds and with formation of C-H and Os-N bonds. Crystals of 3 are monoclinic, space group P21/c, with cell dimensions a =11.308 (2) Å, b = 12.457 (2) Å, c = 15.384 (3) Å, β = 123.59 (2)°, and Z = 8. The structure was refined to Rw = 0.052. The structure is best defined by a model in which the μ3-N==CHCH==CHC ligand is coordinated to one Os atom through a N atom and to the other two through a single C atom forming a μ2-alkylidene bridge. The C4N ring is formally nonaromatic and is oriented vertically to the metal plane. Another nonaromatic derivative formed as a byproduct along with 2 and 3 in the direct reaction of pyrrole with [Os3(CO)12] is the cluster [OS3H(μ-N==CCH2CH==CH) (CO)10] (4). Crystals of 4 are monoclinic, space group P2/b, with cell dimensions a = 28.704 (2) Å, b = 14.377 (3) Å, c = 9.304 (3) Å, γ = 94.16 (2)°, and Z = 8. The structure was refined to RW = 0.064. The stabilization of nonaromatic tautomers of pyrrole by coordination to Os3 groups in clusters 3 and 4 is discussed. © 1990, American Chemical Society. All rights reserved.