Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 91. Steric implications in the reactions of the complexes [M(CR)(CO)2(η-C5H5)](M = Mo or W, R = C6H4Me-4, C6H4OMe-2, or C6H3Me2-2,6) with the compounds [Mo(CO)3(NCMe)3] and [Cu(thf)(η- C5Me5)](thf = tetrahydrofuran); crystal structure of [Mo3(µ-CC6H3Me2-2,6)2(CO)6(η-C5H5)2

Abstract

The compounds [Mo(CO)3(NCMe)3] and [M(CR)(CO)2(η-C5H5)](M = MO or W) in Et2O at room temperature afford the trimetal complexes [MoM2(µ-CR)2(CO)6(η-C5H5)2](M = MO or W, R = C6H4Me2-2,6; M = MO, R = C6H4OMe-2). In contrast, [Mo(CO)3(NCMe)3] and [Mo(CC6H4Me-4)(CO)2(η-C5H5)] yield the µ-alkyne complex [Mo2{µ-C6H4Me-4)2}-(CO)4(C5H5)2]. An X-ray diffraction study established the structure of [MO3(µ-CC6H3Me-2,6)2(CO)6(η-C5H5)2]. The three metal atoms form the spine of the molecule [Mo–Mo 2.802(1)A, MO–MO–MO 124.8(1)°], and the metal–metal bonds are bridged in an essentially symmetrical manner by the alkylidyne groups [µ-C–MO 1.986(5) and 2.100(5)A]. Each metal atom carries two carbonyl groups, but one of these ligands on each of the terminal molybdenum atoms semi-bridges a metal-metal bond [Mo–C–O 169.8(5)°]. The molecule has crystallographic C2 symmetry. The two almost isosceles µ-CMo2 triangles share an Mo apex, with a dihedral angle of 79° between the planes defined by the triangles. Moreover, the two carbonyl groups attached to the central MO atom are each, respectively, coplanar with one of the µ-CMo2 triangles. The arrangement of the ligating groups around the central MO atom is in agreement with extended-Huckel molecular orbital calculations on the model isolobal molecule [Mo(CO)2(η-C2H2)2]. The lowest energy results for a structure in which the alkyne ligands are orthogonal to each other, and are each parallel to one of the CO groups. The reactions of the species [M(CC6H3Me2-2,6)(CO)2(η-C5H5)](M = MO or W) with [Cu(thf)(η-C5Me5](thf = tetrahydrofuran) were also investigated and shown to give the dimetal compounds [MCu(µ-CC6H3Me2-2,6)(CO)2(η-C5H5)(η-C5Me5)].